LINER LT1814 1.3ghz low noise, low distortion differential adc driver for 140mhz if Datasheet

LTC6401-20
1.3GHz Low Noise, Low
Distortion Differential ADC
Driver for 140MHz IF
FEATURES
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DESCRIPTION
1.3GHz –3dB Bandwidth
Fixed Gain of 10V/V (20dB)
–93dBc IMD3 at 70MHz (Equivalent OIP3 = 50.5dBm)
–74dBc IMD3 at 140MHz (Equivalent OIP3 = 41dBm)
1nV/√⎯H⎯z Internal Op Amp Noise
2.1nV/√⎯H⎯z 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
Max Differential Output Swing 4.4VP-P
Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
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-bit ADCs with low noise and low distortion, but can also
be used as a general-purpose broadband gain block.
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 capacitors 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 transformers. 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.
APPLICATIONS
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, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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
3.3V
Equivalent Output IP3 vs Frequency
70
1.25V
0.1μF + 1000pF
(NOTE 7)
60
0.1μF
0.1μF
INPUT
VOCM
10Ω
+IN
66.5Ω
0.1μF
29Ω
+OUT
+OUTF
LTC6401-20
–OUTF
–OUT
–IN
V–
ENABLE
20dB GAIN
AIN+
VCM
VDD
LTC2208
AIN–
OUTPUT IP3 (dBm)
3.3V
V+
50
40
30
20
10Ω
LTC2208 130Msps
16-Bit ADC
10
0
640120 TA01a
0
50
100
150
FREQUENCY (MHz)
200
640120 TA01b
640120f
1
LTC6401-20
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
+IN
+IN
–IN
–IN
TOP VIEW
Supply Voltage (V+ – V–)..........................................3.6V
Input Current (Note 2)..........................................±10mA
Operating Temperature Range
(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
16 15 14 13
12 V–
V+ 1
VOCM 2
11 ENABLE
17
5
6
7
8
–OUT
+OUTF
+OUT
10 V+
9 V–
–OUTF
V+ 3
V– 4
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 150°C, θJA = 68°C/W, θJC = 4.2°C/W
EXPOSED PAD (PIN 17) IS V–, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC6401CUD-20#PBF
LTC6401CUD-20#TRPBF
LCDB
16-Lead (3mm × 3mm) Plastic QFN
0°C to 70°C
LTC6401IUD-20#PBF
LTC6401IUD-20#TRPBF
LCDB
16-Lead (3mm × 3mm) Plastic QFN
–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
PART NUMBER
Please check each datasheet for complete details.
GAIN
(dB)
GAIN
(V/V)
ZIN (DIFFERENTIAL)
(Ω)
ICC
(mA)
LTC6400-20
20
10
200
90
LTC6401-20
20
10
200
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, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless
otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
19.4
20
20.6
UNITS
Input/Output Characteristic
GDIFF
Gain
VIN = ±100mV Differential
●
GTEMP
Gain Temperature Drift
VIN = ±100mV Differential
●
1
VSWINGMIN
Output Swing Low
Each Output, VIN = ±400mV Differential
●
90
VSWINGMAX
Output Swing High
Each Output, VIN = ±400mV Differential
●
2.3
VOUTDIFFMAX
Maximum Differential Output Swing
1dB Compressed
IOUT
Output Current Drive
Single-Ended
●
10
VOS
Input Offset Voltage
Differential
●
–2
TCVOS
Input Offset Voltage Drift
Differential
●
IVRMIN
Input Common Mode Voltage Range, MIN
IVRMAX
Input Common Mode Voltage Range, MAX
RINDIFF
Input Resistance
Differential
CINDIFF
Input Capacitance
Differential, Includes Parasitic
170
V
4.4
VP-P
mA
2
1.4
ROUTDIFF
Output Resistance
Differential
ROUTFDIFF
Filtered Output Resistance
Differential
●
COUTFDIFF
Filtered Output Capacitance
Differential, Includes Parasitic
CMRR
Common Mode Rejection Ratio
Input Common Mode Voltage 1.1V to 1.4V
●
V
V
200
230
1
●
mV
μV/°C
1
170
mV
2.44
1.6
●
dB
mdB/°C
Ω
pF
18
25
32
Ω
85
100
115
Ω
45
2.7
pF
66
dB
1
V/V
Output Common Mode Voltage Control
GCM
Common Mode Gain
VOCM = 1V to 1.6V
VOCMMIN
Output Common Mode Range, MIN
VOCMMAX
Output Common Mode Range, MAX
VOSCM
Common Mode Offset Voltage
TCVOSCM
Common Mode Offset Voltage Drift
●
6
IVOCM
VOCM Input Current
●
5
VIL
⎯E⎯N⎯A⎯B⎯L⎯E Input Low Voltage
●
VIH
⎯E⎯N⎯A⎯B⎯L⎯E Input High Voltage
●
IIL
⎯E⎯N⎯A⎯B⎯L⎯E Input Low Current
⎯E⎯N⎯A⎯B⎯L⎯E = 0.8V
●
IIH
⎯E⎯N⎯A⎯B⎯L⎯E Input High Current
⎯E⎯N⎯A⎯B⎯L⎯E = 2.4V
●
1
1.1
●
VOCM = 1.1V to 1.5V
●
1.6
1.5
●
–15
V
V
V
V
15
mV
μV/°C
15
μA
0.8
V
⎯E⎯N⎯A⎯B⎯L⎯E Pin
2.4
V
±0.5
μA
1.2
3
μA
Power Supply
●
2.85
3
3.5
V
⎯E⎯N⎯A⎯B⎯L⎯E = 0.8V
●
38
50
62
mA
Shutdown Supply Current
⎯E⎯N⎯A⎯B⎯L⎯E = 2.4V
●
1
3
mA
Power Supply Rejection Ratio
(Differential Outputs)
2.85V to 3.5V
●
55
84
VS
Operating Supply Range
IS
Supply Current
ISHDN
PSRR
dB
640120f
3
LTC6401-20
AC ELECTRICAL CHARACTERISTICS
Specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN and –IN
floating, VOCM = 1.25V, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
–3dBBW
–3dB Bandwidth
200mVP-P,OUT (Note 6)
1.25
GHz
0.1dBBW
Bandwidth for 0.1dB Flatness
200mVP-P,OUT (Note 6)
130
MHz
0.5dBBW
Bandwidth for 0.5dB Flatness
200mVP-P,OUT (Note 6)
250
MHz
1/f
1/f Noise Corner
12.5
kHz
SR
Slew Rate
Differential (Note 6)
4500
V/μs
tS1%
1% Settling Time
2VP-P,OUT (Note 6)
2
ns
tOVDR
Output Overdrive Recovery Time
1.9VP-P,OUT (Note 6)
7
ns
tON
Turn-On Time
+OUT, –OUT Within 10% of Final Values
78
ns
tOFF
Turn-Off Time
ICC Falls to 10% of Nominal
146
ns
–3dBBWCM
Common Mode Small Signal –3dB
BW
0.1VP-P at VOCM, Measured Single-Ended at
Output (Note 6)
15
MHz
Second/Third Order Harmonic
Distortion
2VP-P,OUT, RL = 400Ω
–122/–92
dBc
2VP-P,OUT, No RL
–110/–103
dBc
2VP-P,OUTFILT, No RL
–113/–102
dBc
2VP-P,OUT Composite, RL = 400Ω
–96
dBc
2VP-P,OUT Composite, No RL
–108
dBc
2VP-P,OUTFILT Composite, No RL
–105
dBc
58
dBm
dBm
10MHz Input Signal
HD2,10M /HD3,10M
IMD3,10M
Third-Order Intermodulation
(f1 = 9.5MHz f2 = 10.5MHz)
OIP3,10M
Third-Order Output Intercept Point
(f1 = 9.5MHz f2 = 10.5MHz)
2VP-P,OUT Composite, No RL (Note 7)
P1dB,10M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.3
NF10M
Noise Figure
RL = 375Ω (Note 5)
6.2
dB
eIN,10M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.1
nV/√⎯H⎯z
eON,10M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
21
nV/√⎯H⎯z
70MHz Input Signal
HD2,70M /HD3,70M
IMD3,70M
Second/Third Order Harmonic
Distortion
Third-Order Intermodulation
(f1 = 69.5MHz f2 = 70.5MHz)
2VP-P,OUT, RL = 400Ω
–91/–80
dBc
2VP-P,OUT, No RL
–95/–88
dBc
2VP-P,OUTFILT, No RL
–95/–88
dBc
2VP-P,OUT Composite, RL = 400Ω
–88
dBc
2VP-P,OUT Composite, No RL
–93
dBc
2VP-P,OUTFILT Composite, No RL
–92
dBc
2VP-P,OUT Composite, No RL (Note 7)
50.5
dBm
OIP3,70M
Third-Order Output Intercept Point
(f1 = 69.5MHz f2 = 70.5MHz)
P1dB,70M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.3
dBm
NF70M
Noise Figure
RL = 375Ω (Note 5)
6.1
dB
eIN,70M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.1
nV/√⎯H⎯z
eON,70M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
21
nV/√⎯H⎯z
140MHz Input Signal
HD2,140M /HD3,140M Second/Third Order Harmonic
Distortion
2VP-P,OUT, RL = 400Ω
–80/–57
dBc
2VP-P,OUT, No RL
–81/–60
dBc
2VP-P,OUTFILT, No RL
–80/–65
dBc
640120f
4
LTC6401-20
AC ELECTRICAL CHARACTERISTICS
Specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN and –IN
floating, VOCM = 1.25V, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
IMD3,140M
Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)
MIN
TYP
MAX
UNITS
2VP-P,OUT Composite, RL = 400Ω
–71
dBc
2VP-P,OUT Composite, No RL
–74
dBc
2VP-P,OUTFILT Composite, No RL
–72
dBc
2VP-P,OUT Composite, No RL (Note 7)
41
dBm
OIP3,140M
Third-Order Output Intercept Point
(f1 = 139.5MHz f2 = 140.5MHz)
P1dB,140M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
18
dBm
NF140M
Noise Figure
RL = 375Ω (Note 5)
6.4
dB
eIN,140M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.1
nV/√⎯H⎯z
eON,140M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
22
nV/√⎯H⎯z
IMD3,130M/150M
Third-Order Intermodulation
(f1 = 130MHz f2 = 150MHz) Measure
at 170MHz
–69
dBc
2VP-P,OUT Composite, RL = 375Ω (Note 5)
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.
Note 3: The LTC6401C and LTC6401I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
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
–61
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
output voltage swing driving a given RL is converted to OIP3 and P1dB as
if it were driving a 50Ω load. Using this modified convention, 2VP-P is by
definition equal to 10dBm, regardless of the actual RL.
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
25
S21 Phase and Group Delay vs
Frequency
Gain 0.1dB Flatness
1.0
TEST CIRCUIT B
100
TEST CIRCUIT B
1.5
TEST CIRCUIT B
0.8
15
10
5
0.4
PHASE (DEGREE)
NORMALIZED GAIN (dB)
0.6
0.2
0
–0.2
–0.4
–0.6
0
1.2
–100
0.9
–200
0.6
0.3
–300
PHASE
GROUP DELAY
–0.8
0
–1.0
10
100
1000
FREQUENCY (MHz)
3000
640120 G01
–400
10
100
FREQUENCY (MHz)
1000
640120 G02
GROUP DELAY (ns)
GAIN (dB)
20
0
200
400
600
FREQUENCY (MHz)
800
0
1000
640120 G03
640120f
5
LTC6401-20
TYPICAL PERFORMANCE CHARACTERISTICS
0
Input and Output Impedance vs
Frequency
TEST CIRCUIT B
225
IMPEDANCE MAGNITUDE (Ω)
S11
–30
S22
–40
–50
S12
–60
ZIN
200
100
80
90
60
80
40
175
ZOUT
150
125
20
0
ZIN
–20
100
PHASE
IMPEDANCE MAGNITUDE
75
–40
50
–60
–70
25
–80
–80
0
100
1000
FREQUENCY (MHz)
3000
ZOUT
640120 G04
2
eIN
0
1000
1.35
OUTPUT VOLTAGE (V)
NOISE FIGURE
INPUT REFERRED NOISE VOLTAGE (nV/√Hz)
4
100
FREQUENCY (MHz)
30
20
10
0
1
10
100
FREQUENCY (MHz)
Large Signal Transient Response
RL = 87.5Ω PER OUTPUT
RL = 87.5Ω PER OUTPUT
2.0
1.30
+OUT
1.25
1.20
–OUT
5
1.0
–OUT
0.5
1.15
0
+OUT
1.5
10
TIME (ns)
0
20
15
0
5
10
TIME (ns)
640120 G08
20
640120 G09
5
RL = 87.5Ω PER OUTPUT
–OUT
15
1% Settling Time for 2V
Output Step
Overdrive Transient Response
2.5
1000
640120 G06
2.5
640120 G07
RL = 87.5Ω PER OUTPUT
4
2.0
3
2
SETTLING (%)
OUTPUT VOLTAGE (V)
CMRR
40
Small Signal Transient Response
6
10
50
640120 G05
Noise Figure and Input Referred
Noise Voltage vs Frequency
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
60
–100
1000
10
100
FREQUENCY (MHz)
1
PSRR
70
OUTPUT VOLTAGE (V)
10
NOISE FIGURE (dB)
100
IMPEDANCE PHASE (DEGREE)
S PARAMETERS (dB)
–10
–20
PSRR and CMRR vs Frequency
250
PSRR, CMRR (dB)
Input and Output Reflection and
Reverse Isolation vs Frequency
1.5
1.0
1
0
–1
–2
–3
0.5
–4
+OUT
–5
0
0
50
100
TIME (ns)
150
200
640120 G10
0
1
2
3
TIME (ns)
4
5
6
640120 G11
640120f
6
LTC6401-20
TYPICAL PERFORMANCE CHARACTERISTICS
Harmonic Distortion (Unfiltered)
vs Frequency
–60
–70
–80
–90
–100
HD2 NO RL
HD2 200Ω RL
HD3 NO RL
HD3 200Ω RL
–110
–120
0
50
100
150
FREQUENCY (MHz)
–40
DIFFERENTIAL INPUT
= 2VP-P
V
–50 OUT
NO RL
–60
–70
–80
–90
–100
–110
0
50
100
150
FREQUENCY (MHz)
–90
HD2 NO RL
HD2 200Ω RL
HD3 NO RL
HD3 200Ω RL
50
100
150
FREQUENCY (MHz)
200
100
150
FREQUENCY (MHz)
–60
–70
–80
–90
–100
–120
50
100
150
FREQUENCY (MHz)
–60
–70
–80
–90
–100
–110
HD2
HD3
0
UNFILTERED NO RL
UNFILTERED 200Ω RL
FILTERED NO RL
–50
–110
SINGLE-ENDED INPUT
VOUT = 2VP-P COMPOSITE
–120
0
200
50
100
150
FREQUENCY (MHz)
Equivalent Output 1dB
Compression Point vs Frequency
–40
20
DIFFERENTIAL INPUT
VOUT = 2VP-P at 100MHz
–50 RL = 400Ω
–60
HD3
–70
–80
HD2
–90
–100
1.5
1.1
1.2
1.3
1.4
OUTPUT COMMON MODE VOLTAGE (V)
640120 G18
200
640120 G17
640120 G16
Harmonic Distortion vs Output
Common Mode Voltage
(Unfiltered Outputs)
200
Third Order Intermodulation
Distortion vs Frequency
–40
640120 G15
1.0
50
640120 G14
SINGLE-ENDED INPUT
= 2VP-P
V
–50 OUT
NO RL
OUTPUT 1dB COMPRESSION (dBm)
0
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
0
THIRD ORDER IMD (dBc)
–80
HARMONIC DISTORTION (dBc)
–70
DISTORTION (dBc)
HARMONIC DISTORTION (dBc)
–60
–120
–100
–120
–40
–110
–90
Harmonic Distortion (Filtered) vs
Frequency
SINGLE-ENDED INPUT
VOUT = 2VP-P
–100
–80
640120 G13
Harmonic Distortion (Unfiltered)
vs Frequency
–50
–70
200
640120 G12
–40
–60
–110
HD2
HD3
–120
200
UNFILTERED NO RL
UNFILTERED 200Ω RL
FILTERED NO RL
–50
THIRD ORDER IMD (dBc)
HARMONIC DISTORTION (dBc)
–50
Third Order Intermodulation
Distortion vs Frequency
–40
DIFFERENTIAL INPUT
VOUT = 2VP-P
HARMONIC DISTORTION (dBc)
–40
Harmonic Distortion (Filtered) vs
Frequency
19
DIFFERENTIAL INPUT
RL = 400Ω
(NOTE 7)
18
17
16
15
50
80
110
140
FREQUENCY (MHz)
170
200
640020 G19
640120f
7
LTC6401-20
TYPICAL PERFORMANCE CHARACTERISTICS
Equivalent Output Third Order
Intercept vs Frequency
UNFILTERED NO RL
UNFILTERED 200Ω RL
FILTERED NO RL
60
Turn-Off Time
RL = 87.5Ω PER OUTPUT
3.0
ICC
VOLTAGE (V)
40
30
20
2.0
10
0
0
50
100
150
FREQUENCY (MHz)
200
640120 G20
60
3.0
50
2.5
40
–OUT
30
1.5
1.0
20
+OUT
10
0.5
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
(NOTE 7)
3.5
–0.5
–100
0
100
200
300
TIME (ns)
400
50
40
2.0
–OUT
1.5
30
+OUT
1.0
20
10
0.5
0
0
–10
500
–0.5
–100
640120 G21
60
ENABLE
ENABLE
0
70
RL = 87.5Ω PER OUTPUT
ICC
0
100
200
300
TIME (ns)
SUPPLY CURRENT (mA)
2.5
50
70
SUPPLY CURRENT (mA)
OUTPUT IP3 (dBm)
Turn-On Time
3.5
VOLTAGE (V)
70
0
400
–10
500
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 capacitors as close to the pins as possible.
VOCM (Pin 2): This pin sets the output common mode
voltage. A 0.1μF external bypass capacitor is recommended.
V– (Pins 4, 9, 12, 17): Negative Power Supply. All four
pins must be connected to the same voltage/ground.
–OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins
have 12.5Ω series resistors.
–OUTF, +OUTF (Pins 6, 7): Filtered Outputs. These pins have
50Ω series resistors and a 1.7pF shunt capacitance.
⎯E⎯N⎯A⎯B⎯L⎯E (Pin 11): This pin is a logic input referenced to
V–. If low, the part is enabled. If high, the part is disabled
and draws approximately 1mA supply current.
+IN (Pins 13, 14): Positive Input. Pins 13 and 14 are
internally shorted together.
–IN (Pins 15, 16): Negative Input. Pins 15 and 16 are
internally shorted together.
Exposed Pad (Pin 17): V–. The Exposed Pad must be connected to the same voltage/ground as pins 4, 9, 12.
BLOCK DIAGRAM
V–
12
V–
V+
ENABLE
11
10
9
BIAS CONTROL
+IN
13
ROUT
12.5Ω
+OUT
8
RFILT
50Ω
+IN
14
IN+
+OUTF
7
OUT–
CFILT
1.7pF
RFILT
50Ω
–IN
15
–IN
16
RF
1000Ω
RG
100Ω
IN–
OUT+
RF
1000Ω
RG
100Ω
–OUTF
6
ROUT
12.5Ω
–OUT
5
2k
COMMON
MODE CONTROL
5.3pF
1
V+
2
3
VOCM
V+
4
640120 BD
V–
640120f
9
LTC6401-20
APPLICATIONS INFORMATION
Circuit Operation
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
The LTC6401-20 is composed of a fully differential amplifier
with on chip feedback and output common mode voltage
control circuitry. Differential gain and input impedance are
set by 100Ω/1000Ω resistors in the feedback network.
Small output resistors of 12.5Ω improve the circuit stability
over various load conditions. They also provide a possible
external filtering option, which is often desirable when the
load is an ADC.
the differential inputs may need to be terminated to a lower
value impedance, e.g. 50Ω, in order to provide an impedance match to the source. Several choices are available.
One approach is to use a differential shunt resistor (Figure
1). Another approach is to employ a wideband transformer
(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
narrowband impedance match at the inputs of the LTC640120 for frequency selection and/or noise reduction.
Referring to Figure 3, LTC6401-20 can be easily configured
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
the same matching network and a source resistor. Because
the return ratios of the two feedback paths are equal, the
LTC6401-20
25Ω
1000Ω
100Ω
12.5Ω
13 +IN
Filter resistors of 50Ω are available for additional filtering.
Lowpass/bandpass filters are easily implemented with just
a couple of external components. Moreover, they offer
single-ended 50Ω matching in wideband applications and
no external resistor is needed.
+
–
VIN
Input Impedance and Matching
The differential input impedance of the LTC6401-20 is
200Ω. If a 200Ω source impedance is unavailable, then
IN+
OUT–
IN–
OUT+
14 +IN
66.5Ω
+OUTF 7
50Ω
15 –IN
25Ω
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
is automatically biased close to VOCM and thus no external
circuitry is needed for bias. The LTC6401-20 provides an
output common mode voltage set by VOCM, which allows
driving an ADC directly without external components such
as a transformer or AC coupling capacitors. The input
signal can be either single-ended or differential with only
minor differences in distortion performance.
+OUT 8
50Ω
1000Ω
100Ω
1.7pF
–OUTF 6
12.5Ω
–OUT 5
16 –IN
640120 F01
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
LTC6401-20
25Ω
1000Ω
100Ω
12.5Ω
13 +IN
+OUT 8
50Ω
1:4
+
–
VIN
• •
IN+
OUT–
IN–
OUT+
+OUTF 7
14 +IN
50Ω
15 –IN
25Ω
100Ω
16 –IN
1000Ω
1.7pF
–OUTF 6
12.5Ω
–OUT 5
640120 F02
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a 1:4 Balun
640120f
10
LTC6401-20
APPLICATIONS INFORMATION
RS
50Ω
1000Ω
100Ω
12.5Ω
13 +IN
VIN
+
–
LTC6401-20
0.1μF
+OUT 8
50Ω
RT
66.5Ω
IN+
OUT–
+OUTF 7
14 +IN
0.1μF
50Ω
15 –IN
RS
50Ω
RT
66.5Ω
0.1μF
IN–
100Ω
input Smith Chart, based on which users can choose the
optimal source impedance for a given gain and noise
requirement.
Output Match and Filter
1.7pF
–OUTF 6
OUT+
1000Ω
12.5Ω
–OUT 5
16 –IN
640120 F03
Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance
two outputs have the same gain and thus symmetrical
swing. In general, the single-ended input impedance and
termination resistor RT are determined by the combination
of RS, RG and RF. For example, when RS is 50Ω, it is found
that the single-ended input impedance is 200Ω and RT is
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 impedance and load impedance as shown in Figure 4:
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.
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.
LTC6401-20
13 +IN
+OUT 8
IN+
13 +IN
+
–
VIN
Figure 5. LTC6401-20 Internal Filter Topology Modified for Low
Filter Bandwidth (Three External Capacitors)
15 –IN
1/2 RS
IN–
100Ω
16 –IN
1000Ω
100Ω
1000Ω
OUT–
16nH
50Ω
15 –IN
IN–
100Ω
1/2 RL
–OUT 5
4.99Ω
+OUTF 7
14 +IN
1.7pF
12.5Ω
39pF
10Ω
50Ω
–OUTF 6
OUT+
LTC6401-20
12.5Ω
+OUT 8
VOUT
50Ω
8.2pF
12.5Ω
–OUT 5
IN+
+OUTF 7
14 +IN
1000Ω
640120 F05
50Ω
OUT–
FILTERED OUTPUT
12pF (87.5MHz)
–OUTF 6
OUT+
13 +IN
+OUT 8
1.7pF
16 –IN
1/2 RL
12.5Ω
IN–
100Ω
LTC6401-20
IN+
+OUTF 7
50Ω
The noise performance of the LTC6401-20 also depends
upon the source impedance and termination. For example,
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
1000Ω
8.2pF
OUT–
14 +IN
15 –IN
100Ω
12.5Ω
50Ω
V
RL
2000
A V = OUT =
•
VIN
RS + 200 25 + RL
1/2 RS
1000Ω
100Ω
16 –IN
OUT+
1000Ω
1.7pF
LTC2208
39pF
–OUTF 6
12.5Ω
10Ω
–OUT 5
640120 F06
4.99Ω
39pF
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
by the VOCM pin, which is a high impedance input. The
output common mode voltage is capable of tracking VOCM
in a range from 1V to 1.6V. Bandwidth of VOCM control is
typically 15MHz, which is dominated by a low pass filter
connected to the VOCM pin and is aimed to reduce common mode noise generation at the outputs. The internal
common mode feedback loop has a –3dB bandwidth
around 300MHz, allowing fast common mode rejection at
the outputs of the LTC6401-20. The VOCM pin should be
tied to a DC bias voltage where a 0.1μF bypass capacitor
is recommended. When interfacing with A/D converters
such as the LT22xx families, the VOCM can be normally
connected to the VCM pin of the ADC.
Driving A/D Converters
The LTC6401-20 has been specifically designed to interface 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. VOCM of the LTC6401-20 is
connected to VCM of the LTC2208 at 1.25V. Alternatively,
a single-ended input signal can be converted to differential
signal via a balun and fed to the input of the LTC6401-20.
The balun also converts input impedance to match 50Ω
source impedance.
0.1μF
IF IN
VOCM
10Ω
+IN
+OUT
+OUTF
LTC6401-20
–OUTF
–IN
–OUT
66.5Ω
29Ω
AIN+
VCM
LTC2208
AIN–
10Ω
ENABLE
20dB GAIN
LTC2208 130Msps
16-Bit ADC
640120 F07
Figure 7. Single-Ended Input to LTC6401-20 and LTC2208
Test Circuits
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 impedance 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.
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.
640120f
12
LTC6401-20
APPLICATIONS INFORMATION
Top Silkscreen
640120f
13
LTC6401-20
TYPICAL APPLICATION
Demo Circuit 987B Schematic (Test Circuit A)
VCC
ENABLE 1
3 DIS
2 JP1
13
T1
(2)
4
R4
(2)
C21
0.1μF
2
3
R3
(2)
C2
0.1μF
14
R24
(1)
SL1
(2)
+IN
+OUT
+IN
+OUTF
8
R10
86.6Ω
7
R8
(1)
6
R7
(1)
LTC6401-20
15
C1
0.1μF
16
R1
0Ω
–IN
–OUTF
–IN
–OUT
V+
VOCM
1
VCC
C10
0.1μF
VCC
9
V–
2
V+
5
R14
(1)
C4
0.1μF
SL2
(2)
4
C9
1000pF
R12
0Ω
1
5
R11
(1)
C22
0.1μF
R13
0Ω
C3
0.1μF
R9
86.6Ω
V–
3
4
T2
3 TCM 4-19
1:4
2
•
R5
0dB (1)
1
•
•
5
10
V+
C18
0.1μF
•
J2
–IN
R6
0Ω
C17
1000pF
R16
0Ω
12
11
V– ENABLE
R2
(1)
J1
+IN
VCC
J4
+OUT
SL3
(2)
J5
–OUT
VCC
C12
1000pF
C13
0.1μF
R19
1.5k
TP5
VOCM
5
T3
TCM 4-19
1:4
2
C23
0.1μF
C19
0.1μF
R21
(1)
C24
0.1μF
3
3
C5
0.1μF
C20
0.1μF
R22
(1)
C6
0.1μF
T4
TCM 4-19
1:4
4
R18
0Ω
5
R26
0Ω
2
1
•
4
1
•
R25
0Ω
•
R17
0Ω
•
J6
TEST IN
C7
0.1μF
R20
1k
J7
TEST OUT
VCC
TP2
VCC
2.85V TO 3.5V
TP3
GND
C14
4.7μF
NOTE: UNLESS OTHERWISE SPECIFIED.
(1) DO NOT STUFF.
C15
1μF
(2) VERSION
-G
IC
R3
R4
LTC6401CUD-20 OPEN OPEN
SL = SIGNAL LEVEL
T1
SL1
SL2
SL3
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–
11
V–
V+
ENABLE
12
10
9
BIAS CONTROL
RF
1000Ω
RG
100Ω
+IN
13
PORT 1
(50Ω)
ROUT
12.5Ω
RFILT
50Ω
0.1μF
1/2
AGILENT
E5O71A
+IN
14
200Ω
IN+
PORT 3
(50Ω)
+OUTF
IN–
CFILT
1.7pF
1/2
AGILENT
E5O71A
–OUTF
6
OUT+
RF
1000Ω
RG
100Ω
–IN
16
0.1μF
7
OUT–
RFILT
50Ω
–IN
15
PORT 2
(50Ω)
+OUT 37.4Ω
8
ROUT
12.5Ω
–OUT 37.4Ω
PORT 4
(50Ω)
5
0.1μF
0.1μF
COMMON
MODE CONTROL
1
1000pF
2
V+
3
VOCM
0.1μF
VOCM
V+
4
640120 TA02
V–
V+
0.1μF
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
BOTTOM VIEW—EXPOSED PAD
3.00 ± 0.10
(4 SIDES)
0.70 ±0.05
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 ± 0.05
15
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
1
1.45 ± 0.10
(4-SIDES)
3.50 ± 0.05
1.45 ± 0.05
2.10 ± 0.05 (4 SIDES)
16
2
PACKAGE
OUTLINE
(UD16) QFN 0904
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.200 REF
0.00 – 0.05
NOTE:
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
0.25 ± 0.05
0.50 BSC
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 representation 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
800MHz Differential Amplifier/ADC Driver
AV = 2V/V, OIP3 = 38dBm at 70MHz
LT1993-4
900MHz Differential Amplifier/ADC Driver
AV = 4V/V, OIP3 = 40dBm at 70MHz
LT1993-10
700MHz Differential Amplifier/ADC Driver
AV = 10V/V, OIP3 = 40dBm at 70MHz
LT1994
Low Noise, Low Distortion Differential Op Amp
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
1.8GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 20dB, 90mA Supply Current, IMD3 = –65dBc at 300MHz
LT6402-6
300MHz Differential Amplifier/ADC Driver
AV = 6dB, Distortion < –80dBc at 25MHz
LT6402-12
300MHz Differential Amplifier/ADC Driver
AV = 12dB, Distortion < –80dBc at 25MHz
LT6402-20
300MHz Differential Amplifier/ADC Driver
AV = 20dB, Distortion < –80dBc at 25MHz
LTC6406
3GHz Rail-to-Rail Input Differential Op Amp
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, AV = 1, –1 or 2
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
LT1815/LT1816/ Very High Slew Rate Low Cost Single/Dual/Quad Op Amps
LT1817
6nV/√Hz Noise, 1500V/μs, 6.5mA Supply Current
LT1818/LT1819
Ultra High Slew Rate Low Cost Single/Dual Op Amps
6nV/√Hz Noise, 2500V/μs, 9mA Supply Current
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
LT6230/LT6231/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps
LT6232
1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW
LT6233/LT6234/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps
LT6235
1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW
Integrated Filters
LTC1562-2
Very Low Noise, 8th Order Filter Building Block
Lowpass and Bandpass Filters up to 300kHz
LT1568
Very Low Noise, 4th Order Filter Building Block
Lowpass and Bandpass Filters up to 10MHz
LTC1569-7
Linear Phase, Tunable 10th Order Lowpass Filter
Single-Resistor Programmable Cut-Off to 300kHz
LT6600-2.5
Very Low Noise Differential 2.5MHz Lowpass Filter
SNR = 86dB at 3V Supply, 4th Order Filter
LT6600-5
Very Low Noise Differential 5MHz Lowpass Filter
SNR = 82dB at 3V Supply, 4th Order Filter
LT6600-10
Very Low Noise Differential 10MHz Lowpass Filter
SNR = 82dB at 3V Supply, 4th Order Filter
LT6600-15
Very Low Noise Differential 15MHz Lowpass Filter
SNR = 76dB at 3V Supply, 4th Order Filter
LT6600-20
Very Low Noise Differential 20MHz Lowpass Filter
SNR = 76dB at 3V Supply, 4th Order Filter
640120f
16 Linear Technology Corporation
LT 0907 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007
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