🚀 go-pugleaf

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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