LINER LTC6400-8 2.2ghz low noise, low distortion differential adc driver for dc-300mhz Datasheet

LTC6400-8
2.2GHz Low Noise, Low
Distortion Differential ADC
Driver for DC-300MHz
FEATURES
DESCRIPTION
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The LTC®6400-8 is a high-speed differential amplifier targeted at processing signals from DC to 300MHz. 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.
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2.2GHz –3dB Bandwidth
Fixed Gain of 2.5V/V (8dB)
–99dBc IMD3 at 70MHz (Equivalent OIP3 = 53.4dBm)
–61dBc IMD3 at 300MHz (Equivalent OIP3 = 34.8dBm)
1nV/√Hz Internal Op Amp Noise
7.6dB Noise Figure
Differential Inputs and Outputs
400Ω Input Impedance
2.85V to 3.5V Supply Voltage
85mA Supply Current (255mW)
1V to 1.6V Output Common Mode, Adjustable
DC- or AC-Coupled Operation
Max Differential Output Swing 4.8VP-P
Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
APPLICATIONS
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The LTC6400-8 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 8dB (2.5V/V).
The LTC6400-8 saves space and power compared to alternative solutions using IF gain blocks and transformers.
The LTC6400-8 is packaged in a compact 16-lead 3mm ×
3mm QFN package and operates over the –40°C to 85°C
temperature range.
L, 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
3.3V
3.3V
Equivalent Output IP3 vs Frequency
70
C1
1000pF
CF2
33pF
C3
0.1μF
V+
+IN
VIN
R1
59.0Ω
C4
0.1μF
+OUT
LTC6400-8
–IN
R2
27.4Ω
RS3
10Ω
RS1
15Ω
–OUT
VOCM
V–
L1
RS2 24nH
15Ω
COILCRAFT
0603CS
1.25V
CF1
33pF RS4
10Ω
CF3
33pF
AIN+
VDD
LTC2208
AIN–
VCM
LTC2208
130Msps
16-Bit ADC
R3
100Ω
50
40
30
20
10
64008 TA01a
C5
0.1μF
(NOTE 7)
60
OUTPUT IP3 (dBm)
C2
0.1μF
0
0
50
100
150
200
FREQUENCY (MHz)
250
300
64008 TA01b
64008f
1
LTC6400-8
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
+IN
+IN
–IN
–IN
TOP VIEW
Supply Voltage (VCC – VEE) ......................................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
V+ 1
12 V–
VOCM 2
10 V+
9 V–
7
8
+OUT
6
+OUTF
5
–OUT
4
–OUTF
V–
11 ENABLE
17
V+ 3
UD PACKAGE
16-LEAD (3mm s 3mm) PLASTIC QFN
TJMAX = 150°C, θJA = 68°C/W, θJC = 7.5°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
SPECIFIED TEMPERATURE RANGE
LTC6400CUD-8#PBF
LTC6400CUD-8#TRPBF
LCCQ
16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C
LTC6400IUD-8#PBF
LTC6400IUD-8#TRPBF
LCCQ
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)
LTC6401-8
8
2.5
400
45
LTC6401-14
14
5
200
45
LTC6401-20
20
10
200
50
LTC6401-26
26
20
50
45
LTC6400-8
8
2.5
400
85
LTC6400-14
14
5
200
85
LTC6400-20
20
10
200
90
LTC6400-26
26
20
50
85
In addition to the LTC6400 family of amplifiers, a lower power LTC6401 family is available. The LTC6401 is pin compatible to the LTC6400, and has the
same low noise performance. The lower power consumption of the LTC6401 comes at the expense of slightly higher non-linearity, especially at input
frequencies above 140MHz. Please refer to the separate LTC6401 data sheets for complete details.
64008f
2
LTC6400-8
DC ELECTRICAL CHARACTERISTICS + The l –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
8
8.5
UNITS
Input/Output Characteristic
GDIFF
Gain
VIN = ±400mV Differential
l
TCGAIN
Gain Temperature Drift
VIN = ±400mV Differential
l
–0.13
VSWINGMIN
Output Swing Low
Each Output, VIN = ±1.6V Differential
l
74
VSWINGMAX
Output Swing High
Each Output, VIN = ±1.6V Differential
l
7.5
2.3
VOUTDIFFMAX
Maximum Differential Output Swing
1dB Compressed
l
IOUT
Output Current Drive
VOUT > 2VP-P,DIFF
l
20
VOS
Input Offset Voltage
Differential
l
–5
TCVOS
Input Offset Voltage Drift
Differential
l
IVRMIN
Input Common Mode Voltage Range, MIN
IVRMAX
Input Common Mode Voltage Range, MAX
RINDIFF
Input Resistance (+IN, –IN)
Differential
CINDIFF
Input Capacitance (+IN, –IN)
Differential, Includes Parasitic
170
V
4.8
VP-P
mA
5
2
ROUTDIFF
Output Resistance (+OUT, –OUT)
Differential
ROUTFDIFF
Filtered Output Resistance (+OUTF, –OUTF)
Differential
l
COUTFDIFF
Filtered Output Capacitance (+OUTF, –OUTF)
Differential, Includes Parasitic
CMRR
Common Mode Rejection Ratio
Input Common Mode Voltage 1.1V~1.7V
l
V
V
400
460
1
l
mV
μV/°C
1
340
mV
2.48
1.8
l
dB
mdB/°C
Ω
pF
18
25
32
Ω
85
100
115
Ω
39
2.7
pF
55
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
l
6
IVOCM
VOCM Input Current
l
4.5
VIL
ENABLE Input Low Voltage
l
VIH
ENABLE Input High Voltage
l
IIL
ENABLE Input Low Current
ENABLE = 0.8V
l
IIH
ENABLE Input High Current
ENABLE = 2.4V
l
1
1.1
l
VOCM = 1.1V to 1.5V
l
1.6
1.5
l
–15
V
V
V
V
15
mV
μV/°C
15
μA
0.8
V
ENABLE Pin
2.4
V
0.5
μA
1.3
4
μA
3
3.5
V
85
95
mA
0.9
3
mA
Power Supply
VS
Operating Supply Range
l
2.85
70
IS
Supply Current
ENABLE = 0.8V, Input and Output Floating
l
ISHDN
Shutdown Supply Current
ENABLE = 2.4V, Input and Output Floating
l
PSRR
Power Supply Rejection Ratio
(Differential Outputs)
V+ = 2.85V to 3.5V
l
50
68
dB
64008f
3
LTC6400-8
AC ELECTRICAL CHARACTERISTICS
ENABLE = 0V, No RL unless otherwise noted.
Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V,
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
–3dBBW
–3dB Bandwidth
200mVP-P,OUT (Note 6)
1.2
2.2
GHz
0.5dBBW
Bandwidth for 0.5dB Flatness
200mVP-P,OUT (Note 6)
0.43
GHz
0.1dBBW
Bandwidth for 0.1dB Flatness
200mVP-P,OUT (Note 6)
1/f
1/f Noise Corner
SR
Slew Rate
VOUT = 2V Step (Note 6)
tS1%
1% Settling Time
VOUT = 2VP-P (Note 6)
0.2
GHz
16.5
kHz
3810
V/μs
1.8
ns
tOVDR
Overdrive Recovery Time
VOUT = 1.9VP-P (Note 6)
18
ns
tON
Turn-On Time
Differential Output Reaches 90% of
Steady State Value
10
ns
tOFF
Turn-Off Time
Differential Output Drops to 10% of
Original Value
12
ns
–3dBBWVOCM
VOCM Pin Small Signal –3dB BW
0.1VP-P at VOCM, Measured Single-Ended at
Output (Note 6)
14
MHz
–118/–98
dBc
–120/–109
dBc
dBc
10MHz Input Signal
HD2,10M/HD3,10M Second/Third Order Harmonic Distortion VOUT = 2VP-P, RL = 200Ω
VOUT = 2VP-P, No RL
IMD3,10M
Third-Order Intermodulation
(f1 = 9.5MHz f2 = 10.5MHz)
VOUT = 2VP-P Composite, RL = 200Ω
–99
VOUT = 2VP-P Composite, No RL
–112
dBc
OIP3,10M
Equivalent Third-Order Output Intercept
Point (f1 = 9.5MHz f2 = 10.5MHz)
VOUT = 2VP-P Composite, No RL (Note 7)
60
dBm
P1dB,10M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
18.2
dBm
NF10M
Noise Figure
RS = 400Ω, RL = 375Ω
7.6
dB
eIN,10M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
3.7
nV/√Hz
eON,10M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
9.3
nV/√Hz
70MHz Input Signal
HD2,70M/HD3,70M Second/Third Order Harmonic Distortion VOUT = 2VP-P, RL = 200Ω
VOUT = 2VP-P, No RL
–97/–85
dBc
–100/–98
dBc
Third-Order Intermodulation
(f1 = 69.5MHz f2 = 70.5MHz)
VOUT = 2VP-P Composite, RL = 200Ω
–90
dBc
VOUT = 2VP-P Composite, No RL
–99
dBc
OIP3,70M
Equivalent Third-Order Output Intercept
Point (f1 = 69.5MHz f2 = 70.5MHz)
VOUT = 2VP-P Composite, No RL (Note 7)
53.4
dBm
P1dB,70M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
19.2
dBm
NF70M
Noise Figure
RS = 400Ω, RL = 375Ω
7.6
dB
eIN,70M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
3.7
nV/√Hz
eON,70M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
9.3
nV/√Hz
IMD3,70M
140MHz Input Signal
HD2,140M/
HD3,140M
Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 200Ω
2VP-P,OUT, No RL
IMD3,140M
Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)
2VP-P,OUT Composite, RL = 200Ω
–79
dBc
2VP-P,OUT Composite, No RL
–84
dBc
Third-Order Output Intercept Point
(f1 = 139.5MHz f2 = 140.5MHz)
2VP-P,OUT Composite, No RL (Notes 7)
45.8
dBm
OIP3,140M
–86/–71
dBc
–91/–81
dBc
64008f
4
LTC6400-8
AC ELECTRICAL CHARACTERISTICS
ENABLE = 0V, No RL unless otherwise noted.
Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V,
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
P1dB,140M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
19.2
dBm
NF140M
Noise Figure
RS = 400Ω, RL = 375Ω
7.7
dB
eIN,140M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
3.7
nV/√Hz
eON,140M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
9.3
nV/√Hz
HD2,240M/
HD3,240M
Second-Order Harmonic Distortion
2VP-P,OUT, RL = 200Ω
–71/–53
dBc
2VP-P,OUT, No RL
–73/–59
dBc
IMD3,240M
Third-Order Intermodulation
(f1 = 239.5MHz f2 = 240.5MHz)
2VP-P,OUT Composite, RL = 200Ω
–64
dBc
2VP-P,OUT Composite, No RL
–68
dBc
240MHz Input Signal
OIP3,240M
Third-Order Output Intercept Point
(f1 = 239.5MHz f2 = 240.5MHz)
2VP-P,OUT Composite, No RL (Note 7)
37.8
dBm
P1dB,240M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
18.2
dBm
NF240M
Noise Figure
RS = 400Ω, RL = 375Ω
8.1
dB
eN, 240M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
3.7
nV/√Hz
eON,240M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
9.6
nV/√Hz
300MHz Input Signal
HD2,300M/
HD3,300M
Second-Order Harmonic Distortion
IMD3,300M
Third-Order Intermodulation
(f1 = 299.5MHz f2 = 300.5MHz)
OIP3,300M
Third-Order Output Intercept Point
(f1 = 299.5MHz f2 = 300.5MHz)
2VP-P,OUT, RL = 200Ω
–67/–46
dBc
2VP-P,OUT, No RL
–69/–50
dBc
2VP-P,OUT Composite, RL = 200Ω
–57
dBc
2VP-P,OUT Composite, No RL
–61
dBc
2VP-P,OUT Composite, No RL (Note 7)
34.8
dBm
P1dB,300M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.6
dBm
NF300M
Noise Figure
RS = 400Ω, RL = 375Ω
8.5
dB
eN,300M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
3.8
nV/√Hz
eON,300M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
10
nV/√Hz
IMD3,280M/320M
Third-Order Intermodulation
(f1 = 280MHz f2 = 320MHz) Measured
at 360MHz
2VP-P,OUT Composite, RL = 375Ω
–59
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 LTC6400C and LTC6400I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
Note 4: The LTC6400C is guaranteed to meet specified performance from
0°C to 70°C. It is designed, characterized and expected to meet specified
–53
dBc
performance from –40°C to 85°C but is not tested or QA sampled at these
temperatures. The LTC6400I 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. RL = 87.5Ω per output.
Note 7: Since the LTC6400-8 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
LTC6400-8 with amplifiers that require 50Ω output load, the LTC6400-8
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 actual RL.
64008f
5
LTC6400-8
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
1.0
TEST CIRCUIT B
10
0.6
6
4
2
–50
0.4
0.2
0
–0.2
–0.4
0
–0.6
–2
–0.8
100
1000
FREQUENCY (MHz)
10
3000
100
1000
FREQUENCY (MHz)
Input and Output Reflection and
Reverse Isolation vs Frequency
500
TEST CIRCUIT B
IMPEDANCE MAGNITUDE (Ω)
–30
S22
–50
S12
400
ZIN
300
0
200
–20
ZIN
150
ZOUT
10
3000
9.0
4.0
8.5
3.5
EN
3.0
2.5
NOISE FIGURE
7.0
2.0
6.5
1.5
6.0
1.0
5.5
0.5
100
150
200
FREQUENCY (MHz)
250
0
300
64008 G07
1.35
OUTPUT VOLTAGE (V)
NOISE FIGURE (dB)
4.5
INPUT REFERRED NOISE VOLTAGE (nV/√Hz)
9.5
50
50
CMRR
40
30
20
10
–100
1000
0
1
10
100
FREQUENCY (MHz)
1000
64008 G06
Small Signal Transient Response
8.0
0
1000
64008 G05
5.0
NF TEST: RS = 400Ω
800
60
–80
100
FREQUENCY (MHz)
400
600
FREQUENCY (MHz)
PSRR
–60
Noise Figure and Input Referred
Noise Voltage vs Frequency
0
–40
100
64008 G04
5.0
70
20
0
7.5
80
250
–80
10.0
80
40
ZOUT
50
100
1000
FREQUENCY (MHz)
100
60
350
–70
10
200
64008 G03
PHASE (DEGREES)
S PARAMETERS (dB)
S11
–60
0
PSRR and CMRR vs Frequency
PHASE
IMPEDANCE MAGNITUDE
450
–40
–200
3000
0.2
GROUP DELAY
Input and Output Impedance vs
Frequency
–10
–20
0.4
64008 G02
64008 G01
0
–100
PSRR, CMRR (dB)
10
0.6
PHASE
–150
–1.0
–4
Large Signal Transient Response
2.5
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
2.0
1.30
+OUT
1.25
1.20
1.15
0.8
TEST CIRCUIT B
OUTPUT VOLTAGE (V)
GAIN (dB)
8
0
TEST CIRCUIT B
GROUP DELAY (ns)
GAIN FLATNESS (dB)
12
0.8
PHASE (DEGREE)
14
S21 Phase and Group Delay vs
Frequency
Gain 0.1dB Flatness
–OUT
0
2
4
6
TIME (ns)
+OUT
1.5
1.0
–OUT
0.5
8
10
64008 G08
0
0
2
4
6
TIME (ns)
8
10
64008 G09
64008f
6
LTC6400-8
TYPICAL PERFORMANCE CHARACTERISTICS
1% Settling Time for 2V
Output Step
RL = 87.5Ω PER OUTPUT
4 TEST CIRCUIT B
–IN
1
4.5
4
4.0
3
3.5
3.0
+IN
2.5
0
+OUT
–1
2.0
–2
1.5
–3
1.0
–4
–5
1
0
–1
–2
–3
–5
1
0
2
3
TIME (ns)
4
Third Order Intermodulation
Distortion vs Frequency
–40
HARMONIC DISTORTION (dBc)
200Ω RL
–70
NO RL
–80
–90
–100
–110
50
100
150
200
FREQUENCY (MHz)
–90
250
300
HD2 NO RL
HD2 200Ω RL
HD3 NO RL
HD3 200Ω RL
0
50
150
200
100
FREQUENCY (MHz)
250
–50
–70
–80
–90
–110
HD2 NO RL
HD2 200Ω RL
HD3 NO RL
HD3 200Ω RL
0
50
SINGLE-ENDED INPUT
VOUT = 2VP-P COMPOSITE
–50
–60
100
150
200
FREQUENCY (MHz)
250
300
–60
200Ω RL
–70
NO RL
–80
–90
–100
–110
0
50
100
150
200
FREQUENCY (MHz)
250
64008 G14
Equivalent Output 1dB
Compression Point vs Frequency
300
64008 G15
Equivalent Output Third Order
Intercept Point vs Frequency
IMD3 vs VICM and VOCM
70
20
300
Third Order Intermodulation
Distortion vs Frequency
–40
64008 G13
–85
60
–88
19
OUTPUT IP3 (dBm)
OUTPUT 1dB COMPRESSION POINT (dBm)
–80
64008 G12
SINGLE-ENDED INPUT
VOUT = 2VP-P
–100
0
–70
–110
5
18
17
16
15
50
100
150
200
FREQUENCY (MHz)
SWEEP VOCM,
INPUT AC-COUPLE
NO RL
40
200Ω RL
30
–91
SWEEP VICM,
VOCM = 1.25V
–94
20
–97
DIFFERENTIAL INPUT
RL = 375Ω
TEST CIRCUIT A (NOTE 7)
0
50
IMD3 (dBc)
THIRD ORDER IMD (dBc)
–60
–60
Harmonic Distortion vs Frequency
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
–50
–50
64008 G11
64008 G10
–40
DIFFERENTIAL INPUT
VOUT = 2VP-P
–100
–4
0
20 40 60 80 100 120 140 160 180 200
TIME (ns)
0
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
2
0.5
–OUT
Harmonic Distortion vs Frequency
–40
THIRD ORDER IMD (dBc)
2
5
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
3
5.0
SETTLING (%)
5
HARMONIC DISTORTION (dBc)
Overdrive Recovery Response
10
0
250
300
64008 G16
DIFFERENTIAL INPUT
(NOTE 7)
0
50
100
150
200
FREQUENCY (MHz)
250
300
64008 G17
DIFFERENTIAL INPUT, NO RL
VOUT = 100MHz, 2VP-P COMPOSITE
–100
1.0
1.2
1.4
1.6
COMMON MODE VOLTAGE (V)
1.8
64008 G18
64008f
7
LTC6400-8
TYPICAL PERFORMANCE CHARACTERISTICS
Turn-Off Time
3.5
3.0
3.0
2.5
2.5
2.0
+OUT
VOLTAGE (V)
VOLTAGE (V)
Turn-On Time
3.5
1.5
–OUT
1.0
0.5
RL = 87.5Ω PER OUTPUT
2.0
1.5
1.0
+OUT
–OUT
0.5
0
RL = 87.5Ω PER OUTPUT
–0.5
–20
0
20
40
TIME (ns)
0
ENABLE
60
80
64008 G19
ENABLE
–0.5
–20
0
20
40
TIME (ns)
60
80
64008 G20
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 same voltage/ground.
–OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins
have series resistors, ROUT 12.5Ω.
–OUTF, +OUTF (Pins 6, 7): Filtered Outputs. These pins
have 50Ω series resistors and a 2.7pF shunt capacitor.
ENABLE (Pin 11): This pin is a logic input referenced to
VEE. If low, the part is enabled. If high, the part is disabled
and draws very low standby current while the internal op
amp has high output impedance.
+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 same voltage/ground as pins 4, 9, 12.
64008f
8
LTC6400-8
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
2.7pF
RFILT
50Ω
–IN
15
–IN
16
RF
500Ω
RG
200Ω
IN–
RF
500Ω
RG
200Ω
–OUTF
6
OUT+
ROUT
12.5Ω
–OUT
5
2k
COMMON
MODE CONTROL
5.3pF
1
V+
2
3
VOCM
V+
4
64008 BD
V–
APPLICATIONS INFORMATION
Circuit Operation
The LTC6400-8 is a low noise and low distortion fully
differential op amp/ADC driver with:
• Operation from DC to 2.2GHz –3dB bandwidth
• Fixed gain of 2.5V/V (8dB)
• Differential input impedance 400Ω
• Differential output impedance 25Ω
• Differential impedance of output filter 100Ω
The LTC6400-8 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 200Ω/500Ω 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.
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.
The LTC6400-8 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 1.8V for proper operation. If the
inputs are AC-coupled, the input common mode voltage
is automatically biased approximately 450mV above VOCM
and thus no external circuitry is needed for bias. The
LTC6400-8 provides an output common mode voltage
set by VOCM, which allows driving ADC directly without
external components such as transformer or AC coupling
capacitors. The input signal can be either single-ended
or differential with only minor difference in distortion
performance.
Input Impedance and Matching
The differential input impedance of the LTC6400-8 is 400Ω.
Usually the differential inputs need to be terminated to a
lower value impedance, e.g. 50Ω, in order to provide an
impedance match for 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 and shunt resistor (Figure 2). Both methods
provide a wideband match. The termination resistor or
the transformer must be placed close to the input pins in
64008f
9
LTC6400-8
APPLICATIONS INFORMATION
LTC6400-8
500Ω
200Ω
25Ω
13 +IN
+OUT 8
+
–
50Ω
IN+
+
–
VIN
OUT–
14 +IN
57.6Ω
+OUTF 7
50Ω
15 –IN
25Ω
RS
50Ω
12.5Ω
IN–
500Ω
200Ω
2.7pF
0.1μF
LTC6400-8
12.5Ω
13 +IN
+OUT 8
50Ω
1:4
IN+
•
•
+
–
VIN
OUT–
14 +IN
402Ω
15 –IN
25Ω
MINI CIRCUITS
TCM4-19
IN–
200Ω
16 –IN
+OUTF 7
50Ω
500Ω
IN–
OUT+
+OUTF 7
–OUTF 6
500Ω
200Ω
2.7pF
12.5Ω
16 –IN
–OUT 5
27.4Ω
64008 F03
Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance
The LTC6400-8 is unconditionally stable, i.e. differential
stability factor Kf>1 and stability measure B1>0. However,
the overall differential gain is affected by both source
impedance and load impedance as shown in Figure 4:
2.7pF
–OUTF 6
OUT+
OUT–
50Ω
15 –IN
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
500Ω
IN+
0.1μF
–OUT 5
200Ω
+OUT 8
14 +IN
64008 F01
25Ω
12.5Ω
50Ω
RT
59.0Ω
12.5Ω
16 –IN
500Ω
200Ω
13 +IN
VIN
–OUTF 6
OUT+
LTC6400-8
0.1μF
AV =
12.5Ω
VOUT
RL
1000
=
•
VIN
RS + 400 25 + RL
–OUT 5
64008 F02
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a Balun
order to minimize the reflection due to input mismatch.
Alternatively, one could apply a narrowband impedance
match at the inputs of the LTC6400-8 for frequency selection and/or noise reduction.
Referring to Figure 3, LTC6400-8 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
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 322Ω and RT is
59Ω in order to match to a 50Ω source impedance.
The noise performance of the LTC6400-8 also depends upon
the source impedance and termination. For example, an
input 1:4 transformer in Figure 2 improves SNR by adding
6dB 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 input Smith Chart, based
on which users can choose the optimal source impedance
for a given gain and noise requirement.
LTC6400-8
500Ω
200Ω
1/2 RS
12.5Ω
1/2 RL
13 +IN
+OUT 8
50Ω
IN+
+
–
VIN
OUT–
+OUTF 7
14 +IN
VOUT
50Ω
15 –IN
1/2 RS
IN–
200Ω
2.7pF
–OUTF 6
OUT+
500Ω
1/2 RL
12.5Ω
16 –IN
–OUT 5
64008 F04
Figure 4. Calculate Differential Gain
64008f
10
LTC6400-8
APPLICATIONS INFORMATION
Output Impedance Match and Filter
Output Common Mode Adjustment
The LTC6400-8 can drive an ADC directly without external
output impedance matching. Alternatively, the differential
output impedance of 25Ω can be made larger, e.g. 50Ω,
by series resistors or LC network.
The LTC6400-8’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 14MHz, 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 400MHz, allowing fast rejection of any common
mode output voltage disturbance. The VOCM pin should
be tied to a DC bias voltage with a 0.1μF bypass capacitor. When interfacing with 3V A/D converters such as the
LT22xx families, the VOCM pin can be connected to the
VCM pin of the ADC.
The internal low pass filter outputs at +OUTF/–OUTF
have a –3dB bandwidth of 590MHz. External capacitors
can reduce the lowpass filter bandwidth as shown in
Figure 5. A bandpass filter is easily implemented with
LTC6400-8
500Ω
200Ω
12.5Ω
13 +IN
+OUT 8
8pF
50Ω
IN+
OUT–
+OUTF 7
14 +IN
50Ω
15 –IN
IN–
200Ω
2.7pF
FILTERED OUTPUT
12pF (87.5MHz)
–OUTF 6
OUT+
500Ω
8pF
Driving A/D Converters
12.5Ω
16 –IN
–OUT 5
64008 F05
Figure 5. LTC6400-8 Internal Filter Topology Modified for Low
Filter Bandwidth (Three External Capacitors)
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.
500Ω
200Ω
LTC6400-8
12.5Ω
13 +IN
The LTC6400-8 has been specifically designed to interface
directly with high speed A/D converters. Figure 7 shows the
LTC6400-8 with single-ended input driving the LTC2208,
which is a 16-bit, 130Msps ADC. Two external 5Ω resistors
help eliminate potential resonance associated with bond
wires of either the ADC input or the driver output. VOCM
of the LTC6400-8 is connected to VCM of the LTC2208 at
1.25V. Alternatively, an input single-ended signal can be
converted to differential signal via a balun and fed to the
input of the LTC6400-8.
39pF
10Ω
4.99Ω
1.25V
+OUT 8
0.1μF
50Ω
IN+
OUT–
+OUTF 7
14 +IN
15 –IN
IN–
200Ω
16 –IN
0.1μF
16nH
50Ω
OUT+
500Ω
2.7pF
LTC2208
39pF
–OUTF 6
12.5Ω
59.0Ω
10Ω
–OUT 5
64008 F06
4.99Ω
39pF
VOCM
4.99Ω
+IN
IF IN
27.4Ω
0.1μF
+OUT
+OUTF
LTC6400-8
–OUTF
–IN
–OUT
AIN–
VCM
LTC2208
AIN+
4.99Ω
ENABLE
8dB GAIN
LTC2208 130Msps
16-Bit ADC
64008 F07
Figure 6. LTC6400-8 Modified 165MHz for Bandpass Filtering
(Three External Capacitors, One External Inductor)
Figure 7. Single-Ended Input to LTC6400-8 and LTC2208
64008f
11
LTC6400-8
APPLICATIONS INFORMATION
Figure 8 summarizes the IMD3 performance of the whole
system as shown in Figure 7.
–40
SINGLE-ENDED INPUT
FS = 122.8Msps
–50 DRIVER V
OUT = 2VP-P COMPOSITE
IMD3 (dBc)
–60
–70
–80
–90
–100
–110
0
50
100
150
200
FREQUENCY (MHz)
250
300
64008 F08
Figure 8. IMD3 for the Combination of LTC6400-8 and LTC2208
Test Circuits
Due to the fully-differential design of the LTC6400 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 LTC6400 family.
The silkscreen is shown in Figure 9. This circuit includes
input and output transformers (baluns) for single-endedto-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 LTC6400 with a 375Ω differential load, optimizing
distortion performance. Due to the input and output transformers, the –3dB bandwidth is reduced from 2.2GHz to
approximately 1.46GHz.
Figure 9. Top Silkscreen for DC987B. Test Circuit A
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.
64008f
12
LTC6400-8
TYPICAL APPLICATIONS
Demo Circuit 987B Schematic (Test Circuit A)
VCC
3 DIS
2 JP1
VCC
C17
1000pF
R16
0Ω
12
V–
R2
(1)
6
T1
(2)
1
2
C21
0.1μF
4
3
R3
(2)
C2
0.1μF
14
R24
(1)
SL1
(2)
+IN
9
V–
+OUT
+IN
+OUTF
8
R10
86.6Ω
7
R8
(1)
6
R7
(1)
LTC6400-8
15
C1
0.1μF
16
R1
0Ω
–IN
–OUTF
–IN
–OUT
V+
VOCM
1
VCC
C10
0.1μF
VCC
10
V+
V+
2
5
R14
(1)
C4
0.1μF
SL2
(2)
C3
0.1μF
R9
86.6Ω
V–
3
4
C9
1000pF
4
R12
0Ω
1
6
R11
(1)
C22
0.1μF
R13
0Ω
3
2
T2
TCM 4:19
1:4
•
R5
0dB (1)
R4
(2)
•
J2
–IN
R6
0Ω
•
J1
+IN
13
11
ENABLE
C18
0.1μF
•
ENABLE 1
J4
+OUT
SL3
(2)
J5
–OUT
VCC
C12
1000pF
C13
0.1μF
R19
1.5k
TP5
R17
0Ω
6
T3
TCM 4:19
1:4
•
J6
TEST IN
C7
0.1μF
R20
1k
2
C23
0.1μF
C19
0.1μF
4
R21
(1)
C24
0.1μF
3
3
C5
0.1μF
C20
0.1μF
R22
(1)
C6
0.1μF
2
T4
TCM 4:19
1:4
4
R18
0Ω
6
R26
0Ω
•
•
R25
0Ω
1
•
VOCM
1
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
-A
IC
LTC6400CUD-8
SL = SIGNAL LEVEL
R3
R4
T1
SL1
SL2
SL3
200Ω
MINI-CIRCUITS TCM4-19 (1:4)
6dB
8dB
2dB
64008 TA02
64008f
13
LTC6400-8
TYPICAL APPLICATIONS
Test Circuit B, 4-Port Analysis
V+
1000pF
V–
0.1μF
11
V–
V+
ENABLE
12
10
9
BIAS CONTROL
RF
500Ω
RG
200Ω
+IN
13
PORT 1
(50Ω)
ROUT
12.5Ω
RFILT
50Ω
0.1μF
1/2
AGILENT
E5O71A
+IN
14
133Ω
IN+
IN–
+OUTF
CFILT
2.7pF
0.1μF
1/2
AGILENT
E5O71A
–OUTF
6
OUT+
RF
500Ω
RG
200Ω
ROUT
12.5Ω
–OUT 37.4Ω
PORT 4
(50Ω)
5
0.1μF
0.1μF
COMMON
MODE CONTROL
1
1000pF
PORT 3
(50Ω)
7
OUT–
RFILT
50Ω
–IN
15
–IN
16
PORT 2
(50Ω)
+OUT 37.4Ω
8
2
V+
3
VOCM
0.1μF
VOCM
V+
4
64008 TA03
V–
V+
0.1μF
64008f
14
LTC6400-8
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 p0.05
3.50 p 0.05
1.45 p 0.05
2.10 p 0.05 (4 SIDES)
PACKAGE OUTLINE
0.25 p0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 p 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 s 45o CHAMFER
R = 0.115
TYP
0.75 p 0.05
15
16
PIN 1
TOP MARK
(NOTE 6)
0.40 p 0.10
1
1.45 p 0.10
(4-SIDES)
2
(UD16) QFN 0904
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 p 0.05
0.50 BSC
64008f
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
LTC6400-8
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
High-Speed Differential Amplifiers/Differential Op Amps
LT®1993-2
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
LTC6400-14
1.9GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 14dB, 85mA Supply Current, IMD3 = –66dBc at 300MHz
LTC6400-20
1.8GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 20dB, 90mA Supply Current, IMD3 = –65dBc at 300MHz
LTC6400-26
1.9GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 26dB, 85mA Supply Current, IMD3 = –71dBc at 300MHz
LTC6401-8
2.2GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 8dB, 45mA Supply Current, IMD3 = –80dBc at 140MHz
LTC6401-14
2GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 14dB, 45mA Supply Current, IMD3 = –81dBc at 140MHz
LTC6401-20
1.3GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 20dB, 50mA Supply Current, IMD3 = –74dBc at 140MHz
LTC6401-26
1.6GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 26dB, 45mA Supply Current, IMD3 = –72dBc at 140MHz
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
LTC6404-1
600MHz Low Noise Differential ADC Driver
en = 1.5nV/√Hz, Rail-to-Rail Outputs
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
64008f
16 Linear Technology Corporation
LT 0708 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 l FAX: (408) 434-0507 l www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
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