[sdiy] op amp phase inversion

[jhaible at debitel.net]

> I would resort to such measures only if there is no other way. Ask 
> yourself rather: Why would there be a chance that the inputs end up near 
> the rails in the application?

For comparators, a simple resistor divider helps. 
(slightly increasing the effective Vos of course.)

Same for noninverting amps: Divide down by 2, and
amplify by 2* your desired gain. Increased noise
and offset, of course.

Unfortunately, this does not work if you have chosen
the noninverting configuration, because you needed
a high input impedance. Even if your previous stage
allows "some" loading, high resistor values in a 
divider will cause a lot of noise - not good.
And if you buffer a capacitor (filters, S&H, ...)
this is no option anyway.

My choices:

For slow circuits without further demands
on noise or Vos: 741. And 1456, 358, 324.
Don't be a snob - use them if they do what you want. (;->)

For slow circuits, where Vos is important: OP-07
So cheap nowadays.

For fast circuits (audio) with AC couplig (Vos and Ios not
a problem): NE5534 and NE5532.

For audio circuits where a _decent_ Vos and Ios is enough:
RC4558 (dual), RC4136 (quad) 
(is there a single package for these ???)

For applications where no leakage is allowed:
CA3140 and CA3240.
(Especially the 3240 has saved me in applications where
a TL072 would latch up from spikes in the signal that 
were not expected.)

JH.


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