i'm adding DC (4V) to an AC signal. Someone told me that operational amplifiers work well for that; i've been searching for the circuit but i can't find it. Can someone post the circuit, please? Any other suggestions for the same case will be welcomed as well.
There are two inputs in operational amplifier.
If you apply your measured AC on "+" input of op. ampl.
You can add offset voltage to "-" input.
( Of course "+" voltage applied to "-" input shifts op. amp. output "negative".)
You should also take into accoout the amplifier gain.
(add 1 V offset if op ampl. gain = 4)
You insert this voltage not directly to "-" input of op. ampl. but between the GND and fedback resistor.