鈥?/div>
5
C
1
10pF
8
V
OUT
FIGURE 2. SWOP amp with a Gain of +10V/V for Channel
A. Gain of +2V/V for channel B. Connecting
both inputs together yields a programmable gain
amplifier.
By selecting different gains for each channel and connecting
the inputs together, a programmable gain amplifier is real-
ized. The selectable input amplifier can also function as a
gated amplifier, for noise blanking with RF signals, or a
return to zero deglitcher for digital-to-analog converters.
Filtering may be added to any of the circuits shown here,
using standard op amp filter designs.
Figure 3 shows a four channel MUX made with three SWOP
amps. The circuit for each amplifier is shown in Figure 1
with SWOP amps A
1
and A
2
used to MUX the four channels
into two.
A
3
performs the final multiplexing down to one output
channel. The circuit uses two bits for channel select, as
shown in the table in Figure 3. The second bit selects
FIGURE 1. Two-Input Multiplexer with a Gain of +8V/V for
Each Channel. Gain is identical for each channel
without precision resistors. Bandwidth is greater
than 100MHz.
Either channel may be configured as inverting or
noninverting. If different gains are desired for the two
channels, separate feedback networks may be used as shown
in Figure 2. Note that the compensation node is common to
both channels. The capacitor must be large enough to make
the channel with the lowest gain stable. For this reason,
channel B in Figure 2 has R
7
added across the inputs to make
漏
1994 Burr-Brown Corporation
AB-092
Printed in U.S.A. January, 1994
1
2
