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PDF LTC6401-14 Data sheet ( Hoja de datos )
| Número de pieza | LTC6401-14 | |
| Descripción | Low Distortion Differential ADC Driver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC6401-14
2GHz Low Noise, Low
Distortion Differential ADC
Driver for DC-140MHz
FEATURES
■ 2GHz –3dB Bandwidth
■ Fixed Gain of 5V/V (14dB)
■ –91dBc IMD3 at 70MHz (Equivalent OIP3 = 49.3dBm)
■ –81dBc IMD3 at 140MHz (Equivalent OIP3 = 44.5dBm)
■ 1.1nV/√⎯H⎯z Internal Op Amp Noise
■ 7.3dB Noise Figure
■ Differential Inputs and Outputs
■ 200Ω Input Impedance
■ 2.85V to 3.5V Supply Voltage
■ 45mA Supply Current (135mW)
■ 1V to 1.6V Output Common Mode, Adjustable
■ DC- or AC-Coupled Operation
■ Max Differential Output Swing 4.6VP-P
■ Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
APPLICATIONS
■ Differential ADC Driver
■ Differential Driver/Receiver
■ Single Ended to Differential Conversion
■ IF Sampling Receivers
■ SAW Filter Interfacing
DESCRIPTION
The LTC®6401-14 is a high-speed differential amplifier
targeted at processing signals from DC to 140MHz. The
part has been specifically designed to drive 12-, 14- and
16-bit ADCs with low noise and low distortion, but can also
be used as a general-purpose broadband gain block.
The LTC6401-14 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 ca-
pacitors in many applications. The gain is internally fixed
at 14dB (5V/V).
The LTC6401-14 saves space and power compared to
alternative solutions using IF gain blocks and transform-
ers. The LTC6401-14 is packaged in a compact 16-lead
3mm × 3mm QFN package and operates over the –40°C
to 85°C temperature range.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V
C2
0.1μF
C1
1000pF
VIN
R1
68.5Ω
C3
0.1μF
C4
0.1μF
R2
29Ω
V+
+IN +OUT
LTC6401-14
–IN –OUT
VOCM
V–
1.25V
C5
0.1μF
RS1
15Ω
L1
RS2 24nH
15Ω
COILCRAFT
0603CS
R3
100Ω
3.3V
CF2
33pF
RS3
10Ω AIN+ VDD
CF1
33pF RS4
10Ω
CF3
33pF
LTC2208
AIN– VCM
LTC2208
130Msps
16-Bit ADC
640114 TA01a
Equivalent Output IP3 vs Frequency
60 (NOTE 7)
50
40
30
20
10
0
0 20 40 60 80 100 120 140 160 180 200
FREQUENCY (MHz)
640114 TA01b
640114f
1
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LTC6401-14
AC ELECTRICAL CHARACTERISTICS Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V,
⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
140MHz Input Signal
HD2,140M/
HD3,140M
IMD3,140M
Second/Third Order Harmonic Distortion VOUT = 2VP-P, RL = 200Ω
VOUT = 2VP-P, No RL
Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)
VOUT = 2VP-P Composite, RL = 200Ω
VOUT = 2VP-P Composite, No RL
–79/–57
–87/–69
–70
–81
dBc
dBc
dBc
dBc
OIP3,140M
Equivalent Third-Order Output Intercept VOUT = 2VP-P Composite, No RL (Note 7)
Point (f1 = 139.5MHz f2 = 140.5MHz)
44.5 dBm
P1dB,140M
NF140M
eIN,140M
eON,140M
IMD3,130M/150M
1dB Compression Point
Noise Figure
Input Referred Voltage Noise Density
Output Referred Voltage Noise Density
Third-Order Intermodulation
(f1 = 130MHz f2 = 150MHz) Measure at
170MHz
RL = 375Ω (Notes 5, 7)
RL = 375Ω (Note 5)
Includes Resistors (Short Inputs)
Includes Resistors (Short Inputs)
VOUT = 2VP-P Composite, RL = 375Ω
17.7 dBm
7.4 dB
2.5 nV/√⎯H⎯z
12.5 nV/√⎯H⎯z
–70 –61 dBc
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Input pins (+IN, –IN) are protected by steering diodes to either
supply. If the inputs go beyond either supply rail, the input current should
be limited to less than 10mA.
Note 3: The LTC6401C and LTC6401I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
Note 4: The LTC6401C is guaranteed to meet specified performance from
0°C to 70°C. It is designed, characterized and expected to meet specified
performance from –40°C to 85°C but is not tested or QA sampled at these
temperatures. The LTC6401I is guaranteed to meet specified performance
from –40°C to 85°C.
Note 5: Input and output baluns used. See Test Circuit A.
Note 6: Measured using Test Circuit B. RL = 87.5Ω per output.
Note 7: Since the LTC6401-14 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
LTC6401-14 with amplifiers that require 50Ω output load, the LTC6401-14
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
20 TEST CIRCUIT B
18
16
14
12
10
8
6
4
2
0
10 100 1000 3000
FREQUENCY (MHz)
640114 G01
Gain 0.1dB Flatness
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
10
100 1000 3000
FREQUENCY (MHz)
640114 G02
S21 Phase and Group Delay vs
Frequency
0 TEST CIRCUIT B 0.8
–50 0.6
–100
0.4
–150
–200
0
0.2
PHASE
GROUP DELAY
200 400 600
FREQUENCY (MHz)
0
800 1000
640114 G03
640114f
5
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LTC6401-14
APPLICATIONS INFORMATION
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.
200Ω
13 +IN
500Ω
IN+ OUT–
14 +IN
15 –IN
IN–
200Ω
16 –IN
OUT+
500Ω
LTC6401-14
12.5Ω
39pF
10Ω
+OUT 8
50Ω
+OUTF 7
50Ω 1.7pF
16nH
–OUTF 6
12.5Ω
10Ω
–OUT 5
39pF
640114 F06
4.99Ω
39pF
4.99Ω
LTC2208
Figure 6. LTC6401-14 Modified 165MHz for Bandpass
Filtering (Three External Capacitors, One External Inductor)
Output Common Mode Adjustment
The LTC6401-14’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 com-
mon 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 capaci-
tor. 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.
Driving A/D Converters
The LTC6401-14 has been specifically designed to interface
directly with high speed A/D converters. Figure 7 shows the
0.1μF
1.25V
IF IN
68.5Ω
29Ω
0.1μF
0.1μF
VOCM
+IN +OUT
+OUTF
LTC6401-14
–OUTF
–IN –OUT
ENABLE
8dB GAIN
4.99Ω
4.99Ω
AIN– VCM
LTC2208
AIN+
LTC2208 130Msps
16-Bit ADC
640114 F07
Figure 7. Single-Ended Input to LTC6401-14 and LTC2208
LTC6401-14 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 LTC6401-14 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 LTC6401-14.
Figure 8 summarizes the IMD3 performance of the whole
system as shown in Figure 7.
–40
SINGLE-ENDED INPUT
–50
FS = 122.8Msps
DRIVER VOUT = 2VP-P COMPOSITE
–60
–70
–80
–90
–100
–110
0 20 40 60 80 100 120 140 160 180 200
FREQUENCY (MHz)
640114 F08
Figure 8. IMD3 for the Combination of LTC6401-14 and LTC2208
640114f
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| PDF Descargar | [ Datasheet LTC6401-14.PDF ] | |
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