LINER LTC6400-26 1.9ghz low noise, low distortion differential adc driver for dc-300mhz Datasheet

LTC6400-26
1.9GHz Low Noise,
Low Distortion Differential
ADC Driver for DC-300MHz
FEATURES
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DESCRIPTION
The LTC®6400-26 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.
1.9GHz –3dB Bandwidth
Fixed Gain of 20V/V (26dB)
–94dBc IMD3 at 70MHz (Equivalent OIP3 = 51dBm)
–71dBc IMD3 at 300MHz (Equivalent OIP3 = 39.5dBm)
1nV/√Hz Internal Op Amp Noise
1.5nV/√Hz Total Input Referred Noise
6.8dB Noise Figure
Differential Inputs and Outputs
50Ω 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 4.7VP-P
Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
The LTC6400-26 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 of transformers or AC-coupling capacitors in many applications. The gain is internally fixed
at 26dB (20V/V).
The LTC6400-26 saves space and power compared to
alternative solutions using IF gain blocks and transformers. The LTC6400-26 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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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
Single-Ended to Differential ADC Driver at 140MHz IF
Equivalent OIP3 vs Frequency
3.3V
60
3.3V
DIFFERENTIAL INPUT
(NOTE 7)
50
1000pF
33pF
V+
0.1μF
150W
0.1μF
+OUT
LTC6400-26
–IN
37.4Ω
10Ω
15Ω
+IN
VIN
24nH
–OUT
VOCM
V–
1.25V
0.1μF
10Ω
33pF
VDD
LTC2208
33pF
15Ω
COILCRAFT
0603CS
AIN+
AIN–
VCM
40
30
20
10
LTC2208
130Msps
16-BIT ADC
0
640026 TA01a
100Ω
OUTPUT IP3 (dBm)
0.1μF
NO RL
RL = 200Ω
0
50
100
150
200
FREQUENCY (MHz)
250
300
640026 TA01b
640026fa
1
LTC6400-26
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
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
+IN
+IN
–IN
–IN
TOP VIEW
16 15 14 13
12 V–
V+ 1
VOCM 2
11 ENABLE
17
–OUT
7
8
+OUT
6
10 V+
9 V–
+OUTF
5
–OUTF
V+ 3
V– 4
UD PACKAGE
16-LEAD (3mm s 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
LTC6400CUD-26#PBF
LTC6400IUD-26#PBF
PART MARKING*
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LTC6400CUD-26#TRPBF LCCX
16-Lead (3mm × 3mm) Plastic QFN
0°C to 70°C
LTC6400IUD-26#TRPBF LCCX
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)
IS
(mA)
LTC6400-20
20
10
200
90
LTC6400-26
26
20
50
85
LTC6401-8
8
2.5
400
45
LTC6401-20
20
10
200
50
LTC6401-26
26
20
50
45
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. Other gain versions from 8dB to 14dB will follow.
640026fa
2
LTC6400-26
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
26
27
UNITS
Input/Output Characteristic (+IN, –IN, +OUT, –OUT, +OUTF, –OUTF)
GDIFF
Gain
VIN = ±50mV Differential
●
TCGAIN
Gain Temperature Drift
VIN = ±50mV Differential
●
0.0038
VSWINGMIN
Output Swing Low
Each Output, VIN = ±200mV Differential
●
90
VSWINGMAX
Output Swing High
Each Output, VIN = ±200mV Differential
●
2.35
2.48
V
4.38
4.7
VP-P
25
160
VOUTDIFFMAX
Maximum Differential Output Swing
1dB Compressed
●
IOUT
Output Current Drive
Each Output, VIN = ±200mV,
VOUT > 2VP-P
●
20
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 (+IN, –IN)
Differential
CINDIFF
Input Capacitance
Differential, Includes Parasitics
ROUTDIFF
Output Resistance (+OUT, –OUT)
Differential
●
18
25
32
ROUTFDIFF
Filtered Output Resistance (+OUTF, –OUTF)
Differential
●
85
100
115
COUTFDIFF
Filtered Output Capacitance (+OUTF, –OUTF)
Differential, Includes Parasitics
CMRR
Common Mode Rejection Ratio
Input Common Mode Voltage
1.1V to 1.4V
2
1
42.5
50
mV
μV/°C
1
V
57.5
Ω
V
50
1
●
mV
mA
1.6
●
dB
dB/°C
pF
Ω
Ω
2.7
pF
75
dB
1
V/V
Output Common Mode 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
●
3
IVOCM
VOCM Input Current
●
5
VIL
ENABLE Input Low Voltage
●
VIH
ENABLE Input High Voltage
IIL
ENABLE Input Low Current
ENABLE = 0.8V
●
IIH
ENABLE Input High Current
ENABLE = 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
0.5
μA
3
μA
ENABLE Pin
●
2.4
V
1.4
Power Supply
VS
Operating Supply Range
●
2.85
3
3.5
V
IS
Supply Current
ENABLE = 0.8V
●
70
85
102
mA
ISHDN
Shutdown Supply Current
ENABLE = 2.4V
Both Inputs and Outputs Floating
●
0.8
3
mA
PSRR
Power Supply Rejection Ratio
(Differential Outputs)
2.85V to 3.5V
●
65
96
dB
640026fa
3
LTC6400-26
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
1.9
GHz
0.5dBBW
Bandwidth for 0.5dB Flatness
200mVP-P,OUT (Note 6)
0.53
GHz
0.1dBBW
Bandwidth for 0.1dB Flatness
200mVP-P,OUT (Note 6)
0.28
GHz
1/f
1/f Noise Corner
13.9
kHz
SR
Slew Rate
Differential VOUT = 2V Step (Note 6)
6670
V/μs
tS1%
1% Settling Time
VOUT = 2VP-P (Note 6)
2
ns
tOVDR
Overdrive Recovery Time
VOUT = 1.9VP-P (Note 6)
16
ns
tON
Turn-On Time
+OUT, –OUT Within 10% of Final Values
120
ns
tOFF
Turn-Off Time
ICC Falls to 10% of Nominal
166
ns
–3dBBWVOCM
VOCM Pin Small Signal –3dB BW
0.1VP-P at VOCM, Measured Single-Ended
at Output (Note 6)
14.7
MHz
2VP-P,OUT, RL = 200Ω
–99/–90
dBc
2VP-P,OUT, No RL
–98/–99
dBc
–91
dBc
10MHz Input Signal
HD2,10M/HD3,10M Second/Third Order Harmonic Distortion
IMD3,10M
Third-Order Intermodulation
(f1 = 9.5MHz f2 = 10.5MHz)
2VP-P,OUT Composite, RL = 200Ω
2VP-P,OUT Composite, No RL
–93
dBc
OIP3,10M
Equivalent Third-Order Output Intercept
Point
(f1 = 9.5MHz f2 = 10.5MHz)
2VP-P,OUT Composite, No RL (Note 7)
50.5
dBm
P1dB,10M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.8
dBm
NF10M
Noise Figure
RL = 375Ω (Note 5)
6.8
dB
eIN,10M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
1.5
nV/√Hz
eON,10M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
30
nV/√Hz
70MHz Input Signal
HD2,70M/HD3,70M Second/Third Order Harmonic Distortion
2VP-P,OUT, RL = 200Ω
–87/–81
dBc
2VP-P,OUT, No RL
–87/–94
dBc
IMD3,70M
Third-Order Intermodulation
(f1 = 69.5MHz f2 = 70.5MHz)
2VP-P,OUT Composite, RL = 200Ω
–85
dBc
2VP-P,OUT Composite, No RL
–94
dBc
OIP3,70M
Equivalent Third-Order Output Intercept
Point
(f1 = 69.5MHz f2 = 70.5MHz)
2VP-P,OUT Composite, No RL (Note 7)
51
dBm
P1dB,70M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
18.2
dBm
NF70M
Noise Figure
RL = 375Ω (Note 5)
6.7
dB
eIN,70M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
1.4
nV/√Hz
eON,70M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
28
nV/√Hz
HD2,140M/
HD3,140M
Second/Third Order Harmonic Distortion
2VP-P,OUT, RL = 200Ω
–83/–72
dBc
2VP-P,OUT, No RL
–81/–83
dBc
IMD3,140M
Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)
2VP-P,OUT Composite, RL = 200Ω
–80
dBc
2VP-P,OUT Composite, No RL
–88
dBc
Equivalent Third-Order Output Intercept
Point
(f1 = 139.5MHz f2 = 140.5MHz)
2VP-P,OUT Composite, No RL (Note 7)
48
dBm
140MHz Input Signal
OIP3,140M
640026fa
4
LTC6400-26
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)
18.7
NF140M
Noise Figure
RL = 375Ω (Note 5)
6.6
dB
eN,140M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
1.4
nV/√Hz
eON,140M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
28
nV/√Hz
dBm
240MHz Input Signal
2VP-P,OUT, RL = 200Ω
–70/–59
dBc
2VP-P,OUT, No RL
–75/–71
dBc
2VP-P,OUT Composite, RL = 200Ω
–70
dBc
2VP-P,OUT Composite, No RL
–76
dBc
2VP-P,OUT Composite, No RL (Note 7)
42
dBm
RL = 375Ω (Notes 5, 7)
18.1
dBm
RL = 375Ω (Note 5)
6.9
dB
Includes Resistors (Short Inputs)
1.4
nV/√Hz
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
28
nV/√Hz
HD2,300M/
HD3,300M
Second/Third Order Harmonic Distortion
2VP-P,OUT, RL = 200Ω
–66/–54
dBc
2VP-P,OUT, No RL
–76/–62
dBc
IMD3,300M
Third Order Intermodulation
(f1 = 299.5MHz f2 = 300.5MHz)
2VP-P,OUT Composite, RL = 200Ω
–66
dBc
2VP-P,OUT Composite, No RL
–71
dBc
OIP3,300M
Equivalent Third Order Output Intercept
Point
(f1 = 299.5MHz f2 = 300.5MHz)
2VP-P,OUT Composite, No RL (Note 7)
39.5
dBm
P1dB,300M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.7
dBm
NF300M
Noise Figure
RL = 375Ω (Note 5)
7.6
dB
HD2,240M/
HD3,240M
Second/Third Order Harmonic Distortion
IMD3,240M
Third Order Intermodulation
(f1 = 239.5MHz f2 = 240.5MHz)
OIP3,240M
Third Order Output Intercept Point
(f1 = 239.5MHz f2 = 240.5MHz)
P1dB,240M
1dB Compression Point
NF240M
Noise Figure
eN,240M
Input Referred Voltage Noise Density
eON,240M
300MHz Input Signal
eN,300M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
1.5
nV/√Hz
eON,300M
Output Referred Voltage Noise Density
Includes Resistors (Short Inputs)
30
nV/√Hz
IMD3,280M/320M
Third Order Intermodulation
(f1 = 280MHz f2 = 320MHz) Measured at
360MHz
2VP-P,OUT Composite, RL = 375Ω
–68
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 is 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
–62
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 LTC6400-26 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
LTC6400-26 with amplifiers that require 50Ω output load, the LTC6400-26
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.
640026fa
5
LTC6400-26
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
Gain 0.1dB Flatness
30
1.0
0.8
25
GAIN FLATNESS (dB)
0.6
GAIN (dB)
20
15
10
0.2
0
–0.2
–0.4
–0.6
5
0
0.4
–0.8
TEST CIRCUIT B
100
1000
FREQUENCY (MHz)
10
–1.0
3000
10
100
FREQUENCY (MHz)
640026 G01
640026 G02
Input and Output Reflection and
Reverse Isoloation vs Frequency
S21 Phase and Group Delay
vs Frequency
0
1000 2000
TEST CIRCUIT B
0
0.8
GROUP DELAY
0.6
–100
0.4
PHASE
–150
GROUP DELAY (ns)
PHASE (DEGREE)
–50
S PARAMETERS (dB)
–10
–20
S22
–30
–40
S11
–50
–60
0.2
S12
–70
–200
0
200
600
400
FREQUENCY (MHz)
800
–80
0
1000
10
100
1000
FREQUENCY (MHz)
640026 G04
640026 G03
Input and Output Impedance
vs Frequency
ZIN MAG
ZOUT MAG
ZIN PHASE
ZOUT PHASE
90
80
45
70
35
60
30
50
25
40
20
30
15
20
10
10
5
0
10
100
FREQUENCY (MHz)
100
40
0
1000
640026 G05
PHASE (DEGREE)
IMPEDANCE MAGNITUDE (Ω)
PSRR and CMRR vs Frequency
120
50
PSRR, CMRR (dB)
100
3000
80
PSRR
60
CMRR
40
20
0
1
10
100
FREQUENCY (MHz)
1000
640026 G06
640026fa
6
LTC6400-26
TYPICAL PERFORMANCE CHARACTERISTICS
Small Signal Transient Response
2.5
9
2.0
EN
8
1.5
7
1.0
NOISE FIGURE
6
5
10
0.5
1.35
OUTPUT VOLTAGE (V)
10
INPUT REFERRED NOISE VOLTAGE
(nV/√Hz)
NOISE FIGURE (dB)
Noise Figure and Input Referred
Noise Voltage vs Frequency
0
1000
100
FREQUENCY (MHz)
RL = 87.5W PER OUTPUT
TEST CIRCUIT B
–OUT
1.30
1.25
+OUT
1.20
1.15
2
0
6
4
TIME (ns)
8
640026 G07
640026 G08
Large Signal Transient Response
2.5
Overdriven Transient Response
2.5
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
1.5
+OUT
0.5
0
RL = 87.5Ω PER OUTPUT
+OUT
2.0
–OUT
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
2.0
1.0
1.5
1.0
0.5
0
4
12
8
TIME (ns)
16
0
20
–OUT
TEST CIRCUIT B
0
50
150
100
TIME (ns)
640026 G09
HARMONIC DISTORTION (dBc)
3
SETTLING (%)
2
1
0
–1
–2
–3
DIFFERENTIAL INPUT
VOUT = 2VP-P
–50
–60
–70
–80
–90
HD2 NO RL
HD2 RL = 200Ω
HD3 NO RL
HD3 RL = 200Ω
–100
–4
–5
–110
0
1
3
2
TIME (ns)
250
Harmonic Distortion vs Frequency
–40
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
4
200
640026 G10
1% Settling Time for
2V Output Step
5
10
4
5
640026 G11
0
50
200
150
100
FREQUENCY (MHz)
250
300
640026 G12
640026fa
7
LTC6400-26
TYPICAL PERFORMANCE CHARACTERISTICS
Third Order Intermodulation
Distortion vs Frequency
HARMONIC DISTORTION (dBc)
–50
THIRD ORDER IMD (dBc)
–40
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
–60
–70
–80
–90
–100
–110
0
50
200
150
100
FREQUENCY (MHz)
250
–50
–70
–80
–90
–110
300
HD2 NO RL
HD2 RL = 200Ω
HD3 NO RL
HD3 RL = 200Ω
0
50
200
150
100
FREQUENCY (MHz)
250
640026 G13
–70
–80
–90
–100
300
–110
NO RL
RL = 200Ω
0
OUTPUT IP3 (dBm)
17
16
DIFFERENTIAL INPUT
(NOTE 7)
40
30
20
10
250
100
150
200
FREQUENCY (MHz)
0
300
NO RL
RL = 200Ω
0
50
250
100
150
200
FREQUENCY (MHz)
640026 G16
640026 G17
Turn-On Time
Turn-Off Time
140
3.5
3.0
120
3.0
120
100
100
2.5
2.0
–OUT
80
2.0
60
1.5
40
+OUT
0.5
20
ENABLE
0
–0.5
–100
0
0
100
300
200
TIME (ns)
400
500
640026 G18
–20
VOLTAGE (V)
ICC
140
ENABLE
80
–OUT
60
1.5
1.0
40
+OUT
0.5
20
ICC
0
–0.5
–100
ICC (mA)
2.5
ICC (mA)
VOLTAGE (V)
300
3.5
1.0
300
50
18
50
250
640026 G15
60
DIFFERENTIAL INPUT
RL = 3757
TEST CIRCUIT A
19 (NOTE 7)
0
200
150
100
FREQUENCY (MHz)
50
Equivalent Output Third Order
Intercept Point vs Frequency
20
OUTPUT 1dB COMPRESSION POINT (dBm)
–60
640026 G14
Output 1dB Compression Point
vs Frequency
15
SINGLE-ENDED INPUT
VOUT = 2VP-P COMPOSITE
–50
–60
–100
NO RL
RL = 200Ω
–40
SINGLE-ENDED INPUT
VOUT = 2VP-P
THIRD ORDER IMD (dBc)
–40
Third Order Intermodulation
Distortion vs Frequency
Harmonic Distortion vs Frequency
0
100
300
200
TIME (ns)
0
400
–20
500
640026 G19
640026fa
8
LTC6400-26
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. An 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 12.5Ω resistors ROUT.
–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.
BLOCK DIAGRAM
12
V–
11
ENABLE
10
V+
9
V–
BIAS CONTROL
+IN
13
RF
500Ω
RG
25Ω
+OUT
8
RFILT
50Ω
+IN
14
IN+
+OUTF
7
OUT–
CFILT
2.7pF
RFILT
50Ω
–IN
15
–IN
16
ROUT
12.5Ω
IN–
OUT+
RF
500Ω
RG
25Ω
–OUTF
6
ROUT
12.5Ω
–OUT
5
2k
COMMON
MODE CONTROL
5.3pF
1
V+
2
3
VOCM
V+
4
640026 BD
V–
640026fa
9
LTC6400-26
APPLICATIONS INFORMATION
• Operation from DC to 1.9GHz –3dB bandwidth
• Fixed gain of 20V/V (26dB)
• Differential input impedance 50Ω
• Differential output impedance 25Ω
• Differential impedance of output filter 100Ω
The LTC6400-26 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 25Ω/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 LTC6400-26 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 LTC6400-26 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.
Referring to Figure 3, LTC6400-26 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 75Ω and RT is 150Ω in
order to match to a 50Ω source impedance.
LTC6400-26
25Ω
The differential input impedance of the LTC6400-26 is 50Ω.
The interface between the input of LTC6400-26 and 50Ω
source is straightforward. One way is to directly connect
12.5Ω
13 +IN
+OUT 8
50Ω
+
–
VIN
IN+
OUT–
IN–
OUT+
+OUTF 7
14 +IN
50Ω
15 –IN
25Ω
500Ω
25Ω
2.7pF
–OUTF 6
12.5Ω
16 –IN
–OUT 5
640026 F01
Figure 1. Input Termination for Differential 50Ω Input Impedance
LTC6400-26
500Ω
25Ω
50Ω
12.5Ω
13 +IN
+OUT 8
50Ω
+
–
VIN
1:1
IN+
OUT–
IN–
OUT+
+OUTF 7
14 +IN
50Ω
15 –IN
25Ω
Input Impedance and Matching
500Ω
25Ω
•
The LTC6400-26 is a low noise and low distortion fully
differential op amp/ADC driver with:
them if the source is differential (Figure 1). Another approach is to employ a wideband transformer if the source
is single ended (Figure 2). Both methods provide a wideband match. 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 LTC6400-26 for
frequency selection and/or noise reduction.
•
Circuit Operation
16 –IN
MACOM
MABA-007159-000000
500Ω
2.7pF
–OUTF 6
12.5Ω
–OUT 5
640026 F02
Figure 2. Input Termination for Differential 50Ω
Input Impedance Using a Balun
640026fa
10
LTC6400-26
APPLICATIONS INFORMATION
RS
50Ω
VIN
+
–
LTC6400-26
0.1μF
500Ω
25Ω
12.5Ω
13 +IN
RT
150Ω
+OUT 8
50Ω
IN+
OUT–
+OUTF 7
14 +IN
50Ω
15 –IN
0.1μF
IN–
2.7pF
–OUTF 6
OUT+
500Ω
25Ω
12.5Ω
16 –IN
–OUT 5
37.4Ω
640026 F03
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.
Output Common Mode Adjustment
Figure 3. Input Termination for Single-Ended
50Ω Input Impedance
The LTC6400-26 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:
AV =
VOUT
RL
1000
=
•
VIN
RS + 50 25 + RL
The noise performance of the LTC6400-26 also depends
upon the source impedance and termination. A trade-off
between gain and noise is obvious when constant noise
figure circle and constant gain circle are plotted within
the same input Smith Chart, based on which users can
choose the optimal source impedance for a given gain
and noise requirement.
Output Impedance Match and Filter
The LTC6400-26 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 LTC6400-26’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 of
400MHz, allowing fast rejection of any common mode
output disturbance. The VOCM pin should be tied to a DC
bias voltage with a 0.1μF bypass capacitor. When interfacing with A/D converters such as the LTC22xx families, the
VOCM pin can be connected to the VCM pin of the ADC.
Driving A/D Converters
The LTC6400-26 has been specifically designed to interface
directly with high speed A/D converters. Figure 7 shows the
LTC6400-26 with a 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 LTC6400-26 is connected to VCM of the LTC2208
at 1.25V. Alternatively, a single-ended input signal can be
LTC6400-26
1/2 RS
500Ω
25Ω
13 +IN
LTC6400-26
1/2 RL
12.5Ω
+OUT 8
500Ω
25Ω
13 +IN
+OUT 8
50Ω
IN+
+
–
VIN
OUT–
50Ω
15 –IN
1/2 RS
IN–
25Ω
16 –IN
500Ω
IN+
VOUT
OUT–
50Ω
15 –IN
1/2 RL
12.5Ω
–OUT 5
640026 F04
Figure 4. Calculate Differential Gain
+OUTF 7
14 +IN
2.7pF
–OUTF 6
OUT+
8.2pF
50Ω
+OUTP 7
14 +IN
12.5Ω
IN–
25Ω
16 –IN
–OUTF 6
OUT+
500Ω
2.7pF
FILTERED OUTPUT
12pF (87.5MHz)
8.2pF
12.5Ω
–OUT 5
640026 F05
Figure 5. LTC6400-26 Internal Filter Topology Modified
for Low Filter Bandwidth (Three External Capacitors)
640026fa
11
LTC6400-26
APPLICATIONS INFORMATION
–40
LTC6400-26
12.5Ω
500Ω
25Ω
13 +IN
SINGLE-ENDED INPUT
FS = 122.8Msps
–50 DRIVER VOUT = 2VP-P COMPOSITE
39pF
10Ω
4.99Ω
–60
+OUT 8
50Ω
IN+
–70
OUT–
+OUTF 7
14 +IN
15 –IN
IN–
OUT+
500Ω
25Ω
16nH
1.7pF
50Ω
39pF
LTC2208
–80
–90
–OUTF 6
12.5Ω
16 –IN
10Ω
–OUT 5
640026 F06
–100
4.99Ω
–110
39pF
0
50
200
150
100
FREQUENCY (MHz)
250
300
640026 F08
Figure 6. LTC6400-26 with 165MHz Output Bandpass Filter
converted to a differential signal via a balun and fed to the
input of the LTC6400-26. Figure 8 summarizes the IMD3
performance of the whole system in Figure 7.
Test Circuits
Figure 8. IMD3 for the Combination of LTC6400-26 and LTC2208
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.
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 1.9GHz to 1.67GHz.
1.25V
0.1μF
0.1μF
IF IN
VOCM
4.99Ω
+OUT
+OUTF
LTC6400-26
–OUTF
–OUT
–IN
+IN
150Ω
37.4Ω
0.1μF
AIN+
VCM
LTC2208
AIN–
4.99Ω
ENABLE
26dB GAIN
LTC2208 130Msps
16-Bit ADC
640026 F07
Figure 7. Single-Ended Input to LTC6400-26 and LTC2208
Figure 9. Top Silkscreen of DC987B, Test Circuit A
640026fa
12
LTC6400-26
TYPICAL APPLICATION
Demo Circuit 987B Schematic (Test Circuit A)
VCC
ENABLE 1
3 DIS
2 JP1
VCC
C17
1000pF
R16
0W
12
V–
R2
(1)
T1
(2)
R5
0dB (1)
1
•
•
5
4
R4
(2)
2
3
C21
0.1μF
R3
(2)
C2
0.1μF
14
R24
(1)
SL1
(2)
16
R1
0Ω
+IN
+OUTF
–IN
–OUTF
–IN
–OUT
V+
VOCM
1
VCC
R10
86.6Ω
7
R8
(1)
C10
0.1μF
V+
2
6
5
R14
(1)
C4
0.1μF
SL2
(2)
R7
(1)
C3
0.1μF
R9
86.6Ω
V–
3
4
C9
1000pF
T2
TCM 4:19
1:4
4
R12
0Ω
1
6
R11
(1)
C22
0.1μF
R13
0Ω
3
2
J4
+OUT
SL3
(2)
J5
–OUT
VCC
C12
1000pF
C13
0.1μF
R19
1.5k
TP5
VOCM
C7
0.1μF
R20
1k
R17
0Ω
6
T3
TCM 4:19
1:4
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
•
•
J6
TEST IN
+OUT
+IN
8
LTC6400-26
15
C1
0.1μF
VCC
9
V–
•
J2
–IN
R6
0Ω
10
V+
•
J1
+IN
13
11
ENABLE
C18
0.1μF
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
-D
IC
LTC6400CUD-26
SL = SIGNAL LEVEL
R3
R4
T1
OPEN OPEN MACOM MABA-007159-000000
SL1
SL2
SL3
0dB
20dB
14dB
640026 TA02
640026fa
13
LTC6400-26
TYPICAL APPLICATIONS
Test Circuit B, 4-Port Analysis
V+
0.1μF
1000pF
12
V–
11
ENABLE
10
V+
9
V–
BIAS CONTROL
24.9Ω
PORT 1
(50Ω)
RF
500Ω
RG
25Ω
+IN
13
ROUT
12.5Ω
RFILT
50Ω
0.1μF
+IN
14
1/2
AGILENT
E5O71A
IN+
24.9Ω
PORT 3
(50Ω)
+OUTF
IN–
CFILT
2.7pF
1/2
AGILENT
E5O71A
–OUTF
6
OUT+
RF
500Ω
RG
25Ω
–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
2
V+
3
VOCM
0.1μF
1000pF
VOCM
V+
4
640026 TA03
V–
V+
0.1μF
Optical Photodiode Receiver
3V
3V
249Ω
100pF
0.1μF
0.1μF
0.1μF
LTC6400-26
249Ω
640026 TA04
PD:JDSU ETX 100RFC2
–3dB BW: 1.1GHz
RISE TIME: 200ps
640026fa
14
LTC6400-26
PACKAGE DESCRIPTION
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 p 0.05
3.50 p 0.05
1.45 p 0.05
2.10 p 0.05 (4 SIDES)
PACKAGE OUTLINE
0.25 p 0.05
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
640026fa
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
LTC6400-26
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 = 2V/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
LTC6401-8
2.2GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 8dB, 45mA Supply Current, IMD3 = –80dBc 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
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/
LT1814
High Slew Rate Low Cost Single/Dual/Quad Op Amps
8nV/√Hz Noise, 750V/μs, 3mA Supply Current
LT1815/LT1816/
LT1817
Very High Slew Rate Low Cost Single/Dual/Quad Op Amps
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/
LT6204
Rail-to-Rail Input and Output Low Noise Single/Dual/Quad
Op Amps
1.9nV/√Hz Noise, 3mA Supply Current, 100MHz GBW
LT6230/LT6231/
LT6232
Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps
1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW
LT6233/LT6234/
LT6235
Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps
1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW
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
Integrated Filters
640026fa
16 Linear Technology Corporation
LT 1108 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
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