# Offset an input voltage of -2.5V - 2.5V to 0V - 5V? [duplicate]

I have a circuit input which provides a voltage range of negative 2.5 volts to positive 2.5 volts. How do I change this so the output voltage is 0 - 5 volts?

simulate this circuit – Schematic created using CircuitLab

There are several ways to do this, for instance using an opamp to sum 2.5V to your signal:

This is an inverting summing amplifier, so for $R1 = R2 = R4$, the output would be $Vo = -(V_{AC}+V_{DC})$

If you want to keep the phase of the signal, a non-inverting summing amplifier would be like this:

In this, $R_3,R_4$ control the gain of the amplifier, and $R_1,R_2$ act as a resistor divider. Analysing this, we get that the output is $V_{o} = V_ {inop}(\frac{R_3+R_4}{R_3})$, and from the resistor divider $V_{inop} = \frac{V_{s1}R_2+V{s2}R_1}{R_1+R_2}$

If we make $R_2 = 2R_1$ we get $V_{inop} = \frac{2V_{s1}+V_{s2}}{3}$.

Substituting this in the first output equation, and making the gain $2/3$ by choosing $R_3 = 2R_4$, then the final output will be the desired $V_{o} = V_{s1}+\frac{V_{s2}}{2}$, being $V_{s1}$ the -2.5V to 2.5V AC input signal and $V_{s2} = 5V$ in this case.

In page 6 here you can also find a few different examples to offset signals using opamps: http://www.ti.com/ww/en/bobpease/assets/AN-31.pdf

• You should edit the relevant parts into you answer in case those links disappear. – David May 5 '15 at 10:56