MOSFET Biasing
Gate & drain bias
Enter VDD, threshold, transconductance parameter, VGS and the drain/source resistors; the Q-point and region appear live.
Q-point
How to use this calculator
For a MOSFET in the saturation region the drain current is ID = K·(VGS − VT)² where K = ½·µn·Cox·(W/L) and VT is the threshold (positive for enhancement, negative for depletion). Enter VDD, VT, K, the gate-source voltage and the drain/source resistors, and the calculator computes ID, the gate/drain/source voltages, VDS, and whether the device is in saturation (VDS > VGS − VT) or the triode region.
What it means in a real circuit
For VDD = 10 V, VT = 2 V, K = 1 mA/V², VGS = 5 V, the overdrive is 3 V and ID = 1 mA × 9 = 9 mA. With RD = 2 kΩ and RS = 1 kΩ, VDS = 10 − 9 mA × 3 kΩ = −17 V — the calculator flags this as **triode** (actually the device can't sustain that current; in practice it would be in triode with a much smaller ID). Lowering RD/RS or raising VDD moves the Q-point into saturation. Use this to design a MOSFET bias network, to verify a device is in its amplifying region, or to diagnose a switch that's not turning fully on.