What is a Transistor


The Invention
   This unprecedented flow of innovations began in the mid-40s when a team of scientists at Bell Labs set out to find a solution that would replace the vacuum tube and the mechanical relays with something better, something more reliable, more efficient, less costly to maintain. On December 16, 1947, Walter Brattain, backed by his team and the entire pool of Bell Labs science, made another adjustment to his odd-looking contraption consisting of germanium, gold strips, insulators and wires, and typical semiconductor transistorobserved, for the first time, an amplification of the input signal. The transistor was born and unknowingly, the information age. Nobel Prize winners John Bardeen, Walter Brattain, and William Shockley subsequently developed the techniques to make the technology practical, effectively teaching the industrial community how to use it to create applications from hearing aids to telephone switches, from portable radios to television sets.
    Invented at Bell Laboratories in 1947, the transistor resulted from efforts to find a better amplifier and a replacement for mechanical relays. The vacuum tube had amplified music and voice during the first half of the 20th century, and it had made long-distance calling practical. But it consumed lots of power, operated hot and burned out rapidly. The telephone network required hundreds of thousands of relays to connect circuits together to complete calls. Network relays were mechanical devices, requiring regular maintenance to clean and adjust.
Cheaper to make than the vacuum tube and far more reliable, the transistor cut the cost and improved the quality of phone service and, seemingly overnight, spawned countless new products and whole new industries.

How a Transistor Worksschematic symbol for a semiconductor npn transistor
    The transistor has many applications, but only two basic functions: switching and modulation -- the latter often used to achieve amplification.  In the simplest sense, the transistor works like the dimmer in your living room. Push the knob of the dimmer, the light comes on; push it again, the light goes out. Voila! A switch. Rotate the knob back and forth, and the light grows brighter, dimmer, brighter, dimmer. Voila! A modulator. To understand amplification, think of this: a relatively effortless action by you to turn the knob from its low to high setting translates into a much more impressive reaction by the light - the whole room beams with light! Voila! An amplifier.  Both the dimmer and the transistor control current flow, be it through a lamp or a device to be activated. Both act as a switch--on/off--and as a modulator/amplifier-- high/low. The important difference is that the "hand" operating the transistor is millions of times faster. And it's attached to another electrical source--a radio signal in an antenna, for example, a voice in a microphone, or data signal in a computer system, or even another transistor.
    Transistors are made of semi-conductors such as silicon and gallium arsenide. These materials carry electricity moderately well--not well enough to be called a conductor, like copper wires; not badly enough to be called an insulator, like a piece of glass. Hence their name: semi-conductor.
    The 'magic' a transistor performs is in its ability to control its own semi-conductance, namely acting like a conductor when needed, or as an insulator (non-conductor) when that is needed.
Semi-conductors differ in the way they act electrically. Putting a thin piece of semi-conductor of one type between two slices of another type has startling results: a little current in the central slice is able to control the flow of the current between the other two. That little current in the middle slice is the juice that is supplied by an antenna or another transistor for example. Even when the input current is weak, as from a radio signal that's travelled a great distance, the transistor can control a strong current from another circuit through itself. In effect, the current through the 'output side' of the transistor mimics the behaviour of the current through the 'input side'. The result is a strong, amplified version of the weak radio signal.

What Transistors Do
In microchips today, which contain millions of transistors 'integrated' together in a particular pattern or 'design', the amplified output of one transistor drives other transistors that, in turn, drive others, and so on. Build the sequence one way and the chip can be made to amplify weak antenna signals into rich quadraphonic hi-fidelity sound. Build the chip differently, and the transistors interact to create timers to control watches or microwave oven, or sensors to monitor temperatures, detect intruders, or control car wheels from locking (ABS systems). Arrange the transistors in a different array and create arithmetic and logic processors that drive calculators to calculate, computers to compute, 'process' words, search complex data bases for information, networks to 'talk' to each other, or systems that transmit voice, data, graphics and video to make our communications networks.
    It may take a score of transistors, interconnected in teams called logic gates, to accomplish a task as simple as adding one and one. But put enough transistors together in appropriate patterns and transistors end up knock off big jobs by working fast switching on and off 100 million times per second or more--and by working in huge teams.
As discrete components as in the old days, a thousand transistors would occupy dozens of printed circuit boards the size of postcards. But thanks to such techniques as photolithography and computer-aided design, millions of transistors and other electronic components, complete with wiring, can be compactly organized on an integrated circuit smaller than a cornflake.


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