[sdiy] Using Opamps as INV or NON-INV amplifiers

[JH.]

>Analogue guru Jim Williams* points out that  the inverting configuration
>avoids any problems caused by non-ideal common-mode performance of the
>opamp, since there is (pretty much) no common mode signal on the input
pins.
>The non-inverting configuration remains susceptible to such effects.

Yes.
The inverting amp avoids phase reversal, and thus shows better overdrive
performance with most opamp types.

Another benefit of inv config is the protection of the opamp when the psu
voltage is down (switched off, but input still connected).

OTOH, the non-inverting amp can be less noisy.
In general, for a signal gain of A, the non inv configuration has a noise
gain of A,
while the inv configuration has a noise gain of (A+1).

Also, there is the noise of resistors.
Let's look at the unity gain amp:
In the noninverting case, you can use an opamp with -input tied to the
output,
and a large resistor from +input to GND. Now when you connect a low
impedance
source, the resistor noise is defined by this low impedance, not by the
large resistor.
In the inverting case, you decide for a resistance value (for each of the
two resistors),
and these define the resistor noise of your circuit, even when you connect a
low
impedance source.

JH.