Privateline.com's Telephone History Page 8 -- 1948 to 1951
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(Soundwaves) (Life at Western Electric)
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July 1, 1948 the Bell System unveiled the transistor, a joint
invention of Bell Laboratories scientists William Shockley, John
Bardeen, and Walter Brattain. It would revolutionize every aspect
of the telephone industry and all of communications. One engineer
remarked, "Asking us to predict what transistors will do
is like asking the man who first put wheels on an ox cart to
foresee the automobile, the wristwatch, or the high speed generator."
Others were less restrained.
In 1954, recently retired Chief of Engineering for AT&T,
Dr. Harold Osborne, predicted, "Let us say that in the ultimate,
whenever a baby is born anywhere in the world, he is given at
birth a number which will be his telephone number for life. As
soon as he can talk, he is given a watchlike device with 10 little
buttons on one side and a screen on the other. Thus equipped,
at any time when he wishes to talk with anyone in the world,
he will pull out the device and punch on the keys the number
of his friend. Then turning the device over, he will hear the
voice of his friend and see his face on the screen, in color
and in three dimensions. If he does not see and hear him he will
know that the friend is dead." [Conly]Sheesh.
The first transistor looking
as crude, perhaps, as the first
telephone. The point contact transistor pictured here is now
Capitalizing on a flowing stream of electrons, along with
the special characteristics of silicon and germanium, the transistor
was built into amplifiers and switching equipment. Hearing aids,
radios, phonographs, computers, electronic telephone switching
equipment, satellites and moon rockets would all be improved
or made possible because of the transistor. Let's depart again
from the narrative to see how a transistor works.
Transistor stands for transit resistor, the temporary name,
now permanent, that the inventors gave it. These semidconductors
control the electrical current flowing between two terminals
by applying voltage to a third terminal. You now have a minature
switch, presenting either a freeway to electrons or a brick wall
to them, depending on whether a signal voltage exists. Bulky
mechanical relays that used to switch calls, like the crossbar
shown above, could now be replaced with transistors. There's
Transistors amplify when built into a proper circuit. A weak
signal can be boosted tremendously. Let's say you have ten watts
flowing into one side of the transistor. Your current stops because
silicon normally isn't a good conducter. You now introduce a
signal into the middle of the transistor, say, at one watt. That
changes the transistor's internal crystalline structure, causing
the silicon to go from an insulator to a conductor. It now allows
the larger current to go through, picking up your weak signal
along the way, impressing it on the larger voltage. Your one
watt signal is now a ten watt signal.
Transistors use the properties of semi-conductors, seemingly
innocuous materials like geranium and now mostly silicon. Materials
like silver and copper conduct electricity well. Rubber and porcelain
conduct electricity poorly. The difference between electrical
conductors and insulators is their molecular structure, the stuff
that makes them up. Weight, size, or shape doesn't matter, it's
how tightly the material holds on to its electrons, preventing
them from freely flowing through its atoms.
Silicon by itself is an ordinary element, a common part of
sand. If you introduce impurities like arsenic or boron, though,
you can turn it into a conductor with the right electrical charge.
Selectively placing precise impurities into a silicon chip produces
an electronic circuit. It's like making a magnetically polarized,
multi-layered chemical cake. Vary the ingredients or elements
and you can make up many kinds of cakes or transistors. And each
will taste or operate a little differently.
As I've just hinted, there are many kinds of transistors,
just as there are many different kinds of tubes. It's the triode's
solid state equivalent: the field effect transistor or FET. The
FET we'll look at goes by an intimidating name, MOSFET for Metal
Oxide Semiconductor Field Effect Transistor. Whew! That's a big
name but it describes what it does: a metal topped device working
by a phenomenon called a field effect.
A silicon chip makes up the FET. Three separate wires are
welded into different parts. These electrode wires conduct electricity.
The source wire takes current in and the drain wire takes current
out. A third wire is wired into the top. In our example the silicon
wafer is positively charged. Further, the manufacturer makes
the areas holding the source and drain negative. These two negative
areas are thus surrounded by a positive.
A much more accurate transistor explanation here
Now we introduce our weak signal current, say a telephone
call that needs amplifying. The circuit is so arranged that its
current is positive. It goes into the gate where it pushes against
the positive charge of the silicon chip. That's like two positive
magnets pushing against each other. If you've ever tried to hold
two like magnets together you know it's hard to do -- there's
always a space between them. Similarly, a signal voltage pushing
against the chip's positive charge gives space to let the current
go from the source to the drain. It picks up the signal along
the way. Check out this diagram, modified only slightly from
Lucent's excellent site:
As Louis Bloomfield of Virginia puts it:"The MOSFET goes
from being an insulating device when there is no charge on the
gate to a conductor when there is charge on the gate! This property
allows MOSFETs to amplify signals and control the movements of
electric charge, which is why MOSFETs are so useful in electronic
devices such as stereos, televisions, and computers."
I know that this is a simple explanation to a forbiddingly
difficult topic, but I think it's enough for a history article.
Thanks to Australia's John Wong for help with his section. If
you'd like to read further, check out Lucent's transistor page
by searching their site: http://www.lucent.com (external link)
If you have a better explanation or something to add, please contact me And now back to the narrative.
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