Quote:
Originally posted by Groth
This is what I used for the difference stage. I actually used a 200 Ohm trimmer in series with a 9.9k resistor where it shows the 10k's. With precision resistors/amps, you could get away without the timming. Plus I'm just lazy with the drawing...
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I'd suggest the circuit below. (Largely because I have access to laser trimmed 20K center tapped resistor networks, with very good ratio accuracy and ratio tempco specs. I like to avoid trimming as well.)
I think it would be a good idea to up the capacitance to roll off at 10kHz. (or even lower depending on the A/D used) It's a good idea to filter out the current ripple as soon as possible.
I'd also swap the two input signals to put the 'noisier' signal into the noninverting input. (The way I've redrawn the circuit, the noninverting input will do a better job of filtering at high frequency because the cap goes to ground rather than the output. The amp will have a significant output impedance at high frequencies.)
Anyway, once again it's late. I hope I'm actually making sense. Enough for tonight.