# Create a differential Op Amp Subtractor With Single Supply?

Is it possible to create a subtractor op amp circuit using a single supply? For example, if I am using a non-inverting op amp to buffer a DC signal, how can I offset this voltage by 1V?

My voltage supply to my op amp is 3.3v (V+) and GND (V-).

• What's the range of the input signal and which way is the offset? -1 V or +1 V? – Transistor Jun 9 '17 at 19:58
• I had an easier time implementing a single supply subtractor using a switched mode capacitor for charge control rather than standard resistor style subtractor – jbord39 Jun 9 '17 at 20:15

For sure it's possible!

Check here: http://www.ti.com/lit/an/sloa030a/sloa030a.pdf Page 11. Case 2

Vout = m*Vin - b. This means m, some gain and b some offset.

You can ignore the cap and rl for interpretation purposes.

I highly suggest reading that whole document since it has a lot of knowledge.

Cheers!

• I've always loved that TI reference – Scott Seidman Jun 9 '17 at 20:13

Here's a single-supply op-amp circuit that produces a 1.052 V offset for a 3.3V single-supply system. Click and open it in CircuitLab to try the time-domain simulation to see the shifted sine wave, or run the DC Sweep to see the overall input-output shifted characteristic! (You can adjust R3 and R4 to adjust the offset; see notes on schematic.)

simulate this circuit – Schematic created using CircuitLab

The key here is using two different inverting gain-of-negative-one amplifiers with two different reference voltages, V(VMID) and V(VREL). This produces an offset so the overall input-output characteristic is:

$$V_{\text{out}} = V_{\text{in}} - 2(V_\text{mid} - V_\text{rel})$$

With the resistors configured as shown (R3=91k, R4=47k), you'll get:

$$V_{\text{out}} = V_{\text{in}} - 1.052$$