Subtractor using Op Amp or Difference Amplifier Circuit:

Similar to the summer circuit, the subtraction of 2 input voltages is possible with the help of op-amp circuit called subtractor or difference amplifier circuit. The Subtractor using Op Amp circuit diagram is shown in the Fig. 2.31.

To find the relation between the inputs and output let us use Superposition principle.

Let V_o1 be the output, with input V₁ acting, assuming V₂ to be zero. And V_o2 be the output, with input V₂ acting, assuming V₁ to be zero.

With V₂ zero, the circuit acts as an inverting amplifier. Hence we can write

While with V₁ as zero, the circuit reduces to as shown in the Fig. 2.32.

Let potential of node B be V_B. The potential of node A is same as B i.e. V_A = V_B. Applying voltage divider rule to the input V₂ loop,

Equating the equations (3) and (4),

Substituting V_B from (2) in (5) we get,

Hence using Superposition principle,

Now if the resistances are selected as R₁ = R₂,

Thus the output voltage is proportional to the difference between the two input voltages. Thus it acts as a Subtractor using Op Amp circuit or difference amplifier.

If R₁ = R₂ = R_f is selected,

But by selecting proper values of R₁, R₂ and R_f, we can have the subtraction of two inputs with appropriate strengths like