Overdrive voltage

Overdrive voltage, usually abbreviated as VOV, is typically referred to in the context of MOSFET transistors. The overdrive voltage is defined as the voltage between transistor gate and source (VGS) in excess of the threshold voltage (Vt) where Vt is defined as the minimum voltage required between gate and source to turn the transistor on (allow it to conduct electricity). Due to this definition, overdrive voltage is also known as "excess gate voltage" or "effective voltage."[1] Overdrive voltage can be found using the simple equation: VOV = VGS - Vt.


VOV is important as it directly affects the output current (ID) of the transistor, an important property of amplifier circuits. By increasing VOV, ID can be increased until saturation is reached.

Overdrive voltage is also important because of its relationship to VDS, the drain voltage relative to the source, which can be used to determine the region of operation of the MOSFET. The table below shows how to use overdrive voltage to understand what region of operation the MOSFET is in:

Conditions Region of Operation Description
VDS > VOV; VGS > Vt Saturation (CCR) The MOSFET is delivering a high amount of current, and changing VDS won't do much.
VDS < VOV; VGS > Vt Triode (Linear) The MOSFET is delivering current in a linear relationship to the voltage (VDS).
VGS < Vt Cutoff The MOSFET is turned off, and should not be delivering any current.

A more physics-related explanation follows:

In an NMOS transistor, the channel region under zero bias has an abundance of holes (ie, it is p-type silicon). By applying a negative gate bias (VGS < 0) we attract MORE holes, and this is called accumulation. A positive gate voltage (VGS > 0) will attract electrons and repel holes, and this is called depletion because we are depleting the number of holes. At a critical voltage called the THRESHOLD VOLTAGE (Vt or Vth) the channel will actually be so depleted of holes and rich in electrons that it will INVERT to being n-type silicon, and this is called the inversion region.

As we increase this voltage, VGS, beyond Vt, we are said to be then OVERDRIVING the gate by creating a stronger channel, hence the OVERDRIVE VOLTAGE (Called often Vov, Vod, or Von) is defined as (VGS - Vt)


  1. ^ Sedra and Smith, Microelectronic Circuits, Fifth Edition, (2004) Chapter 4, ISBN 978-0-19-533883-6

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Current–voltage characteristic — Figure 1. I–V curve of a P–N junction diode (not to scale). A current–voltage characteristic is a relationship, typically represented as a chart or graph, between an electric current and a corresponding voltage, or potential difference. In… …   Wikipedia

  • Pentium OverDrive — The Pentium OverDrive was a microprocessor marketing brand name used by Intel, to cover a variety of consumer upgrade products sold in the mid 1990s. It was originally released for 486 motherboards, and later some Pentium sockets. Intel dropped… …   Wikipedia

  • Intel 80486 OverDrive — The Intel s i486 OverDrive processors are a category of various Intel 80486s that were produced with the designated purpose of being used to upgrade personal computers. The OverDrives typically possessed qualities different from standard i486s… …   Wikipedia

  • MOSFET — Two power MOSFETs in the surface mount package D2PAK. Operating as switches, each of these components can sustain a blocking voltage of 120 volts in the OFF state, and can conduct a continuous current of 30 amperes in the ON state, dissipating up …   Wikipedia

  • Transconductance — Transconductance, also known as mutual conductance[citation needed], is a property of certain electronic components. Conductance is the reciprocal of resistance; transconductance, meanwhile, is the ratio of the current change at the output port… …   Wikipedia

  • Hybrid-pi model — The hybrid pi model is a popular circuit model used for analyzing the small signal behavior of transistors. The model can be quite accurate for low frequency circuits and can easily be adapted for higher frequency circuits with the addition of… …   Wikipedia

  • Distortion (music) — Fuzzbox redirects here. For other uses, see Fuzzbox (disambiguation). Distortion (music) Boss distortion pedal Notes A well used Turbo Distortion guitar effect pedal made by Boss Distortion effects create warm , dirty and fuzzy sounds by… …   Wikipedia

  • List of Intel microprocessors — For a list of Intel s microcontrollers, see List of common microcontrollers#Intel. This generational and chronological list of Intel microprocessors attempts to present all of Intel s processors from the pioneering 4 bit 4004 (1971) to the… …   Wikipedia

  • P5 (microarchitecture) — The Intel P5 Pentium family Produced From 1993 to 1999 Common manufacturer(s) Intel Max. CPU clock rate 60 MH …   Wikipedia

  • List of Intel Core 2 microprocessors — The Core 2 brand refers to Intel s x86/x86 64 microprocessors with the Core microarchitecture targeted at the consumer and business markets (except servers) above Pentium. The Core 2 solo branch covered single core CPUs for notebook computers,… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.