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PDF LTC6421-20 Data sheet ( Hoja de datos )
| Número de pieza | LTC6421-20 | |
| Descripción | Dual Matched 1.3GHz Differential Amplifier/ADC Drivers | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Matched Gain ±0.1dB
n Matched Phase ±0.2° at 100MHz
n Channel Separation 80dB at 100MHz
n 1.3GHz –3dB Bandwidth; Fixed Gain of 10V/V (20dB)
n IMD3 = –76dBc at 100MHz, 2VP-P
n Equivalent OIP3 = 42dBm at 100MHz
n 1nV/√Hz Internal Op Amp Noise
n 6.2dB Noise Figure
n Differential Inputs and Outputs
n Rail-to-Rail Output Swing
n 40mA Supply Current (120mW) per Amplifier
n 1V to 1.6V Output Common Mode Voltage,
Adjustable
n DC- or AC-Coupled Operation
n 20-Lead 3mm × 4mm × 0.75mm QFN Package
APPLICATIONS
n Differential ADC Driver
n Differential Driver/Receiver
n Single Ended to Differential Conversion
n IF Sampling (Diversity) Receivers
LTC6421-20
Dual Matched
1.3GHz Differential
Amplifiers/ADC Drivers
DESCRIPTION
The LTC®6421-20 is a dual 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 LTC6421-20 is easy to use, with minimal support
circuitry required. The output common mode voltage
is set using an external pin, independent of the inputs,
which eliminates the need for transformers or AC-coupling
capacitors in many applications. The gain is internally
fixed at 20dB (10V/ V).
The LTC6421-20 saves space and power compared to
alternative solutions using IF gain blocks and transformers.
The LTC6421-20 is packaged in a compact 20-lead
3mm × 4mm 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.
TYPICAL APPLICATION
Matched Dual Amplifiers with Output Common Mode Biasing
3V
1000pF 0.1μF
VOCMA
V+ A
ZIN = 200Ω LTC6421-20
0.1μF
–INA 100Ω
VINA 0.1μF
+INA 100Ω
V–
VOCMA
1000Ω
1000Ω
0.1μF
+INB 100Ω
1000Ω
VINB 0.1μF
– INB 100Ω
ZIN = 200Ω
V+ B
1000pF 0.1μF
1000Ω
VOCMB
VOCMB
ENABLEA
12.5Ω +OUTA
12.5Ω – OUTA
V–
12.5Ω – OUTB
12.5Ω +OUTB
VOCMA
VOCMA
±0.1dB GAIN MATCHING
±0.1° PHASE MATCHING
AT 100MHz
VOCMB
VOCMB
ENABLEB
642120 TA01a
3V
Distribution of Gain Match
40
35
30
25
20
15
10
5
0
– 0.25 – 0.15 – 0.05 0.05 0.15 0.25
CHANNEL-TO-CHANNEL GAIN MATCH (dB)
642120 TA01b
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC6421-20
Channel-to-Channel Gain Match
vs Frequency
0.5
0.4
0.3
0.2
0.1
0
– 0.1
– 0.2
– 0.3
– 0.4
– 0.5
10
100
FREQUENCY (MHz)
1000 2000
642120 G01
Channel-to-Channel Group Delay
Match vs Frequency
0.5
0.4
0.3
0.2
0.1
0
– 0.1
– 0.2
– 0.3
– 0.4
– 0.5
10
100
FREQUENCY (MHz)
1000 2000
642120 G02
Frequency Response
25 TEST CIRCUIT B
S21 Phase and Group Delay
vs Frequency
100 TEST CIRCUIT B
1.5
20 0 1.2
PHASE
15
–100
0.9
GROUP DELAY
10
–200
0.6
5
– 300
0.3
0
– 400
0
10
100
1000 3000
0 200 400 600 800 1000
FREQUENCY (MHz)
642120 G04
FREQUENCY (MHz)
642120 G05
Input and Output Impedance
vs Frequency
250 100
225 80
ZIN
200 60
175 40
150
ZOUT
20
125 ZIN
100
75 PHASE
IMPEDANCE MAGNITUDE
50
0
–20
– 40
– 60
25
0
1
ZOUT
10 100
FREQUENCY (MHz)
– 80
–100
1000
642120 G07
Noise Figure and Input Referred
Noise Voltage vs Frequency
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
10
6
NOISE FIGURE
eIN
4
2
100
FREQUENCY (MHz)
0
1000
642120 G08
Channel-to-Channel Phase Match
vs Frequency
1.0
0.5
0
– 0.5
–1.0
10
100
FREQUENCY (MHz)
500
642120 G03
Input and Output Reflection and
Reverse Isolation vs Frequency
0 TEST CIRCUIT B
–10
–20 S11
– 30
S22
– 40
– 50
–60 S12
–70
– 80
10
100 1000 3000
FREQUENCY (MHz)
642120 G06
Small-Signal Transient Response
1.35 RL = 87.5Ω PER OUTPUT
1.30
+OUT
1.25
1.20
1.15
0
– OUT
5 10 15 20
TIME (ns)
642120 G09
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LTC6421-20
APPLICATIONS INFORMATION
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 LTC6421-20 has been specifically designed to interface
directly with high speed A/D converters. The back page of
this data sheet shows the LTC6421-20 driving an LTC2285,
which is a dual 14-bit, 125Msps ADC.
The VOCM pins of the LTC6421-20 are connected to the
VCM pins of the LTC2285, which provide a DC voltage
level of 1.5V. Both ICs are powered from the same 3V
supply voltage.
The inputs to the LTC6421-20 can be configured in various
ways, as described in the Input Impedance and Matching
section of this datasheet. The outputs of the LTC6421-20
may be connected directly to the analog inputs of an ADC,
or a simple lowpass or bandpass filter network may be
inserted to reduce out-of-band noise.
Test Circuits
Due to the fully-differential design of the LTC6421 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 DC1299, a
two-port demonstration circuit for the LTC6420/LTC6421
family. The schematic and silkscreen are shown in Figure 4.
This circuit includes input and output transformers (baluns)
for single-ended-to-differential conversion and impedance
transformation, allowing direct hook-up to a 2-port network
analyzer. There are also series resistors at the output to
avoid loading the amplifier directly with a 50Ω load. Due
to the input and output transformers, the –3dB bandwidth
is reduced from 1.3GHz to approximately 1.1GHz.
Test Circuit B uses a 4-port network analyzer to measure
S-parameters and gain/phase response. This removes the
effects of the wideband baluns and associated circuitry,
for a true picture of the >1GHz S-parameters and AC
characteristics.
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC6421-20.PDF ] | |
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