p-MOSFET

Observe the complementary voltage polarities and current direction of a p-channel MOSFET.

The source connects to +5 V and RD = 1 kΩ connects the drain to ground. V1 sweeps the gate from 0 to 5 V. Threshold is −2 V, and the magnitude of KP is 2 mA/V² with equal channel width and length.

$$V_{GS}=V_G-5\,\mathrm{V}$$ $$|I_D|\approx\frac{|K_P|}{2}\frac WL(V_{SG}-|V_T|)^2\quad\text{(saturation)}$$

Vgs is green and Vds red, both measured relative to the source using the shared reference marker. Positive blue Id flows from the drain through RD to ground. The device conducts at low gate voltage and turns off as the gate approaches the source voltage. This is the complementary polarity to the n-channel example.

Read the results. The saved DC sweep chart and table show each bias point. 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 generic level-1 MOSFET model is intended to explain bias and low-frequency behavior. It omits detailed subthreshold conduction, gate charge, body effects and thermal behavior; these are not part-specific design results.

Try it. Set M1 threshold voltage VTO to −3 V; a larger source-to-gate voltage is needed for conduction. Restore the original values after comparing the results.