Wednesday, February 16, 2011

The Transistor

What we all should know and understand. 

How the first transistor worked

Transcript: "This doesn't look like it would change the world, but this first transistor did just that. This replica is a bit larger than the original, but otherwise a pretty faithful representation. In 1947 Walter Brattain at Bell Lab fashioned it out of plastic stand, a chunk of germanium, a triangular piece of plastic with a layer of gold on each side, and a "spring" on top to press the gold at the apex of the triangle into the germanium - that's why its called a "point contact" transistor.
Here's what Bardeen and Brattain actually did with this device on December 23, 1947.
They hooked up a microphone to the left side, and an oscilloscope to the right side. As they spoke into the microphone they could see the voice signal being amplified. As Brattain wrote in his lab notebook "This circuit was actually spoken over and by switching the device in and out a distinct gain in speech level could be hear and seen on the scope ...."
Now, that amplification is still one of the main uses for a transistor. Think of your cell phone: It detects a low-power signal from the cell tower and then its circuity amplifies the signal until you can hear it.
But how does this klutzy looking contraption work its magic? They key lies in this chunk of semi-conducting germanium.
Recall that there are three ways we can classify material in terms of their ability to conduct electricity.
Conductors like metals that readily transport electricity with negative charge carriers. Insulators which refuse to allow current to flow. And a third class, which make possible the transistor: semiconductors. As the name implies they they conduct better than insulators, but not as well as conductors. But more importantly unlike metals semiconductors have two different ways to conduct electricity - effectively negative and positive charge carriers.
That property lies at the heart of a transistor. It allows an engineer to make a highly reliable device that allows current to flow in only one direction. We can make a "sandwich" of the two types of semiconductors. Here the negative charge carrier one on the left and the positive one on the right. The semiconductor sandwich allows electricity to flow. Reverse the battery and the current grinds to a halt.
Other devices can do this, for example, vacuum tubes, but they had many part, were unreliable, overheated, and were expensive to produce and likely impossible to miniaturize." Bill Hammack 

Nowaday's chips in computers hold hundreds of millions of transistors, soon billions! How many transistors in a computer chip?
  • Intel 4004 2,300 (first intel chip)
  • Pentium 3,100,000 (windows 95)
  • core i7 quad: 731,000,000 (best personal chip out now)
  • 8-Core Xeon Nehalem-EX 2,300,000,000 (supercomputer chip)