MOSFET Transistor Operation

Change Vd and Vgs via the sliders below, and observe the field buildup inside the device and the accompanying parametric changes.


This interactive simulation was written to gain an understanding of transconductance (or Gm). When is it fixed?, When does it vary?

Parametric (or Etest) testing sweeps the Vgs (gate to source) voltage for a given Vd (drain) voltage, to derive the (curve sweep) plot on the right. The transistor does not " Turn-on " (or conduct current through the drain = Id) until Vgs reaches the " Threshold Voltage " (or Vt).

Note that Vd changes only effect Id in the " Linear " region (hence " Saturation " means Vd changes do not effect the Id current flow through the transistor).

Vd (the drain voltage, or voltage across the whole transistor) must be less than Vgs (the gate to source voltage) - Vt (the theshold or turn on voltage) to be in this (ohmic or) linear region.

If this does not make sense to you, please see Semiconductor Basics under Ken's Technology Notes (for an explaination of how transistors are used in analog amplifier and digital circuits).

Links to Other (Similar) Interactive Simulations

How a BJT Works This one has the best (electron flow in a) field animation work I've seen in a device demo. I hope to replicate it on a future project.Flash
How a JFET Works Similar interactive application, no GmFlash
MOSFET Operation-1 Basic Vgs, Vd interactivity.Java Applet
MOSFET Operation-2 Basic Vgs, Vd interactivity, nice curve tracing (better than mine!)Java Applet
Semiconductor Simulation Library Extensive (and good!) library demonstrating most of the basicsJava Applet
Funktionsweise des MOS-Transistors German website containing a series demosJava Applet