Sawtooth Wave Generator

Charge and discharge an integrator at different nearly constant rates to generate a sawtooth-like ramp.

A2 integrates a −1 V reference through 100 kΩ, producing a slow positive ramp. When the ramp reaches about +1 V, the Schmitt trigger switches positive and D1 adds a larger opposing current through another 100 kΩ resistor. The output then ramps down rapidly until about −1 V, when D1 turns off.

$$\left.\frac{dV}{dt}\right|_{\mathrm{rise}}\approx\frac{1\,\mathrm{V}}{100\,\mathrm{k\Omega}\cdot100\,\mathrm{nF}}=100\,\mathrm{V/s}$$ $$\left.\frac{dV}{dt}\right|_{\mathrm{fall}}\approx-\frac{12-V_F-1}{100\,\mathrm{k\Omega}\cdot100\,\mathrm{nF}}$$

The green ramp takes about 20 ms to rise through 2 V and about 2 ms to return. The red control output marks the short reset interval. The finite return slope makes a sawtooth-like waveform rather than a mathematically instantaneous reset. Diode drop and amplifier limits determine the exact duty cycle.

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 C1 to 200 nF; both ramp times approximately double. Restore the original values after comparing the results.