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Difference amplifier

Op-amps and analog ICs · Intermediate · about 15 minutes · part of Zen’s Electronics Design Mastery

Feed one signal to each input through matched resistors and the op-amp amplifies only their difference: V_out = (R_f / R1) · (V2 − V1). Anything common to both (noise, an offset) cancels.

Difference amplifier: the circuit on the simulator's bench

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How it works

With R_f/R1 = R4/R3 = 1.00:

Vout = 1.00 × (5 − 3) = 2 V

Try it on the bench

  1. Raise both V1 and V2 by 2 V: the output does not move (common-mode rejection).
  2. Set R_f and R4 to 47 kΩ for a gain of 4.7.
  3. Unbalance it by changing only R4: now part of the common voltage leaks through.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Op-Amps & Analog ICs”.

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