ADC14161CIMDC [TI]
IC,A/D CONVERTER,SINGLE,14-BIT,CMOS,DIE;
| 型号： | ADC14161CIMDC |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | IC,A/D CONVERTER,SINGLE,14-BIT,CMOS,DIE |
| 文件： | 总20页 (文件大小：474K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
July 2001
ADC14161
Low-Distortion, Self-Calibrating 14-Bit, 2.5 MSPS,
390 mW A/D Converter
General Description
The ADC14161 is a self-calibrating 14-bit, 2.5 Megasample
per second analog to digital converter. It operates on a single
+5V supply, consuming just 390mW (typical).
Features
n Single +5V Operation
n Auto-Calibration
n Power Down Mode
n TTL/CMOS Input/Output compatible
The ADC14161 provides an easy and affordable upgrade
from 12 bit converters. The ADC14161 may also be used to
replace many hybrid converters with a resultant saving of
space, power and cost.
Key Specifications
n Resolution
n Conversion Rate
n DNL
n SNR (fIN = 500 kHz)
n ENOB
n Supply Voltage
n Power Consumption
14 Bits
2.5 Msps (min)
0.3 LSB (typ)
80 dB (typ)
1
The ADC14161 operates with input frequencies up to ⁄
2
the
clock frequency. The calibration feature of the ADC14161
can be used to get more consistent and repeatable results
over the entire operating temperature range. On-command
self-calibration reduces many of the effects of
temperature-induced drift, resulting in more repeatable con-
versions.
12.8 Bits (typ)
±
+5V 5%
390mW (typ)
Tested and guaranteed dynamic performance specifications
provide the designer with known performance.
Applications
n Instrumentation
n PC-Based Data Acquisition
n Data Communications
n Blood Analyzers
The Power Down feature reduces power consumption to
less than 2mW.
The ADC14161 comes in a TQFP and is designed to operate
over the industrial temperature range of −40˚C to +85˚C.
n Sonar/Radar
Connection Diagram
10015401
© 2001 National Semiconductor Corporation
DS100154
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Ordering Information
Industrial
(−40˚C ≤ TA ≤ +85˚C)
ADC14161CIVT
Package
VEG52A 52 Pin Thin Quad Flat Pack
Evaluation Board
ADC14161EVAL
Block Diagram
10015402
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2
Pin Descriptions and Equivalent Circuits
Pin
No.
Symbol
Equivalent Circuit
Description
Analog I/O
Non-Inverting analog signal Input. With a 2.0V reference voltage and a 2.0V
common mode voltage, VCM, the input signal voltage range is from 1.0 volt
to 3.0 Volts.
1
VIN+
Inverting analog signal Input. With a 2.0V reference voltage and a 2.0V
common mode voltage, VCM, the input signal voltage range is from 1.0 Volt
to 3.0 Volts. The input signal should be balanced for best performance.
Positive reference input. This pin should be bypassed to AGND with a 0.1
µF monolithic capacitor. VREF+ minus VREF− IN should be a minimum of 1.8V
4
VIN
−
48
VREF+
IN
and a maximum of 2.2V. The full-scale input voltage is equal to VREF
minus VREF
+
IN
−
.
IN
Negative reference input. In most applications this pin should be connected
to AGND and the full reference voltage applied to VREF IN. If the
application requires that VREF be offset from AGND, this pin should be
+
−
IN
47
VREF−
IN
bypassed to AGND with a 0.1 µF monolithic capacitor. VREF
+
minus
IN
VREF− should be a minimum of 1.8V and a maximum of 2.2V. The full-scale
IN
input voltage is equal to VREF
+
minus VREF
−
.
IN
IN
Output of the high impedance positive reference buffer. With a 2.0V
reference input, and with a VCM of 2.0V, this pin will have a 3.0V output
voltage. This pin should be bypassed to AGND with a 0.1 µF monolithic
capacitor in parallel with a 10 µF capacitor.
50
49
VREF
+
−
OUT
The output of the negative reference buffer. With a 2.0V reference and a
VCM of 2.0V, this pin will have a 1.0V output voltage. This pin should be
bypassed to AGND with a 0.1 µF monolithic capacitor in parallel with a 10
µF capacitor.
REF OUT
Output of the reference mid-point, nominally equal to 0.4 VA (2.0V). This pin
should be bypassed to AGND with a 0.1 µF monolithic capacitor. This
52
VREF (MID)
voltage is derived from VCM
.
Input to the common mode buffer, nominally equal to 40% of the supply
voltage (2.0V). This pin should be bypassed to AGND with a 0.1 µF
monolithic capacitor. Best performance is obtained if this pin is driven with a
low impedance source of 2.0V.
51
VCM
Digital I/O
Digital clock input. The input voltage is captured tAD after the fall of the clock
signal. The range of frequencies for this input is 300 kHz to 2.5 MHz. The
clock frequency should not be changed or interrupted during conversion or
while reading data output.
10
Clock
3
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Pin Descriptions and Equivalent Circuits (Continued)
Pin
No.
Symbol
Equivalent Circuit
Description
CAL is a level-sensitive digital input that, when pulsed high for at least two
clock cycles, puts the ADC into the CALIBRATE mode. Calibration should
be performed upon ADC power-up (after asserting a reset) and each time
the temperature changes by more than 50˚C since the ADC14161 was last
calibrated. See Section 2.3 for more information.
11
CAL
RESET is a level-sensitive digital input that, when pulsed high for at least 2
CLOCK cycles, results in the resetting of the ADC. This reset pulse must be
applied after ADC power-up, before calibration.
40
18
44
RESET
RD
RD is the (READ) digital input that, when low, enables the output data
buffers. When this input pin is high, the output data bus is in a high
impedance state.
PD is the Power Down input that, when low, puts the converter into the
power down mode. When this pin is high, the converter is in the active
mode.
PD
EOC is a digital output that, when low, indicates the availability of new
conversion results at the data output pins.
17
EOC
Digital data outputs that make up the 14-bit TRI-STATE conversion results.
D00 is the LSB, while D13 is the MSB (SIGN bit) of the two’s complement
output word.
23-32
35-38
D00-13
Analog Power
Positive analog supply pins. These pins should be connected to a clean,
quiet +5V source and bypassed to AGND with 0.1 µF monolithic capacitors
in parallel with 10 µF capacitors, both located within 1 cm of these power
pins.
6, 7, 45
VA
The ground return for the analog supply. AGND and DGND should be
connected together directly beneath the ADC14161 package. See Section 5
(Layout and grounding) for more details).
5, 8, 46
AGND
Digital Power
Positive digital supply pin. This pin should be connected to the same clean,
quiet +5V source of as is VA and bypassed to DGND with a 0.1 µF
monolithic capacitor in parallel with a 10µF capacitor, both located within 1
cm of the power pin.
20
VD
12,13
14,19
The ground return for the digital supply. AGND and DGND should be
connected together directly beneath the ADC14161 package. See Section 5
(Layout and Grounding) for more details.
DGND
41,42
43
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Pin Descriptions and Equivalent Circuits (Continued)
Pin
No.
Symbol
Equivalent Circuit
Description
Positive digital supply pin for the ADC14161’s output drivers. This pin should
be connected to a +3V to +5V source and bypassed to DGND I/O with a 0.1
µF monolithic capacitor. If the supply for this pin is different from the supply
used for VA and VD, it should also be bypassed with a 10 µF capacitor. All
bypass capacitors should be located within 1 cm of the supply pin.
The ground return for the digital supply for the ADC14161’s output drivers.
This pin should be connected to the system digital ground, but not be
connected in close proximity to the ADC14161’s DGND or AGND pins. See
Section 5.0 (Layout and Grounding) for more details.
34
VD I/O
33
DGND I/O
NC
2, 3,
9,15,
16,21
22,39
All pins marked NC (no connect) should be left floating. Do not connect the
NC pins to ground, power supplies, or any other potential or signal. These
pins are used for test in the manufacturing process.
NC
5
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Absolute Maximum Ratings (Note 1)
Storage Temperature
−65˚C to +150˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Ratings(Notes 1, 2)
Operating Temperature
Range
−40˚C ≤ TA ≤ +85˚C
Supply Voltage (VA, VD, VD I/O)
Voltage on Any I/O Pin
6.5V
−0.3V to V+ +0.3V
VA, VD
+4.75V to +5.25V
2.7V to VD
±
±
Input Current at Any Pin (Note 3)
Package Input Current (Note 3)
Power Dissipation at TA = 25˚C
ESD Susceptibility (Note 5)
Human Body Model
25mA
50mA
V
D I/O
VREF − IN
REF− IN
1.0V to 3.0V
(Note 4)
V
AGND to 1.0V
−0.05V to VD + 0.05V
≤ 100 mV
Digital Inputs
|VA − VD|
1500V
200V
Machine Model
|AGND - DGND |
0V to 100 mV
Soldering Temp., Infrared, 10 sec. (Note 6)
300˚C
Converter Electrical Characteristics
The following specifications apply for AGND = DGND = DGND I/O = 0V, V+ = VA = VD = +5.0V, VD I/O = 3.0V or 5.0V,
@
PD = +5V, VREF+ IN = +2.0V, VREF− IN = AGND, fCLK = 2.5 MHz, CL = 50 pF/pin. After Auto-Cal Temperature. Boldface
limits apply for TA = TJ = TMIN to TMAX: all other limits TA = TJ = 25˚C(Notes 7, 8, 9)
Typical
Limits
Symbol
Parameter
Conditions
Units
(Note 10)
(Note 11)
Static Converter Characteristics
Resolution with No
14
Bits(min)
Missing Codes
±
±
±
±
±
INL
Integral Non Linearity
Differential Non Linearity
Full-Scale Error
0.75
2.5
1.0
2.8
0.6
LSB(max)
LSB(max)
% FS(max)
% FS(max)
±
DNL
0.3
0.4
±
Zero Error
+0.1
Reference and Analog Input Characteristics
VIN
Input Voltage Range (VIN+
− VIN−
1.8
V(min) V(max)
VREF = VREF
+
− VREF+
IN IN
2.0
)
2.2
(CLK LOW)
(CLK HIGH)
12
28
pF
pF
CIN
Input Capacitance
VIN = 1.0V + 0.7Vrms
Reference Voltage Range
1.8
2.2
V(min)
V(max)
VREF
[( VREF
+
IN) − (VREF
−IN)]
2.00
3.5
(Note 14)
Reference Input
Resistance
KΩ
Dynamic Converter Characteristics
BW
Full Power Bandwidth
Signal-to-Noise Ratio
Signal-to-Noise &
45
80
MHz
SNR
fIN = 500 kHz, VIN = 1.9VP-P
fIN = 500 kHz, VIN = 1.9VP-P
77
76
dB(min)
SINAD
79
dB(min)
Distortion
ENOB
THD
Effective Number of Bits
Total Harmonic Distortion
Spurious Free Dynamic
Range
fIN = 500 kHz, VIN = 1.9VP-P
fIN = 500 kHz, VIN = 1.9VP-P
12.8
−88
12.3
−80
Bits(min)
dB(min)
SFDR
IMD
fIN = 500 kHz, VIN = 1.9VP-P
90
dB
dB
Intermodulation Distortion
fIN1 = 95 kHz
fIN2 = 105 kHz
−97
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6
DC and Logic Electrical Characteristics
The following specifications apply for AGND = DGND = DGND I/O = 0V, V+ = VA = VD = +5.0V, VD I/O = 3.0V or 5.0V,
@
PD = +5V, VREF+ = +2.0V, VREF IN = AGND, fCLK = 2.5 MHz, RS = 25Ω, CL = 50 pF/pin. After Auto-Cal Temperature.
Boldface limits apply for TA = TJ = TMIN to TMAX: all other limits TA = TJ = 25˚C(Notes 7, 8, 9)
Typical
Limits
Symbol
Parameter
Conditions
Units
(Note 10)
(Note 11)
CLOCK, RD, PD Digital Input Characteristics
VIN(1)
VIN(0)
IIN(1)
IIN(0)
CIN
Logical ″1″ Input Voltage
Logical ″0″ Input Voltage
Logical ″1″ Input Current
Logical ″0″ Input Current
VIN Input Capacitance
V+ = 5.25V
V+ = 4.75V
VIN = 5.0V
VIN = 0V
2.0
0.8
V(min)
V(max)
µA
5
−5
5
µA
pF
CAL, RESET Digital Input Characteristics
VIN(1)
VIN(0)
IIN(1)
IIN(0)
CIN
Logical ″1″ Input Voltage
Logical ″0″ Input Voltage
Logical ″1″ Input Current
Logical ″0″ Input Current
Input Capacitance
V+ = 5.25V
V+ = 4.75V
VIN = 5.0V
VIN = 0V
3.5
1.0
V(min)
V(max)
µA
5
−5
5
µA
pF
D00 - D13 Digital Output Characteristics
Logical ″1″ Output
VOUT(1)
Voltage
VD I/O = 4.75V, IOUT = −360 µA
VD I/O = 2.7V, IOUT = −360 mA
4.5
2.5
V(min)
V(min)
Logical ″1″ Output
VOUT(1)
Voltage
VD I/O = 5.25V, IOUT = 1.6 mA
VD I/O = 3.3V, IOUT = 1.6 mA
VOUT = 3V or 5V
0.4
0.4
V(max)
V(max)
nA
Logical ″0″ Output
VOUT(0)
Voltage
100
TRI-STATE Output
IOZ
Current
VOUT = 0V
−100
nA
+ISC
−ISC
Output Short Circuit
Source Current
VOUT = 0V, VD I/O = 3V
VOUT = VD I/O = 3V
−10
12
mA
mA
Output Short Circuit Sink
Current
Power Supply Characteristics
IA
ID
Analog Supply Current
Digital Supply Current
Output Bus Supply
Current
PD = VD I/O
PD = VD I/O
70
7
85
8
mA(max)
mA(max)
ID I/O
PD = VD I/O
1
2
mA(max)
PD = VD I/O
390
475
mW(max)
mW
Total Power Consumption
<
PD = DGND
2
Power Supply Rejection
Ratio
250 mVPP 100kHz riding on VA
PSRR
54
dB
AC Electrical Characteristics
The following specifications apply for AGND = DGND = DGND I/O = 0V, V+ = VA = VD = +5.0V, VD I/O = 3.0V or 5.0V,
+
@
PD = +5V, VREF = +2.0V, VREF IN = AGND, fCLK = 2.5 MHz, RS = 25Ω, CL = 50 pF/pin. After Auto-Cal Temperature.
Boldface limits apply for TA = TJ = TMIN to TMAX: all other limits TA = TJ = 25˚C(Notes 7, 8, 9)
Typical
Limits
Units
(Limits)
kHz(min)
MHz(max
%(min)
Symbol
fCLK
Parameter
Conditions
(Note 10)
(Note 11)
Conversion Clock (CLOCK)
Frequency
300
3
2.5
45
55
13
9
Conversion Clock Duty Cycle
%(max)
Clock Cycles
ns
tCONV
tAD
Conversion Latency
Aperture Delay
7
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AC Electrical Characteristics (Continued)
The following specifications apply for AGND = DGND = DGND I/O = 0V, V+ = VA = VD = +5.0V, VD I/O = 3.0V or 5.0V,
+
@
PD = +5V, VREF = +2.0V, VREF IN = AGND, fCLK = 2.5 MHz, RS = 25Ω, CL = 50 pF/pin. After Auto-Cal Temperature.
Boldface limits apply for TA = TJ = TMIN to TMAX: all other limits TA = TJ = 25˚C(Notes 7, 8, 9)
Typical
Limits
Units
Symbol
Parameter
Conditions
(Note 10)
(Note 11)
(Limits)
Falling edge of CLK to Data
Valid
tOD
50
ns
Falling edge of CLK to falling
edge of EOC
90
130
38
ns(min)
ns(max)
ns(min)
ns(max)
tEOCL
1/(4fCLK
1/(8fCLK
23
)
)
Falling edge of CLOCK to Data
Valid
tDATA_VALID
tON
tOFF
tCAL
95
RD low to data valid on D00
-D13
33
33
ns(max)
RD high to D00 -D13 in
TRI-STATE
25
ns(max)
ms
Calibration Time
110
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: All voltages are measured with respect to GND = AGND = DGND I/O = 0V, unless otherwise specified.
<
>
V
A
Note 3: When the input voltage at any pin exceeds the power supplies (that is, V
AGND or V
or V ), the current at that pin should be limited to 25 mA.
D
IN
IN
The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 25 mA to two.
Note 4: The absolute maximum junction temperature (T max) for this device is 150˚C. The maximum allowable power dissipation is dictated by TJmax, the
J
junction-to-ambient thermal resistance (θ ), and the ambient temperature (T ), and can be calculated using the formula P MAX = (T max - T )/θ . In the 52-pin
JA
A
D
J
A
JA
TQFP, θ is 70˚C/W, so P MAX = 1,785 mW at 25˚C and 982 mW at the maximum operating ambient temperature of 85˚C. Note that the power dissipation of this
JA
D
device under normal operation will typically be about 410 mW (390 mW quiescent power + 20 mW due to 1 TTL load on each digital output. The values for maximum
power dissipation listed above will be reached only when the ADC14161 is operated in a severe fault condition (e.g. when input or output pins are driven beyond
the power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided.
Note 5: Human body model is 100 pF capacitor discharged through a 1.5kΩ resistor. Machine model is 220 pF discharged through ZERO Ω.
Note 6: See AN450, ″Surface Mounting Methods and Their Effect on Product Reliability″, or the section entitled ″Surface Mount″ found in any post 1986 National
Semiconductor Linear Data Book, for other methods of soldering surface mount devices.
Note 7: The inputs are protected as shown below. Input voltage magnitudes up to 5V above V or to 5V below GND will not damage this device, provided current
A
is limited per Note 3. However, errors in the A/D conversion can occur if the input goes above V or below GND by more than 100 mV. As an example, if V is 4.75
A
A
V , the full-cale input voltage must be ≤4.85V
DC
to ensure accurate conversions
DC
10015412
ESD Protection Scheme for Analog Input and Digital
Output pins
10015411
ESD Protection Scheme for Digital Input pins
+
Note 8: To guarantee accuracy, it is required that V and V be connected together and to the same power supply with separate bypass capacitors at each V pin.
A
D
Note 9: With the test condition for V
= (V
+ − V −) given as +2.0V, the 14-bit LSB is 122 µV.
REF
REF
REF
Note 10: Typical figures are at T = T = 25˚C, and represent most likely parametric norms.
A
J
Note 11: Tested limits are guaranteed to Nationsl’s AOQL (Average Outgoing Quality Level).
Note 12: Integral Non Linearity is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through positive full-scale and
negative full-scale.
Note 13: Timing specifications are tested at the TTL logic levels, V = 0.4V for a falling edge and V = 2.4V for a rising edge. TRI-STATE output voltage is forced
IL
IH
to 1.4V.
Note 14: Optimum SNR performance will be obtained by keeping the reference input in the 1.8V to 2.2V range. The LM4041CIM3-ADJ (SOT-23 package) or the
LM4041CIZ-ADJ (TO-92 package), bandgap voltage reference is recommended for this application.
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10015413
FIGURE 1. Transfer Characteristics
10015414
FIGURE 2. Simplified Error Curve vs. Output Code after Auto-Cal cycle
9
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Typical Performance Characteristics
INL vs Temperature
DNL vs Temperature
SNR vs Temperature
10015425
10015426
10015427
INL vs VREF and Temperature
DNL vs VREF and Temperature
THD vs Temperaure
10015428
10015435
10015434
SINAD & ENOB vs Temperature
SINAD & ENOB vs Clock Duty Cycle
SFDR vs Temperature and fIN
10015429
10015430
10015431
IMD
Spectral Response
10015432
10015433
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10
OUTPUT DELAY is the time delay after the falling edge of
the input clock before the data update is present at the
output pins.
Specification Definitions
APERTURE JITTER is the variation in aperture delay from
sample to sample. Aperture jitter shows up as input noise.
PIPELINE DELAY (LATENCY) is the number of clock cycles
between initiation of conversion and when that data is pre-
sented to the output stage. Data for any given sample is
available the Pipeline Delay plus the Output Delay after that
sample is taken. New data is available at every clock cycle,
but the data lags the conversion by the pipeline delay.
APERTURE DELAY is the time required after the falling
edge of the clock for the sampling switch to open. In other
words, for the Track/Hold circuit to go from ″track″ mode into
the ″hold″ mode. The Track/Hold circuit effectively stops
capturing the input signal and goes into the ″hold″ mode tAD
after the fall of the clock.
POWER SUPPLY REJECTION RATIO (PSRR) is a mea-
sure of how well an a.c. signal riding upon the power supply
is rejected at the output.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE
BITS) is another method of specifying Signal-to-Noise and
Distortion Ratio, or SINAD. ENOB is defined as (SINAD
−1.76) / 6.02.
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in
dB, of the rms value of the input signal to the rms value of the
sum of all other spectral components below one-half the
sampling frequency, not including harmonics or dc.
FULL SCALE ERROR is the difference between the input
voltage [(VIN+) − (VIN−)] just causing a transition to positive
SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SI-
NAD)) Is the ratio, expressed in dB, of the rms value of the
input signal to the rms value of all of the other spectral
components below half the clock frequency, including har-
monics but excluding dc.
full scale and VREF − 1.5 LSB, where VREF is ( VREF
(VREF IN).
+ IN) −
−
FULL POWER BANDWIDTH is a measure of the frequency
at which the reconstructed output fundamental drops 3 dB
below its low frequency value for a full scale input.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-
ence, expressed in dB, between the rms values of the input
signal and the peak spurious signal, where a spurious signal
is any signal present in the output spectrum that is not
present at the input.
INTERMODULATION DISTORTION (IMD) is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to the ADC input at the same time.
It is defined as the ratio of the power in the intermodulation
products to the total power in the original frequencies. IMD is
usually expressed in dB.
TOTAL HARMONIC DISTORTION (THD) is the ratio, ex-
pressed in dB or dBc, of the rms total of the first six harmonic
components, to the rms value of the input signal.
INTEGRAL NON-LINEARITY (INL) is a measure of the
ZERO ERROR is the difference between the ideal differen-
deviation of each individual code from a line drawn from
tial input voltage (1⁄
LSB) and the actual input voltage that
2
negative full scale (1⁄
LSB below the first code transition)
2
just causes a transition from an output code of 2047 to an
output code of 2048.
through positive full scale (the last code transition). The
deviation of any given code from this straight line is mea-
sured from the center of that code value.
MISSING CODES are those output codes that are skipped
and will never appear at the ADC outputs. These codes can
not be reached by any input value.
11
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Timing Diagrams
10015415
TIMING DIAGRAM 1. Output Timing
Minimum fCLK is 300 kHz
10015416
TIMING DIAGRAM 2. Reset and Calibration
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12
VREF
V
is the reference mid-point and is derived from
CM. This point is brought out only to be by passed. By pass
this pin with 0.1µF capacitor to ground. Do not load this pin.
(MID)
Functional Description
Operating on a single +5V supply, the ADC14161 uses a
pipelined architecture and has error correction circuitry and a
calibration mode to help ensure maximum performance at all
times.
It is very important that all grounds associated with the
reference voltage make connection to the analog ground
plane at a single point to minimize the effects of noise
currents in the gound path.
Balanced analog signals with a peak-to-peak voltage equal
to the input reference voltage, VREF, and centered around
the common mode input voltage, VCM, are digitized to 14 bits
(13 bits plus sign). Neglecting offsets, positive input signal
1.3 Signal Inputs
The signal inputs are VIN+ and VIN −. The signal input, VIN
,
is defined as
>
voltages (VIN+ − VIN
data and negative input signal voltages (VIN+ − VIN
−
0) produce positive digital output
<
−
0)
VIN = (VIN+) − (VIN −).
produce negative output data. The input signal can be digi-
tized at any clock rate between 300 Ksps and 2.5 Msps.
Figure 3 indicates the relationship between the input voltage
and the reference voltages. Figure 4 shows the expected
input signal range.
Input voltages below the negative full scale value will cause
the output word to take on the negative full scale value of
10,0000,0000,0000. Input voltage above the positive full
scale value will cause the output word to take on the positive
full scale value of 01,1111,1111,1111.
The output word rate is the same as the clock frequency. The
analog input voltage is acquired at the falling edge of the
clock and the digital data for that sample is delayed by the
pipeline for 13 clock cycles plus tDATA_VALID. The digital
output is undefined if the chip is being reset or is in the
calibration mode. The output signal may be inhibited by the
RD pin while the converter is in one of these modes.
The RD pin must be low to enable the digital outputs. A logic
low on the power down (PD) pin reduces the converter
power consumption to less than two milliwatts.
Applications Information
1.0 OPERATING CONDITIONS
10015417
We recommend that the following conditions be observed for
operation of the ADC14161:
FIGURE 3. Typical Input to Reference Relationaship.
4.75V ≤ VA ≤ 5.25V
5.25V ≤ VD ≤ 5.25V
3.0V ≤ VD I/O ≤ VD
0.3MHz ≤ fCLK ≤ 2.5 MHz
VCM = 2.0V (forced)
V
REF IN+ = 2.0V
REF IN−= AGND
V
1.1 The Analog Inputs
The ADC14161 has two analog signal inputs, VIN+ and VIN−.
These two pins form a balanced signal input. There are two
reference pins, VREF
+
and VREF− IN. These pins form a
IN
differential input reference.
1.2 Reference Inputs
VREF+ IN should always be more positive than VREF− IN. The
10015418
effective reference voltage, VREF, is the difference between
these two voltages:
FIGURE 4. Expected Input Signal Range.
VREF = (VREF
The operational voltage range of VREF
+3.0 Volts. The operational voltage range of VREF
ground to 1.0V. For best performance, the difference be-
tween VREF IN and VREF IN should remain within the range
+
IN) − (VREF
−
IN).
The ADC14161 performs best with a balanced input cen-
tered around VCM. The peak-to-peak voltage swing at either
IN+ or VIN− should be less than the reference voltage and
each signal input pin should be centered on the VCM voltage.
The two VCM-centered input signals should be exactly 180˚
out of phase from each other. As a simple check to ensure
this, be certain that the average voltage at the ADC iinput
pins is equal to VCM. Drive the analog inputs with a source
impedance less than 100 Ohms.
+
is +1.8 Volts to
IN
−
is
IN
V
+
−
of 1.8V to 2.2V. Reducing the reference voltage below 1.8V
will decrease the signal-to-noise ratio (SNR) of the
ADC14161. Increasing the reference voltage (and, conse-
quently, the input signal swing) above 2.2V will increase
THD.
13
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reference voltage is different from the desired VCM, that
desired VCM voltage may be derived from the reference or
from another stable source.
Applications Information (Continued)
The sign bit of the output word will be a logic low when VIN
+
is greater than VIN− . When VIN+ is less than VIN−, the sign
bit of the output word will be a logic high.
Note that the buffer used for this purpose should be a slow,
low noise amplifier. The LMC660, LMC662, LMC272 and
LMC7101 are good choices for driving the VCM pin of the
ADC14161.
For single ended operation, one of the analog inputs should
be connected to VCM. However, SNR and SINAD are re-
duced by about 12dB with a single ended input as compared
with differential inputs.
If it is desired to use a multiplexer at the analog input, that
multiplexer should be switched at the rising edge of the clock
signal.
An input voltage of VIN = (VIN+) − (VIN−) = 0 will be inter-
preted as mid-scale and will thus be converted to
00,0000,0000,0000, plus any offset error.
2.0 DIGITAL INPUTS
Digital Inputs consist of CLOCK, RESET, CAL, RD and PD.
All digital input pins should remain stable from the fall of the
clock until 30ns after the fall of the clock to minimize digital
noise corruption of the input signal on the die.
The VIN+ and the VIN− inputs of the ADC14161 consist of an
analog switch followed by a switched-capacitor amplifier.
The capacitance seen at the analog input pins changes with
the clock level, appearing as 12 pF when the clock is low,
and 28 pF when the clock is high. It is recommended that the
ADC14161 be driven with a low impedance source of 100
Ohms or less.
2.1 The CLOCK signal drives an internal phase delay loop to
create timing for the ADC. Drive the clock input with a stable,
low phase jitter clock signal in the range of 300 kHz to 2.5
MHz. The trace carrying the clock signal should be as short
as possible. This trace should not cross any other signal line,
analog or digital, not even at 90˚.
A simple application circuit is shown in Figure 6 and Figure 7.
Here we use two LM6172 dual amplifiers to provide a bal-
anced input to the ADC14161. Note that better noise perfor-
mance is achieved when VREF
well-bypassed resistive divider. The resulting offset and off-
set drift is minimal.
+
voltage is forced with a
IN
The CLOCK signal also drives the internal state machine. If
the clock is interrupted, the data within the pipeline could
become corrupted.
Since a dynamic capacitance is more difficult to drive than is
a fixed capacitance, choose driving amplifiers carefully. The
CLC427, CLC440, LM6152, LM6154, LM6172, LM6181 and
LM6182 are excellent amplifiers for driving the ADC14161.
A 100 Ohm damping resistor should be placed in series with
the CLOCK pin to prevent signal undershoot at that input.
2.2 The RESET input is level sensitive and must be pulsed
high for at least two clock cycles to reset the ADC after
power-up and before calibration (See Timing Diagram 2).
1.4 VCM Analog Inputs
The VCM input of the ADC14161 is internally biased to 40%
of the VA supply with on-chip resistors, as shown in Figure 5.
The VCM pin must be bypassed to prevent any power supply
noise from modulating this voltage. Modulation of the VCM
potential will result in the introduction of noise into the input
signal. The advantage of simply bypassing VCM (without
driving it) is the circuit simplicity. On the other hand, if the VA
supply can vary for any reason, VCM will also vary at a rate
and amplitude related to the RC filter created by the bypass
capacitor and the internal divider resistors. However, perfor-
mance of this approach will be adequate for many applica-
tions.
2.3 The CAL input is level sensitive and must be pulsed high
for at least two clock cycles to begin ADC calibration (See
Timing Diagram 2). Reset the ADC14161 before calibrating.
Re-calibrate after the temperature has changed by more
than 50˚C since the last calibration was performed and after
return from power down.
During calibration, use the same clock frequency that will be
used for conversions to avoid excessive offset errors.
Calibration takes 272,800 clock cycles. Irrelevant data may
appear at the data outputs during RESET or CAL and for 13
clock cycles thereafter. Calibration should not be started until
the reference outputs have settled (100mS with 1µF capaci-
tors on these outputs) after power up or coming out of the
power down mode.
2.4 RD pin is used to READ the conversion data. When the
RD pin is low, the output buffers go into the active state.
When the RD input is high, the output buffers are in the high
impedance state.
2.5 The PD pin, when low, holds the ADC14161 in a
power-down mode where power consumption is typically
less than 2mW to conserve power when the converter is not
being used. The ADC14161 will begin normal operation
within tWU after this pin is brought high, provided a valid
CLOCK input is present. Power dissipation during shut-down
is not affected by the clock frequency, or by whether there is
a clock signal present. The data in the pipeline is corrupted
while in the power down mode. The ADC14161 should be
reset and calibrated upon returning to normal operation after
a power down.
10015421
FIGURE 5. VCM input to the ADC14161 VCM is set to
40% of VA with on-chip resistors. Performance is
improved when VCM is driven with a stable, low
impedance source
By forcing VCM to a fixed potential, you can avoid the prob-
lems mentioned above. One such approach is to buffer the
2.0 Volt reference voltage to drive the VCM input, holding it at
a constant potential as shown in Figure 6 and Figure 8. If the
3.0 OUTPUTS
The ADC14161 has four analog outputs: VREF
VREF OUT, VREF (MID) and VCM .There are 15 digital outputs:
EOC (End of Conversion) and 14 Data Output pins.
+
,
OUT
−
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14
each output pin. Additionally, inserting series resistors of 47
or 56 Ohms at the digital outputs, close to the ADC pins, will
isolate the outputs from other circuitry and limit output cur-
rents. (See Figure 6).
Applications Information (Continued)
3.1 The reference output voltages are made available only
for the purpose of bypassing with capacitors. These pins
should not be loaded with more than 10 µA DC. These output
voltages are described as
4.0 POWER SUPPLY CONSIDERATIONS
1
Each power supply pin should be bypassed with a parallel
combination of a 10 µF capacitor and a 0.1 µF ceramic chip
VREF
VREF
+
−
= VCM + ⁄
2
VREF
VREF
OUT
OUT
1
= VCM − ⁄
2
capacitor. The chip capacitors should be within 1⁄
centimeter
2
where VREF = (VREF
+
IN) − (VREF+ IN)
+ VREF OUT) / 2.
of the power pins. Leadless chip capacitors are preferred
because they provide low lead inductance.
VREF (MID) = (VREF
+
−
OUT
While a single 5V source is used for the analog and digital
supplies of the ADC14161, these supply pins should be well
isolated from each other to prevent any digital noise from
being coupled to the analog power pins. Supply isolation
with ferrite beads is shown in Figure 6 and Figure 8.
To avoid signal clipping and distortion, VREF
+ OUT should not
exceed 3.3V, VREF should not be below 750 mV and
−
OUT
VCM should be held in the range of 1.8V to 2.2V.
3.2 The /EOC output goes low to indicate the presence of
valid data at the output data lines. Valid data is present the
entire time that this signal is low except during reset. Corrupt
or irrelevant data may appear at the data outputs when the
RESET pin or the CAL pin is high.
As is the case with all high-speed converters, the ADC14161
is sensitive to power supply noise. Accordingly, the noise on
the analog supply pin should be kept below 100 mVP-P
.
No pin should ever have a voltage on it that is in excess of
the supply voltages, not even at power up.
3.3 The Data Outputs are TTL/CMOS compatible. The out-
put data format is two’s complement. Valid data is present at
these outputs while the EOC pin is low. While the tEOCL time
and the tDATA_VALID time provide information about output
timing, a simple way to capture a valid output is to latch the
data on the rising edge of the CLOCK (pin 10).
The VD I/O provides power for the output drivers and may be
operated from a supply in the range of 3.0V to the VD supply
(nominal 5V). This can simplify interfacing to 3.0 Volt devices
and systems. Powering VD I/O from 3 Volts will also reduce
power consumption and noise generation due to output
switching. DO NOT operate the VD I/O at a voltage higher
than VD or VA.
Also helpful in minimizing noise due to output switching is to
minimize the load currents at the digital outputs. This can be
done by connecting buffers between the ADC outputs and
any other circuitry. Only one input should be connected to
10015419
FIGURE 6. Simple application circuit with single-ended to differential buffer.
15
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Applications Information (Continued)
10015420
FIGURE 7. Differential drive circuit of Figure 6. All 5k resistors are 0.1%. Tolerance of the other resistors is not
critical.
10015422
FIGURE 8. Driving the signal inputs with a transformer.
www.national.com
16
rest of the ground plane. A typical width is 3/16 inch (4 to 5
mm).This narrowing beneath the converter provides a fairly
high impedance to the high frequency components of the
digital switching currents, directing them away from the ana-
log pins. The relatively lower frequency analog ground cur-
rents see a relatively low impedance across this narrow
ground connection.
Applications Information (Continued)
5.0 LAYOUT AND GROUNDING
Proper grounding and proper routing of all signals are es-
sential to ensure accurate conversion. Separate analog and
digital ground planes that are connected beneath the
ADC14161 are required to achieve specified performance.
The analog and digital grounds may be in the same layer, but
Generally, analog and digital lines should cross each other at
90 degrees to avoid getting digital noise into the analog path.
To maximize accuracy in high speed, high resolution sys-
tems, however, avoid crossing analog and digital lines alto-
gether. It is important to keep any clock lines isolated from
ALL other lines, including other digital lines. Even the gen-
erally accepted 90 degree crossing should be avoided as
even a little coupling can cause problems at high frequen-
cies. This is because other lines can introduce phase noise
(jitter) into the clock line, which can lead to degradation of
SNR.
should be separated from each other and should never
1
overlap each other. Separation should be at least
where possible.
⁄8 inch,
The ground return for the digital supply (DGND I/O ) carries
the ground current for the output drivers. This output current
can exhibit high transients that could add noise to the con-
version process. To prevent this from happening, the DGND
I/O pin should NOT be connected in close proximity to any of
the ADC14161’s ground pins.
Capacitive coupling between the typically noisy digital
ground plane and the sensitive analog circuitry can lead to
poor performance that may seem impossible to isolate and
remedy. The solution is to keep the analog circuitry sepa-
rated from the digital circuitry and from the digital ground
plane.
Best performance at high frequencies and at high resolution
is obtained with a straight signal path. That is, the signal path
through all components should form a straight line wherever
possible.
Be especially careful with the layout of inductors. Mutual
inductance can change the characteristics of the circuit in
which they are used. Inductors should not be placed side by
side, even with just a small part of their bodies beside each
other.
Digital circuits create substantial supply and ground current
transients. The logic noise thus generated could have sig-
nificant impact upon system noise performance. The best
logic family to use in systems with A/D converters is one
which employs non-saturating transistor designs, or has low
noise characteristics, such as the 74LS, 74HC(T) and
74AC(T)Q families. The worst noise generators are logic
families that draw the largest supply current transients dur-
ing clock or signal edges, like the 74F and the 74AC(T)
families.
The analog input should be isolated from noisy signal traces
to avoid coupling of spurious signals into the input. Any
external component (e.g., a filter capacitor) connected be-
tween the converter’s input and ground should be connected
to a very clean point in the analog ground plane.
Figure 9 gives an example of a suitable layout. All analog
circuitry (input amplifiers, filters, reference components, etc.)
should be placed on or over the analog ground plane. All
digital circuitry and I/O lines should be placed over the digital
ground plane.
Since digital switching transients are composed largely of
high frequency components, total ground plane copper
weight will have little effect upon the logic-generated noise.
This is because of the skin effect. Total surface area is more
important than is total ground plane volume.
All ground connections should have a low inductance path to
ground.
An effective way to control ground noise is by connecting the
analog and digital ground planes together beneath the ADC
with a copper trace that is very narrow compared with the
17
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Applications Information (Continued)
10015423
FIGURE 9. Example at a suitable layout.
7.0 COMMON APPLICATION PITFALLS
6.0 DYNAMIC PERFORMANCE
The ADC14161 can achieve impressive dynamic perfor-
mance. To achieve the best dynamic performance with the
ADC14161, the clock source driving the CLK input must be
free of jitter. For best ac performance, isolate the ADC clock
from any digital circuitry with buffers, as with the clock tree
shown in Figure 10.
Driving the inputs (analog or digital) beyond the power
supply rails. For proper operation, all inputs should not go
more than 100 mV beyond the supply rails (more than 100
mV below the ground pins or 100 mV above the supply pins).
Exceeding these limits on even a transient basis may cause
faulty or erratic operation. It is not uncommon for high speed
digital circuits (e.g., 74F and 74AC devices) to exhibit under-
shoot that goes more than a volt below ground. A resistor of
about 50 to 100Ω in series with the offending digital input will
eliminate the problem.
As mentioned in section 5.0, it is good practice to keep the
ADC clock line as short as possible and to keep it well away
from any other signals. Other signals can introduce phase
noise (jitter) into the clock signal, which can lead to in-
creased distortion. Even lines with 90˚ crossings have ca-
pacitive coupling, so try to avoid even these 90˚ crossings of
the clock line.
Do not allow input voltages to exceed the supply voltage
during power up.
Be careful not to overdrive the inputs of the ADC14161 with
a device that is powered from supplies outside the range of
the ADC14161 supply. Such practice may lead to conversion
inaccuracies and even to device damage.
Attempting to drive a high capacitance digital data bus.
The more capacitance the output drivers must charge for
each conversion, the more instantaneous digital current
flows through VD I/O and DGND I/O. These large charging
current spikes can couple into the analog circuitry of the
ADC14161, degrading dynamic performance. Adequate by-
passing and maintaining separate analog and digital ground
planes will reduce this problem. The digital data outputs
should be buffered (with 74ACQ541, for example). Dynamic
performance can also be improved by adding series resis-
tors at each digital output, close to the ADC14161, which
reduces the energy coupled back into the converter output
pins by limiting the output current. A reasonable value for
these resistors is 47Ω.
10015424
FIGURE 10. Isolating the ADC clock from other
circuitry with a clock tree.
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18
1.8V ≤ VREF ≤ 2.2V
Applications Information (Continued)
with VREF
−
IN ≤ 1.0V. Operating outside of these limits could
Using an inadequate amplifier to drive the analog input.
As explained in Section 1.2, the capacitance seen at the
input alternates between 12 pF and 28 pF, depending upon
the phase of the clock. This dynamic loaad is more difficult to
drive than is a fixed capacitance.
lead to signal distortion.
Using a clock source with excessive jitter, using exces-
sively long clock signal trace, or having other signals
coupled to the clock signal trace. This will cause the
sampling interval to vary, causing excessive output noise
and a reduction in SNR performance.
If the amplifier exhibits overshoot, ringing, or any evidence of
instability, even at a very low level, it will degrade perfor-
mance. Amplifiers that have been used sucessfully to dirve
the analog inputs of the ADC14161 include the CLC427,
CLC440, LM6152, LM6154, LM6181 and the LM6182. A
small series reistor at each amplifier output and a capacitor
across the analog inputs (as shown in Figure 7) will often
improve performance.
Connecting pins marked ″NC″ to any potential. Some of
these pins are used for factory testing. They should all be left
floating. Connecting them to ground, power supply, or some
other voltage could result in a non-functional device.
Operating with the reference pins outside of the speci-
fied range. As mentioned in section 1.1, VREF should be in
the range of
19
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Physical Dimensions inches (millimeters)
unless otherwise noted
52-Lead Thin Quad Flat Pack
Ordering Information Package ADC14161CIVT
NS Package Number VEG52A
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
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Response Group
Tel: 65-2544466
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