OPA3693_07 Datasheet, PDF (19/31 Pages) Burr-Brown (TI) – Triple, Ultra-Wideband, Fixed-Gain, VIDEO BUFFER with Disable

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HIGH-SPEED INSTRUMENTATION
AMPLIFIER
Figure 51 shows an instrumentation amplifier based
on the OPA3693. The offset matching between
inputs makes this configuration an attractive input
stage
for
this
application.
The
differential-to-single-ended gain for this circuit is
2V/V. The inputs are high-impedance, with only
1.2pF to ground at each input. The loads on the
OPA3693 outputs are equal for the best harmonic
distortion possible.
V₁
1/3
OPA3693
300W
300W
300W
300W
1/3
OPA3693
V₂
150W
150W
1/3
OPA3693
300W
300W
V_OUT
Figure 51. High-Speed Instrumentation Amplifier
As shown in Figure 52, the OPA3693 used as an
instrumentation amplifier has a 420MHz, –3dB
bandwidth. This plot has been made for a 1V_PP
output signal using a low-impedance differential input
source.
9
6
3
0
-3
-6
-9
20log ^VOUT
-12
|V₁ - V₂|
-15
1
10M
100M
1G
Frequency (Hz)
Figure 52. High-Speed Instrumentation Amplifier
Response
OPA3693
SBOS353 – DECEMBER 2006
MULTIPLEXED CONVERTER DRIVER
The converter driver in Figure 53 multiplexes among
the three input signals. The OPA3693 enable and
disable times support multiplexing among video
signals. The make-before-break disable
characteristic of the OPA3693 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 does not exceed the
±1.2V maximum allowed.
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.
LOW-PASS FILTER
The circuit in Figure 54 realizes a 7th-order
Butterworth low-pass filter with a –3dB bandwidth of
20MHz. This filter is based on the KRC active filter
topology that uses an amplifier with the fixed gain ≥
1. The OPA3693 makes a good amplifier for this type
of filter. The component values have been adjusted
to compensate for the parasitic effects of the op
amp.
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