An inverting operational amplifier

Amplify a signal and flip it

Op amp is short for operational amplifier: a powered circuit that amplifies the difference between two inputs. Negative feedback returns the output to the subtracting input. An inverting amplifier changes the signal sign; gain is output voltage divided by input voltage. Clipping means the requested output exceeds the supply limits. Av labels the linear voltage gain, in V/V: volts out per volt in, before clipping.

Open interactive experiment

EXPERIMENT BENCH

Change the circuit settings, predict the readings, then check a challenge. These are learning models, with the assumptions explained in each lesson.

Open laboratory in a full window

How it works

Ideal amplifier powered at +5 V and −5 V; output is limited to these rails. No bandwidth, speed or current limits. Actual parts have other limits; this teaching model is not hardware tested.

Requested Vout = −Vin × Rf/Rin. Vin is input voltage, Rf feedback resistance and Rin input resistance. In the linear negative-feedback region, the subtracting input is near 0 V: a virtual ground, not a wire to ground. When clipped, that approximation fails. The input-current meter is source current through Rin, not current into the ideal op-amp terminal, which is zero. If clipped, Iin = (Vin − Vout)/(Rin + Rf), using actual Vout.

Difficulty

Build · Observe
Power on at input +1 V, input resistor 10 kΩ and feedback 20 kΩ. Read output −2 V.
Need a hint?
+1 V; Rin 10 kΩ; Rf 20 kΩ → −2 V
Explore · Adjust
At input +0.5 V, obtain output −1.9 to −2.1 V without clipping.
Need a hint?
+0.5 V; Rin 10 kΩ; Rf 40 kΩ → −2 V
Solve it · Discover the limit
At input +1 V, choose resistors requesting gain magnitude at least 6. Observe output clipped at −5 V.
Need a hint?
+1 V; Rin 5 kΩ; Rf 30 kΩ → requested −6 V, actual −5 V

Extra reading and circuit recipes