opamp circuit offsets

John Larkin · 2017-04-15T14:03:16+00:00

I have a fairly bizarre 4-opamp circuit with differential output, and I need to calculate the worst-case DC offset. The math is a nuisance, and I'll have to repeat it if I change anything. So, Spice. The issue is now how to program the four opamp DC offset sources. One way is to use four asynchronous sine waves, and run it and see how things eventually spike. Sort of a cheap Monte Carlo. There must be some number-theory choice of frequencies that's best, but a few guesses seem to make peak DIFF offsets just below +-8 mV, so that seems to be the answer. Eyeballing the graph sort of suggests the probability that any given offset could ever really happen. I doubt that we'd ever have all four amps at 2 mV in the worst-case directions; the typ offset is 0.5 mV. So I guess I'll never see more than, say, +-5 out. -- John Larkin Highland Technology, Inc lunatic fringe electronics

Apr 15, 2017 102 Replies

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John Larkin 9 years ago

I probably shouldn't post that in public. NDAs and stuff.

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com

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Jim Thompson 9 years ago

Without that information, and assigning randomness to desired signals, a pot (actually probably two pots) looks like the only solution. ...Jim Thompson

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John Larkin 9 years ago

The alternatives are

Autozero servo. Tricky.

Nonvolatile DPOT, SPI or I2C programmed somehow.

Real pot.

I'm going to fight for the pot. I like pots.

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com

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