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Summing amplifier

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

Several inputs, each through its own resistor, meet at the virtual ground. Their currents add in R_f, so the output is the negative weighted sum: V_out = −R_f · (V1/R1 + V2/R2). Audio mixers work this way.

Summing amplifier: the circuit on the simulator's bench

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How it works

I1 = V1/R1 = 100 µA, I2 = V2/R2 = 200 µA

Vout = −Rf(I1 + I2) = -3 V

Try it on the bench

  1. Set R1 to 5.1 kΩ: V1 now counts double.
  2. Push V1 and V2 up until the sum passes −10.5 V and the output saturates.

Parts on the bench

In the course

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

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