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Transistor can be categorized based on semiconductor material used, structure, and power rating operation frequency, amplification factor, electrical polarity or application. Although one of the above basis categorizes transistor, the major types falls to junction transistor and field effect transistor (FET) categorized mainly based on the structure.
The transistor is an arrangement of semiconductor materials that share common physical boundaries. Materials most commonly used are silicon, gallium-arsenide, and germanium, into which impurities have been introduced by a process called "doping." In n -type semiconductors the impurities or dopants result in an excess of electrons, or negative charges; in p -type semiconductors the dopants lead to a deficiency of electrons and therefore an excess of positive charge carriers or "holes" [8].
Junction Transistor
The transferred resistance or transistor is a multi-junction device that is capable of Current gain, Voltage gain, and Signal power gain Invented in 1948 by Bardeen, Brattain and Shockley. Contains three adjoining, alternately doped semiconductor regions: Emitter (E), Base (B), and Collector (C) The middle region, base, is very thin compared to the diffusion length of minority carriers Two kinds: npn and pnp.
The Bipolar junction transistor is an active device that works as a voltage controlled current source and whose basic action is control of current at one terminal by controlling voltage applied at other two terminals. Emitter is heavily doped compared to collector. So, emitter and collector are not interchangeable. The base width is small compared to the minority carrier diffusion length. If the base is much larger, then this will behave like back-to-back diodes.[9]
Figure 4. NPN and PNP Junction transistor
FET transistor
FET transistor commonly called as unipolar transistor since it contains one type of carrier electrons or holes (unipolar). The conventional bipolar transistor has two type of current carriers of both polarities (majority and minority) and FET has only one type of current carriers, p or n (holes or electrons). The BJT is current controlled and FET is voltage controlled current between two other terminals.
Field effect transistor is a unipolar transistor, which acts as a voltage controlled current device and is a device in which current at two electrodes is controlled by the action of an electric field at another electrode. Field effect transistor is a device in which the current is controlled and transported by carriers of one polarity (majority) only and an electric field near the one terminal controls the current between other two.
Family of FET
Junction FET (JFET)
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JFET is a unipolar transistor, which acts as a voltage controlled current device and is a device in which current at two electrodes is controlled by the action of an electric field at a pn junction. In addition to the channel, a JFET contains two ohmic contacts: the source and the drain. The JFET will conduct current equally well in either direction and the source and drain leads are usually interchangeable.
JFET consists of a piece of high resistivity semiconductor material (usually Si) which constitutes a channel for the majority carrier flow and a gate. Conducting semiconductor channel between two ohmic contacts source & drain. The magnitude of this current is controlled by a voltage applied to a gate, which is a reverse biased. (Ohmic contacts means following Ohm's law current proportional to V under constant physical condition. [9]
MOSFET
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Field effect transistor is a unipolar transistor, which acts as a voltage controlled current device and is a device in which current at two electrodes drain and source is controlled by the action of an electric field at another electrode gate having in between semiconductor and metal very a thin metal oxide layer.[9]
CPU Transistor Technology
CPU architecture design, implementation and form have changed through time. However fundamental operation principle remain almost unchanged. CPU has the following most principal components:
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