dje@datacube.UUCP (01/27/89)
I designed a pressure transducer amplifier a few years ago. It too
was a bridge. I used AC square wave drive and then used an AC
coupled amplifier followed by a synchronous demod. The advantage of
AC was that there were no dc coupled stages until the last: offset,
drift, bias, all gone.
For an AC square wave, I used a cmos gate with it's VCC (VDD) hooked
to a +5V reference. this makes a really accurate square wave if you
don't load it much.
sq. wave --> cmos gate --> op-amp -->/\
/ \
sig-___/ \__sig+
\ /
\ /
\/
gnd
sig+ --||----- --||--
diff amp, AV=30 diff amp, AV=30 -- synchronous demod--out
sig- --||----- --||--
The first diff amp is two op-amps, the second is one or three in the
classic instrumentation amplifier configuration. Gain may vary
depending on the transducer.
My application was medical so the whole thing had to be isolated as
well. Let me know if you need a schematic.
Dave Erickson
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