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A power MOSFET is a specific type of metal–oxide–semiconductor field-effect transistor (MOSFET) designed to handle significant power levels. Compared to the other power semiconductor devices , such as an insulated-gate bipolar transistor (IGBT) or a thyristor , its main advantages are high switching speed and good efficiency at low voltages.
Like other MOSFETs, PMOS transistors have four modes of operation: cut-off (or subthreshold), triode, saturation (sometimes called active), and velocity saturation. While PMOS logic is easy to design and manufacture (a MOSFET can be made to operate as a resistor, so the whole circuit can be made with PMOS FETs), it has several shortcomings as well.
where the combination V ov = V GS − V th is called the overdrive voltage, [41] and where V DSsat = V GS − V th accounts for a small discontinuity in which would otherwise appear at the transition between the triode and saturation regions. Another key design parameter is the MOSFET output resistance r out given by:
Cross-sectional view of a MOSFET type field-effect transistor, showing source, gate and drain terminals, and insulating oxide layer. The field-effect transistor (FET) is a type of transistor that uses an electric field to control the current through a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET ...
The MOSFETs are n-type enhancement mode transistors, arranged in a so-called "pull-down network" (PDN) between the logic gate output and negative supply voltage (typically the ground). A pull up (i.e. a "load" that can be thought of as a resistor, see below) is placed between the positive supply voltage and each logic gate output.
Overdrive voltage, usually abbreviated as V OV, is typically referred to in the context of MOSFET transistors.The overdrive voltage is defined as the voltage between transistor gate and source (V GS) in excess of the threshold voltage (V TH) where V TH is defined as the minimum voltage required between gate and source to turn the transistor on (allow it to conduct electricity).
Velocity saturation greatly affects the voltage transfer characteristics of a field-effect transistor, which is the basic device used in most integrated circuits. If a semiconductor device enters velocity saturation, an increase in voltage applied to the device will not cause a linear increase in current as would be expected by Ohm's law .
In semiconductor electronics, Dennard scaling, also known as MOSFET scaling, is a scaling law which states roughly that, as transistors get smaller, their power density stays constant, so that the power use stays in proportion with area; both voltage and current scale (downward) with length.