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A CDE Definition

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(1) A starting or reference point.

(2) In a bipolar transistor, the elements that act as a switch. In NMOS and PMOS transistors, which make up CMOS circuits, the base is called the "gate." See transistor.

(3) A multiplier in a numbering system. In a decimal system, each digit position is worth 10x the position to its right. In binary, each digit position is worth 2x the position to its right.


In the analog world of continuously varying signals, a transistor is a device used to amplify its electrical input. In the digital world, a transistor is a binary switch and the fundamental building block of computer circuitry. Like a light switch on the wall, the transistor either prevents or allows current to flow through. A single modern CPU can have hundreds of millions or even billions of transistors.

Made of Semiconductor Material
The active part of the transistor is made of silicon or some other semiconductor material that can change its electrical state when pulsed. In its normal state, the material may be nonconductive or conductive, either impeding or letting current flow. When voltage is applied to the gate, the transistor changes its state. To learn more about the transistor, see transistor concept and chip. See active area, phototransistor and High-K/Metal Gate.

From Transistors to Systems
Transistors, along with resistors, capacitors and diodes, are wired in patterns that make up logic gates. Logic gates wired in patterns make up circuits, and circuits wired in patterns make up electronic systems. See Boolean logic.

Conceptual View of a Transistor
In a digital circuit, a transistor is an on/off switch becoming conductive for a moment when it is pulsed with electricity. However, it can also function like a relay to amplify analog signals such as from an audio source, transferring a low voltage at the gate to a larger voltage at the drain.

The First Silicon Transistor
Today, billions of transistors could fit into the space taken up by the first transistor. In 1954, Texas Instruments pioneered the commercial production of silicon transistors. See transistor concept. (Image courtesy of Texas Instruments, Inc.)

Transistors Get Smaller
When IBM announced the System/360 in 1964, its Solid Logic technology tied three transistors together. With the top of the module removed, you can see the three silvery transistors. This half square inch of space today can hold more than a billion transistors. See active area. (Image courtesy of IBM.)

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