LTC6401IUD-8#PBF Linear Technology, LTC6401IUD-8#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC6401IUD-8#PBF
• Description: IC ADC DRIVER DIFF 16-QFN
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LTC6401IUD-8#PBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
Circuit Operation
The LTC6401-8 is a low noise and low distortion fully
differential op amp/ADC driver with:
The LTC6401-8 is composed of a fully differential amplifi er
with on chip feedback and output common mode voltage
control circuitry. Differential gain and input impedance
are set by 200Ω/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 fi ltering option, which is often desirable when the
load is an ADC.
Filter resistors of 50Ω are available for additional fi ltering.
Lowpass/bandpass fi lters 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 LTC6401-8 is very fl exible 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 approximately 250mV above V
and thus no external circuitry is needed for bias. The
LTC6401-8 provides an output common mode voltage
set by V
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.
• Operation from DC to 2.2GHz –3dB bandwidth
• Fixed gain of 2.5V/V (8dB)
• Differential input impedance 400Ω
• Differential output impedance 25Ω
• Differential impedance of output fi lter 100Ω
OCM
, which allows driving ADC directly without
OCM
Input Impedance and Matching
The differential input impedance of the LTC6401-8 is 400Ω.
Usually the differential inputs 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 avail-
able. One approach is to use a differential shunt resistor
(Figure 1). Another approach is to employ a wideband
transformer and shunt resistor (Figure 2). Both methods
provide a wideband match. The termination resistor or
the transformer must be placed close to the input pins in
order to minimize the refl ection due to input mismatch.
Alternatively, one could apply a narrowband impedance
match at the inputs of the LTC6401-8 for frequency selec-
tion and/or noise reduction.
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a Balun
+
–
V
25Ω
25Ω
IN
MINI CIRCUITS
TCM4-19
+
–
V
25Ω
25Ω
•
IN
1:4
•
57.6Ω
402Ω
13
14
15
16
13
14
15
16
+IN
+IN
–IN
–IN
+IN
+IN
–IN
–IN
200Ω
200Ω
200Ω
200Ω
IN+
IN–
IN+
IN–
500Ω
500Ω
500Ω
500Ω
OUT–
OUT+
OUT–
OUT+
LTC6401-8
12.5Ω
12.5Ω
12.5Ω
12.5Ω
50Ω
50Ω
50Ω
50Ω
LTC6401-8
LTC6401-8
2.7pF
2.7pF
+OUTF
–OUTF
+OUTF
–OUTF
+OUT
–OUT
+OUT
–OUT
64018 F01
64018 F02
64018f
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8
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6
5
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6
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