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Thread: DC (0 to 0,2V) voltage amplifier with single +5V power supply
www.piclist.com/techref/power.htm?key=power
picon face BY : Russell McMahon email (remove spam text)



I'm not too happy with the 324's performance near ground.
With ground referenced input signals you may find the overall performance
imperfect for low signal levels.
One solution is to provide an input  pullup from  a higher voltage through a
higher value resistor. This provides a known positive input offset which can
be subtracted from the final result.

eg if R in -ve is Rin and input pullup is Rpullup, bias voltage is Vpullup,
then effective input voltage from the pullup is
Vpullup x Rin/(Rin + Rpullup). Multiply this by G (here = 30) to get the
constant output pullup voltage. Vpullup can just be Vcc but variations in
Vcc will be reflected in the accuracy of Voffset. A stabilised offset
voltage helps. Even a zener derived Vpullup may be OK IF you can measure the
zero offset at startup with software in the absence of input voltage.


     Russell McMahon
_____________________________



{Original Message removed}
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