Datasheet
HIGH-SPEED INSTRUMENTATION MULTIPLEXED CONVERTER DRIVER
1/3
OPA3695
1/3
OPA3695
1/3
OPA3695
604W604W
604W
604W 604W
301W 301W
604W
V
2
V
OUT
V
1
1/3
OPA3695
R
604
F
W
100W
V
1
1/3
OPA3695
100W
V
2
1/3
OPA3695
100W
V
3
Selection
Logic
ADS828
10-Bit
75MSPS
0.1 Fm
0.1 Fm
4.99kW
0.1 Fm
4.99kW
0.1 Fm
100pF
REFT
+3.5V
REFB
+1.5V
+In
-In
CM
+5V
R
604
G
W
R
511
F
W
R
169
G
W
R
402
F
W
R
57.6
G
W
OPA3695
SBOS355A – APRIL 2008 – REVISED SEPTEMBER 2008 ...............................................................................................................................................
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AMPLIFIER
The converter driver in Figure 42 multiplexes among
Figure 41 shows an instrumentation amplifier circuit the three input signals with gains of +2V/V, +4V/V,
based on the OPA3695. Because all three amplifiers and +8V/V. The OPA3695 enable and disable times
are on the same silicon die, the offset matching support multiplexing among video signals. The
between inputs makes this configuration an attractive make-before-break disable characteristic of the
input stage for this application. The OPA3695 ensures that the output is always under
differential-to-single-ended gain for this circuit is control. To avoid large switching glitches, it is best to
2V/V. The inputs are high-impedance, with only 1.2pF switch when the signal on the amplifier inputs are
to ground at each input. The loads on the OPA3695 very close to each other.
outputs are equal for the best harmonic distortion
The voltage difference appearing between the
possible.
inverting node and the noninverting node should not
exceed ± 1.2V. This difference can occur when the
individual amplifier is disabled and a voltage is
applied at the summing node of the three amplifiers.
The resulting inverting node voltage of the disabled
amplifier is easily calculated by using simple resistor
voltage divider methods. In general, as the gain of the
amplifier increases, the less impact this issue has on
the system because of the increased R
F
/R
G
ratio.
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.
Figure 41. High-Speed Instrumentation Amplifier
Figure 42. Multiplexed Converter Driver
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