LT1814 [Linear]
1.3GHz Low Noise, Low Distortion Differential ADC Driver for 140MHz IF; 1.3GHz的低噪声,低失真差分ADC驱动器为140MHz的IF型号: | LT1814 |
厂家: | Linear |
描述: | 1.3GHz Low Noise, Low Distortion Differential ADC Driver for 140MHz IF |
文件: | 总16页 (文件大小:221K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC6401-20
1.3GHz Low Noise, Low
Distortion Differential ADC
Driver for 140MHz IF
FEATURES
DESCRIPTION
The LTC®6401-20 is a high-speed differential amplifier
targeted at processing signals from DC to 140MHz. The
part has been specifically designed to drive 12-, 14- and
16-bitADCswithlownoiseandlowdistortion,butcanalso
be used as a general-purpose broadband gain block.
■
1.3GHz –3dB Bandwidth
■
Fixed Gain of 10V/V (20dB)
■
–93dBc IMD at 70MHz (Equivalent OIP = 50.5dBm)
3
3
■
■
■
■
■
■
■
■
■
–74dBc IMD at 140MHz (Equivalent OIP = 41dBm)
3
3
1nV/√Hz Internal Op Amp Noise
2.1nV/√Hz Total Input Noise
6.2dB Noise Figure
Differential Inputs and Outputs
200Ω Input Impedance
2.85V to 3.5V Supply Voltage
50mA Supply Current (150mW)
1V to 1.6V Output Common Mode Voltage,
Adjustable
DC- or AC-Coupled Operation
The LTC6401-20 is easy to use, with minimal support
circuitry required. The output common mode voltage is
set using an external pin, independent of the inputs, which
eliminates the need for transformers or AC-coupling ca-
pacitors in many applications. The gain is internally fixed
at 20dB (10V/V).
The LTC6401-20 saves space and power compared to
alternative solutions using IF gain blocks and transform-
ers. The LTC6401-20 is packaged in a compact 16-lead
3mm × 3mm QFN package and operates over the –40°C
to 85°C temperature range.
■
■
■
Max Differential Output Swing 4.4V
P-P
Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIONS
■
Differential ADC Driver
■
Differential Driver/Receiver
■
Single Ended to Differential Conversion
IF Sampling Receivers
■
■
SAW Filter Interfacing
TYPICAL APPLICATION
Single-Ended to Differential ADC Driver
Equivalent Output IP3 vs Frequency
70
(NOTE 7)
3.3V
1.25V
60
0.1μF + 1000pF
0.1μF
3.3V
50
+
V
0.1μF
0.1μF
V
OCM
40
10Ω
10Ω
V
V
DD
CM
+
–
INPUT
66.5Ω
+IN
+OUT
+OUTF
AIN
AIN
30
20
10
0
LTC6401-20
LTC2208
–OUTF
–OUT
–IN
ENABLE
–
V
29Ω
LTC2208 130Msps
16-Bit ADC
20dB GAIN
640120 TA01a
0
50
100
150
200
FREQUENCY (MHz)
640120 TA01b
640120f
1
LTC6401-20
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
+
–
Supply Voltage (V – V )..........................................3.6V
Input Current (Note 2).......................................... 10mA
Operating Temperature Range
16 15 14 13
+
–
V
1
2
3
4
12 V
(Note 3) ............................................... –40°C to 85°C
Specified Temperature Range
(Note 4) ............................................... –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
Maximum Junction Temperature........................... 150°C
V
11 ENABLE
+
OCM
+
17
V
V
V
10
9
–
–
V
5
6
7
8
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
= 150°C, θ = 68°C/W, θ = 4.2°C/W
T
JMAX
JA
JC
–
EXPOSED PAD (PIN 17) IS V , MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC6401CUD-20#PBF
LTC6401IUD-20#PBF
TAPE AND REEL
LTC6401CUD-20#TRPBF LCDB
LTC6401IUD-20#TRPBF LCDB
PART MARKING*
PACKAGE DESCRIPTION
16-Lead (3mm × 3mm) Plastic QFN
16-Lead (3mm × 3mm) Plastic QFN
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LTC6400 AND LTC6401 SELECTOR GUIDE Please check each datasheet for complete details.
PART NUMBER
GAIN
(dB)
GAIN
(V/V)
Z
IN
(DIFFERENTIAL)
I
CC
(mA)
(Ω)
LTC6400-20
LTC6401-20
20
20
10
10
200
200
90
50
In addition to the LTC6401 family of amplifiers, a lower distortion LTC6400 family is available. The LTC6400 is pin compatible to the LTC6401, and has the
same low noise performance. The low distortion of the LTC6400 comes at the expense of higher power consumption. Please refer to the separate LTC6400
data sheets for complete details. Other gain versions from 8dB to 26dB will follow.
640120f
2
LTC6401-20
DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN = –IN = VOCM = 1.25V, ENABLE = 0V, No RL unless
otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
20.6
170
UNITS
Input/Output Characteristic
●
●
●
●
G
G
Gain
V
V
=
=
100mV Differential
100mV Differential
19.4
20
1
dB
mdB/°C
mV
DIFF
IN
Gain Temperature Drift
Output Swing Low
TEMP
IN
V
V
V
Each Output, V
Each Output, V
=
=
400mV Differential
400mV Differential
90
SWINGMIN
SWINGMAX
OUTDIFFMAX
OUT
IN
IN
Output Swing High
2.3
2.44
4.4
V
Maximum Differential Output Swing
Output Current Drive
1dB Compressed
Single-Ended
Differential
V
P-P
●
●
●
I
10
–2
mA
mV
μV/°C
V
V
Input Offset Voltage
2
1
OS
TCV
Input Offset Voltage Drift
Input Common Mode Voltage Range, MIN
Input Common Mode Voltage Range, MAX
Input Resistance
Differential
1.4
OS
VRMIN
VRMAX
I
I
1.6
V
●
Ω
R
Differential
170
200
1
230
INDIFF
INDIFF
C
Input Capacitance
Differential, Includes Parasitic
Differential
pF
●
●
Ω
R
R
Output Resistance
18
85
25
32
OUTDIFF
OUTFDIFF
OUTFDIFF
Ω
Filtered Output Resistance
Filtered Output Capacitance
Common Mode Rejection Ratio
Differential
100
2.7
66
115
C
Differential, Includes Parasitic
Input Common Mode Voltage 1.1V to 1.4V
pF
●
CMRR
45
dB
Output Common Mode Voltage Control
G
Common Mode Gain
V
= 1V to 1.6V
1
V/V
CM
OCM
OCM
V
V
V
Output Common Mode Range, MIN
1
V
V
OCMMIN
●
1.1
Output Common Mode Range, MAX
1.6
1.5
V
V
OCMMAX
●
●
●
●
Common Mode Offset Voltage
V
= 1.1V to 1.5V
–15
15
15
mV
μV/°C
μA
OSCM
TCV
Common Mode Offset Voltage Drift
6
5
OSCM
IV
V
Input Current
OCM
OCM
ENABLE Pin
●
●
●
●
V
V
ENABLE Input Low Voltage
ENABLE Input High Voltage
ENABLE Input Low Current
ENABLE Input High Current
0.8
V
V
IL
2.4
IH
I
IL
I
IH
ENABLE = 0.8V
ENABLE = 2.4V
0.5
3
μA
μA
1.2
Power Supply
●
●
●
●
V
Operating Supply Range
Supply Current
2.85
38
3
50
1
3.5
62
3
V
mA
mA
dB
S
I
I
ENABLE = 0.8V
ENABLE = 2.4V
2.85V to 3.5V
S
Shutdown Supply Current
SHDN
PSRR
Power Supply Rejection Ratio
(Differential Outputs)
55
84
640120f
3
LTC6401-20
AC ELECTRICAL CHARACTERISTICS Specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN and –IN
floating, VOCM = 1.25V, ENABLE = 0V, No RL unless otherwise noted.
SYMBOL
–3dBBW
0.1dBBW
0.5dBBW
1/f
PARAMETER
CONDITIONS
MIN
TYP
1.25
130
250
12.5
4500
2
MAX
UNITS
GHz
MHz
MHz
kHz
V/μs
ns
–3dB Bandwidth
200mV
200mV
200mV
(Note 6)
(Note 6)
(Note 6)
P-P,OUT
P-P,OUT
P-P,OUT
Bandwidth for 0.1dB Flatness
Bandwidth for 0.5dB Flatness
1/f Noise Corner
SR
Slew Rate
Differential (Note 6)
2V (Note 6)
t
t
t
t
1% Settling Time
S1%
OVDR
ON
P-P,OUT
Output Overdrive Recovery Time
Turn-On Time
1.9V
(Note 6)
7
ns
P-P,OUT
+OUT, –OUT Within 10% of Final Values
Falls to 10% of Nominal
78
ns
Turn-Off Time
I
146
15
ns
OFF
CC
–3dBBW
Common Mode Small Signal –3dB
BW
0.1V at V , Measured Single-Ended at
OCM
MHz
CM
P-P
Output (Note 6)
10MHz Input Signal
HD /HD
Second/Third Order Harmonic
Distortion
2V
2V
2V
2V
2V
2V
2V
, R = 400Ω
–122/–92
–110/–103
–113/–102
–96
dBc
dBc
dBc
dBc
dBc
dBc
dBm
2,10M
3,10M
P-P,OUT
L
, No R
P-P,OUT
L
, No R
P-P,OUTFILT
L
IMD
Third-Order Intermodulation
(f1 = 9.5MHz f2 = 10.5MHz)
Composite, R = 400Ω
P-P,OUT L
3,10M
Composite, No R
–108
P-P,OUT
L
Composite, No R
–105
P-P,OUTFILT
L
OIP
Third-Order Output Intercept Point
(f1 = 9.5MHz f2 = 10.5MHz)
Composite, No R (Note 7)
58
3,10M
P-P,OUT
L
P
1dB Compression Point
Noise Figure
R = 375Ω (Notes 5, 7)
17.3
6.2
2.1
21
dBm
dB
1dB,10M
L
NF
R = 375Ω (Note 5)
L
10M
e
e
Input Referred Voltage Noise Density Includes Resistors (Short Inputs)
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
nV/√Hz
nV/√Hz
IN,10M
ON,10M
70MHz Input Signal
HD /HD
Second/Third Order Harmonic
Distortion
2V
2V
2V
2V
2V
2V
2V
, R = 400Ω
–91/–80
–95/–88
–95/–88
–88
dBc
dBc
dBc
dBc
dBc
dBc
dBm
2,70M
3,70M
P-P,OUT
L
, No R
P-P,OUT
L
, No R
P-P,OUTFILT
L
IMD
Third-Order Intermodulation
(f1 = 69.5MHz f2 = 70.5MHz)
Composite, R = 400Ω
P-P,OUT L
3,70M
Composite, No R
–93
P-P,OUT
L
Composite, No R
–92
P-P,OUTFILT
L
OIP
Third-Order Output Intercept Point
(f1 = 69.5MHz f2 = 70.5MHz)
Composite, No R (Note 7)
50.5
3,70M
P-P,OUT
L
P
1dB Compression Point
Noise Figure
R = 375Ω (Notes 5, 7)
17.3
6.1
2.1
21
dBm
dB
1dB,70M
L
NF
R = 375Ω (Note 5)
L
70M
e
e
Input Referred Voltage Noise Density Includes Resistors (Short Inputs)
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
nV/√Hz
nV/√Hz
IN,70M
ON,70M
140MHz Input Signal
HD /HD
Second/Third Order Harmonic
Distortion
2V
2V
2V
, R = 400Ω
–80/–57
–81/–60
–80/–65
dBc
dBc
dBc
2,140M
3,140M
P-P,OUT
L
, No R
P-P,OUT
L
, No R
P-P,OUTFILT
L
640120f
4
LTC6401-20
AC ELECTRICAL CHARACTERISTICS Specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN and –IN
floating, VOCM = 1.25V, ENABLE = 0V, No RL unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
–71
–74
–72
41
MAX
UNITS
dBc
IMD
Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)
2V
2V
2V
2V
Composite, R = 400Ω
3,140M
P-P,OUT L
Composite, No R
dBc
P-P,OUT
L
Composite, No R
dBc
P-P,OUTFILT
L
OIP
Third-Order Output Intercept Point
(f1 = 139.5MHz f2 = 140.5MHz)
Composite, No R (Note 7)
dBm
3,140M
P-P,OUT
L
P
1dB Compression Point
Noise Figure
R = 375Ω (Notes 5, 7)
18
6.4
2.1
22
dBm
dB
1dB,140M
L
NF
R = 375Ω (Note 5)
L
140M
e
e
Input Referred Voltage Noise Density Includes Resistors (Short Inputs)
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
nV/√Hz
nV/√Hz
dBc
IN,140M
ON,140M
IMD
Third-Order Intermodulation
(f1 = 130MHz f2 = 150MHz) Measure
at 170MHz
2V
P-P,OUT
Composite, R = 375Ω (Note 5)
–61
–69
3,130M/150M
L
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Input pins (+IN, –IN) are protected by steering diodes to either
supply. If the inputs go beyond either supply rail, the input current should
be limited to less than 10mA.
temperatures. The LTC6401I is guaranteed to meet specified performance
from –40°C to 85°C.
Note 5: Input and output baluns used. See Test Circuit A.
Note 6: Measured using Test Circuit B.
Note 7: Since the LTC6401-20 is a feedback amplifier with low output
impedance, a resistive load is not required when driving an AD converter.
Therefore, typical output power is very small. In order to compare the
LTC6401-20 with amplifiers that require 50Ω output load, the LTC6401-20
Note 3: The LTC6401C and LTC6401I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
output voltage swing driving a given R is converted to OIP and P as
L
3
1dB
Note 4: The LTC6401C is guaranteed to meet specified performance from
0°C to 70°C. It is designed, characterized and expected to meet specified
performance from –40°C to 85°C but is not tested or QA sampled at these
if it were driving a 50Ω load. Using this modified convention, 2V is by
P-P
definition equal to 10dBm, regardless of the actual R .
L
TYPICAL PERFORMANCE CHARACTERISTICS
S21 Phase and Group Delay vs
Frequency
Frequency Response
Gain 0.1dB Flatness
25
20
15
10
5
1.0
0.8
100
0
1.5
1.2
0.9
0.6
0.3
0
TEST CIRCUIT B
TEST CIRCUIT B
TEST CIRCUIT B
0.6
0.4
0.2
–100
–200
–300
–400
0
–0.2
–0.4
–0.6
–0.8
–1.0
PHASE
GROUP DELAY
0
10
100
1000
3000
10
100
1000
0
200
400
600
800
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (MHz)
640120 G03
640120 G01
640120 G02
640120f
5
LTC6401-20
TYPICAL PERFORMANCE CHARACTERISTICS
Input and Output Reflection and
Reverse Isolation vs Frequency
Input and Output Impedance vs
Frequency
PSRR and CMRR vs Frequency
0
–10
–20
–30
–40
–50
–60
–70
–80
250
225
200
175
150
125
100
75
100
80
100
90
80
70
60
50
40
30
20
10
0
TEST CIRCUIT B
Z
IN
60
PSRR
CMRR
S11
S22
40
Z
OUT
20
0
Z
IN
–20
–40
–60
–80
–100
PHASE
IMPEDANCE MAGNITUDE
S12
50
25
Z
OUT
0
10
100
1000
3000
1
10
100
1000
1
10
100
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (MHz)
640120 G04
640120 G05
640120 G06
Noise Figure and Input Referred
Noise Voltage vs Frequency
Small Signal Transient Response
Large Signal Transient Response
1.35
1.30
1.25
1.20
1.15
2.5
15
14
13
12
11
10
9
8
7
6
5
6
4
2
R
= 87.5Ω PER OUTPUT
R
= 87.5Ω PER OUTPUT
L
L
2.0
1.5
1.0
0.5
0
+OUT
+OUT
NOISE FIGURE
e
IN
4
3
2
1
–OUT
–OUT
0
0
1000
0
5
10
TIME (ns)
15
20
0
5
10
TIME (ns)
15
20
10
100
FREQUENCY (MHz)
640120 G08
640120 G09
640120 G07
1% Settling Time for 2V
Output Step
Overdrive Transient Response
2.5
2.0
1.5
1.0
0.5
0
5
4
R
= 87.5Ω PER OUTPUT
R = 87.5Ω PER OUTPUT
L
L
–OUT
3
2
1
0
–1
–2
–3
–4
–5
+OUT
50
0
100
TIME (ns)
150
200
0
1
2
3
4
5
6
TIME (ns)
640120 G10
640120 G11
640120f
6
LTC6401-20
TYPICAL PERFORMANCE CHARACTERISTICS
Harmonic Distortion (Unfiltered)
vs Frequency
Harmonic Distortion (Filtered) vs
Frequency
Third Order Intermodulation
Distortion vs Frequency
–40
–50
–40
–50
–40
–50
DIFFERENTIAL INPUT
DIFFERENTIAL INPUT
UNFILTERED NO R
L
V
= 2V
V
= 2V
L
UNFILTERED 200Ω R
L
OUT
P-P
OUT
P-P
NO R
FILTERED NO R
L
–60
–60
–60
–70
–70
–70
–80
–80
–80
–90
–90
–90
–100
–110
–120
–100
–110
–120
–100
–110
–120
HD2 NO R
L
HD2 200Ω R
L
HD3 NO R
L
HD3 200Ω R
DIFFERENTIAL INPUT
HD2
HD3
V
= 2V COMPOSITE
L
OUT
P-P
0
50
100
FREQUENCY (MHz)
150
200
0
50
100
150
200
0
50
100
150
200
FREQUENCY (MHz)
FREQUENCY (MHz)
640120 G12
640120 G13
640120 G14
Harmonic Distortion (Unfiltered)
vs Frequency
Harmonic Distortion (Filtered) vs
Frequency
Third Order Intermodulation
Distortion vs Frequency
–40
–50
–40
–50
–40
–50
UNFILTERED NO R
L
SINGLE-ENDED INPUT
SINGLE-ENDED INPUT
UNFILTERED 200Ω R
FILTERED NO R
L
V
= 2V
V
= 2V
L
L
OUT
P-P
OUT P-P
NO R
–60
–60
–60
–70
–70
–70
–80
–80
–80
–90
–90
–90
–100
–110
–120
–100
–110
–120
–100
–110
–120
HD2 NO R
L
HD2 200Ω R
L
SINGLE-ENDED INPUT
HD3 NO R
L
HD3 200Ω R
HD2
HD3
V
= 2V COMPOSITE
OUT
P-P
L
0
50
100
150
200
0
50
100
FREQUENCY (MHz)
150
200
0
50
100
150
200
FREQUENCY (MHz)
FREQUENCY (MHz)
640120 G17
640120 G15
640120 G16
Harmonic Distortion vs Output
Common Mode Voltage
(Unfiltered Outputs)
Equivalent Output 1dB
Compression Point vs Frequency
–40
–50
–60
–70
–80
–90
–100
20
19
18
17
16
15
DIFFERENTIAL INPUT
DIFFERENTIAL INPUT
V
R
= 2V at 100MHz
R
= 400Ω
OUT
L
P-P
L
= 400Ω
(NOTE 7)
HD3
HD2
1.0
1.1
1.2
1.3
1.4
1.5
50
80
110
140
170
200
OUTPUT COMMON MODE VOLTAGE (V)
FREQUENCY (MHz)
640020 G19
640120 G18
640120f
7
LTC6401-20
TYPICAL PERFORMANCE CHARACTERISTICS
Equivalent Output Third Order
Intercept vs Frequency
Turn-On Time
Turn-Off Time
70
60
50
40
30
20
10
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
70
60
50
40
30
20
10
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
70
60
50
40
30
20
10
0
UNFILTERED NO R
R
= 87.5Ω PER OUTPUT
R = 87.5Ω PER OUTPUT
L
L
L
UNFILTERED 200Ω R
L
FILTERED NO R
L
I
CC
ENABLE
–OUT
–OUT
+OUT
+OUT
ENABLE
I
CC
DIFFERENTIAL INPUT
V
= 2V COMPOSITE
OUT
P-P
(NOTE 7)
–0.5
–10
–0.5
–10
0
50
100
150
200
–100
0
100
200
TIME (ns)
300
400
500
–100
0
100
200
TIME (ns)
300
400
500
FREQUENCY (MHz)
640120 G20
640120 G21
640120 G22
640120f
8
LTC6401-20
PIN FUNCTIONS
V (Pins 1, 3, 10): Positive Power Supply (Normally tied
to 3V or 3.3V). All three pins must be tied to the same
voltage. Bypass each pin with 1000pF and 0.1μF capaci-
tors as close to the pins as possible.
+
–OUTF,+OUTF(Pins6,7):FilteredOutputs.Thesepinshave
50Ω series resistors and a 1.7pF shunt capacitance.
ENABLE (Pin 11): This pin is a logic input referenced to
–
V . If low, the part is enabled. If high, the part is disabled
V
(Pin 2): This pin sets the output common mode
and draws approximately 1mA supply current.
OCM
voltage. A 0.1μF external bypass capacitor is recom-
+IN (Pins 13, 14): Positive Input. Pins 13 and 14 are
internally shorted together.
mended.
–
V (Pins 4, 9, 12, 17): Negative Power Supply. All four
–IN (Pins 15, 16): Negative Input. Pins 15 and 16 are
internally shorted together.
pins must be connected to the same voltage/ground.
–OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins
have 12.5Ω series resistors.
–
Exposed Pad (Pin 17): V . The Exposed Pad must be con-
nected to the same voltage/ground as pins 4, 9, 12.
BLOCK DIAGRAM
–
+
–
V
ENABLE
V
V
12
11
10
9
BIAS CONTROL
R
F
R
R
OUT
G
+IN
13
+OUT
1000Ω
100Ω
12.5Ω
8
7
R
FILT
+OUTF
50Ω
+IN
–IN
IN+
IN–
OUT–
14
15
C
FILT
R
FILT
1.7pF
–OUTF
–OUT
50Ω
6
5
OUT+
R
R
G
100Ω
R
OUT
12.5Ω
F
–IN
16
1000Ω
2k
COMMON
MODE CONTROL
5.3pF
640120 BD
1
2
3
4
+
+
–
V
V
V
V
OCM
640120f
9
LTC6401-20
APPLICATIONS INFORMATION
Circuit Operation
thedifferentialinputsmayneedtobeterminatedtoalower
value impedance, e.g. 50Ω, in order to provide an imped-
ance match to the source. Several choices are available.
One approach is to use a differential shunt resistor (Figure
1).Anotherapproachistoemployawidebandtransformer
(Figure 2). Both methods provide a wideband match. The
termination resistor or the transformer must be placed
close to the input pins in order to minimize the reflection
due to input mismatch. Alternatively, one could apply a
narrowbandimpedancematchattheinputsoftheLTC6401-
20 for frequency selection and/or noise reduction.
The LTC6401-20 is a low noise and low distortion fully
differential op amp/ADC driver with:
• Operation from DC to 1.3GHz –3dB bandwidth
impedance
• Fixed gain of 10V/V (20dB)
• Differential input impedance 200Ω
• Differential output impedance 25Ω
• Differential impedance of output filter 100Ω
ReferringtoFigure3,LTC6401-20canbeeasilyconfigured
for single-ended input and differential output without a
balun. The signal is fed to one of the inputs through a
matching network while the other input is connected to
thesamematchingnetworkandasourceresistor.Because
the return ratios of the two feedback paths are equal, the
TheLTC6401-20iscomposedofafullydifferentialamplifier
with on chip feedback and output common mode voltage
controlcircuitry. Differentialgainandinputimpedanceare
set by 100Ω/1000Ω resistors in the feedback network.
Smalloutputresistorsof12.5Ωimprovethecircuitstability
over various load conditions. They also provide a possible
external filtering option, which is often desirable when the
load is an ADC.
LTC6401-20
1000Ω
25Ω
100Ω
12.5Ω
50Ω
13 +IN
+OUT
8
7
Filter resistors of 50Ω are available for additional filtering.
Lowpass/bandpassfiltersareeasilyimplementedwithjust
a couple of external components. Moreover, they offer
single-ended 50Ω matching in wideband applications and
no external resistor is needed.
IN+
IN–
OUT–
+OUTF
V
IN
14 +IN
+
66.5Ω
–
50Ω
1.7pF
15 –IN
–OUTF
6
5
OUT+
1000Ω
25Ω
100Ω
12.5Ω
The LTC6401-20 is very flexible in terms of I/O coupling.
It can be AC- or DC-coupled at the inputs, the outputs or
both. Due to the internal connection between input and
output, users are advised to keep input common mode
voltage between 1V and 1.6V for proper operation. If the
inputs are AC-coupled, the input common mode voltage
16 –IN
–OUT
640120 F01
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
LTC6401-20
1000Ω
25Ω
100Ω
12.5Ω
50Ω
is automatically biased close to V
and thus no external
OCM
13 +IN
+OUT
8
7
circuitry is needed for bias. The LTC6401-20 provides an
output common mode voltage set by V , which allows
1:4
• •
OCM
IN+
IN–
OUT–
+OUTF
V
IN
drivinganADCdirectlywithoutexternalcomponentssuch
as a transformer or AC coupling capacitors. The input
signal can be either single-ended or differential with only
minor differences in distortion performance.
14 +IN
15 –IN
+
–
50Ω
1.7pF
–OUTF
6
5
OUT+
1000Ω
25Ω
100Ω
12.5Ω
16 –IN
–OUT
640120 F02
Input Impedance and Matching
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a 1:4 Balun
The differential input impedance of the LTC6401-20 is
200Ω. If a 200Ω source impedance is unavailable, then
640120f
10
LTC6401-20
APPLICATIONS INFORMATION
R
LTC6401-20
S
input Smith Chart, based on which users can choose the
optimal source impedance for a given gain and noise
requirement.
0.1μF
1000Ω
50Ω
100Ω
12.5Ω
13 +IN
+OUT
8
7
V
IN
+
50Ω
–
R
T
IN+
IN–
OUT–
66.5Ω
+OUTF
14 +IN
15 –IN
0.1μF
50Ω
1.7pF
Output Match and Filter
–OUTF
6
5
OUT+
1000Ω
R
S
50Ω
The LTC6401-20 can drive an ADC directly without
external output impedance matching. Alternatively, the
differential output impedance of 25Ω can be matched to
higher value impedance, e.g. 50Ω, by series resistors or
an LC network.
0.1μF
100Ω
12.5Ω
16 –IN
–OUT
640120 F03
R
T
66.5Ω
Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance
The internal low pass filter outputs at +OUTF/–OUTF
have a –3dB bandwidth of 590MHz. External capacitor
can reduce the low pass filter bandwidth as shown in
Figure 5. A bandpass filter is easily implemented with
only a few components as shown in Figure 6. Three
39pF capacitors and a 16nH inductor create a bandpass
filter with 165MHz center frequency, –3dB frequencies at
138MHz and 200MHz.
two outputs have the same gain and thus symmetrical
swing. In general, the single-ended input impedance and
terminationresistorR aredeterminedbythecombination
T
of R , R and R . For example, when R is 50Ω, it is found
S
G
F
S
that the single-ended input impedance is 200Ω and R is
T
66.5Ω in order to match to a 50Ω source impedance.
The LTC6401-20 is unconditionally stable. However, the
overall differential gain is affected by both source imped-
ance and load impedance as shown in Figure 4:
LTC6401-20
1000Ω
100Ω
12.5Ω
50Ω
13 +IN
+OUT
8
7
8.2pF
FILTERED OUTPUT
IN+
IN–
OUT–
VOUT
RL
RS + 200 25+RL
2000
+OUTF
14 +IN
15 –IN
AV =
=
•
12pF
(87.5MHz)
50Ω
V
1.7pF
IN
–OUTF
6
5
OUT+
1000Ω
8.2pF
100Ω
12.5Ω
The noise performance of the LTC6401-20 also depends
uponthesourceimpedanceandtermination. Forexample,
an input 1:4 balun transformer in Figure 2 improves SNR
by adding 6dB of gain at the inputs. A trade-off between
gain and noise is obvious when constant noise figure
circle and constant gain circle are plotted within the same
16 –IN
–OUT
640120 F05
Figure 5. LTC6401-20 Internal Filter Topology Modified for Low
Filter Bandwidth (Three External Capacitors)
39pF
LTC6401-20
12.5Ω
LTC6401-20
1000Ω
100Ω
10Ω
4.99Ω
1000Ω
1/2 R
S
100Ω
12.5Ω
50Ω
1/2 R
L
13 +IN
+OUT
8
7
13 +IN
+OUT
8
7
50Ω
IN+
IN–
OUT–
+OUTF
IN+
IN–
OUT–
+OUTF
14 +IN
15 –IN
V
IN
16nH
LTC2208
14 +IN
15 –IN
V
+
OUT
1.7pF
39pF
50Ω
–
50Ω
1.7pF
OUT+
1000Ω
–OUTF
6
5
–OUTF
6
5
OUT+
1000Ω
100Ω
12.5Ω
10Ω
4.99Ω
1/2 R
S
100Ω
12.5Ω
1/2 R
L
16 –IN
–OUT
39pF
16 –IN
–OUT
640120 F06
640120 F04
Figure 4. Calculate Differential Gain
Figure 6. LTC6401-20 Application Circuit for Bandpass
Filtering (Three External Capacitors, One External Inductor)
640120f
11
LTC6401-20
APPLICATIONS INFORMATION
Output Common Mode Adjustment
1.25V
0.1μF
The LTC6401-20’s output common mode voltage is set
0.1μF
by the V
pin, which is a high impedance input. The
V
OCM
+OUT
+OUTF
OCM
10Ω
V
+
–
CM
IF IN
66.5Ω
+IN
AIN
output common mode voltage is capable of tracking V
OCM
control is
LTC6401-20
LTC2208
in a range from 1V to 1.6V. Bandwidth of V
–OUTF
–OUT
OCM
–IN
ENABLE
AIN
typically 15MHz, which is dominated by a low pass filter
connected to the V pin and is aimed to reduce com-
10Ω
29Ω
LTC2208 130Msps
16-Bit ADC
OCM
20dB GAIN
640120 F07
mon mode noise generation at the outputs. The internal
common mode feedback loop has a –3dB bandwidth
around 300MHz, allowing fast common mode rejection at
Figure 7. Single-Ended Input to LTC6401-20 and LTC2208
Test Circuits
the outputs of the LTC6401-20. The V
pin should be
OCM
tied to a DC bias voltage where a 0.1μF bypass capacitor
is recommended. When interfacing with A/D converters
Due to the fully-differential design of the LTC6401 and
its usefulness in applications with differing characteristic
specifications, two test circuits are used to generate the
information in this datasheet. Test Circuit A is DC987B,
a two-port demonstration circuit for the LTC6401 family.
The schematic and silkscreen are shown below. This
circuit includes input and output transformers (baluns)
for single-ended-to-differential conversion and imped-
ance transformation, allowing direct hook-up to a 2-port
network analyzer. There are also series resistors at the
output to present the LTC6401 with a 375Ω differential
load, optimizing distortion performance. Due to the input
and output transformers, the –3dB bandwidth is reduced
from 1.3GHz to approximately 1.1GHz.
such as the LT22xx families, the V
can be normally
OCM
connected to the V pin of the ADC.
CM
Driving A/D Converters
The LTC6401-20 has been specifically designed to inter-
face directly with high speed A/D converters. In Figure 7,
an example schematic shows the LTC6401-20 with a
single-ended input driving the LTC2208, which is a 16-bit,
130Msps ADC. Two external 10Ω resistors help eliminate
potential resonance associated with stray capacitance of
PCB traces and bond wire inductance of either the ADC
input or the driver output. V
of the LTC6401-20 is
OCM
connected to V of the LTC2208 at 1.25V. Alternatively,
CM
Test Circuit B uses a 4-port network analyzer to measure
S-parameters and gain/phase response. This removes the
effects of the wideband baluns and associated circuitry,
for a true picture of the >1GHz S-parameters and AC
characteristics.
asingle-endedinputsignalcanbeconvertedtodifferential
signal via a balun and fed to the input of the LTC6401-20.
The balun also converts input impedance to match 50Ω
source impedance.
640120f
12
LTC6401-20
APPLICATIONS INFORMATION
Top Silkscreen
640120f
13
LTC6401-20
TYPICAL APPLICATION
Demo Circuit 987B Schematic (Test Circuit A)
V
CC
ENABLE
DIS
1
3
V
CC
2
JP1
C17
1000pF
C18
0.1μF
R16
0Ω
12
–
11
10
+
9
–
V
ENABLE
V
V
R10
R2
(1)
R14
(1)
86.6Ω
13
14
15
16
8
7
6
5
+IN
+IN
–IN
+OUT
+OUTF
–OUTF
–OUT
R6
0Ω
R12
0Ω
T2
TCM 4-19
1:4
R8
(1)
C2
0.1μF
C4
R4
(2)
T1
(2)
5
4
1
2
3
3
2
1
4
J1
+IN
J4
+OUT
0.1μF
C21
0.1μF
R24
(1)
SL1
(2)
SL2
(2)
R7
(1)
LTC6401-20
R5
(1)
R11
(1)
SL3
(2)
J5
–OUT
0dB
5
J2
–IN
R3
(2)
C1
0.1μF
C3
0.1μF
R9
86.6Ω
–IN
V
R13
0Ω
C22
R1
0Ω
+
+
–
V
OCM
V
V
0.1μF
1
2
3
4
V
CC
V
CC
C10
0.1μF
C9
1000pF
C12
1000pF
C13
0.1μF
V
CC
R19
1.5k
TP5
V
OCM
R20
1k
C7
0.1μF
T3
TCM 4-19
1:4
T4
TCM 4-19
1:4
R17
R18
0Ω
0Ω
5
4
1
2
3
3
2
1
4
J6
TEST IN
J7
C23
C5
C19
0.1μF
C20
0.1μF
TEST OUT
0.1μF
0.1μF
R21
(1)
R22
(1)
R25
0Ω
R26
0Ω
C24
0.1μF
C6
0.1μF
5
V
CC
TP2
V
CC
NOTE: UNLESS OTHERWISE SPECIFIED.
(1) DO NOT STUFF.
C14
4.7μF
C15
1μF
2.85V TO 3.5V
(2) VERSION
-G
SL = SIGNAL LEVEL
IC
R3
R4
T1
SL1
SL2
SL3
TP3
GND
LTC6401CUD-20 OPEN OPEN MINI-CIRCUITS TCM4-19 (1:4) 6dB
20dB 14dB
640120 TA03
640120f
14
LTC6401-20
TYPICAL APPLICATION
Test Circuit B, 4-Port Analysis
+
V
1000pF
0.1μF
–
+
V
–
V
V
ENABLE
12
G
11
10
9
BIAS CONTROL
R
F
1000Ω
R
R
OUT
12.5Ω
+IN
13
+OUT
100Ω
37.4Ω
PORT 1
(50Ω)
0.1μF
PORT 3
(50Ω)
8
7
R
FILT
50Ω
0.1μF
+OUTF
+IN
–IN
IN+
IN–
OUT–
14
15
1/2
AGILENT
E5O71A
1/2
AGILENT
E5O71A
C
FILT
1.7pF
R
FILT
200Ω
–OUTF
–OUT
50Ω
6
5
OUT+
R
R
G
100Ω
R
OUT
12.5Ω
F
–IN
16
1000Ω
37.4Ω
PORT 2
(50Ω)
PORT 4
(50Ω)
0.1μF
0.1μF
COMMON
MODE CONTROL
640120 TA02
1
2
3
4
+
+
V
–
V
V
V
OCM
1000pF
0.1μF
0.1μF
+
V
V
OCM
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 ± 0.05
3.00 ± 0.10
(4 SIDES)
15 16
0.70 ±0.05
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
1
2
1.45 ± 0.10
(4-SIDES)
3.50 ± 0.05
2.10 ± 0.05
1.45 ± 0.05
(4 SIDES)
PACKAGE
OUTLINE
(UD16) QFN 0904
0.200 REF
0.25 ± 0.05
0.25 ±0.05
0.50 BSC
0.00 – 0.05
0.50 BSC
NOTE:
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
640120f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC6401-20
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
High-Speed Differential Amplifiers/Differential Op Amps
LT1993-2
LT1993-4
LT1993-10
LT1994
800MHz Differential Amplifier/ADC Driver
900MHz Differential Amplifier/ADC Driver
700MHz Differential Amplifier/ADC Driver
Low Noise, Low Distortion Differential Op Amp
A = 2V/V, OIP3 = 38dBm at 70MHz
V
A = 4V/V, OIP3 = 40dBm at 70MHz
V
A = 10V/V, OIP3 = 40dBm at 70MHz
V
16-Bit SNR and SFDR at 1MHz, Rail-to-Rail Outputs
LT5514
Ultralow Distortion IF Amplifier/ADC Driver with Digitally
Controlled Gain
OIP3 = 47dBm at 100MHz, Gain Control Range 10.5dB to 33dB
LT5524
Low Distortion IF Amplifier/ADC Driver with Digitally
Controlled Gain
OIP3 = 40dBm at 100MHz, Gain Control Range 4.5dB to 37dB
LTC6400-20
LT6402-6
LT6402-12
LT6402-20
LTC6406
1.8GHz Low Noise, Low Distortion, Differential ADC Driver
300MHz Differential Amplifier/ADC Driver
300MHz Differential Amplifier/ADC Driver
300MHz Differential Amplifier/ADC Driver
3GHz Rail-to-Rail Input Differential Op Amp
A = 20dB, 90mA Supply Current, IMD = –65dBc at 300MHz
V 3
A = 6dB, Distortion < –80dBc at 25MHz
V
A = 12dB, Distortion < –80dBc at 25MHz
V
A = 20dB, Distortion < –80dBc at 25MHz
V
1.6nV/√Hz Noise, –72dBc Distortion at 50MHz, 18mA
LT6411
Low Power Differential ADC Driver/Dual Selectable Gain
Amplifier
16mA Supply Current, IMD3 = –83dBc at 70MHz, A = 1, –1 or 2
V
High-Speed Single-Ended Output Op Amps
LT1812/LT1813/ High Slew Rate Low Cost Single/Dual/Quad Op Amps
LT1814
8nV/√Hz Noise, 750V/μs, 3mA Supply Current
6nV/√Hz Noise, 1500V/μs, 6.5mA Supply Current
6nV/√Hz Noise, 2500V/μs, 9mA Supply Current
LT1815/LT1816/ Very High Slew Rate Low Cost Single/Dual/Quad Op Amps
LT1817
LT1818/LT1819 Ultra High Slew Rate Low Cost Single/Dual Op Amps
LT6200/LT6201 Rail-to-Rail Input and Output Low Noise Single/Dual Op Amps 0.95nV/√Hz Noise, 165MHz GBW, Distortion = –80dBc at 1MHz
LT6202/LT6203/ Rail-to-Rail Input and Output Low Noise Single/Dual/Quad
LT6204 Op Amps
1.9nV/√Hz Noise, 3mA Supply Current, 100MHz GBW
1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW
1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW
LT6230/LT6231/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps
LT6232
LT6233/LT6234/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps
LT6235
Integrated Filters
LTC1562-2
LT1568
Very Low Noise, 8th Order Filter Building Block
Very Low Noise, 4th Order Filter Building Block
Linear Phase, Tunable 10th Order Lowpass Filter
Very Low Noise Differential 2.5MHz Lowpass Filter
Very Low Noise Differential 5MHz Lowpass Filter
Very Low Noise Differential 10MHz Lowpass Filter
Very Low Noise Differential 15MHz Lowpass Filter
Very Low Noise Differential 20MHz Lowpass Filter
Lowpass and Bandpass Filters up to 300kHz
Lowpass and Bandpass Filters up to 10MHz
Single-Resistor Programmable Cut-Off to 300kHz
SNR = 86dB at 3V Supply, 4th Order Filter
SNR = 82dB at 3V Supply, 4th Order Filter
SNR = 82dB at 3V Supply, 4th Order Filter
SNR = 76dB at 3V Supply, 4th Order Filter
SNR = 76dB at 3V Supply, 4th Order Filter
LTC1569-7
LT6600-2.5
LT6600-5
LT6600-10
LT6600-15
LT6600-20
640120f
LT 0907 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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