bipolar transistor


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Related to bipolar transistor: Field effect transistor, unipolar transistor

bipolar transistor

[bī′pō·lər tranz′is·tər]
(electronics)
A transistor that uses both positive and negative charge carriers.

bipolar transistor

(electronics)
A transistor made from a sandwich of n- and p-type semiconductor material: either npn or pnp. The middle section is known as the "base" and the other two as the "collector" and "emitter". When used as an amplifying element, the base to emitter junction is in a "forward-biased" (conducting) condition, and the base to collector junction is "reverse-biased" or non-conducting. Small changes in the base to emitter current (the input signal) cause either holes (for pnp devices) or free electrons (for npn) to enter the base from the emitter. The attracting voltage of the collector causes the majority of these charges to cross into and be collected by the collector, resulting in amplification.

Contrast field effect transistor.

bipolar transistor

Also called a "bipolar junction transistor" (BJT), it is one of two major transistor categories; the other is "field effect transistor" (FET). Although the first transistors and first silicon chips used bipolar transistors, most chips today are field effect transistors wired as CMOS logic, which consume less power (see FET and MOSFET).

Bipolar transistors are available as individually packaged discrete components as well as by the hundreds of thousands on a single chip.

High Power, High Frequency
Although the overall market for bipolar transistors has decreased, they are still used for high power applications and high radio frequency (RF) applications that reach into the gigahertz range. For example, from 1997 to 2002, worldwide sales of bipolar chips dropped from USD $1.5 billion to $226 million, the latter out of a total semiconductor market of $136 billion. See transistor, IGBT and BiCMOS.


The First Transistor Was Bipolar
In 1954, Texas Instruments pioneered the bipolar transistor. Although BJTs are fabricated in microscopic proportions on chips, individual discrete BJTs similar to this one are still in common use. (Image courtesy of Texas Instruments, Inc.)







NPN Bipolar Transistor
BJTs are either a sandwich of p-type silicon surrounded by n-type regions or n-type surrounded by p-type. To turn an NPN BJT on (example above), a negative potential is applied to the emitter terminal and a positive potential to the collector. When a positive voltage is applied to the base, it allows electrons to flow from the emitter to collector. For the PNP BJT, the polarities are reversed. The "bipolar" name comes from using both mobile carriers (electrons and holes).







Bipolars Use More Power
BJTs require continuous voltage at the base to keep the transistor closed (on) and current flowing from emitter to collector. In the field effect transistors (FETs) used in CMOS chips, the transistor is closed (turned on) by charging the gate, and current is only used during the gate charging period (see FET and MOSFET).































References in periodicals archive ?
The hook up of an active inductive element on the basis of the bipolar transistor VT4 and R11C1-circuit to a drain field two-gate transistor VT2 and to a common bus through capacity C2 establishes a tuned circuit, the power losses in which are cancelled by negative resistance.
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2 SCIENCE, Lieber's group reported using its silicon nanowires to create a bipolar transistor, a workhorse of microelectronics technologies.
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Designing bipolar transistor radio frequency integrated circuits.
One such device was the heterostructure bipolar transistor. The presence of germanium accelerated the motion of electrons across the device, boosting the transistor's speed by roughly 60 percent.
Pursuant to the order and to satisfy the FTC's remaining concerns before the acquisition of Fairchild, the company is required to sell its planar insulated gate bipolar transistor (Ignition IGBT) business with revenues of under USD25m during fiscal year 2015, it said.
They have retained the basic physics of classic devices and added material on such areas of contemporary interest as three-dimensional MOSFETs (metal-oxide-semiconductor field-effect transistors), nonvolatile memory, modulation-doped field effect transistor, single-electron transistor, resonant-tunneling diode, insulated-gate bipolar transistor, quantum cascade laser, and semiconductor sensors.
This two-stage amplifier, which operates in the 1850 to 1910 MHz frequency range, is an In-GaP heterojunction bipolar transistor device and is internally matched to 50 [ohm] to minimize the use of external components.
The 75 contributions are divided into eight sections on epitaxial growth techniques, SiGe heterojunction bipolar transistor (HBT) operation, BiCMOS technology, heterostructure field-effect transistors, optoelectronic components, measurement and modeling, and circuits.