The Wien Bridge Oscillator problem (your Sunday ruined part1)

Oct 20, 2024 Last reply: 1 year ago 3 Replies

Gentlemen,



How critical is the choice of thermistor for a WB oscillator? Stability is desired; we know that much (along with minimal distortion of course). The usual problem with WB oscillators is they are not amplitude stable and either die out or saturate. However, by means of a non-linear negative f/b arrangement, they *can* be made stable. One common solution is to use a thermistor, usually one with a positive temperature coefficient. The issue is, that it must be 'nimble' enough to regulate the output level without being *so* 'nimble' as to respond to peaks and troughs of the output signal's cycles. I'm going to call this 'nimbleness' "tau" for the time being. I know it's not the right Greek letter, but no doubt some helpful soul will point out the correct one. So the question is, how the hell do you select a thermistor with the optimum 'tau' for any given wideband WB oscillator?



Your pal,



CD.


I think they should all get there in the end but a longer tau thermistor will take longer to settle.

You could always use a large bulky thermistor which does not self-heat and then heat it with a resistor fed from a power amplifier. That would trade off distortion against settling time.

It would be constantly hunting unless the resolution was infinely small and there was absolutely no mechanical backlash..

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