Datasheet
OPA3692
SBOS228E
12
www.ti.com
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.
1/3
OPA3692
1/3
OPA3692
1/3
OPA3692
402Ω402Ω
402Ω
402Ω 402Ω
200Ω 200Ω
402Ω
V
2
V
OUT
V
1
1/3
OPA3692
402Ω402Ω
100Ω
V
1
1/3
OPA3692
402Ω402Ω
100Ω
V
2
1/3
OPA3692
402Ω402Ω
100Ω
V
3
Selection
Logic
ADS826
10-Bit
60MSPS
0.1µF
0.1µF
4.99kΩ
0.1µF
4.99kΩ
0.1µF
100pF
REFT
+3.5V
REFB
+1.5V
+In
–In
CM
FIGURE 3. High-Speed Instrumentation Amplifier.
FIGURE 5. Multiplexed Converter Driver.
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.
FIGURE 4. High-Speed Instrumentation Amplifier Response.
7
6
5
4
3
2
1
0
–1
–2
–3
Frequency (MHz)
140010 100
Gain (dB)
20log
V
OUT
|V
1
– V
2
|
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.