LINER LT6600-2.5 2.4ghz low noise, low distortion differential adc driver for 300mhz if Datasheet

LTC6400-14
2.4GHz Low Noise, Low
Distortion Differential ADC
Driver for 300MHz IF
FEATURES
DESCRIPTION
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The LTC®6400-14 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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2.4GHz –3dB Bandwidth
Fixed Gain of 5V/V (14dB)
–97dBc IMD3 at 70MHz (Equivalent OIP3 = 52.4dBm)
–66dBc IMD3 at 300MHz (Equivalent OIP3 = 36.9dBm)
1.1nV/√Hz Internal Op Amp Noise
2.5nV/√Hz Total Input Noise
7.5dB Noise Figure
Differential Inputs and Outputs
200Ω Input Impedance
2.85V to 3.5V Supply Voltage
85mA Supply Current (255mW)
1V to 1.6V Output Common Mode Voltage,
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 LTC6400-14 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 14dB (5V/V).
The LTC6400-14 saves space and power compared to
alternative solutions using IF gain blocks and transformers.
The LTC6400-14 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
Equivalent Output IP3 vs
Frequency
Single-Ended to Differential ADC Driver
3.3V
70
3.3V
(NOTE 7)
C2
0.1μF
C1
1000pF
CF2
33pF
C3
0.1μF
V+
+OUT
+IN
VIN
R1
68.5Ω
C4
0.1μF
LTC6400-14
–IN
R2
29Ω
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–
R3
100Ω
50
40
30
20
10
VCM
LTC2208
130Msps
16-Bit ADC
0
0
64014 TA01a
C5
0.1μF
OUTPUT IP3 (dBm)
60
50
100
150
200
FREQUENCY (MHz)
250
300
640020 TA01b
640014fb
1
LTC6400-14
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
Lead Temperature (Soldering, 10 sec) .................. 300°C
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
PART MARKING*
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LTC6400CUD-14#PBF
LTC6400CUD-14#TRPBF
LCCR
16-Lead (3mm × 3mm) Plastic QFN
0°C to 70°C
LTC6400IUD-14#PBF
LTC6400IUD-14#TRPBF
LCCR
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)
LTC6400-8
8
2.5
400
85
LTC6400-14
14
5
200
85
LTC6400-20
20
10
200
90
LTC6400-26
26
20
50
85
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
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.
640014fb
2
LTC6400-14
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
14
14.5
UNITS
Input/Output Characteristic
GDIFF
Gain
VIN = ±200mV Differential
l
TCGAIN
Gain Temperature Drift
VIN = ±200mV Differential
l
–0.9
VSWINGMIN
Output Swing Low
Each Output, VIN = ±800mV Differential
l
77
VSWINGMAX
Output Swing High
Each Output, VIN = ±800mV Differential
l
13.5
2.35
VOUTDIFFMAX
Maximum Differential Output Swing
1dB Compressed
l
IOUT
Output Current Drive
Each Output
l
20
VOSDIFF
Input Differential Offset Voltage
l
–3
TCVOSDIFF
Input Differential Offset Voltage Drift
TMIN to TMAX
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
l
160
V
4.8
VP-P
mA
3
0.7
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
200
230
1
l
mV
μV/°C
1
170
mV
2.48
1.8
l
dB
mdB/°C
Ω
pF
18
25
32
Ω
85
100
115
Ω
40
2.7
pF
62
dB
1
V/V
Output Common Mode Voltage Control
GCM
Common Mode Gain
VOCMMIN
Output Common Mode Range, MIN
VOCMMAX
Output Common Mode Range, MAX
VOSCM
Common Mode Offset Voltage
TCVOSCM
Common Mode Offset Voltage Drift
IVOCM
VOCM = 1V to 1.6V
1
1.1
l
l
1.6
1.5
VOCM = 1.1V to 1.5V
l
–15
TMIN to TMAX
l
9
VOCM Input Current
l
4
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
V
V
V
V
15
mV
μV/°C
15
μA
0.8
V
ENABLE Pin
2.4
V
0.5
μA
1.3
3
μA
3
3.5
V
85
96
mA
0.9
3
mA
Power Supply
VS
Operating Supply Range
l
2.85
70
IS
Supply Current
ENABLE = 0.8V
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
55
76
dB
640014fb
3
LTC6400-14
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
–3dBBW
–3dB Bandwidth
200mVP-P, OUT (Note 6)
1.2
2.37
MAX
UNITS
GHz
0.1dBBW
Bandwidth for 0.1dB Flatness
200mVP-P, OUT (Note 6)
200
MHz
0.5dBBW
Bandwidth for 0.5dB Flatness
200mVP-P, OUT (Note 6)
377
MHz
1/f
1/f Noise Corner
15
kHz
SR
Slew Rate
Differential (Note 6)
6000
V/μs
tS1%
1% Settling Time
2VP-P, OUT (Note 6)
1.7
ns
tOVDR
Overdrive Recovery Time
1.9VP-P, OUT (Note 6)
17
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)
16
MHz
2VP-P, OUT, RL = 200Ω
–107/–96
dBc
2VP-P, OUT, No RL
–110/–108
dBc
10MHz Input Signal
HD2,10M/HD3,10M
IMD3,10M
OIP3,10M
Second/Third Order Harmonic
Distortion
Third-Order Intermodulation
(f1 = 9.5MHz f2 = 10.5MHz)
2VP-P, OUT Composite, RL = 200Ω
–99
dBc
2VP-P, OUT Composite, No RL
–110
dBc
Third-Order Output Intercept Point
(f1 = 9.5MHz f2 = 10.5MHz)
2VP-P, OUT Composite, No RL (Note 7)
59.1
dBm
P1dB,10M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.8
dBm
NF10M
Noise Figure
RL = 375Ω (Note 5)
7.5
dB
eIN,10M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.5
nV/√Hz
eON,10M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
13
nV/√Hz
70MHz Input Signal
HD2,70M/HD3,70M
Second/Third Order Harmonic
Distortion
2VP-P, OUT, RL = 200Ω
–86/–85
dBc
2VP-P, OUT, No RL
–89/–94
dBc
–91
dBc
IMD3,70M
Third-Order Intermodulation
(f1 = 69.5MHz f2 = 70.5MHz)
2VP-P, OUT Composite, RL = 200Ω
2VP-P, OUT Composite, No RL
–97
dBc
OIP3,70M
Third-Order Output Intercept Point
(f1 = 69.5MHz f2 = 70.5MHz)
2VP-P, OUT Composite, No RL (Note 7)
52.4
dBm
P1dB,70M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
18.5
dBm
NF70M
Noise Figure
RL = 375Ω (Note 5)
7.5
dB
eIN,70M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.5
nV/√Hz
eON,70M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
12.5
nV/√Hz
640014fb
4
LTC6400-14
AC ELECTRICAL CHARACTERISTICS
ENABLE = 0V, No RL unless otherwise noted.
SYMBOL
Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V,
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Second/Third Order Harmonic
Distortion
2VP-P, OUT, RL = 200Ω
–78/–74
dBc
2VP-P, OUT, No RL
–81/–79
dBc
140MHz Input Signal
HD2,140M/HD3,140M
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
–85
dBc
OIP3,140M
Third-Order Output Intercept Point
(f1 = 139.5MHz f2 = 140.5MHz)
2VP-P, OUT Composite, No RL (Notes 7)
46.5
dBm
P1dB,140M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
18.8
dBm
NF140M
Noise Figure
RL = 375Ω (Note 5)
7.7
dB
eIN,140M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.5
nV/√Hz
eON,140M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
12.6
nV/√Hz
240MHz Input Signal
2VP-P, OUT, RL = 200Ω
–63/–57
dBc
2VP-P, OUT, No RL
–67/–63
dBc
2VP-P, OUT Composite, RL = 200Ω
–68
dBc
2VP-P, OUT Composite, No RL
–71
dBc
Third-Order Output Intercept Point
(f1 = 239.5MHz f2 = 240.5MHz)
2VP-P, OUT Composite, No RL (Note 7)
39.6
dBm
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.9
dBm
HD2,240M/HD3,240M
Second/Third-Order Harmonic
Distortion
IMD3, 240M
Third-Order Intermodulation
(f1 = 239.5MHz f2 = 240.5MHz)
OIP3, 240M
P1dB, 240M
8
dB
NF240M
Noise Figure
RL = 375Ω (Note 5)
eN, 240M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.5
nV/√Hz
eON, 240M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
12.9
nV/√Hz
640014fb
5
LTC6400-14
AC ELECTRICAL CHARACTERISTICS
ENABLE = 0V, No RL unless otherwise noted.
SYMBOL
Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V,
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Second/ Third-Order Harmonic
Distortion
2VP-P, OUT, RL = 200Ω
–61/–51
dBc
2VP-P, OUT, No RL
–61/–55
dBc
300MHz Input Signal
HD2,300M/HD3,300M
IMD3,300M
Third-Order Intermodulation
(f1 = 299.5MHz f2 = 300.5MHz)
2VP-P, OUT Composite, RL = 200Ω
–62
dBc
2VP-P, OUT Composite, No RL
–66
dBc
OIP3,300M
Third-Order Output Intercept Point
(f1 = 299.5MHz f2 = 300.5MHz)
2VP-P, OUT Composite, No RL (Note 7)
36.9
dBm
P1dB,300M
1dB Compression Point
RL = 375Ω (Notes 5, 7)
17.4
dBm
NF300M
Noise Figure
RL = 375Ω (Note 5)
8.2
dB
eN, 300M
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs)
2.5
nV/√Hz
eON, 300M
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
13.9
nV/√Hz
IMD3,280M/320M
Third-Order Intermodulation
(f1 = 280MHz f2 = 320MHz)
Measured at 360MHz
–63
2VP-P, OUT Composite, RL = 375Ω
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
performance from –40 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.
–55
dBc
Note 5: Input and output baluns used. See Test Circuit A.
Note 6: Measured using Test Circuit B.
Note 7: Since the LTC6400-14 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
LTC6400-14 with amplifiers that require 50Ω output load, the LTC6400-14
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.
640014fb
6
LTC6400-14
TYPICAL PERFORMANCE CHARACTERISTICS
20
18
12
10
8
6
4
0
TEST CIRCUIT B
10
100
1000
FREQUENCY (MHz)
3000
0
TEST CIRCUIT B
–50
PHASE
GROUP DELAY
–200
10
100
1000
FREQUENCY (MHz)
225
IMPEDANCE MAGNITUDE (Ω)
–10
–20
–30
–40
–50
– 60
S11
S22
S11
200
ZOUT
150
100
50
–40
100
FREQUENCY (MHz)
50
30
10
–100
1000
0
1
13
4.0
12
3.5
3.0
EN
2.5
10
9
2.0
NOISE FIGURE
1.5
7
1.0
6
0.5
0
1000
640014 G07
10
100
FREQUENCY (MHz)
1000
640014 G06
Large Signal Transient Response
1.35
2.50
–OUT
+OUT
–OUT
+OUT
2.00
1.30
OUTPUT VOLTAGE (V)
4.5
CMRR
40
20
–60
–80
ZOUT
OUTPUT VOLTAGE (V)
NOISE FIGURE (dB)
–20
ZIN
PHASE
IMPEDANCE MAGNITUDE
75
0.0
1000
640014 G05
INPUT REFERRED NOISE VOLTAGE (nV/√Hz)
14
800
PSRR
60
Small Signal Transient Response
5.0
100
FREQUENCY (MHz)
70
0
Noise Figure and Input Referred
Noise Voltage vs Frequency
10
80
20
125
640014 G04
5
80
40
10
100
1000
FREQUENCY (MHz)
100
60
175
25
15
400
600
FREQUENCY (MHz)
PSRR and CMRR vs Frequency
ZIN
0
8
200
640014 G03
PHASE (DEGREES)
S PARAMETERS (dB)
250
11
0
Input and Output Impedance vs
Frequency
0
10
3000
640014 G02
Input and Output Reflection and
Reverse Isolation vs Frequency
–80
0.2
–100
–150
640014 G01
–70
0.4
TEST CIRCUIT B
PSRR, CMRR (dB)
GAIN (dB)
14
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
–0.7
–0.8
–0.9
–1
GROUP DELAY (ns)
GAIN FLATNESS (dB)
16
2
S21 Phase and Group Delay vs
Frequency
Gain 0.1dB Flatness
PHASE (DEGREE)
Frequency Response
1.25
1.20
1.15
1.50
1.00
0.50
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
0
2
4
6
TIME (ns)
8
10
640014 G08
0.00
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
0
2
4
6
TIME (ns)
8
10
640014 G09
640014fb
7
LTC6400-14
TYPICAL PERFORMANCE CHARACTERISTICS
1% Settling Time for 2V
Output Step
RL = 87.5Ω PER OUTPUT
4 TEST CIRCUIT B
+IN
4.5
4
4.0
3
3.5
1
3.0
–IN
0
–1
2.5
2.0
+OUT
–2
1.5
–3
1.0
–OUT
–4
0
20
40
60
TIME (ns)
1
0
–1
–2
–3
–5
1
0
640014 G10
HARMONIC DISTORTION (dBc)
THIRD ORDER IMD (dBc)
–40
–60
–70
–80
–90
–100
–110
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
0
50
100
150
200
FREQUENCY (MHz)
–60
–70
–80
–90
2
3
TIME (ns)
4
–110
5
250
300
640014 G13
HD2 NO RL
HD2 200Ω RL
HD3 NO RL
HD3 200Ω RL
0
50
100
150
200
FREQUENCY (MHz)
250
–50
Third Order Intermodulation
Distortion vs Frequency
–40
SINGLE-ENDED INPUT
VOUT = 2VP-P
–70
–80
–90
HD2 NO RL
HD2 200Ω RL
HD3 NO RL
HD3 200Ω RL
–100
–110
0
50
NO RL
200Ω RL
–50
–60
100
150
200
FREQUENCY (MHz)
250
300
640014 G14
300
640014 G12
Harmonic Distortion vs Frequency
NO RL
200Ω RL
–50
–50
640014 G11
Third Order Intermodulation
Distortion vs Frequency
–40
DIFFERENTIAL INPUT
VOUT = 2VP-P
–100
–4
0
100
80
RL = 87.5Ω PER OUTPUT
TEST CIRCUIT B
2
0.5
–5
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
–60
–70
–80
–90
–100
–110
SINGLE-ENDED INPUT
VOUT = 2VP-P COMPOSITE
0
50
100
150
200
FREQUENCY (MHz)
250
300
640014 G15
640014fb
8
LTC6400-14
TYPICAL PERFORMANCE CHARACTERISTICS
Equivalent Output 1dB
Compression Point vs Frequency
Equivalent Output Third Order
Intercept vs Frequency
70
IMD3 vs VICM and VOCM
–85
NO RL
200Ω RL
60
SWEEP VOCM
INPUT AC-COUPLED
–88
18
17
DIFFERENTIAL INPUT
16 R = 375Ω
L
TEST CIRCUIT A
(NOTE 7)
15
0
50
100
150
200
FREQUENCY (MHz)
50
IMD3 (dBc)
OUTPUT IP3 (dBm)
19
40
30
250
300
0
VOUT = 2VP-P COMPOSITE at 100MHz
DIFFERENTIAL INPUT NO RL
DIFFERENTIAL INPUT
(NOTE 7)
–100
0
50
100
150
200
FREQUENCY (MHz)
250
300
1.0
1.2
1.4
1.6
COMMON MODE VOLTAGE (V)
640014 G17
Turn-On Time
1.8
640014 G18
Turn-Off Time
3.0
3.0
2.5
2.5
2.0
2.0
VOLTAGE (V)
3.5
+OUT
1.0
–OUT
0.5
SWEEP VICM
VOCM = 1.25V
–94
–97
10
3.5
1.5
–91
20
640014 G16
VOLTAGE (V)
OUTPUT 1dB COMPRESSION POINT (dBm)
20
RL = 87.5Ω PER OUTPUT
ENABLE
1.5
+OUT
1.0
–OUT
0.5
ENABLE
0
0
RL = 87.5Ω PER OUTPUT
–0.5
–20
0
20
40
TIME (ns)
60
80
640014 G19
–0.5
–20
0
20
40
TIME (ns)
60
80
640014 G20
640014fb
9
LTC6400-14
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 (GND). 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 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 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
2.7pF
RFILT
50Ω
–IN
15
–IN
16
RF
500Ω
RG
100Ω
IN–
OUT+
RF
500Ω
RG
100Ω
–OUTF
6
ROUT
12.5Ω
–OUT
5
2k
COMMON
MODE CONTROL
5.3pF
1
V+
2
VOCM
3
V+
4
640014 BD
V–
640014fb
10
LTC6400-14
APPLICATIONS INFORMATION
Circuit Operation
The LTC6400-14 is a low noise and low distortion fully
differential op amp/ADC driver with:
• Operation from DC to 2.4GHz (–3dB bandwidth)
• Fixed gain of 5V/V (14dB)
• Differential input impedance 200Ω
• Differential output impedance 25Ω
• On-Chip 590MHz output filter
The LTC6400 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.
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 LTC6400-14 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
LTC6400-14 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.
Input Impedance and Matching
The differential input impedance of the LTC6400-14 is
200Ω. If a 200Ω source impedance is unavailable, then
the differential inputs may 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 wide band transformer
(Figure 2). Both methods provide a wide band impedance
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 LTC6400-14 for frequency selection and/or noise
reduction.
Referring to Figure 3, LTC6400-14 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.
LTC6400-14
25Ω
500Ω
100Ω
12.5Ω
13 +IN
+OUT 8
50Ω
IN+
+
–
VIN
OUT–
14 +IN
66.5Ω
50Ω
15 –IN
25Ω
+OUTF 7
IN–
500Ω
100Ω
2.7pF
–OUTF 6
OUT+
12.5Ω
16 –IN
–OUT 5
640014 F01
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
LTC6400-14
25Ω
500Ω
100Ω
12.5Ω
13 +IN
+OUT 8
50Ω
1:4
+
–
VIN
IN+
• •
OUT–
+OUTF 7
14 +IN
50Ω
15 –IN
25Ω
MINI-CIRCUITS
TCM4-19
IN–
100Ω
16 –IN
500Ω
2.7pF
–OUTF 6
OUT+
12.5Ω
–OUT 5
640014 F02
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a 1:4 Balun
640014fb
11
LTC6400-14
APPLICATIONS INFORMATION
RS
50Ω
1000Ω
100Ω
12.5Ω
13 +IN
VIN
+
–
LTC6400-14
0.1μF
+OUT 8
50Ω
RT
68.5Ω
IN+
OUT–
+OUTF 7
14 +IN
0.1μF
50Ω
15 –IN
0.1μF
RT
29Ω
IN–
2.7pF
–OUTF 6
OUT+
1000Ω
100Ω
12.5Ω
–OUT 5
16 –IN
640014 F03
Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance
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 202Ω and RT is
68.5Ω in order to match to a 50Ω source impedance.
The LTC6400-14 is unconditionally stable under normal
bias conditions. However, the overall differential gain is
affected by both source impedance and load impedance
as shown in Figure 4:
Output Match and Filter
The LTC6400-14 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 capacitors 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
The 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. The bandwidth of VOCM control is typically 16MHz,
LTC6400-14
V
RL
1000
A V = OUT =
•
VIN
RS + 200 25 + RL
500Ω
100Ω
12.5Ω
13 +IN
+OUT 8
IN+
The noise performance of the LTC6400-14 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 voltage 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 input Smith Chart, based on which users can
choose the optimal source impedance for a given gain
and noise requirement.
OUT–
+OUTF 7
14 +IN
50Ω
15 –IN
IN–
100Ω
12.5Ω
13 +IN
–OUT 5
640014 F05
Figure 5. LTC6400-14 Internal Filter Topology Modified for Low
Filter Bandwidth (Three External Capacitors)
500Ω
100Ω
LTC6400-14
12.5Ω
+
–
VIN
IN+
OUT–
+OUTF 7
14 +IN
16nH
50Ω
15 –IN
IN–
OUT+
2.7pF
15 –IN
IN–
100Ω
2.7pF
–OUTF 6
OUT+
16 –IN
500Ω
–OUTF 6
12.5Ω
10Ω
–OUT 5
640014 F06
100Ω
16 –IN
LTC2208
39pF
VOUT
50Ω
1/2 RS
4.99Ω
50Ω
+OUTF 7
14 +IN
39pF
10Ω
+OUT 8
50Ω
OUT–
8.2pF
12.5Ω
16 –IN
1/2 RL
+OUT 8
IN+
FILTERED OUTPUT
12pF (87.5MHz)
–OUTF 6
500Ω
LTC6400-14
500Ω
100Ω
2.7pF
OUT+
13 +IN
1/2 RS
8.2pF
50Ω
500Ω
4.99Ω
39pF
1/2 RL
12.5Ω
–OUT 5
640014 F04
Figure 4. Calculate Differential Gain
Figure 6. LTC6400-14 Internal Filter Topology Modified
for Bandpass Filtering (Three External Capacitors, One
External Inductor)
640014fb
12
LTC6400-14
APPLICATIONS INFORMATION
–40
SINGLE-ENDED INPUT
fS = 122.8Msps
–50 DRIVER V
OUT = 2VP-P COMPOSITE
–60
IMD3 (dBc)
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 common mode rejection at the outputs of
the LTC6400-14. 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.
–70
–80
–90
–100
–110
Driving A/D Converters
0
The LTC6400-14 has been specifically designed to interface directly with high speed A/D converters. In Figure 7,
an example schematic shows the LTC6400-14 with a
single-ended input driving the LTC2208, which is a 16-bit,
130Msps ADC. Two external 4.99Ω resistors help eliminate
potential resonance associated with stray capacitance of
PCB traces and bond wires of either the ADC input or the
driver output. VOCM of the LTC6400-14 is connected to VCM
of the LTC2208 VCM pin at 1.25V. Alternatively, a singleended input signal can be converted to a differential signal
via a balun and fed to the input of the LTC6400-14.
50
100
150
200
FREQUENCY (MHz)
250
300
640014 F08
Figure 8. IMD3 for the Combination of LTC6400-14 and LTC2208
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 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
Top Silkscreen
Figure 8 summarizes the IMD3 of the whole system in
Figure 7. Note that Figure 7 shows a direct connection
to the LTC2208, but in many applications an anti-alias
filter would be desirable to limit the wideband noise of
the amplifier. This is especially true in high performance
16-bit designs.
Test Circuits
Due to the fully-differential design of the LTC6400 and
its usefulness in applications with differing characteristic
1.25V
0.1μF
0.1μF
+IN
IF IN
66.5Ω
29Ω
0.1μF
VOCM
4.99Ω
+OUT
+OUTF
LTC6400-14
–OUTF
–IN
–OUT
AIN–
VCM
LTC2208
AIN+
4.99Ω
ENABLE
14dB GAIN
LTC2208 130Msps
16-Bit ADC
640014 F07
Figure 7. Single-Ended Input to LTC6400-14 and LTC2208
640014fb
13
LTC6400-14
APPLICATIONS INFORMATION
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 2.4GHz to approximately 1.8GHz.
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.
TYPICAL APPLICATIONS
Demo Circuit 987B Schematic (Test Circuit A)
VCC
ENABLE 1
3 DIS
2 JP1
VCC
C17
1000pF
R16
0Ω
12
V–
R2
(1)
T1
(2)
4
R4
(2)
2
3
C21
0.1μF
R3
(2)
C2
0.1μF
14
R24
(1)
SL1
(2)
+IN
+OUT
+IN
+OUTF
8
R10
86.6Ω
7
R8
(1)
LTC6400-14
15
C1
0.1μF
16
R1
0Ω
–IN
–OUTF
–IN
–OUT
V+
VOCM
1
VCC
C10
0.1μF
VCC
9
V–
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
4
R12
0Ω
1
5
R11
(1)
C22
0.1μF
R13
0Ω
3
2
•
R5
0dB (1)
1
•
5
10
V+
•
J2
–IN
R6
0Ω
•
J1
+IN
13
11
ENABLE
C18
0.1μF
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
-B
IC
LTC6400CUD-14
R3
R4
OPEN OPEN
T1
SL1
SL2
SL3
MINI-CIRCUITS TCM4-19 (1:4)
6dB
14dB
8dB
SL = SIGNAL LEVEL
SL LEVELS DO NOT INCLUDE TRANSFORMER LOSS IN T1 AND T2
640014 TA03
640014fb
14
LTC6400-14
TYPICAL APPLICATIONS
Test Circuit B, 4-Port Analysis
V+
1000pF
V–
0.1μF
11
V–
V+
ENABLE
12
10
9
LTC6400-14
BIAS CONTROL
RF
500Ω
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)
IN–
CFILT
2.7pF
1/2
AGILENT
E5O71A
–OUTF
6
OUT+
RF
500Ω
RG
100Ω
–IN
16
0.1μF
+OUTF
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
640014 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 16
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)
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
640014fb
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
LTC6400-14
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
LTC6400-8
2.2GHz Low Noise, Low Distortion, Differential ADC Driver
AV = 8dB, 85mA Supply Current, IMD3 = –61dBc 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
640014fb
16 Linear Technology Corporation
LT 0908 REV B • 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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