Hello all,

I have a project which will have both a PIC and some op-amps to
amplify/filter the signal from a 40kHz ultrasonic transducer.

It would be convenient to have a negative supply for the analog side,
and since I've got a PIC handy I wondered about generating the negative
supply with a simple capacitor/diode charge pump.  That would give me
roughly -3.6 (or -4.3 with Schottky diodes) to +5V which would be just
fine.  I would imagine I'd want to avoid running the charge pump at,
say, 40kHz.

The question is how much of a problem would the relatively poor
regulation of the negative supply likely to cause me?  The op-amp
circuits will all have feedback and will be referenced to 0V.

Best regards,

Chris
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