AD9255-105EBZ [ADI]
14-Bit, 125 MSPS/105 MSPS/80 MSPS; 14位， 125 MSPS / 105 MSPS / 80 MSPS
| 型号： | AD9255-105EBZ |
| 厂家： | 
ADI |
| 描述： | 14-Bit, 125 MSPS/105 MSPS/80 MSPS |
| 文件： | 总44页 (文件大小：1757K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
14-Bit, 125 MSPS/105 MSPS/80 MSPS,
1.8 V Analog-to-Digital Converter
Data Sheet
AD9255
FEATURES
APPLICATIONS
SNR = 78.3 dBFS at 70 MHz and 125 MSPS
SFDR = 93 dBc at 70 MHz and 125 MSPS
Low power: 371 mW at 125 MSPS
Communications
Multimode digital receivers (3G)
GSM, EDGE, W-CDMA, LTE, CDMA2000, WiMAX, and
TD-SCDMA
1.8 V analog supply operation
1.8 V CMOS or LVDS output supply
Smart antenna systems
Integer 1-to-8 input clock divider
General-purpose software radios
Broadband data applications
Ultrasound equipment
IF sampling frequencies to 300 MHz
−153.4 dBm/Hz small signal input noise with 200 Ω input
impedance at 70 MHz and 125 MSPS
Optional on-chip dither
PRODUCT HIGHLIGHTS
1. On-chip dither option for improved SFDR performance
with low power analog input.
2. Proprietary differential input that maintains excellent SNR
performance for input frequencies up to 300 MHz.
3. Operation from a single 1.8 V supply and a separate digital
output driver supply accommodating 1.8 V CMOS or
LVDS outputs.
4. Standard serial port interface (SPI) that supports various
product features and functions, such as data formatting
(offset binary, twos complement, or gray coding), enabling
the clock DCS, power-down, test modes, and voltage
reference mode.
Programmable internal ADC voltage reference
Integrated ADC sample-and-hold inputs
Flexible analog input range: 1 V p-p to 2 V p-p
Differential analog inputs with 650 MHz bandwidth
ADC clock duty cycle stabilizer
Serial port control
User-configurable, built-in self-test (BIST) capability
Energy-saving power-down modes
5. Pin compatibility with the AD9265, allowing a simple
migration up to 16 bits.
FUNCTIONAL BLOCK DIAGRAM
SENSE RBIAS PDWN
AGND AVDD (1.8V)
LVDS LVDS_RS
REFERENCE
VREF
AD9255
VCM
DRVDD (1.8V)
D13 TO D0
VIN+
TRACK-AND-HOLD
VIN–
OUTPUT
ADC
14
STAGING
CMOS OR
LVDS
14
14-BIT
DITHER
CORE
(DDR)
CLK+
CLOCK
MANAGEMENT
OR
CLK–
OEB
SYNC
SERIAL PORT
DCO
SVDD SCLK/ SDIO/ CSB
DFS DCS
Figure 1.
Rev. C
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Technical Support
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AD9255
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Voltage Reference ....................................................................... 28
Clock Input Considerations...................................................... 29
Power Dissipation and Standby Mode .................................... 31
Digital Outputs ........................................................................... 32
Timing ......................................................................................... 32
Built-In Self-Test (BIST) and Output Test .................................. 33
Built-In Self-Test (BIST)............................................................ 33
Output Test Modes..................................................................... 33
Serial Port Interface (SPI).............................................................. 34
Configuration Using the SPI..................................................... 34
Hardware Interface..................................................................... 34
Configuration Without the SPI ................................................ 35
SPI Accessible Features.............................................................. 35
Memory Map .................................................................................. 36
Reading the Memory Map Register Table............................... 36
Memory Map Register Table..................................................... 37
Memory Map Register Descriptions........................................ 39
Applications Information .............................................................. 40
Design Guidelines ...................................................................... 40
Outline Dimensions....................................................................... 41
Ordering Guide .......................................................................... 41
Applications....................................................................................... 1
Product Highlights ........................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
General Description......................................................................... 3
Specifications..................................................................................... 4
ADC DC Specifications................................................................. 4
ADC AC Specifications ................................................................. 5
Digital Specifications ................................................................... 6
Switching Specifications ................................................................ 8
Timing Specifications .................................................................. 9
Absolute Maximum Ratings.......................................................... 10
Thermal Characteristics ............................................................ 10
ESD Caution................................................................................ 10
Pin Configurations and Function Descriptions ......................... 11
Typical Performance Characteristics ........................................... 15
Equivalent Circuits......................................................................... 23
Theory of Operation ...................................................................... 25
ADC Architecture ...................................................................... 25
Analog Input Considerations.................................................... 25
REVISION HISTORY
7/13—Rev. B to Rev. C
Changes to Data Clock Output (DCO) Section......................... 32
3/13—Rev. A to Rev. B
Changes to Table 17.......................................................................... 1
Updated Outline Dimensions ....................................................... 41
1/10—Rev. 0 to Rev. A
Changes to Worst Other (Harmonic or Spur) Parameter,
Table 2 ................................................................................................ 6
Changes to Figure 77...................................................................... 29
Changes to Input Clock Divider Section..................................... 30
Changes to Table 17........................................................................ 37
Updated Outline Dimensions ....................................................... 41
10/09—Revision 0: Initial Version
Rev. C | Page 2 of 44
Data Sheet
AD9255
GENERAL DESCRIPTION
The AD9255 is a 14-bit, 125 MSPS analog-to-digital converter
(ADC). The AD9255 is designed to support communications
applications where high performance combined with low cost,
small size, and versatility is desired.
A differential clock input controls all internal conversion cycles. A
duty cycle stabilizer provides the means to compensate for vari-
ations in the ADC clock duty cycle, allowing the converters to
maintain excellent performance over a wide range of input
clock duty cycles. An integrated voltage reference eases design
considerations.
The ADC core features a multistage, differential pipelined
architecture with integrated output error correction logic to
provide 14-bit accuracy at 125 MSPS data rates and guarantees
no missing codes over the full operating temperature range.
The ADC output data format is either parallel 1.8 V CMOS or
LVDS (DDR). A data output clock is provided to ensure proper
latch timing with receiving logic.
The ADC features a wide bandwidth differential sample-and-
hold analog input amplifier supporting a variety of user-selectable
input ranges. It is suitable for multiplexed systems that switch
full-scale voltage levels in successive channels and for sampling
single-channel inputs at frequencies well beyond the Nyquist rate.
Combined with power and cost savings over previously available
ADCs, the AD9255 is suitable for applications in communications,
instrumentation, and medical imaging.
Programming for setup and control is accomplished using a 3-wire
SPI-compatible serial interface. Flexible power-down options
allow significant power savings, when desired. An optional on-
chip dither function is available to improve SFDR performance
with low power analog input signals.
The AD9255 is available in a Pb-free, 48-lead LFCSP and is
specified over the industrial temperature range of −40°C to +85°C.
Rev. C | Page 3 of 44
AD9255
Data Sheet
SPECIFICATIONS
ADC DC SPECIFICATIONS
AVDD = 1.8 V, DRVDD = 1.8 V, SVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference, DCS
enabled, unless otherwise noted.
Table 1.
AD9255BCPZ-801
Temp Min Typ Max
AD9255BCPZ-1051
AD9255BCPZ-1251
Parameter
Min Typ
Max
Min Typ
Max
Unit
RESOLUTION
Full
14
14
14
Bits
ACCURACY
No Missing Codes
Offset Error
Gain Error
Full
Full
Full
Full
ꢀ0°C
Full
ꢀ0°C
Guaranteed
±±.±0 ±±.ꢀ0
Guaranteed
±±.±0
Guaranteed
±±.ꢀ0
±ꢀ.0
±±.4
±±.±0
±±.4
±±.ꢀ0 ꢁ FSR
±ꢀ.0 ꢁ FSR
±±.ꢀ
±±.ꢀ
±±.ꢃ0
±ꢀ.0
±±.4
±±.ꢀ
±±.ꢀ
±±.40
Differential Nonlinearity (DNL)ꢀ
±±.40 LSB
LSB
±1.ꢀ
±±.ꢀ0
±±.ꢄ
Integral Nonlinearity (INL)ꢀ
±±.ꢂ
±±.ꢂ
LSB
LSB
TEMPERATURE DRIFT
Offset Error
Gain Error
Full
Full
±ꢀ
±10
±ꢀ
±10
±ꢀ
±10
ppm/°C
ppm/°C
INTERNAL VOLTAGE REFERENCE
Output Voltage Error (1 V Mode)
Load Regulation at 1.± mA
INPUT REFERRED NOISE
VREF = 1.± V
Full
Full
+8
ꢃ
±1ꢀ
+8
ꢃ
±1ꢀ
+8
ꢃ
±1ꢀ
mV
mV
ꢀ0°C
±.6ꢀ
±.6ꢃ
±.61
LSB rms
ANALOG INPUT
ꢀ
8
±.ꢂ
6
ꢀ
8
±.ꢂ
6
Input Span, VREF = 1.± V
Input Capacitanceꢃ
Input Common-Mode Voltage
REFERENCE INPUT RESISTANCE
POWER SUPPLIES
Supply Voltage
Full
Full
Full
Full
ꢀ
8
±.ꢂ
6
V p-p
pF
V
kΩ
1.ꢄ
1.ꢄ
1.ꢄ
1.8
1.8
1.ꢂ
1.ꢂ
ꢃ.0
1.ꢄ
1.ꢄ
1.ꢄ
1.8
1.8
1.ꢂ
1.ꢂ
ꢃ.0
AVDD
DRVDD
SVDD
Full
Full
Full
1.ꢄ
1.ꢄ
1.ꢄ
1.8
1.8
1.ꢂ
1.ꢂ
ꢃ.0
V
V
V
Supply Current
IAVDDꢀ
Full
Full
Full
1ꢂ4
ꢀꢃ
44
ꢀ±ꢀ
ꢃ8ꢀ
mA
mA
mA
1ꢀ6
1ꢃ
ꢃꢂ
1ꢃ1
16ꢂ
1ꢂ
4ꢀ
1ꢄ6
IDRVDDꢀ (1.8 V CMOS)
IDRVDDꢀ (1.8 V LVDS)
POWER CONSUMPTION
DC Input
ꢀꢃꢂ
ꢀ48
ꢃꢀ1
ꢃꢃꢀ
Full
ꢃꢄ1
mW
Sine Wave Inputꢀ
CMOS Output Mode
LVDS Output Mode
Standby Power4
ꢀ0ꢀ
ꢃ±6
04
ꢃꢃ8
ꢃ84
04
Full
Full
Full
Full
ꢃꢂ1
4ꢃꢄ
04
mW
mW
mW
mW
±.±0
±.10
±.±0
±.10
Power-Down Power
±.±0
±.10
1 The suffix following the part number refers to the model found in the Ordering Guide section.
ꢀ Measured with a low input frequency, full-scale sine wave, with approximately 0 pF loading on each output bit.
ꢃ Input capacitance refers to the effective capacitance between one differential input pin and AGND.
4 Standby power is measured with a dc input, the CLK pins (CLK+, CLK−) inactive (set to AVDD or AGND).
Rev. C | Page 4 of 44
Data Sheet
AD9255
ADC AC SPECIFICATIONS
AVDD = 1.8 V, DRVDD = 1.8 V, SVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference, DCS
enabled, unless otherwise noted.
Table 2.
AD9255BCPZ-802
AD9255BCPZ-1052
AD9255BCPZ-1252
Parameter1
Temp Min
Typ
Max Min
Typ
Max Min
Typ
Max Unit
SIGNAL-TO-NOISE-RATIO (SNR)
fIN = 2.4 MHz
fIN = 70 MHz
25°C
25°C
Full
25°C
25°C
79.2
78.9
78.9
78.5
78.3
78.3
dBFS
dBFS
dBFS
dBFS
dBFS
78.1
77.9
77.6
77.3
76.9
76.7
fIN = 140 MHz
fIN = 200 MHz
78.0
76.9
77.7
76.4
77.1
75.5
SIGNAL-TO-NOISE-AND DISTORTION (SINAD)
fIN = 2.4 MHz
fIN = 70 MHz
25°C
25°C
Full
25°C
25°C
78.7
78.7
78.6
78.0
78.0
78.0
dBFS
dBFS
dBFS
dBFS
dBFS
fIN = 140 MHz
fIN = 200 MHz
76.8
75.8
77.0
75.3
76.7
74.3
EFFECTIVE NUMBER OF BITS (ENOB)
fIN = 2.4 MHz
fIN = 70 MHz
fIN = 140 MHz
fIN = 200 MHz
12.8
12.8
12.5
12.3
12.8
12.7
12.5
12.2
12.7
12.7
12.4
12.0
Bits
Bits
Bits
Bits
25°C
25°C
25°C
25°C
WORST SECOND OR THIRD HARMONIC
fIN = 2.4 MHz
fIN = 70 MHz
dBc
dBc
dBc
dBc
dBc
25°C
25°C
Full
25°C
25°C
−88
−94
−90
−89
−88
−93
−91
−88
−85
fIN = 140 MHz
fIN = 200 MHz
−82
−81
−86
−81
−89
−80
SPURIOUS-FREE DYNAMIC RANGE (SFDR)
fIN = 2.4 MHz
fIN = 70 MHz
dBc
dBc
dBc
dBc
dBc
25°C
25°C
Full
25°C
25°C
88
94
90
89
88
93
91
88
85
fIN = 140 MHz
fIN = 200 MHz
82
81
86
81
89
80
SPURIOUS-FREE DYNAMIC RANGE (SFDR)
Without Dither (AIN at −23 dBFS)
fIN = 2.4 MHz
dBFS
dBFS
dBFS
dBFS
25°C
25°C
25°C
25°C
102
103
104
102
99
97
97
101
96
99
98
97
fIN = 70 MHz
fIN = 140 MHz
fIN = 200 MHz
With On-Chip Dither (AIN at −23 dBFS)
fIN = 2.4 MHz
fIN = 70 MHz
fIN = 140 MHz
fIN = 200 MHz
dBFS
dBFS
dBFS
dBFS
25°C
25°C
25°C
25°C
110
110
110
110
109
108
108
109
108
109
109
109
Rev. C | Page 5 of 44
AD9255
Data Sheet
AD9255BCPZ-802
AD9255BCPZ-1052
AD9255BCPZ-1252
Parameter1
Temp Min
Typ
Max Min
Typ
Max Min
Typ
Max Unit
WORST OTHER (HARMONIC OR SPUR)
Without Dither
dBc
dBc
dBc
dBc
dBc
fIN = 2.4 MHz
fIN = 70 MHz
25°C
25°C
Full
25°C
25°C
−106
−106
−105
−104
−101
−104
−94
−97
−95
−99
−91
−98
fIN = 140 MHz
fIN = 200 MHz
With On-Chip Dither
fIN = 2.4 MHz
−104
−102
−104
−103
−103
−100
dBc
dBc
dBc
dBc
dBc
25°C
25°C
Full
25°C
25°C
−105
−106
−106
−105
−101
−104
fIN = 70 MHz
fIN = 140 MHz
fIN = 200 MHz
−103
−100
−103
−101
−103
−100
TWO-TONE SFDR
Without Dither
93
80
90
78
dBc
dBc
MHz
fIN = 29 MHz (−7 dBFS ), 32 MHz (−7 dBFS )
fIN = 169 MHz (−7 dBFS ), 172 MHz (−7 dBFS )
ANALOG INPUT BANDWIDTH
25°C
25°C
25°C
95
79
650
650
650
1 See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for a complete set of definitions.
2 The suffix following the part number refers to the model found in the Ordering Guide section.
DIGITAL SPECIFICATIONS
AVDD = 1.8 V, DRVDD = 1.8 V, SVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference, and DCS
enabled, unless otherwise noted.
Table 3.
Parameter
Temperature
Min
Typ
Max
Unit
DIFFERENTIAL CLOCK INPUTS (CLK+, CLK−)
Logic Compliance
CMOS/LVDS/LVPECL
Internal Common-Mode Bias
Differential Input Voltage
Input Voltage Range
Input Common-Mode Range
High Level Input Current
Low Level Input Current
Input Capacitance
Full
Full
Full
Full
Full
Full
Full
Full
0.9
3.6
V
V p-p
V
0.3
AGND
0.9
−100
−100
AVDD
1.4
+100
+100
V
μA
μA
pF
kΩ
4
Input Resistance
8
10
12
SYNC INPUT
Logic Compliance
Internal Bias
CMOS
0.9
Full
Full
Full
Full
Full
Full
Full
Full
V
Input Voltage Range
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
Input Capacitance
AGND
1.2
AGND
−100
−100
AVDD
AVDD
0.6
V
V
V
+100
+100
μA
μA
pF
kΩ
1
16
Input Resistance
12
20
Rev. C | Page 6 of 44
Data Sheet
AD9255
Parameter
LOGIC INPUT (CSB)1
Temperature
Min
Typ
Max
Unit
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
Input Resistance
Full
Full
Full
Full
Full
Full
1.22
0
SVDD
0.6
V
V
−10
40
+10
132
µA
µA
kΩ
pF
26
2
Input Capacitance
LOGIC INPUT (SCLK/DFS)2
High Level Input Voltage
Low Level Input Voltage
High Level Input Current (VIN = 1.8 V)
Low Level Input Current
Input Resistance
Full
Full
Full
Full
Full
Full
1.22
0
−92
−10
SVDD
0.6
−135
+10
V
V
µA
µA
kΩ
pF
26
2
Input Capacitance
LOGIC INPUT/OUTPUT (SDIO/DCS)1
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
Input Resistance
Full
Full
Full
Full
Full
Full
Full
Full
1.22
0
−10
38
SVDD
0.6
+10
128
V
V
µA
µA
kΩ
pF
V
26
5
Input Capacitance
High Level Output Voltage
Low Level Output Voltage
LOGIC INPUTS (OEB, PDWN, DITHER, LVDS, LVDS_RS)2
High Level Input Voltage
Low Level Input Voltage
High Level Input Current (VIN = 1.8 V)
Low Level Input Current
Input Resistance
1.70
0.2
V
Full
Full
Full
Full
Full
Full
1.22
0
−90
−10
2.1
0.6
−134
+10
V
V
µA
µA
kΩ
pF
26
5
Input Capacitance
DIGITAL OUTPUTS (DRVDD = 1.8 V)
CMOS Mode
High Level Output Voltage
IOH = 50 µA
IOH = 0.5 mA
Full
Full
1.79
1.75
V
V
Low Level Output Voltage
IOL = 1.6 mA
IOL = 50 µA
Full
Full
0.2
0.05
V
V
LVDS Mode
ANSI Mode
Differential Output Voltage (VOD)
Output Offset Voltage (VOS)
Reduced Swing Mode
Differential Output Voltage (VOD)
Output Offset Voltage (VOS)
Full
Full
290
1.15
345
1.25
400
1.35
mV
V
Full
Full
160
1.15
200
1.25
230
1.35
mV
V
1 Pull-up.
2 Pull-down.
Rev. C | Page 7 of 44
AD9255
Data Sheet
SWITCHING SPECIFICATIONS
AVDD = 1.8 V, DRVDD = 1.8 V, SVDD = 1.8 V, maximum sample rate, VIN = −1.0 dBFS differential input, 1.0 V internal reference, and
DCS enabled, unless otherwise noted.
Table 4.
AD9255BCPZ-801
Temp Min Typ Max Min Typ
AD9255BCPZ-1051 AD9255BCPZ-1251
Max Min Typ Max Unit
Parameter
CLOCK INPUT PARAMETERS
Input Clock Rate
Conversion Rate2
DCS Enabled
DCS Disabled
CLK Period—Divide-by-1 Mode (tCLK
Full
625
625
625
MHz
Full
Full
Full
20
10
12.5
80
80
20
10
9.5
105
105
20
10
8
125
125
MSPS
MSPS
ns
)
CLK Pulse Width High (tCH
)
Divide-by-1 Mode
DCS Enabled
DCS Disabled
Divide-by-3 Mode, Divide-by-5 Mode, and
Divide-by-7 Mode, DCS Enabled3
Divide-by-2 Mode, Divide-by-4 Mode, Divide-
by-6 Mode, and Divide-by-8 Mode, DCS
Enabled or DCS Disabled3
Full
3.75 6.25 8.75 2.85 4.75 6.65
2.4
3.8
0.8
4
4
5.6
4.2
ns
ns
ns
5.9
0.8
6.25 6.6
4.5
0.8
4.75 5.0
Full
Full
0.8
0.8
0.8
ns
Aperture Delay (tA)
Aperture Uncertainty (Jitter, tJ)
DATA OUTPUT PARAMETERS
CMOS Mode
Full
Full
1.0
0.07
1.0
0.07
1.0
0.07
ns
ps rms
Data Propagation Delay (tPD
DCO Propagation Delay (tDCO
)
Full
Full
Full
Full
2.4
2.7
0.3
2.8
3.4
0.6
12
3.4
4.2
0.9
2.4
2.7
0.3
2.8
3.4
0.6
12
3.4
4.2
0.9
2.4
2.7
0.3
2.8
3.4
0.6
12
3.4
4.2
0.9
ns
ns
ns
Cycles
4
)
DCO to Data Skew (tSKEW
)
Pipeline Delay (Latency)
LVDS Mode
Data Propagation Delay (tPD
DCO Propagation Delay (tDCO
)
Full
Full
2.6
3.3
3.4
3.8
4.2
4.3
2.6
3.3
3.4
3.8
4.2
4.3
2.6
3.3
3.4
3.8
4.2
4.3
ns
ns
4
)
DCO to Data Skew (tSKEW
)
−0.3 +0.4 +1.2 −0.3 +0.4 +1.2
−0.3 +0.4 +1.2
Pipeline Delay (Latency)
Wake-Up Time5
Full
Full
Full
12.5
500
2
12.5
500
2
12.5
500
2
Cycles
μs
OUT-OF-RANGE RECOVERY TIME
Cycles
1 The suffix following the part number refers to the model found in the Ordering Guide section.
2 Conversion rate is the clock rate after the divider.
3 See the Input Clock Divider section for additional information on using the DCS with the input clock divider.
4 Additional DCO delay can be added by writing to Bit 0 through Bit 4 in SPI Register 0x17 (see Table 17).
5 Wake-up time is defined as the time required to return to normal operation from power-down mode.
Rev. C | Page 8 of 44
Data Sheet
AD9255
TIMING SPECIFICATIONS
Table 5.
Parameter
Conditions
Min
Typ
Max
Unit
SYNC TIMING REQUIREMENTS
tSSYNC
tHSYNC
SYNC to rising edge of CLK setup time
SYNC to rising edge of CLK hold time
0.30
0.40
ns
ns
SPI TIMING REQUIREMENTS1
tDS
tDH
tCLK
tS
tH
tHIGH
tLOW
tEN_SDIO
Setup time between the data and the rising edge of SCLK
Hold time between the data and the rising edge of SCLK
Period of the SCLK
Setup time between CSB and SCLK
Hold time between CSB and SCLK
SCLK pulse width high
SCLK pulse width low
Time required for the SDIO pin to switch from an input to an
output relative to the SCLK falling edge
2
2
40
2
2
10
10
10
ns
ns
ns
ns
ns
ns
ns
ns
tDIS_SDIO
Time required for the SDIO pin to switch from an output to an
input relative to the SCLK rising edge
10
ns
1 Refer to Figure 84 for a detailed timing diagram.
Timing Diagrams
N – 1
N + 4
tA
N + 5
N
N + 3
VIN
N + 1
N + 2
tCH
tCL
tCLK
CLK+
CLK–
tDCO
DCO/DCO+
DCO–
tSKEW
LVDS (DDR) MODE
CMOS MODE
tPD
D0/1+ TO D12/D13+
D0/1– TO D12/D13–
DEx
– 12
DOx
– 12
DEx
– 11
DOx
– 11
DEx
– 10
DOx
– 10
DEx
– 9
DOx
– 9
DEx
– 8
DOx
– 8
D0 TO D13
NOTES
1. DEx DENOTES EVEN BIT.
2. DOx DENOTES ODD BIT.
Dx – 12
Dx – 11
Dx – 10
Dx – 9
Dx – 8
Figure 2. LVDS (DDR) and CMOS Output Mode Data Output Timing
CLK+
SYNC
tSSYNC
tHSYNC
Figure 3. SYNC Input Timing Requirements
Rev. C | Page 9 of 44
AD9255
Data Sheet
ABSOLUTE MAXIMUM RATINGS
Table 6.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Parameter
Rating
Electrical
AVDD to AGND
DRVDD to AGND
SVDD to AGND
VIN+, VIN− to AGND
CLK+, CLK− to AGND
SYNC to AGND
VREF to AGND
SENSE to AGND
VCM to AGND
RBIAS to AGND
CSB to AGND
SCLK/DFS to AGND
SDIO/DCS to AGND
OEB to AGND
PDWN to AGND
LVDS to AGND
LVDS_RS to AGND
DITHER to AGND
D0 through D13 to AGND
DCO to AGND
−0.3 V to +2.0 V
−0.3 V to +2.0V
−0.3 V to +3.6 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to SVDD +0.3 V
−0.3 V to SVDD +0.3 V
−0.3V to SVDD + 0.3 V
−0.3 V to DRVDD + 0.2 V
−0.3 V to DRVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to DRVDD + 0.2 V
−0.3 V to DRVDD + 0.2 V
THERMAL CHARACTERISTICS
The exposed paddle must be soldered to the ground plane for
the LFCSP package. Soldering the exposed paddle to the customer
board increases the reliability of the solder joints and maximizes
the thermal capability of the package.
Typical θJA is specified for a 4-layer PCB with a solid ground
plane. As shown, airflow improves heat dissipation, which
reduces θJA. In addition, metal in direct contact with the package
leads from metal traces, through holes, ground, and power
planes, reduces the θJA.
Table 7. Thermal Resistance
Airflow
Velocity
(m/s)
1, 2
1, 3
1, 4
Package Type
θJA
θJC
θJB
Unit
48-Lead LFCSP
(CP-48-8)
0
24.5 1.3
21.4
12.7 °C/W
°C/W
Environmental
1.0
2.5
Operating Temperature Range
(Ambient)
Maximum Junction Temperature
Under Bias
−40°C to +85°C
150°C
19.2
°C/W
1 Per JEDEC 51-7, plus JEDEC 25-5 2S2P test board.
2 Per JEDEC JESD51-2 (still air) or JEDEC JESD51-6 (moving air).
3 Per MIL-Std 883, Method 1012.1.
4 Per JEDEC JESD51-8 (still air).
Storage Temperature Range
(Ambient)
−65°C to +150°C
ESD CAUTION
Rev. C | Page 10 of 44
Data Sheet
AD9255
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
SYNC
CLK+
CLK–
AVDD
AVDD
OEB
1
2
3
4
5
6
7
8
9
36 AVDD
35 DITHER
34 AVDD
33 SVDD
32 CSB
PIN 1
INDICATOR
AD9255
PARALLEL
31 SCLK/DFS
30 SDIO/DCS
29 DRVDD
28 DNC
DNC
CMOS
DCO
TOP VIEW
(Not to Scale)
DNC
DNC 10
D0 (LSB) 11
D1 12
27 OR
26 D13 (MSB)
25 D12
NOTES
1. DNC = DO NOT CONNECT.
2. THE EXPOSED THERMAL PAD ON THE BOTTOM OF THE PACKAGE
PROVIDES THE ANALOG GROUND FOR THE INPUT. THIS EXPOSED
PAD MUST BE CONNECTED TO GROUND FOR PROPER OPERATION.
Figure 4. LFCSP Parallel CMOS Pin Configuration (Top View)
Table 8. Pin Function Descriptions (Parallel CMOS Mode)
Pin No.
Mnemonic
Type
Description
ADC Power Supplies
13, 20, 29
4, 5, 34, 36, 45
33
DRVDD
AVDD
SVDD
Supply
Supply
Supply
Digital Output Driver Supply (1.8 V Nominal).
Analog Power Supply (1.8 V Nominal).
SPI Input/Output Voltage
7, 9, 10, 28, 39, 40 DNC
Do Not Connect.
0
AGND
Ground
Analog Ground. The exposed thermal pad on the bottom of the package provides
the analog ground for the input. This exposed pad must be connected to ground for
proper operation.
ADC Analog
42
43
38
37
47
46
2
3
VIN+
VIN−
VREF
SENSE
RBIAS
VCM
Input
Input
Differential Analog Input Pin (+).
Differential Analog Input Pin (−).
Input/output Voltage Reference Input/Output.
Input
Input/output External Reference Bias Resistor.
Output
Input
Voltage Reference Mode Select. See Table 11 for details.
Common-Mode Level Bias Output for Analog Inputs.
ADC Clock Input—True.
ADC Clock Input—Complement.
CLK+
CLK−
Input
Digital Input
1
SYNC
Input
Digital Synchronization Pin. Slave mode only.
Digital Outputs
11
12
14
15
16
17
18
19
21
D0 (LSB)
D1
D2
D3
D4
D5
D6
D7
D8
Output
Output
Output
Output
Output
Output
Output
Output
Output
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
Rev. C | Page 11 of 44
AD9255
Data Sheet
Pin No.
Mnemonic
D9
D10
D11
D12
D13 (MSB)
OR
DCO
Type
Description
22
23
24
25
26
27
8
Output
Output
Output
Output
Output
Output
Output
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
CMOS Output Data.
Overrange Output.
Data Clock Output.
SPI Control
31
30
32
SCLK/DFS
SDIO/DCS
CSB
Input
SPI Serial Clock/Data Format Select Pin in External Pin Mode.
Input/output SPI Serial Data I/O/Duty Cycle Stabilizer Pin in External Pin Mode.
Input
SPI Chip Select (Active Low).
ADC Configuration
6
35
OEB
DITHER
Input
Input
Output Enable Input (Active Low).
In external pin mode, this pin sets dither to on (active high). Pull low for control via
SPI in SPI mode.
41
44
48
LVDS_RS
LVDS
Input
Input
Input
In external pin mode, this pin sets LVDS reduced swing output mode (active high).
Pull low for control via SPI in SPI mode.
In external pin mode, this pin sets LVDS output mode (active high). Pull low for
control via SPI in SPI mode.
Power-down input in external pin mode. In SPI mode, this input can be configured
as power-down or standby.
PDWN
Rev. C | Page 12 of 44
Data Sheet
AD9255
SYNC
CLK+
CLK–
AVDD
AVDD
OEB
1
2
3
4
5
6
7
8
9
36 AVDD
PIN 1
35 DITHER
34 AVDD
INDICATOR
33 SVDD
32 CSB
AD9255
INTERLEAVED
31 SCLK/DFS
30 SDIO/DCS
29 DRVDD
28 OR+
DCO–
DCO+
DNC
LVDS
TOP VIEW
(Not to Scale)
DNC 10
D0/1– 11
D0/1+ 12
27 OR–
26 D12/13+
25 D12/13–
NOTES
1. DNC = DO NOT CONNECT.
2. THE EXPOSED THERMAL PAD ON THE BOTTOM OF THE PACKAGE
PROVIDES THE ANALOG GROUND FOR THE PART. THIS EXPOSED PAD
MUST BE CONNECTED TO GROUND FOR PROPER OPERATION.
Figure 5. LFCSP Interleaved Parallel LVDS Pin Configuration (Top View)
Table 9. Pin Function Descriptions (Interleaved Parallel LVDS Mode)
Pin No.
Mnemonic
Type
Description
ADC Power Supplies
13, 20, 29
DRVDD
Supply
Supply
Supply
Digital Output Driver Supply (1.8 V Nominal).
Analog Power Supply (1.8 V Nominal).
SPI Input/Output Voltage.
4, 5, 34, 36, 45 AVDD
33
SVDD
DNC
9, 10, 39, 40
0
Do Not Connect.
AGND
Ground
Analog Ground. The exposed thermal pad on the bottom of the package provides the
analog ground for the input. This exposed pad must be connected to ground for proper
operation.
ADC Analog
42
43
38
37
47
46
2
3
VIN+
VIN−
VREF
SENSE
RBIAS
VCM
Input
Input
Differential Analog Input Pin (+).
Differential Analog Input Pin (−).
Input/output Voltage Reference Input/Output.
Input
Input/output External Reference Bias Resistor.
Output
Input
Voltage Reference Mode Select. See Table 11 for details.
Common-Mode Level Bias Output for Analog Inputs.
ADC Clock Input—True.
ADC Clock Input—Complement.
CLK+
CLK−
Input
Digital Input
1
SYNC
Input
Digital Synchronization Pin. Slave mode only.
Digital Outputs
12
11
15
14
17
16
19
18
22
21
D0/1+
D0/1−
D2/3+
D2/3−
D4/5+
D4/5−
D6/7+
D6/7−
D8/9+
D8/9−
Output
Output
Output
Output
Output
Output
Output
Output
Output
Output
LVDS Output Data Bit 0/Bit 1 (LSB)—True.
LVDS Output Data Bit 0/Bit 1 (LSB)—Complement.
LVDS Output Data Bit 2/Bit 3—True.
LVDS Output Data Bit 2/Bit 3—Complement.
LVDS Output Data Bit 4/Bit 5—True.
LVDS Output Data Bit 4/Bit 5—Complement.
LVDS Output Data Bit 6/Bit 7—True.
LVDS Output Data Bit 6/Bit 7—Complement.
LVDS Output Data Bit 8/Bit 9 —True.
LVDS Output Data Bit 8/Bit 9—Complement.
Rev. C | Page 13 of 44
AD9255
Data Sheet
Pin No.
Mnemonic
D10/11+
D10/11−
D12/13+ (MSB) Output
D12/13− (MSB) Output
OR+
OR−
DCO+
DCO−
Type
Description
24
23
26
25
28
27
8
7
Output
Output
LVDS Output Data Bit 10/Bit 11—True.
LVDS Output Data Bit 10/Bit 11—Complement.
LVDS Output Data Bit 12/Bit 13—True.
LVDS Output Data Bit 12/Bit 13—Complement.
LVDS Overrange Output—True.
LVDS Overrange Output—Complement.
LVDS Data Clock Output—True.
LVDS Data Clock Output—Complement.
Output
Output
Output
Output
SPI Control
31
30
32
SCLK/DFS
SDIO/DCS
CSB
Input
SPI Serial Clock/Data Format Select Pin in External Pin Mode.
Input/output SPI Serial Data I/O/Duty Cycle Stabilizer Pin in External Pin Mode.
Input
SPI Chip Select (Active Low).
ADC Configuration
6
35
OEB
Input
Input
Output Enable Input (Active Low).
In external pin mode, this pin sets dither to on (active high). Pull low for control via SPI
in the SPI mode.
In external pin mode, this pin sets LVDS reduced swing output mode (active high). Pull
low for control via SPI in the SPI mode.
In external pin mode, this pin sets LVDS output mode (active high). Pull low for control
via SPI in the SPI mode.
DITHER
LVDS_RS
LVDS
41
44
48
Input
Input
Input
PDWN
Power-Down Input in External Pin Mode. In SPI mode, this input can be configured as
power-down or standby.
Rev. C | Page 14 of 44
Data Sheet
AD9255
TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = 1.8 V, DRVDD = 1.8 V, SVDD = 1.8 V, sample rate = 125 MSPS, DCS enabled, 1.0 V internal reference, 2 V p-p differential input,
VIN = −1.0 dBFS, and 32k sample, TA = 25°C, unless otherwise noted.
0
–20
0
80MSPS
80MSPS
2.4MHz @ –1dBFS
SNR = 78.2dB (79.2dBFS)
SFDR = 89dBc
200.3MHz @ –1dBFS
SNR = 75.9dB (76.9dBFS)
SFDR = 81dBc
–20
–40
–40
–60
–60
THIRD
HARMONIC
SECOND
HARMONIC
–80
–80
THIRD
HARMONIC
SECOND
HARMONIC
–100
–120
–140
–100
–120
–140
0
10
20
FREQUENCY (MHz)
30
40
0
10
20
FREQUENCY (MHz)
30
40
Figure 6. AD9255-80 Single-Tone FFT with fIN = 2.4 MHz
Figure 9. AD9255-80 Single-Tone FFT with fIN = 200.3 MHz
0
–20
0
80MSPS
80MSPS
70.1MHz @ –1dBFS
SNR = 77.8dB (78.8dBFS)
SFDR = 93.6dBc
70.1MHz @ –6dBFS
SNR = 73.2dB (79.2dBFS)
–20
SFDR = 99dBc
–40
–40
–60
–60
THIRD
HARMONIC
–80
–80
THIRD
HARMONIC
SECOND
HARMONIC
SECOND
HARMONIC
–100
–120
–140
–100
–120
–140
0
10
20
30
40
0
10
20
30
40
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 7. AD9255-80 Single-Tone FFT with fIN = 70.1 MHz
Figure 10. AD9255-80 Single-Tone FFT with fIN = 70.1 MHz at −6 dBFS with
Dither Enabled
120
0
80MSPS
SFDR (dBFS)
140.1MHz @ –1dBFS
SNR = 77.0dB (78.0dBFS)
SFDR = 82.1dBc
–20
–40
100
SNR (dBFS)
80
–60
THIRD
HARMONIC
60
SFDR (dBc)
SECOND
HARMONIC
–80
40
–100
–120
–140
SNR (dBc)
20
0
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
0
10
20
FREQUENCY (MHz)
30
40
INPUT AMPLITUDE (dBFS)
Figure 11. AD9255-80 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 98.12 MHz
Figure 8. AD9255-80 Single-Tone FFT with fIN = 140.1 MHz
Rev. C | Page 15 of 44
AD9255
Data Sheet
120
110
100
90
1.6M
1.4M
1.2M
1.0M
800k
600k
400k
200k
0
0.62 LSB RMS
SFDRFS (DITHER ON)
SFDRFS (DITHER OFF)
SNRFS (DITHER OFF)
SNRFS (DITHER ON)
80
70
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
N – 3
N – 2
N – 1
N
N + 1
N + 2
N + 3
INPUT AMPLITUDE (dBFS)
OUTPUT CODE
Figure 12. AD9255-80 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 30 MHz with and without Dither Enabled
Figure 15. AD9255-80 Grounded Input Histogram
100
1.0
0.8
SFDR @ –40°C
INL WITHOUT DITHER
INL WITH DITHER
95
SFDR @ +25°C
0.6
90
0.4
SFDR @ +85°C
0.2
85
SNR @ –40°C
0
80
–0.2
–0.4
–0.6
–0.8
75
70
65
SNR @ +25°C
SNR @ +85°C
–1.0
0
0
50
100
150
200
250
300
2000 4000 6000 8000 10,000 12,000 14,000 16,000
OUTPUT CODE
INPUT FREQUENCY (MHz)
Figure 13. AD9255-80 Single-Tone SNR/SFDR vs.
Input Frequency (fIN) and Temperature with 2 V p-p Full Scale
Figure 16. AD9255-80 INL with fIN = 12.5 MHz
105
0.50
0.25
0
100
95
90
SFDR
85
80
–0.25
SNR
75
25
–0.50
0
30
35
40
45
50
55
60
65
70
75
80
2000 4000 6000 8000 10,000 12,000 14,000 16,000
OUTPUT CODE
SAMPLE RATE (MSPS)
Figure 14. AD9255-80 Single-Tone SNR/SFDR vs. Sample Rate (fS)
with fIN = 70.1 MHz
Figure 17. AD9255-80 DNL with fIN = 12.5 MHz
Rev. C | Page 16 of 44
Data Sheet
AD9255
0
–20
–40
–60
0
–20
105MSPS
105MSPS
2.4MHz @ –1dBFS
SNR = 77.9dB (78.9dBFS)
SFDR = 91dBc
200.3MHz @ –1dBFS
SNR = 75.4dB (76.4dBFS)
SFDR = 81.6dBc
–40
–60
THIRD
HARMONIC
SECOND
HARMONIC
SECOND
HARMONIC
–80
–100
–120
–140
–80
THIRD
HARMONIC
–100
–120
–140
0
10
20
30
40
50
0
10
20
30
40
50
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 18. AD9255-105 Single-Tone FFT with fIN = 2.4 MHz
Figure 21. AD9255-105 Single-Tone FFT with fIN = 200.3 MHz
0
0
105MSPS
105MSPS
70.1MHz @ –1dBFS
70.1MHz @ –6dBFS
SNR = 77.4dB (78.4dBFS)
SFDR = 88.7dBc
SNR = 72.9dB (78.9dBFS)
SFDR = 91dBc
–20
–40
–20
–40
–60
–60
SECOND
HARMONIC
–80
–80
SECOND
HARMONIC
THIRD
HARMONIC
THIRD
HARMONIC
–100
–120
–140
–100
–120
–140
0
10
20
30
40
50
0
10
20
30
40
50
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 19. AD9255-105 Single-Tone FFT with fIN = 70.1 MHz
Figure 22. AD9255-105 Single-Tone FFT with fIN = 70.1 MHz at −6 dBFS with
Dither Enabled
120
0
105MSPS
SFDR (dBFS)
140.1MHz @ –1dBFS
SNR = 76.7dB (77.7dBFS)
SFDR = 86.4dBc
–20
–40
100
SNR (dBFS)
80
–60
THIRD
HARMONIC
SECOND
HARMONIC
60
SFDR (dBc)
–80
40
–100
–120
–140
SNR (dBc)
20
0
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
0
10
20
30
40
50
INPUT AMPLITUDE (dBFS)
FREQUENCY (MHz)
Figure 23. AD9255-105 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 98.12 MHz
Figure 20. AD9255-105 Single-Tone FFT with fIN = 140.1 MHz
Rev. C | Page 17 of 44
AD9255
Data Sheet
120
110
100
90
1.4M
1.2M
1.0M
800k
600k
400k
200k
0
0.63 LSB RMS
SFDRFS (DITHER ON)
SFDRFS (DITHER OFF)
SNRFS (DITHER OFF)
SNRFS (DITHER ON)
80
70
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
N – 3
N – 2
N – 1
N
N + 1
N + 2
N + 3
INPUT AMPLITUDE (dBFS)
OUTPUT CODE
Figure 24. AD9255-105 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 30 MHz with and without Dither Enabled
Figure 27. AD9255-105 Grounded Input Histogram
100
1.0
0.8
SFDR @ –40°C
INL WITHOUT DITHER
INL WITH DITHER
SFDR @ +25°C
95
0.6
SFDR @ +85°C
90
0.4
0.2
85
SNR @ –40°C
80
0
–0.2
–0.4
–0.6
–0.8
–1.0
75
70
65
SNR @ +25°C
SNR @ +85°C
0
50
100
150
200
250
300
0
2000 4000 6000 8000 10,000 12,000 14,000 16,000
OUTPUT CODE
INPUT FREQUENCY (MHz)
Figure 25. AD9255-105 Single-Tone SNR/SFDR vs.
Input Frequency (fIN) and Temperature with 2 V p-p Full Scale
Figure 28. AD9255-105 INL with fIN = 12.5 MHz
105
0.50
0.25
0
100
SFDR
95
90
85
–0.25
–0.50
80
SNR
75
25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105
0
2000 4000 6000 8000 10,000 12,000 14,000 16,000
OUTPUT CODE
SAMPLE RATE (MSPS)
Figure 26. AD9255-105 Single-Tone SNR/SFDR vs. Sample Rate (fS)
with fIN = 70.1 MHz
Figure 29. AD9255-105 DNL with fIN = 12.5 MHz
Rev. C | Page 18 of 44
Data Sheet
AD9255
0
–20
–40
–60
0
–20
125MSPS
125MSPS
2.4MHz @ –1dBFS
SNR = 77.2dB (78.2dBFS)
SFDR = 88dBc
140.1MHz @ –1dBFS
SNR = 76.2dB (77.2dBFS)
SFDR = 88.9dBc
–40
–60
SECOND
HARMONIC
SECOND
HARMONIC
THIRD
HARMONIC
–80
–100
–120
–140
–80
THIRD
HARMONIC
–100
–120
–140
0
10
20
30
40
50
60
0
10
20
30
40
50
60
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 30. AD9255-125 Single-Tone FFT with fIN = 2.4 MHz
Figure 33. AD9255-125 Single-Tone FFT with fIN = 140.1 MHz
0
0
125MSPS
125MSPS
30.3MHz @ –1dBFS
200.3MHz @ –1dBFS
SNR = 77.7dB (78.7dBFS)
SFDR = 95dBc
SNR = 74.5dB (75.5dBFS)
SFDR = 80.0dBc
–20
–40
–20
–40
–60
–60
THIRD
HARMONIC
SECOND
HARMONIC
THIRD
HARMONIC
–80
–80
SECOND
HARMONIC
–100
–120
–140
–100
–120
–140
0
10
20
30
40
50
60
0
10
20
30
40
50
60
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 31. AD9255-125 Single-Tone FFT with fIN = 30.3 MHz
Figure 34. AD9255-125 Single-Tone FFT with fIN = 200.3 MHz
0
0
125MSPS
125MSPS
70.1MHz @ –1dBFS
220.1MHz @ –1dBFS
SNR = 77.3dB (78.3dBFS)
SFDR = 93.9dBc
SNR = 74.2dB (75.2dBFS)
SFDR = 79.8dBc
–20
–40
–20
–40
–60
–60
THIRD
HARMONIC
SECOND
HARMONIC
–80
–80
SECOND
HARMONIC
THIRD
HARMONIC
–100
–120
–140
–100
–120
–140
0
10
20
30
40
50
60
0
10
20
30
40
50
60
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 32. AD9255-125 Single-Tone FFT with fIN = 70.1 MHz
Figure 35. AD9255-125 Single-Tone FFT with fIN = 220.1 MHz
Rev. C | Page 19 of 44
AD9255
Data Sheet
0
120
100
80
60
40
20
0
125MSPS
SFDR (dBFS)
70.1MHz @ –6dBFS
SNR = 72.6dB (78.6dBFS)
SFDR = 99.7dBc
–20
–40
SNR (dBFS)
–60
SFDR (dBc)
–80
SECOND
HARMONIC
THIRD
HARMONIC
–100
–120
–140
SNR (dBc)
0
10
20
30
40
50
60
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
FREQUENCY (MHz)
INPUT AMPLITUDE (dBFS)
Figure 36. AD9255-125 Single-Tone FFT with fIN = 70.1 MHz at −6 dBFS with
Dither Enabled
Figure 39. AD9255-125 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 2.4 MHz
120
125MSPS
70.1MHz @ –23dBFS
0
SFDR (dBFS)
SNR = 56.4dBc (79.4dBFS)
SFDR = 75.8dBc
–30
–15
100
SNR (dBFS)
80
–45
–60
–75
60
SFDR (dBc)
–90
2
40
5
–105
3
+
6
SNR (dBc)
4
–120
–135
20
0
6
12
18
24
30
36
42
48
54
60
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
FREQUENCY (MHz)
INPUT AMPLITUDE (dBFS)
Figure 40. AD9255-125 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 98.12 MHz
Figure 37. AD9255-125 Single-Tone FFT with fIN = 70.1 MHz at −23 dBFS with
Dither Disabled, 1M Sample
120
125MSPS
70.1MHz @ –23dBFS
0
SFDRFS (DITHER ON)
SNR = 55.9dBc (78.9dBFS)
–15
SFDR = 86.6dBc
–30
110
100
–45
–60
–75
SFDRFS (DITHER OFF)
90
–90
–105
2
4
+
3
SNRFS (DITHER OFF)
80
5
6
–120
–135
SNRFS (DITHER ON)
70
6
12
18
24
30
36
42
48
54
60
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
FREQUENCY (MHz)
INPUT AMPLITUDE (dBFS)
Figure 38. AD9255-125 Single-Tone FFT with fIN = 70.1 MHz at −23 dBFS with
Dither Enabled, 1M Sample
Figure 41. AD9255-125 Single-Tone SNR/SFDR vs. Input Amplitude (AIN) with
fIN = 30 MHz With and Without Dither Enabled
Rev. C | Page 20 of 44
Data Sheet
AD9255
100
0
–20
SFDR @ –40°C
95
SFDR (dBc)
SFDR @ +25°C
SFDR @ +85°C
90
–40
IMD3 (dBc)
85
–60
SNR @ –40°C
80
75
70
65
–80
–100
–120
–140
SNR @ +25°C
SFDR (dBFS)
IMD3 (dBFS)
SNR @ +85°C
0
50
100
150
200
250
300
–90
–78
–66
–54
–42
–30
–18
–6
INPUT FREQUENCY (MHz)
INPUT AMPLITUDE (dBFS)
Figure 42. AD9255-125 Single-Tone SNR/SFDR vs.
Figure 45. AD9255-125 Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN
)
Input Frequency (fIN) and Temperature with 2 V p-p Full Scale
with fIN1 = 169.1 MHz, fIN2 = 172.1 MHz, fS = 125 MSPS
95
0
125MSPS
29.1MHz @ –7dBFS
32.1MHz @ –7dBFS
SFDR = 94.4dBc
(101.4dBFS)
–20
–40
90
85
SFDR
–60
80
–80
75
–100
–120
–140
SNR
70
65
0
50
100
150
200
250
300
0
10
20
30
40
50
60
INPUT FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 43. AD9255-125 Single-Tone SNR/SFDR vs.
Input Frequency (fIN) with 1 V p-p Full Scale
Figure 46. AD9255-125 Two-Tone FFT with fIN1 = 29.1 MHz and fIN2 = 32.1 MHz
0
–20
0
125MSPS
169.1MHz @ –7dBFS
172.1MHz @ –7dBFS
SFDR = 79.5dBc (86.5dBFS)
SFDR (dBc)
IMD3 (dBc)
–20
–40
–40
–60
–60
–80
–80
SFDR (dBFS)
–100
–120
–140
–100
–120
–140
IMD3 (dBFS)
–90
–78
–66
–54
–42
–30
–18
–6
0
10
20
30
40
50
60
INPUT AMPLITUDE (dBFS)
FREQUENCY (MHz)
Figure 44. AD9255-125 Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN
)
Figure 47. AD9255-125 Two-Tone FFT with fIN1 = 169.1 MHz and
IN2 = 172.1 MHz
with fIN1 = 29.1 MHz, fIN2 = 32.1 MHz, fS = 125 MSPS
f
Rev. C | Page 21 of 44
AD9255
Data Sheet
105
100
95
0.50
0.25
0
90
SFDR
85
–0.25
–0.50
80
SNR
75
75
25
35
45
55
65
85
95
105 115 125
0
2000 4000 6000 8000 10,000 12,000 14,000 16,000
SAMPLE RATE (MSPS)
OUTPUT CODE
Figure 48. AD9255-125 Single-Tone SNR/SFDR vs. Sample Rate (fS)
with fIN = 70.1 MHz
Figure 51. AD9255-125 DNL with fIN = 12.5 MHz
100
90
80
70
60
50
40
1.4M
0.63 LSB RMS
SFDR (dBc)
1.2M
1.0M
800k
600k
400k
200k
0
SFDR (dBFS)
0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20
N – 3
N – 2
N – 1
N
N + 1
N + 2
N + 3
INPUT COMMON-MODE VOLTAGE (V)
OUTPUT CODE
Figure 52. AD9255-125 SNR/SFDR vs. Input Common Mode (VCM)
with fIN = 30 MHz
Figure 49. AD9255-125 Grounded Input Histogram
1.0
0.8
INL WITHOUT DITHER
INL WITH DITHER
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
0
2000 4000 6000 8000 10,000 12,000 14,000 16,000
OUTPUT CODE
Figure 50. AD9255-125 INL with fIN = 12.5 MHz
Rev. C | Page 22 of 44
Data Sheet
AD9255
EQUIVALENT CIRCUITS
DRVDD
VIN+ OR
VIN–
PAD
Figure 57. Digital Output
Figure 53. Equivalent Analog Input Circuit
AVDD
SVDD
0.9V
26kΩ
10kΩ
10kΩ
350Ω
CLK–
CLK+
SDIO/DCS
Figure 58. Equivalent SDIO/DCS Circuit
Figure 54. Equivalent Clock Input Circuit
AVDD
SVDD
350Ω
VREF
SCLK/DFS
6kΩ
26kΩ
Figure 55. Equivalent VREF Circuit
Figure 59. Equivalent SCLK/DFS Input Circuit
AVDD
SVDD
26kΩ
350Ω
350Ω
SENSE
CSB
Figure 56. Equivalent SENSE Circuit
Figure 60. Equivalent CSB Input Circuit
Rev. C | Page 23 of 44
AD9255
Data Sheet
AVDD
DITHER,
LVDS OR
LVDS_RS
350Ω
350Ω
PDWN
26kΩ
26kΩ
Figure 61. Equivalent PDWN Circuit
Figure 63. Equivalent DITHER, LVDS, and LVDS_RS Input Circuit
DRVDD
26kΩ
350Ω
OEB
Figure 62. Equivalent OEB Input Circuit
Rev. C | Page 24 of 44
Data Sheet
AD9255
THEORY OF OPERATION
A small resistor in series with each input can help reduce the
With the AD9255, the user can sample any fS/2 frequency
segment from dc to 200 MHz, using appropriate low-pass or
band-pass filtering at the ADC inputs with little loss in ADC
performance. Operation to 300 MHz analog input is permitted,
but occurs at the expense of increased ADC noise and distortion.
peak transient current required from the output stage of the
driving source. A shunt capacitor can be placed across the
inputs to provide dynamic charging currents. This passive
network creates a low-pass filter at the ADC input; therefore,
the precise values are dependent on the application.
Synchronization capability is provided to allow synchronized
timing between multiple devices.
In intermediate frequency (IF) undersampling applications, any
shunt capacitors should be reduced. In combination with the
driving source impedance, the shunt capacitors limit the input
bandwidth. Refer to AN-742 Application Note, Frequency
Domain Response of Switched-Capacitor ADCs; AN-827
Application Note, A Resonant Approach to Interfacing Amplifiers to
Switched-Capacitor ADCs; and the Analog Dialogue article,
“Transformer-Coupled Front-End for Wideband A/D Converters,”
for more information on this subject (see www.analog.com).
BIAS
Programming and control of the AD9255 are accomplished
using a 3-wire SPI-compatible serial interface.
ADC ARCHITECTURE
The AD9255 architecture consists of a front-end sample-and-
hold input network, followed by a pipelined, switched-capacitor
ADC. The quantized outputs from each stage are combined into
a final 14-bit result in the digital correction logic. The pipelined
architecture permits the first stage to operate on a new input
sample and the remaining stages to operate on the preceding
samples. Sampling occurs on the rising edge of the clock.
S
S
C
C
FB
S
VIN+
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC connected to a switched-capacitor digital-
to-analog converter (DAC) and an interstage residue amplifier.
The residue amplifier magnifies the difference between the
reconstructed DAC output and the flash input for the next stage
in the pipeline. One bit of redundancy is used in each stage to
facilitate digital correction of flash errors. The last stage simply
consists of a flash ADC.
C
C
PAR1
PAR2
H
S
S
S
C
S
VIN–
C
FB
C
C
PAR1
PAR2
S
BIAS
Figure 64. Switched-Capacitor Input
The input stage can be ac- or dc-coupled in differential or
single-ended modes. The output staging block aligns the data,
corrects errors, and passes the data to the output buffers. The
output buffers are powered from a separate supply, allowing
adjustment of the output voltage swing. During power-down,
the output buffers go into a high impedance state.
For best dynamic performance, the source impedances driving
VIN+ and VIN− should be matched, and the inputs should be
differentially balanced.
An internal differential reference buffer creates positive and
negative reference voltages that define the input span of the ADC
core. The span of the ADC core is set by this buffer to 2 × VREF.
ANALOG INPUT CONSIDERATIONS
Input Common Mode
The analog input to the AD9255 is a differential switched-
capacitor network that has been designed for optimum
performance while processing a differential input signal.
The analog inputs of the AD9255 are not internally dc biased.
In ac-coupled applications, the user must provide this bias
externally. Setting the device so that VCM = 0.5 × AVDD is
recommended for optimum performance, but the device
functions over a wider range with reasonable performance (see
Figure 52). An on-board common-mode voltage reference is
included in the design and is available from the VCM pin.
Optimum performance is achieved when the common-mode
voltage of the analog input is set by the VCM pin voltage
(typically 0.5 × AVDD). The VCM pin must be decoupled to
ground by a 0.1 µF capacitor, as described in the Applications
Information section.
The clock signal alternatively switches between sample mode
and hold mode (see Figure 64). When the input is switched into
sample mode, the signal source must be capable of charging the
sample capacitors and settling within 1/2 of a clock cycle.
Rev. C | Page 25 of 44
AD9255
Data Sheet
Static Linearity
Dither
The AD9255 has an optional dither mode that can be selected
either using the DITHER pin or using the SPI bus. Dithering is
the act of injecting a known but random amount of white noise,
commonly referred to as dither, into the input of the ADC.
Dithering has the effect of improving the local linearity at
various points along the ADC transfer function. Dithering can
significantly improve the SFDR when quantizing small signal
inputs, typically when the input level is below −6 dBFS.
Dithering also removes sharp local discontinuities in the INL
transfer function of the ADC and reduces the overall peak-to-
peak INL.
In receiver applications, utilizing dither helps to reduce DNL errors
that cause small signal gain errors. Often, this issue is overcome
by setting the input noise at 5 dB to 10 dB above the converter
noise. By utilizing dither within the converter to correct the
DNL errors, the input noise requirement can be reduced.
As shown in Figure 65, the dither that is added to the input of
the ADC through the dither DAC is precisely subtracted out
digitally to minimize SNR degradation. When dithering is
enabled, the dither DAC is driven by a pseudorandom number
generator (PN gen). In the AD9255, the dither DAC is precisely
calibrated to result in only a very small degradation in SNR and
SINAD. The typical SNR and SINAD degradation values, with
dithering enabled, are only 1 dB and 0.8 dB, respectively.
Differential Input Configurations
Optimum performance is achieved while driving the AD9255 in a
differential input configuration. For baseband applications, the
AD8138, ADA4937-2, and ADA4938-2 differential drivers provide
excellent performance and a flexible interface to the ADC.
The output common-mode voltage of the ADA4938-2 is easily
set with the VCM pin of the AD9255 (see Figure 66), and the
driver can be configured in the filter topology shown to provide
band limiting of the input signal.
VIN
DOUT
ADC CORE
15pF
200Ω
33Ω
5pF
15Ω
15Ω
90Ω
VIN–
VIN+
DITHER
DAC
AVDD
ADC
VCM
76.8Ω
VIN
ADA4938-2
0.1µF
33Ω
PN GEN
DITHER ENABLE
120Ω
15pF
200Ω
Figure 65. Dither Block Diagram
Large Signal FFT
Figure 66. Differential Input Configuration Using the ADA4938-2
In most cases, dithering does not improve SFDR for large signal
inputs close to full scale, for example, with a −1 dBFS input. For
large signal inputs, the SFDR is typically limited by front-end
sampling distortion, which dithering cannot improve. However,
even for such large signal inputs, dithering may be useful for
certain applications because it makes the noise floor whiter.
As is common in pipeline ADCs, the AD9255 contains small
DNL errors caused by random component mismatches that
produce spurs or tones that make the noise floor somewhat
randomly colored part-to-part. Although these tones are typically
at very low levels and do not limit SFDR when the ADC is
quantizing large-signal inputs, dithering converts these tones to
noise and produces a whiter noise floor.
For baseband applications where SNR is a key parameter,
differential transformer coupling is the recommended input
configuration. An example is shown in Figure 67. To bias the
analog input, the VCM voltage can be connected to the center
tap of the secondary winding of the transformer.
C2
R2
VIN+
R1
2V p-p
49.9Ω
C1
R1
ADC
VCM
R2
VIN–
0.1µF
C2
Figure 67. Differential Transformer-Coupled Configuration
Small Signal FFT
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few megahertz (MHz). Excessive signal power can also
cause core saturation, which leads to distortion.
For small signal inputs, the front-end sampling circuit typically
contributes very little distortion, and, therefore, the SFDR is likely
to be limited by tones caused by DNL errors due to random com-
ponent mismatches. Therefore, for small signal inputs (typically,
those below −6 dBFS), dithering can significantly improve
SFDR by converting these DNL tones to white noise.
At input frequencies in the second Nyquist zone and above, the
noise performance of most amplifiers is not adequate to achieve
the true SNR performance of the AD9255. For applications in
Rev. C | Page 26 of 44
Data Sheet
AD9255
which SNR is a key parameter, differential double balun coupling
is the recommended input configuration (see Figure 68). In this
configuration, the input is ac-coupled and the CML is provided
to each input through a 33 Ω resistor. These resistors compensate
for losses in the input baluns to provide a 50 Ω impedance to
the driver.
Table 10. Example RC Network
Frequency
Range
(MHz)
R1 Series C1 Differential R2 Series C2 Shunt
(Ω Each) (pF)
(Ω Each)
(pF Each)
Open
10
0 to 100
100 to 300 10
15
18
10
15
10
An alternative to using a transformer-coupled input at frequencies
in the second Nyquist zone and higher is to use the ADL5562
differential driver. The ADL5562 provides three selectable gain
options up to 15.5 dB. An example circuit is shown in Figure 69;
additional filtering between the ADL5562 output and the AD9255
input may be required to reduce out-of-band noise. See the
ADL5562 data sheet for more information.
In the double balun and transformer configurations, the value of
the input capacitors and resistors is dependent on the input fre-
quency and source impedance and may need to be reduced or
removed. Table 10 displays recommended values to set the RC
network. However, these values are dependent on the input
signal and should be used only as a starting guide.
C2
0.1µF
0.1µF
0.1µF
R1
R2
R2
VIN+
VIN–
2V p-p
33Ω
33Ω
P
A
S
S
P
C1
R1
ADC
0.1µF
VCM
C2
Figure 68. Differential Double Balun Input Configuration
V
CC
10pF
0.1µF
0.1µF
5, 6, 7, 8
0Ω
2
1
0.1µF
0.1µF
ANALOG INPUT
ANALOG INPUT
20Ω
15Ω
15Ω
11
VIN+
100Ω
5pF
AD9255
ADL5562
10
100Ω
4
3
15Ω
15Ω
VCM
VIN–
20Ω
9
0Ω
0.1µF
0.1µF
10pF
0.1µF
Figure 69. Differential Input Configuration Using the ADL5562
Rev. C | Page 27 of 44
AD9255
Data Sheet
the reference amplifier in a noninverting mode with the VREF
output defined as follows:
VOLTAGE REFERENCE
A stable and accurate voltage reference is built into the AD9255.
The input range can be adjusted by varying the reference voltage
applied to the AD9255, using either the internal reference or an
externally applied reference voltage. The input span of the ADC
tracks reference voltage changes linearly. The various reference
modes are summarized in the sections that follow. The Reference
Decoupling section describes the best practices PCB layout of
the reference.
R2
R1
VREF = 0.5× 1+
The input range of the ADC always equals twice the voltage at
the reference pin for either an internal or an external reference.
VIN+
VIN–
Internal Reference Connection
ADC
CORE
A comparator within the AD9255 detects the potential at the
SENSE pin and configures the reference into four possible modes,
which are summarized in Table 11. If SENSE is grounded, the
reference amplifier switch is connected to the internal resistor
divider (see Figure 70), setting VREF to 1.0 V for a 2.0 V p-p full-
scale input. In this mode, with SENSE grounded, the full scale can
also be adjusted through the SPI port by adjusting Bit 6 and Bit 7 of
Register 0x18. These bits can be used to change the full scale to
1.25 V p-p, 1.5 V p-p, 1.75 V p-p, or to the default of 2.0 V p-p,
as shown in Table 17.
VREF
1.0µF
0.1µF
R2
SELECT
LOGIC
SENSE
0.5V
R1
ADC
Figure 71. Programmable Reference Configuration
Connecting the SENSE pin to the VREF pin switches the reference
amplifier output to the SENSE pin, completing the loop and
providing a 0.5 V reference output for a 1 V p-p full-scale input.
If the internal reference of the AD9255 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 72 shows
how the internal reference voltage is affected by loading.
VIN+
VIN–
0
ADC
CORE
–0.5
VREF = 0.5V
VREF
–1.0
1.0µF
0.1µF
SELECT
LOGIC
VREF = 1V
–1.5
SENSE
0.5V
ADC
–2.0
–2.5
–3.0
Figure 70. Internal Reference Configuration
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
If a resistor divider is connected external to the chip, as shown
in Figure 71, the switch again sets to the SENSE pin. This puts
LOAD CURRENT (mA)
Figure 72. VREF Accuracy vs. Load
Table 11. Reference Configuration Summary
Selected Mode
SENSE Voltage
Resulting VREF (V)
Resulting Differential Span (V p-p)
External Reference
AVDD
N/A
2 × external reference
Internal Fixed Reference
Programmable Reference
Internal Fixed Reference
VREF
0.5
1.0
R2
R1
(see Figure 71)
0.5× 1+
0.2 V to VREF
AGND to 0.2 V
2 × VREF
2.0
1.0
Rev. C | Page 28 of 44
Data Sheet
AD9255
External Reference Operation
Clock Input Options
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift charac-
teristics. Figure 73 shows the typical drift characteristics of the
internal reference in 1.0 V mode.
The AD9255 has a very flexible clock input structure. Clock input
can be a CMOS, LVDS, LVPECL, or sine wave signal. Regardless of
the type of signal being used, clock source jitter is of the most
concern, as described in the Jitter Considerations section.
2.0
Figure 75 and Figure 76 show two preferred methods for clocking
the AD9255. A low jitter clock source is converted from a single-
ended signal to a differential signal using either an RF
transformer or an RF balun.
1.5
VREF = 1.0V
1.0
0.5
0
The RF balun configuration is recommended for clock frequencies
at 625 MHz and the RF transformer is recommended for clock
frequencies from 10 MHz to 200 MHz. The back-to-back
Schottky diodes across the transformer/balun secondary limit
clock excursions into the AD9255 to approximately 0.8 V p-p
differential.
–0.5
–1.0
–1.5
–2.0
This limit helps prevent the large voltage swings of the clock
from feeding through to other portions of the AD9255 while
preserving the fast rise and fall times of the signal that are critical
to low jitter performance.
–40
–20
0
20
40
60
80
TEMPERATURE (°C)
Figure 73. Typical VREF Drift
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
6 kΩ load (see Figure 55). The internal buffer generates the
positive and negative full-scale references for the ADC core.
Therefore, the external reference must be limited to a maximum
of 1.0 V.
®
Mini-Circuits
ADC
ADT1-1WT, 1:1Z
AD9255
0.1µF
0.1µF
XFMR
CLOCK
INPUT
CLK+
CLK–
100Ω
50Ω
0.1µF
SCHOTTKY
DIODES:
HSMS2822
0.1µF
Figure 75. Transformer-Coupled Differential Clock (Up to 200 MHz)
CLOCK INPUT CONSIDERATIONS
For optimum performance, the AD9255 sample clock inputs,
CLK+ and CLK−, should be clocked with a differential signal.
The signal is typically ac-coupled into the CLK+ and CLK− pins
via a transformer or capacitors. These pins are biased internally
(see Figure 74) and require no external bias.
ADC
AD9255
1nF
50Ω
1nF
0.1µF
0.1µF
CLOCK
INPUT
CLK+
CLK–
AVDD
SCHOTTKY
DIODES:
HSMS2822
Figure 76. Balun-Coupled Differential Clock (625 MHz)
0.9V
If a low jitter clock source is not available, another option is to
ac couple a differential PECL signal to the sample clock input
pins, as shown in Figure 77. The AD9510/AD9511/AD9512/
AD9513/AD9514/AD9515/AD9516/AD9517/AD9518/AD9520/
AD9522 clock drivers offer excellent jitter performance.
CLK+
CLK–
4pF
4pF
Figure 74. Equivalent Clock Input Circuit
0.1µF
0.1µF
CLK+
CLOCK
INPUT
ADC
AD9255
AD95xx
PECL DRIVER
100Ω
0.1µF
0.1µF
CLOCK
CLK–
INPUT
240Ω
240Ω
50kΩ
50kΩ
Figure 77. Differential PECL Sample Clock (Up to Rated Sample Rate)
Rev. C | Page 29 of 44
AD9255
Data Sheet
0.1µF
0.1µF
CLOCK
INPUT
CLK+
ADC
AD9255
AD95xx
LVDS DRIVER
100Ω
0.1µF
0.1µF
CLOCK
INPUT
CLK–
50kΩ
50kΩ
Figure 78. Differential LVDS Sample Clock (Up to the Rated Sample Rate)
also be disabled in some cases when using the input clock
A third option is to ac couple a differential LVDS signal to the
sample clock input pins, as shown in Figure 78. The AD9510/
AD9511/AD9512/AD9513/AD9514/AD9515/AD9516/AD9517/
AD9518/AD9520/AD9522 clock drivers offer excellent jitter
performance.
divider circuit, see the Input Clock Divider section for addi-
tional information. In all other applications, enabling the DCS
circuit is recommended to maximize ac performance.
The DCS is enabled by setting the SDIO/DCS pin high when
operating in the external pin mode (see Table 12). If the SPI
mode is enabled, the DCS is enabled by default and can be
disabled by writing a 0x00 to Address 0x09.
In some applications, it may be acceptable to drive the sample
clock inputs with a single-ended CMOS signal. In such applica-
tions, drive the CLK+ pin directly from a CMOS gate, and bypass
the CLK− pin to ground with a 0.1 μF capacitor (see Figure 79).
Input Clock Divider
The AD9255 contains an input clock divider with the ability to
divide the input clock by integer values between 2 and 8. For
clock divide ratios of 2, 4, 6, or 8, the duty cycle stabilizer (DCS)
is not required because the output of the divider inherently pro-
duces a 50% duty cycle. Enabling the DCS with the clock divider in
these divide modes may cause a slight degradation in SNR so
disabling the DCS is recommended. For other divide ratios,
divide-by-3, divide-by-5, and divide-by-7 the duty cycle output
from the clock divider is related to the input clock’s duty cycle.
In these modes, if the input clock has a 50% duty cycle, the DCS
is again not required. However, if a 50% duty cycle input clock
is not available the DCS must be enabled for proper part
operation.
V
CC
OPTIONAL
100Ω
0.1µF
1
0.1µF
1kΩ
1kΩ
AD95xx
CMOS DRIVER
CLOCK
INPUT
CLK+
ADC
AD9255
50Ω
CLK–
0.1µF
1
50Ω RESISTOR IS OPTIONAL.
Figure 79. Single-Ended 1.8 V CMOS Input Clock (Up to 200 MHz)
Clock Duty Cycle
Typical high speed ADCs use both clock edges to generate
a variety of internal timing signals and, as a result, may be
sensitive to clock duty cycle. Commonly, a 5% tolerance is
required on the clock duty cycle to maintain dynamic
performance characteristics.
To synchronize the AD9255 clock divider, use an external sync
signal applied to the SYNC pin. Bit 1 and Bit 2 of Register 0x100
allow the clock divider to be resynchronized on every SYNC
signal or only on the first SYNC signal after the register is written.
A valid signal at the SYNC pin causes the clock divider to reset
to its initial state. This synchronization feature allows multiple
parts to have their clock dividers aligned to guarantee simulta-
neous input sampling. If the SYNC pin is not used, it should be
tied to AGND.
The AD9255 contains a duty cycle stabilizer (DCS) that retimes
the nonsampling (falling) edge, providing an internal clock
signal with a nominal 50% duty cycle. This allows the user to
provide a wide range of clock input duty cycles without affecting
the performance of the AD9255. Noise and distortion perform-
ance are nearly flat for a wide range of duty cycles with the DCS
enabled. Jitter in the rising edge of the input is still of paramount
concern and is not easily reduced by the internal stabilization
circuit.
Jitter Considerations
High speed, high resolution ADCs are sensitive to the quality
of the clock input. The degradation in SNR from the low fre-
quency SNR (SNRLF) at a given input frequency (fINPUT) due to
jitter (tJRMS) can be calculated by
The duty cycle control loop does not function for clock rates
less than 20 MHz nominally. The loop has a time constant
associated with it that must be considered in applications in
which the clock rate can change dynamically. A wait time of
1.5 µs to 5 µs is required after a dynamic clock frequency increase
or decrease before the DCS loop is relocked to the input signal.
During the time period that the loop is not locked, the DCS loop is
bypassed, and the internal device timing is dependent on the duty
cycle of the input clock signal. In such applications, it may be
appropriate to disable the duty cycle stabilizer. The DCS can
SNRHF = −10 log[(2π × fINPUT × tJRMS)2 + 10 (/SNR /10)
]
LF
In this equation, the rms aperture jitter represents the clock
input jitter specification. IF undersampling applications are
particularly sensitive to jitter, as illustrated in Figure 80.
Rev. C | Page 30 of 44
Data Sheet
AD9255
80
0.5
0.4
0.3
0.2
0.1
0
0.20
0.05ps
IAVDD
75
0.16
0.12
0.08
0.04
MEASURED
70
0.20ps
0.50ps
TOTAL
POWER
65
60
55
50
1.00ps
1.50ps
IDRVDD
0
125
1
10
100
1k
25
50
75
100
INPUT FREQUENCY (MHz)
CLOCK FREQUENCY (MSPS)
Figure 80. SNR vs. Input Frequency and Jitter
Figure 81. AD9255-125 Power and Current vs. Sample Rate
0.5
0.4
0.3
0.2
0.1
0
0.20
Treat the clock input as an analog signal in cases in which
aperture jitter may affect the dynamic range of the AD9255. To
avoid modulating the clock signal with digital noise, separate
power supplies for clock drivers from the ADC output driver
supplies. Low jitter, crystal controlled oscillators make the best
clock sources. If the clock is generated from another type of source
(by gating, dividing, or another method), the output clock should
be retimed by the original clock at the last step.
0.16
0.12
0.08
0.04
0
IAVDD
TOTAL
POWER
Refer to AN-501 Application Note, Aperture Uncertainty and ADC
System Performance, and AN-756 Application Note, Sampled
Systems and the Effects of Clock Phase Noise and Jitter (see
www.analog.com) for more information about jitter performance
as it relates to ADCs.
IDRVDD
65
25
35
45
55
75
85
95
105
CLOCK FREQUENCY (MSPS)
POWER DISSIPATION AND STANDBY MODE
Figure 82. AD9255-105 Power and Current vs. Sample Rate
As shown in Figure 81, the power dissipated by the AD9255 is
proportional to its sample rate. In CMOS output mode, the digital
power dissipation is determined primarily by the strength of the
digital drivers and the load on each output bit.
0.5
0.4
0.3
0.2
0.1
0
0.15
0.12
0.09
0.06
0.03
0
IAVDD
The maximum DRVDD current (IDRVDD) can be approximately
calculated as
TOTAL
POWER
IDRVDD = VDRVDD × CLOAD × fCLK × N
where N is the number of output bits (14 output bits plus
one DCO).
This maximum current occurs when every output bit switches on
every clock cycle, that is, a full-scale square wave at the Nyquist
frequency of fCLK/2. In practice, the DRVDD current is established
by the average number of output bits switching, which is deter-
mined by the sample rate and the characteristics of the analog
input signal.
IDRVDD
55
25
35
45
65
75
ENCODE FREQUENCY (MSPS)
Figure 83. AD9255-80 Power and Current vs. Sample Rate
By asserting PDWN (either through the SPI port or by asserting
the PDWN pin high), the AD9255 is placed in power-down
mode. In this state, the ADC typically dissipates 0.05 m W.
During power-down, the output drivers are placed in a high
impedance state; asserting the PDWN pin low returns the
AD9255 to its normal operating mode.
Reducing the capacitive load presented to the output drivers
can minimize digital power consumption. The data in Figure 81,
Figure 82, and Figure 83 was taken using a 70 MHz analog input
signal, with a 5 pF load on each output driver.
Rev. C | Page 31 of 44
AD9255
Data Sheet
Low power dissipation in power-down mode is achieved by
shutting down the reference, reference buffer, biasing networks,
and clock. Internal capacitors are discharged when entering power-
down mode and then must be recharged when returning to normal
operation.
Table 12. SCLK/DFS Mode Selection (External Pin Mode)
Voltage
at Pin
AGND
SVDD
SCLK/DFS
Offset binary (default) DCS disabled
Twos complement DCS enabled (default)
SDIO/DCS
Digital Output Enable Function (OEB)
When using the SPI port interface, the user can place the ADC
in power-down mode or standby mode. Standby mode allows
the user to keep the internal reference circuitry powered when
faster wake-up times are required. In addition, when using the SPI
mode, the user can change the function of the external PDWN pin
to either place the part in power-down or standby mode. See the
Memory Map Register Descriptions section for more details.
The AD9255 has a flexible three-state ability for the digital output
pins. The three-state mode is enabled using the OEB pin or
through the SPI interface. If the OEB pin is low, the output data
drivers and DCOs are enabled. If the OEB pin is high, the output
data drivers and DCOs are placed in a high impedance state. This
OEB function is not intended for rapid access to the data bus.
Note that OEB is referenced to the digital output driver supply
(DRVDD) and should not exceed that supply voltage.
DIGITAL OUTPUTS
The AD9255 output drivers can be configured to interface with
1.8 V CMOS logic families. The AD9255 can also be configured
for LVDS outputs using a DRVDD supply voltage of 1.8 V. The
AD9255 defaults to CMOS output mode but can be placed into
LVDS mode either by setting the LVDS pin high or by using the
SPI port to place the part into LVDS mode. Because most users do
not toggle between CMOS and LVDS mode during operation, use
of the LVDS pin is recommended to avoid any power-up loading
issues on the CMOS configured outputs.
When using the SPI interface, the data and DCO outputs can be
three-stated by using the output enable bar bit in Register 0x14.
TIMING
The AD9255 provides latched data with a pipeline delay of
12 clock cycles (12.5 clock cycles in LVDS mode). Data outputs
are available one propagation delay (tPD) after the rising edge of
the clock signal.
Minimize the length of the output data lines and loads placed
on them to reduce transients within the AD9255. These tran-
sients can degrade converter dynamic performance.
In CMOS output mode, the output drivers are sized to provide
sufficient output current to drive a wide variety of logic families.
However, large drive currents tend to cause current glitches on
the supplies, which may affect converter performance. Applications
requiring the ADC to drive large capacitive loads or large
fanouts may require external buffers or latches.
The lowest typical conversion rate of the AD9255 is 10 MSPS.
At clock rates below 10 MSPS, dynamic performance can degrade.
Data Clock Output (DCO)
In LVDS output mode, two output drive levels can be selected,
either ANSI LVDS or reduced swing LVDS mode. Using the
reduced swing LVDS mode lowers the DRVDD current and
reduces power consumption. The reduced swing LVDS mode
can be selected by asserting the LVDS_RS pin or by selecting
this mode via the SPI port.
The AD9255 provides a single data clock output (DCO) pin in
CMOS output mode and two differential data clock output (DCO)
pins in LVDS mode intended for capturing the data in an external
register. In CMOS output mode, the data outputs are valid on the
rising edge of DCO, unless the DCO clock polarity has been
changed via the SPI. In LVDS output mode, data is output as
double data rate with the odd numbered output bits transitioning
near the rising edge of DCO and the even numbered output bits
transitioning near the falling edge of DCO. See Figure 2 for a
graphical timing description.
The output data format is selected for either offset binary or
twos complement by setting the SCLK/DFS pin when operating in
the external pin mode (see Table 12).
As detailed in AN-877 Application Note, Interfacing to High
Speed ADCs via SPI, the data format can be selected for offset
binary, twos complement, or gray code when using the SPI control.
Table 13. Output Data Format
Input (V)
Condition (V)
< −VREF − 0.5 LSB
= −VREF
Offset Binary Output Mode
00 0000 0000 0000
00 0000 0000 0000
10 0000 0000 0000
11 1111 1111 1111
11 1111 1111 1111
Twos Complement Mode
10 0000 0000 0000
10 0000 0000 0000
00 0000 0000 0000
01 1111 1111 1111
01 1111 1111 1111
OR
1
0
0
0
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
= 0
= +VREF − 1.0 LSB
> +VREF − 0.5 LSB
1
Rev. C | Page 32 of 44
Data Sheet
AD9255
BUILT-IN SELF-TEST (BIST) AND OUTPUT TEST
The AD9255 includes built-in self-test features designed to
enable verification of the integrity of the part as well as facilitate
board level debugging. A built-in self-test (BIST) feature is included
that verifies the integrity of the digital datapath of the AD9255.
Various output test options are also provided to place predictable
values on the outputs of the AD9255.
continued from its last value or reset from the beginning, based
on the value programmed in Register 0x0E, Bit 2. The BIST
signature result varies based on the part configuration.
OUTPUT TEST MODES
The output test options are shown in Table 17. When an output
test mode is enabled, the analog section of the ADC is discon-
nected from the digital back end blocks and the test pattern is run
through the output formatting block. Some of the test patterns are
subject to output formatting, and some are not. The seed value for
the PN sequence tests can be forced if the PN reset bits are used
to hold the generator in reset mode by setting Bit 4 or Bit 5 of
Register 0x0D. These tests can be performed with or without
an analog signal (if present, the analog signal is ignored), but
they do require an encode clock. For more information, see
AN-877 Application Note, Interfacing to High Speed ADCs via SPI.
BUILT-IN SELF-TEST (BIST)
The BIST is a thorough test of the digital portion of the selected
AD9255 signal path. When enabled, the test runs from an internal
pseudorandom noise (PN) source through the digital datapath
starting at the ADC block output. The BIST sequence runs for
512 cycles and stops. The BIST signature value is placed in
Register 0x24 and Register 0x25.
The outputs are not disconnected during this test, so the PN
sequence can be observed as it runs. The PN sequence can be
Rev. C | Page 33 of 44
AD9255
Data Sheet
SERIAL PORT INTERFACE (SPI)
The AD9255 serial port interface (SPI) allows the user to configure
the converter for specific functions or operations through a
structured register space provided inside the ADC. The SPI
gives the user added flexibility and customization, depending on
the application. Addresses are accessed via the serial port and
can be written to, or read from, via the port. Memory is organized
into bytes that can be further divided into fields, which are docu-
mented in the Memory Map section. For detailed operational
information, see AN-877Application Note, Interfacing to High
Speed ADCs via SPI.
All data is composed of 8-bit words. The first bit of the first byte in
a multibyte serial data transfer frame indicates whether a read
command or a write command is issued. This allows the serial
data input/output (SDIO) pin to change direction from an input
to an output.
In addition to word length, the instruction phase determines
whether the serial frame is a read or write operation, allowing
the serial port to be used both to program the chip and to read
the contents of the on-chip memory. If the instruction is a readback
operation, performing a readback causes the serial data input/
output (SDIO) pin to change direction from an input to an output
at the appropriate point in the serial frame.
CONFIGURATION USING THE SPI
Three pins define the SPI of this ADC: the SCLK/DFS pin, the
SDIO/DCS pin, and the CSB pin (see Table 14). The SCLK/DFS
(a serial clock) is used to synchronize the read and write data
presented from and to the ADC. The SDIO/DCS (serial data
input/output) is a dual-purpose pin that allows data to be sent
and read from the internal ADC memory map registers. The
CSB (chip select bar) is an active low control that enables or
disables the read and write cycles.
Data can be sent in MSB-first mode or in LSB-first mode. MSB
first is the default on power-up and can be changed via the SPI
port configuration register. For more information about this
and other features, see AN-877 Application Note, Interfacing to
High Speed ADCs via SPI.
HARDWARE INTERFACE
The pins described in Table 14 comprise the physical interface
between the user programming device and the serial port of the
AD9255. When using the SPI interface, the SCLK pin and the
CSB pin function as inputs. The SDIO pin is bidirectional, func-
tioning as an input during write phases and as an output during
readback.
Table 14. Serial Port Interface Pins
Pin Mnemonic Function
SCLK/DFS
Serial clock. The SCLK function of the pin is for
the serial shift clock input, which is used to
synchronize serial interface reads and writes.
SDIO is the serial data input/output function
of the pin. A dual-purpose pin that typically
serves as an input or an output, depending on
the instruction being sent and the relative
position in the timing frame.
SDIO/DCS
The AD9255 has a separate supply pin for the SPI interface, SVDD.
The SVDD pin can be set at any level between 1.8 V and 3.3 V
to enable operation with a SPI bus at these voltages without
requiring level translation. If the SPI port is not used, SVDD
can be tied to the DRVDD voltage.
CSB
Chip select bar. An active low control that
gates the read and write cycles.
The SPI interface is flexible enough to be controlled by either
FPGAs or microcontrollers. One method for SPI configuration
is described in detail in AN-812 Application Note, Microcontroller-
Based Serial Port Interface (SPI) Boot Circuit.
The falling edge of the CSB, in conjunction with the rising edge
of the SCLK, determines the start of the framing. See Figure 84
and Table 5 for an example of the serial timing and its definitions.
Other modes involving the CSB are available. The CSB can be
held low indefinitely, which permanently enables the device;
this is called streaming. The CSB can stall high between bytes
to allow for additional external timing. When CSB is tied high
at power-up, SPI functions are placed in high impedance mode.
This mode turns on any SPI pin secondary functions. When
CSB is toggled low after power-up, the part remains in SPI
mode and does not revert back to pin mode.
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK signal, the CSB signal, and the SDIO signal are typically
asynchronous to the ADC clock, noise from these signals can
degrade converter performance. If the on-board SPI bus is used for
other devices, it may be necessary to provide buffers between
this bus and the AD9255 to prevent these signals from transi-
tioning at the converter inputs during critical sampling periods.
During an instruction phase, a 16-bit instruction is transmitted.
Data follows the instruction phase, and its length is determined
by the W0 and W1 bits.
Some pins serve a dual function when the SPI interface is not
being used. When the pins are tied to AVDD or ground during
device power-on, they are associated with a specific function.
The Digital Outputs section describes the alternate functions
that are supported on the AD9255.
Rev. C | Page 34 of 44
Data Sheet
AD9255
CONFIGURATION WITHOUT THE SPI
SPI ACCESSIBLE FEATURES
In applications that do not interface to the SPI control registers,
the SDIO/DCS pin and the SCLK/DFS pin serve as standalone
CMOS-compatible control pins. When the device is powered
up, it is assumed that the user intends to use the pins as static
control lines for the duty cycle stabilizer and output data format
feature control. In this mode, connect the CSB chip select to
AVDD, which disables the serial port interface.
Table 16 provides a brief description of the general features that
are accessible via the SPI. These features are described in detail
in AN-877 Application Note, Interfacing to High Speed ADCs via
SPI. The AD9255 part-specific features are described in detail
following Table 17, the external memory map register table.
Table 16. Features Accessible Using the SPI
Feature Name
Description
The OEB pin, the DITHER pin, the LVDS pin, the LVDS_RS
pin, and the PDWN pin are active control lines in both external
pin mode and SPI mode. The input from these pins or the SPI
register setting (the logical OR of the SPI bit and the pin function)
is used to determine the mode of operation for the part.
Mode
Allows the user to set either power-down mode
or standby mode
Allows the user to access the DCS, set the
clock divider, set the clock divider phase, and
enable the SYNC input
Clock
Offset
Allows the user to digitally adjust the
converter offset
Table 15. Mode Selection
External
Voltage
Test I/O
Allows the user to set test modes to have
known data on output bits
Pin
Configuration
SDIO/DCS
SVDD (default) Duty cycle stabilizer enabled
Output Mode
Output Phase
Output Delay
VREF
Allows the user to set the output mode
Allows the user to set the output clock polarity
Allows the user to vary the DCO delay
Allows the user to set the reference voltage
AGND
SVDD
Duty cycle stabilizer disabled
Twos complement enabled
SCLK/DFS
OEB
AGND (default) Offset binary enabled
DRVDD Outputs in high impedance
AGND (default) Outputs enabled
AVDD
Chip in power-down or
standby mode
PDWN
AGND (default) Normal operation
AGND (default) CMOS output mode
LVDS
AVDD
LVDS output mode
LVDS_RS
AGND (default) ANSI LVDS output levels
AVDD
Reduced swing LVDS
output levels
DITHER
AGND (default) Dither disabled
AVDD
Dither enabled
tHIGH
tDS
tCLK
tH
tS
tDH
tLOW
CSB
SCLK DON’T CARE
SDIO DON’T CARE
DON’T CARE
R/W
W1
W0
A12
A11
A10
A9
A8
A7
D5
D4
D3
D2
D1
D0
DON’T CARE
Figure 84. Serial Port Interface Timing Diagram
Rev. C | Page 35 of 44
AD9255
Data Sheet
MEMORY MAP
valid address location should be written with 0s. Writing to these
locations is required only when part of an address location is
open (for example, Address 0x18). If the entire address location
is open (for example, Address 0x13), this address location should
not be written.
READING THE MEMORY MAP REGISTER TABLE
Each row in the memory map register table has eight bit locations.
The memory map is roughly divided into four sections: the chip
configuration registers (Address 0x00 to Address 0x02); the
transfer register (Address 0xFF); the ADC functions registers,
including setup, control, and test (Address 0x08 to Address 0x30);
and the digital feature control registers (Address 0x100).
Default Values
After the AD9255 is reset, critical registers are loaded with
default values. The default values for the registers are given in
the memory map register table, Table 17.
The memory map register table (see Table 17) documents the
default hexadecimal value for each hexadecimal address shown.
The column with the heading, Bit 7 (MSB), is the start of the
default hexadecimal value given. For example, Address 0x18, the
VREF select register, has a hexadecimal default value of 0xC0. This
means that Bit 7 = 1, Bit 6 = 1, and the remaining bits are 0s. This
setting is the default reference selection setting. The default value
uses a 2.0 V p-p reference. For more information on this function
and others, see AN-877 Application Note, Interfacing to High Speed
ADCs via SPI. This document details the functions controlled by
Register 0x00 to Register 0x30. The remaining register, at
Register 0x100, is documented in the Memory Map Register
Descriptions section.
Logic Levels
An explanation of logic level terminology follows:
•
“Bit is set” is synonymous with “bit is set to Logic 1” or
“writing Logic 1 for the bit.”
•
“Clear a bit” is synonymous with “bit is set to Logic 0” or
“writing Logic 0 for the bit.”
Transfer Register Map
Address 0x08 to Address 0x18 are shadowed. Writes to these
addresses do not affect part operation until a transfer command
is issued by writing 0x01 to Address 0xFF, setting the transfer bit.
This allows these registers to be updated internally and simulta-
neously when the transfer bit is set. The internal update takes
place when the transfer bit is set, and the bit autoclears.
Open Locations
All address and bit locations that are not included in Table 17
are not currently supported for this device. Unused bits of a
Rev. C | Page 36 of 44
Data Sheet
AD9255
MEMORY MAP REGISTER TABLE
All address and bit locations that are not included in Table 17 are not currently supported for this device.
Table 17. Memory Map Registers
Default
Value
Bit 0 (LSB) (Hex)
Addr. Register
Default Notes/
Comments
(Hex)
Name
Bit 7 (MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Chip Configuration Registers
0x00
SPI port
configuration
0
LSB first
Soft reset
1
1
Soft reset LSB
first
0
0x18
The nibbles are
mirrored so
LSB-first mode
or MSB-first
mode registers
correctly,
regardless of
shift mode
0x01
0x02
Chip ID
8-Bit Chip ID[7:0], AD9255 = 0x65 (default)
0x65
Read only
Chip grade
Open
Open
Open
Open
Speed grade ID
01 = 125 MSPS
10 = 105 MSPS
11 = 80 MSPS
Open Open
Open
Open
Open
Speed grade ID
used to
differentiate
devices; read
only
Transfer Register
0xFF Transfer
Open
Open
Open Open
Transfer
0x00
0x80
Synchronously
transfers data
from the
master shift
register to the
slave
ADC Functions Registers
0x08
Power
modes
1
Open
External power- Open
down pin
Open Open
Internal
Determines
various generic
modes of chip
operation
power-down
mode
function
0 = power-
down
00 = normal
operation
1 = standby
01 = full power-
down
10 = standby
11 = normal
operation
0x09
0x0B
Global clock
Open
Open
Open
Open
Open
Open
Open
Open
Open Open
Open
Open
Duty
cycle
stabilizer
(default)
0x01
0x00
Clock divide
(global)
Clock divide ratio
Clock divide
values other
than 000
automatically
cause the duty
stabilizer to
become active.
000 = divide by 1
001 = divide by 2
010 = divide by 3
011 = divide by 4
100 = divide by 5
101 = divide by 6
110 = divide by 7
111 = divide by 8
0x0D
Test mode
Open
Open
Reset PN23
generator
Reset PN9
generator
Open
Output test mode
000 = off (default)
001 = midscale short
010 = positive FS
011 = negative FS
0x00
When this
register is set,
the test data is
placed on the
output pins in
place of normal
data
100 = alternating checkerboard
101 = PN 23 sequence
110 = PN 9 sequence
111 = one/zero word toggle
0x0E
BIST enable
Open
Open
Open
Open
Open Reset BIST Open
sequence
BIST
enable
0x04
Rev. C | Page 37 of 44
AD9255
Data Sheet
Default
Addr. Register
Value
Bit 0 (LSB) (Hex)
Default Notes/
Comments
(Hex)
Name
Bit 7 (MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
0x14
Output
mode
Drive
strength
Output
type
Open
Output
enable
bar
Open Output
invert
Output
format
0x00
Configures the
outputs and
the format of
the data
0 = ANSI
LVDS
0 =
CMOS
00 = offset
binary
1 = reduced 1 = LVDS
LVDS
01 = twos
complement
01 = gray code
11 = offset binary
0x16
Clock phase
control
Invert DCO
clock
Open
Open
Open
Open
Input clock divider phase adjust
000 = no delay
0x00
Allows
selection of
clock delays
into the input
clock divider
001 = 1 input clock cycle
010 = 2 input clock cycles
011 = 3 input clock cycles
100 = 4 input clock cycles
101 = 5 input clock cycles
110 = 6 input clock cycles
111 = 7 input clock cycles
DCO clock delay
0x17
DCO output
delay
Open
Open
Open
0x00
(delay = 2500 ps × register value/31)
00000 = 0 ps
00001 = 81 ps
00010 = 161 ps
…
11110 = 2419 ps
11111 = 2500 ps
0x18
VREF select
Reference voltage
selection
Open
Open
Open Open
Open
Open
0xC0
00 = 1.25 V p-p
01 = 1.5 V p-p
10 = 1.75 V p-p
11 = 2.0 V p-p (default)
0x24
0x25
BIST
signature LSB
BIST Signature[7:0]
BIST Signature[15:8]
0x00
0x00
Read only
Read only
BIST
signature
MSB
0x30
Dither
enable
Open
Open
Open
Dither
enable
Open Open
Open
Clock
Open
0x00
0x00
Digital Feature Control Register
0x100 Sync control Open
Open
Open
Open
Open Clock
divider
Master
divider sync
next sync
only
sync
enable
enable
Rev. C | Page 38 of 44
Data Sheet
AD9255
and to ignore the rest. The clock divider sync enable bit
(Address 0x100, Bit 1) resets after it syncs.
MEMORY MAP REGISTER DESCRIPTIONS
For additional information about functions controlled in
Register 0x00 to Register 0xFF, see AN-877 Application Note,
Interfacing to High Speed ADCs via SPI.
Bit 1—Clock Divider Sync Enable
Bit 1 gates the sync pulse to the clock divider. The sync signal is
enabled when Bit 1 is high and Bit 0 is high. This is continuous
sync mode.
Sync Control (Register 0x100)
Bits[7:3]—Reserved
Bit 0—Master Sync Enable
These bits are reserved.
Bit 0 must be high to enable any of the sync functions. If the
sync capability is not used, this bit should remain low to
conserve power.
Bit 2—Clock Divider Next Sync Only
If the master sync enable bit (Address 0x100, Bit 0) and the
clock divider sync enable bit (Address 0x100, Bit 1) are high, Bit 2
allows the clock divider to sync to the first sync pulse it receives
Rev. C | Page 39 of 44
AD9255
Data Sheet
APPLICATIONS INFORMATION
should have several vias to achieve the lowest possible resistive
thermal path for heat dissipation to flow through the bottom of
the PCB. Fill or plug these vias with nonconductive epoxy.
DESIGN GUIDELINES
Before starting design and layout of the AD9255 as a system, it
is recommended that the designer become familiar with these
guidelines, which discuss the special circuit connections and
layout requirements that are needed for certain pins.
To maximize the coverage and adhesion between the ADC and
the PCB, overlay a silkscreen to partition the continuous plane on
the PCB into several uniform sections. This provides several tie
points between the ADC and the PCB during the reflow process.
Using one continuous plane with no partitions guarantees only one
tie point between the ADC and the PCB. For detailed information
about packaging and PCB layout of chip scale packages, see the
AN-772 Application Note, A Design and Manufacturing Guide for
the Lead Frame Chip Scale Package (LFCSP), at www.analog.com.
Power and Ground Recommendations
When connecting power to the AD9255, it is recommended that
two separate 1.8 V supplies be used. Use one supply for analog
(AVDD); use a separate supply for the digital outputs (DRVDD).
Several different decoupling capacitors can be used to cover both
high and low frequencies. Locate these capacitors close to the
point of entry at the PCB level and close to the pins of the part,
with minimal trace length. The power supply for the SPI port,
SVDD, should not contain excessive noise and should also be
bypassed close to the part.
VCM
Decouple the VCM pin to ground with a 0.1 μF capacitor, as
shown in Figure 67.
RBIAS
A single PCB ground plane should be sufficient when using the
AD9255. With proper decoupling and smart partitioning of the
PCB analog, digital, and clock sections, optimum performance
is easily achieved.
The AD9255 requires that a 10 kΩ resistor be placed between
the RBIAS pin and ground. This resistor sets the master current
reference of the ADC core and should have at least a 1% tolerance.
Reference Decoupling
LVDS Operation
Decouple the VREF pin externally to ground with a low ESR,
1.0 μF capacitor in parallel with a low ESR, 0.1 μF ceramic
capacitor.
The AD9255 can be configured for CMOS or LVDS output mode
on power-up using the LVDS pin, Pin 44. If LVDS operation is
desired, connect Pin 44 to AVDD. LVDS operation can also be
enabled through the SPI port. If CMOS operation is desired,
connect Pin 44 to AGND.
SPI Port
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK, CSB, and SDIO signals are typically asynchronous to the
ADC clock, noise from these signals can degrade converter per-
formance. If the on-board SPI bus is used for other devices, it
may be necessary to provide buffers between this bus and the
AD9255 to keep these signals from transitioning at the converter
inputs during critical sampling periods.
Exposed Paddle Thermal Heat Slug Recommendations
It is mandatory that the exposed paddle on the underside of the
ADC be connected to the analog ground (AGND) to achieve
the best electrical and thermal performance. A continuous,
exposed (no solder mask) copper plane on the PCB should mate
to the AD9255 exposed paddle, Pin 0. The copper plane
Rev. C | Page 40 of 44
Data Sheet
AD9255
OUTLINE DIMENSIONS
7.10
7.00 SQ
6.90
0.30
0.23
0.18
0.60 MAX
0.60 MAX
PIN 1
37
48
INDICATOR
1
36
PIN 1
INDICATOR
0.50
REF
6.85
6.75 SQ
6.65
*
5.55
5.50 SQ
5.45
EXPOSED
PAD
25
12
24
13
0.50
0.40
0.30
0.22 MIN
TOP VIEW
BOTTOMVIEW
5.50 REF
0.80 MAX
0.65 TYP
12° MAX
1.00
0.85
0.80
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
0.05 MAX
0.02 NOM
COPLANARITY
SECTION OF THIS DATA SHEET.
SEATING
PLANE
0.08
0.20 REF
*
COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2
WITH EXCEPTION TO EXPOSED PAD DIMENSION
Figure 85. 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
7 mm × 7 mm Body, Very Thin Quad
(CP-48-8)
Dimensions shown in millimeters
ORDERING GUIDE
Model1
Temperature Range
Package Description
Package Option
AD9255BCPZ-125
AD9255BCPZRL7-125
AD9255BCPZ-105
AD9255BCPZRL7-105
AD9255BCPZ-80
AD9255BCPZRL7-80
AD9255-125EBZ
AD9255-105EBZ
AD9255-80EBZ
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
Evaluation Board
CP-48-8
CP-48-8
CP-48-8
CP-48-8
CP-48-8
CP-48-8
Evaluation Board
Evaluation Board
1 Z = RoHS Compliant Part.
Rev. C | Page 41 of 44
AD9255
NOTES
Data Sheet
Rev. C | Page 42 of 44
Data Sheet
NOTES
AD9255
Rev. C | Page 43 of 44
AD9255
NOTES
Data Sheet
©2009–2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08505-0-7/13(C)
Rev. C | Page 44 of 44
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