# Voltage follower with shift

I am trying to figure out a simple application/ circuit that would allow me to shift the voltage a little bit. Lets say we have an input voltage of range from 0 to 1 V. I need an output voltage of 0.2 to 1.2 V. This is just an example but I am looking for a generic solution. There is no negative voltage available in the circuit.

• @le_top: No, that won't work at all. Draw it out on paper and maybe you'll see why. – Dave Tweed Oct 12 '19 at 20:01
• Ok, maybe I wrote it out wrong - so I'll delete my comment as your drawing is what I meant to describe. – le_top Oct 12 '19 at 21:02

The classic 4-resistor difference amplifier will do what you want:

simulate this circuit – Schematic created using CircuitLab

This circuit keeps the difference between Vout and Vref equal to the difference between V+ and V-, effectively adding Vref to V+ if V- is grounded.

The opamp tries to keep its two input terminals at the same potential using negative feedback:

$$\frac{V_{out} + V_-}{2} = \frac{V_{ref} + V_+}{2}$$

Multiply both sides by 2 and rearrange the terms to get:

$$V_{out} - V_{ref} = V_+ - V_-$$

• Yes, I messed up the terminals. I think its the simplest way, thanks. – Bremen Oct 12 '19 at 20:24