Drain current (ID): definition

Beginner

How much electricity flows through a transistor, from one end of the switch to the other.

Novice

The current flowing from drain to source through the channel, written $I_{\mathrm{D}}$ or $I_{\mathrm{DS}}$ . It depends on the gate-to-source voltage $V_{\mathrm{GS}}$ and the drain-to-source voltage $V_{\mathrm{DS}}$ .

Expert

$I_{\mathrm{D}}(V_{\mathrm{GS}}, V_{\mathrm{DS}}, V_{\mathrm{BS}})$ , usually quoted per micrometer of width because it scales linearly with $W$ . The function is what every MOSFET model, from the square law to BSIM, tries to reproduce.