I want to offset an AC signal from +/- 2.5 V to 0-5 V.
you can use an offset-circuit ... can be done with a couple of resistors, and is probably the simplest solution.
Consider a clamping circuit
https://electronics.stackexchange.com/questions/37095/level-shifting-a-2-5v-signal-to-0-5v
Simulate this on Falstad.
What are the proper resistor values? Let's do some calculation. Say we have V~IN~ (+/- 2.5 V) and V~S~ (of 5 V), resistors R~IN~, R~S~ and R~G~ (connected to ground).
I continued this idea on the 'resistor threeway' page without satisfactory results.
Simulate this on Falstad. Here is the source.
This is a non-inverting summing amplifier. You would think that we simply have to add 2.5 V, but do you have that? I'm assuming you have 5 V, so let's use that and see where it gets us. If we have -2.5 V on the Vin input the non-inverting input should be zero if you want 0 V out, regardless of the values of R3 and R4. So R1 and R2 form a voltage divider, and R2 should be twice R1 to get the 0 V.
$ A_V = \dfrac{R3 + R4}{R3} $
If we have 2.5 V on the Vin input and with R2 = 2 ┬×┬×R1 we get 3.33 V on the non-inverting input of the opamp. To make that 5 V out we have to amplify by 1.5, so R3 must be twice R4.
I have not tested this yet.