Field-effect transistor

The field-effect transistor (FET) is a transistor that uses an electric field to control the shape and hence the electrical conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are also known as unipolar transistors as they involve single-carrier-type operation. The FET has several forms, but all have high input impedance. While the conductivity of a non-FET transistor is regulated by the input current (the emitter to base current) and so has a low input impedance, a FET's conductivity is regulated by a voltage applied to a terminal (the gate) which is insulated from the device. The applied gate voltage imposes an electric field into the device, which in turn attracts or repels charge carriers to or from the region between a source terminal and a drain terminal. The density of charge carriers in turn influences the conductivity between the source and drain.

History

The field-effect transistor was first patented by Julius Edgar Lilienfeld in 1926 and by Oskar Heil in 1934, but practical semiconducting devices (the JFET) were developed only much later after the transistor effect was observed and explained by the team of William Shockley at Bell Labs in 1947, immediately after the 20-year patent period eventually expired. The MOSFET, which largely superseded the JFET and had a profound effect on digital electronic development, was invented by Dawon Kahng and Martin Atalla in 1959.

Channel

Channel, channels, and similar terms may refer to:

Places

Channel (programming)

In computing, a channel is a model for interprocess communication and synchronization via message passing. A message may be sent over a channel, and another process or thread is able to receive messages sent over a channel it has a reference to, as a stream. Different implementations of channels may be buffered or not, and either synchronous or asynchronous.

Channels are fundamental to the process calculus approach to concurrency, and originated in communicating sequential processes (CSP), a formal model for concurrency, and has been used in many derived languages, such as occam, and Limbo programming language (via Newsqueak and the Alef programming language). They are also used in the C programming language threading library libthread, and in Plan 9 from Bell Labs, which uses libthread, as well as in Stackless Python and the Go programming language.

Channel implementations

Channels modeled after the CSP model are inherently synchronous: a process waiting to receive an object from a channel will block until the object is sent. This is also called rendezvous behaviour. Typical supported operations are presented below using the example of the libthread channel API.

Price channels

A price channel is a pair of parallel trend lines that form a chart pattern for a stock or commodity. Channels may be horizontal, ascending or descending. When prices pass through and stay through a trendline representing support or resistance, the trend is said to be broken and there is a "breakout".

References

See also