Op-Amp Full-Wave Rectifier

Combine a precision half-wave stage and a weighted summer to obtain the absolute value of a small signal.

A1 and its two diodes produce a negative half-wave H from a 0.2 V peak, 100 Hz input. A2 sums the original input through 10 kΩ and H through 5 kΩ, with 10 kΩ feedback. These weights convert both input polarities to a positive output.

$$H\approx\min(-V_{\mathrm{in}},0)$$ $$V_{\mathrm{out}}=-V_{\mathrm{in}}-2H\approx|V_{\mathrm{in}}|$$

The red output has two positive crests per input period and reaches about 0.2 V. The blue load current peaks near 20 µA. Small transition glitches reveal finite amplifier bandwidth and diode switching; this is not an ideal absolute-value operator.

Read the results. The saved transient chart uses separate voltage and current panels; the table provides numerical samples. The first voltage probe is green and the second red. The first current probe is blue; a second current probe is purple.

Model limits. The three-terminal op-amp model has implicit ±12 V output limits, 200,000 low-frequency gain and 10 MHz gain-bandwidth product. Supply pins are intentionally absent in this functional model. In Schmitt-trigger and relaxation/integrator oscillator examples, the switching amplifier uses a 100 kHz gain-bandwidth setting to resolve transitions cleanly at the saved time step. It omits detailed slew-rate, input common-mode, output-current and thermal limits.

Try it. Set V1 peak voltage to 20 mV; both half-cycles are still rectified. Restore the original values after comparing the results.