OPA3692IDBQT Datasheet, PDF (12/26 Pages) Texas Instruments – Triple, Wideband, Fixed Gain Video BUFFER AMPLIFIER With Disable

HIGH-SPEED INSTRUMENTATION AMPLIFIER
Figure 3 shows an instrumentation amplifier based on the
OPA3692. The offset matching between inputs makes this an
attractive input stage for this application. The differential-to-
single-ended gain for this circuit is 2.0V/V. The inputs are high
impedance, with only 1pF to ground at each input. The loads
on the OPA3692 outputs are equal for the best harmonic
distortion possible.
V₁
1/3
OPA3692
402Ω
402Ω
402Ω
402Ω
1/3
OPA3692
V₂
200Ω
200Ω
1/3
OPA3692
402Ω
402Ω
V_OUT
FIGURE 3. High-Speed Instrumentation Amplifier.
As shown in Figure 4, the OPA3692 used as an instrumenta-
tion amplifier has a 240MHz, –3dB bandwidth. This plot has
been made for a 1Vp-p output signal using a low-impedance
differential input source.
7
6
5
4
3
2
1
0
–1
V_OUT
20log
–2
|V₁ – V₂|
–3
1
10
100
400
Frequency (MHz)
FIGURE 4. High-Speed Instrumentation Amplifier Response.
MULTIPLEXED CONVERTER DRIVER
The converter driver in Figure 5 multiplexes among the three
input signals. The OPA3692s enable and disable times
support multiplexing among video signals. The make-before-
break disable characteristic of the OPA3692 ensures that the
output is always under control. To avoid large switching
glitches, switch during the sync or retrace portions of the
video signal—the two inputs should be almost equal at these
times. The output is always under control, so the switching
glitches for two 0V inputs are < 20mV. With standard
video signals levels at the inputs, the maximum differential
voltage across the disabled inputs will not exceed the ±1.2V
maximum rating.
The output resistors isolate the outputs from each other
when switching between channels. The feedback network of
the disabled channels forms part of the load seen by the
enabled amplifier, attenuating the signal slightly.
V₁
1/3
OPA3692
402Ω
402Ω
100Ω
4.99kΩ
0.1µF
4.99kΩ
0.1µF
V₂
1/3
OPA3692
402Ω
402Ω
V₃
1/3
OPA3692
100Ω
0.1µF
100pF
100Ω
0.1µF
REFT REFB
+3.5V +1.5V
+In
–In
CM
ADS826
10-Bit
60MSPS
402Ω
402Ω
Selection
Logic
FIGURE 5. Multiplexed Converter Driver.
12
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OPA3692
SBOS228E