555 Negative supply woes...

[gildasd]

The ripple will be similar when using a 7660. It can be quite difficult to get a clean output voltage:
https://www.eevblog.com/forum/projects/an-evening-with-the-icl7660/

Thanks for the head up, saved me a few hours of pain.
I've checked that, and come to the conclusion that with a moderate amount of filtering, this will work for me.
However, If I was to use the -V to power a sensor, I'd run it through a 741 1to1 negative amp on the -VCC. That is best way to clean a low energy power source (in my limited knowledge).

[IanB]

The ground really has to be ground, negative has to be negative for consistent results.
I tried again today to to a 10x signal amplifier using a voltage divider, not so good, worked great with the 555 negative generator.

But a simple voltage divider does not make a good virtual ground. It has a relatively high output impedance so any current flowing to or from the ground node will cause the voltage to swing. If you buffer the virtual ground you should get better results.

[electrolust]

I tried again today to to a 10x signal amplifier using a voltage divider, not so good, worked great with the 555 negative generator.

How about TLE2426?

[Zero999]

I tried again today to to a 10x signal amplifier using a voltage divider, not so good, worked great with the 555 negative generator.

How about TLE2426?

A voltage divider/rail splitter is no good if the total supply voltage is not enough.

[electrolust]

A voltage divider/rail splitter is no good if the total supply voltage is not enough.

OP said he has a 20mV signal and needs 2V, and that he has a 5V supply.  Is 5V/2 = 2.5V not ok for this purpose?

Apologies if this is a bit of a hijack.  Given that the original signal would fall into the negative side of the virtual ground, is that a problem?  Wouldn't an op amp make a [now] negative voltage, MORE negative?  I'll start a new thread if I have further questions.

[electrolust]

To answer my own question, I found some documentation that confirms the shift of the ground reference with a rail splitter or voltage divider indeed requires that the signal be biased to compensate.

Rather than delete my earlier post I'll just leave this here in case it's useful to someone in the future.

[IanB]

If the signal to be amplified is independently generated it can be referenced to the virtual ground.

More significantly, most op amps do not operate right up to the supply rails. The supply rails usually should have some margin beyond the swing of the output voltage. Depending on the amplifier a +/- 2 V output with a +/- 2.5 V supply may work, but it is not leaving much headroom.