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PDF LTC6400-14 Data sheet ( Hoja de datos )
| Número de pieza | LTC6400-14 | |
| Descripción | Low Distortion Differential ADC Driver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC6400-14
2.4GHz Low Noise, Low
Distortion Differential ADC
Driver for 300MHz IF
FEATURES
n 2.4GHz –3dB Bandwidth
n Fixed Gain of 5V/V (14dB)
n –97dBc IMD3 at 70MHz (Equivalent OIP3 = 52.4dBm)
n –66dBc IMD3 at 300MHz (Equivalent OIP3 = 36.9dBm)
n 1.1nV/√Hz Internal Op Amp Noise
n 2.5nV/√Hz Total Input Noise
n 7.5dB Noise Figure
n Differential Inputs and Outputs
n 200Ω Input Impedance
n 2.85V to 3.5V Supply Voltage
n 85mA Supply Current (255mW)
n 1V to 1.6V Output Common Mode Voltage,
Adjustable
n DC- or AC-Coupled Operation
n Max Differential Output Swing 4.8VP-P
n Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
APPLICATIONS
n Differential ADC Driver
n Differential Driver/Receiver
n Single Ended to Differential Conversion
n IF Sampling Receivers
n SAW Filter Interfacing
DESCRIPTION
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.
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 ca-
pacitors 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.
TYPICAL APPLICATION
Single-Ended to Differential ADC Driver
3.3V
3.3V
C2
0.1μF
C1
1000pF
VIN
R1
68.5Ω
C3
0.1μF
C4
0.1μF
R2
29Ω
V+
+IN +OUT
LTC6400-14
–IN –OUT
VOCM
V–
1.25V
C5
0.1μF
RS1
15Ω
L1
RS2 24nH
15Ω
COILCRAFT
0603CS
R3
100Ω
CF2
33pF
RS3
10Ω AIN+ VDD
CF1
33pF RS4
10Ω
CF3
33pF
LTC2208
AIN– VCM
LTC2208
130Msps
16-Bit ADC
64014 TA01a
Equivalent Output IP3 vs
Frequency
70
(NOTE 7)
60
50
40
30
20
10
0
0 50 100 150 200 250 300
FREQUENCY (MHz)
640020 TA01b
640014fb
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LTC6400-14
AC ELECTRICAL CHARACTERISTICSENABLE = 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
140MHz Input Signal
HD2,140M/HD3,140M Second/Third Order Harmonic
Distortion
IMD3,140M
Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)
OIP3,140M
Third-Order Output Intercept Point
(f1 = 139.5MHz f2 = 140.5MHz)
2VP-P, OUT, RL = 200Ω
2VP-P, OUT, No RL
2VP-P, OUT Composite, RL = 200Ω
2VP-P, OUT Composite, No RL
2VP-P, OUT Composite, No RL (Notes 7)
–78/–74
–81/–79
–80
–85
46.5
dBc
dBc
dBc
dBc
dBm
P1dB,140M
NF140M
eIN,140M
eON,140M
240MHz Input Signal
1dB Compression Point
Noise Figure
Input Referred Voltage Noise Density
RL = 375Ω (Notes 5, 7)
RL = 375Ω (Note 5)
Includes Resistors (Short Inputs)
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
18.8 dBm
7.7 dB
2.5 nV/√Hz
12.6 nV/√Hz
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)
2VP-P, OUT, RL = 200Ω
2VP-P, OUT, No RL
2VP-P, OUT Composite, RL = 200Ω
2VP-P, OUT Composite, No RL
2VP-P, OUT Composite, No RL (Note 7)
– 63/–57
– 67/–63
– 68
–71
39.6
dBc
dBc
dBc
dBc
dBm
P1dB, 240M
NF240M
eN, 240M
eON, 240M
1dB Compression Point
Noise Figure
Input Referred Voltage Noise Density
RL = 375Ω (Notes 5, 7)
RL = 375Ω (Note 5)
Includes Resistors (Short Inputs)
Output Referred Voltage Noise Density Includes Resistors (Short Inputs)
17.9 dBm
8 dB
2.5 nV/√Hz
12.9 nV/√Hz
640014fb
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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 of-
fer 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 imped-
ance 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.
25Ω 100Ω
13 +IN
500Ω
–+ VIN
14 +IN
66.5Ω
15 –IN
IN+ OUT–
IN– OUT+
LTC6400-14
12.5Ω
+OUT 8
50Ω
+OUTF 7
50Ω 2.7pF
–OUTF 6
25Ω 100Ω
16 –IN
500Ω
12.5Ω
–OUT 5
640014 F01
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
25Ω 100Ω
13 +IN
–+ VIN
1:4
••
14 +IN
IN+
15 –IN
IN–
500Ω
OUT–
OUT+
LTC6400-14
12.5Ω
+OUT 8
50Ω
+OUTF 7
50Ω 2.7pF
–OUTF 6
25Ω
MINI-CIRCUITS
TCM4-19
100Ω
16 –IN
500Ω
12.5Ω
–OUT 5
640014 F02
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a 1:4 Balun
640014fb
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC6400-14.PDF ] | |
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