cgs

Cgs is an abbreviation most commonly encountered in electronics to denote the gate-to-source capacitance of a transistor, especially a metal-oxide-semiconductor field-effect transistor (MOSFET). It is part of the transistor's input capacitance and represents the capacitance between the gate terminal and the source terminal, arising from the oxide layer between gate and channel and from depletion regions at the junctions.

In operation, Cgs is bias-dependent. Its value changes as the transistor moves from cut-off through triode to saturation as the channel forms under the gate. In small-signal models, Cgs is modeled as a capacitor connected between the gate and source, contributing to the overall input capacitance Ciss, while a separate capacitance Cgd exists between gate and drain. The total gate capacitance is commonly approximated as Ciss ≈ Cgs + Cgd. The presence of Cgd enables Miller effect, which can magnify the apparent input capacitance during large-signal switching, influencing propagation delay and switching speed.

Cgs values vary with device geometry and technology, typically spanning femto- to pico-farads for small devices and up to pico- or even nano-farads for larger, higher-capacitance parts. In circuit design and simulation, Cgs is specified in device models (for example, CGS in SPICE) and is incorporated into time-domain and frequency-domain analyses.

Other uses of the acronym Cgs exist in unrelated fields, but in electronics, Cgs almost always refers to gate-to-source capacitance. If a different context is intended, clarification is needed from the surrounding material.