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Whats the point of transistors?

  1. Mar 4, 2015 #1
    Since you can make all the logic gates with diodes instead, what is the point of transistors considering they take more semiconductor material to construct?

  2. jcsd
  3. Mar 4, 2015 #2


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    Transistors are active control elements. Try making an amplifier with diodes.
  4. Mar 4, 2015 #3
    I see, so they pass a higher voltage with a lower trigger voltage. But why are they used in CPUs? Is it just more energy efficient?
  5. Mar 4, 2015 #4
    The problem is that the output of a logic gate using diodes will have a lower voltage than the input, because of the forward voltage drop of diodes.. This is bad if you need to use the output from one gate to feed the input of the next one. You'll need voltage amplification for that.
  6. Mar 4, 2015 #5


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    Amplification of signal is just one use to which transistors can be put.

    When transistors are used to fashion logic circuits, the ability of a transistor to turn on and off is quite handy.

    Prior to transistors, vacuum tubes were used for signal amplification and to interrupt signals by turning on and off. Early computers were constructed using vacuum tubes, but these machines were huge, required kilowatts of power to function, and gave off large quantities of heat. Tubes also tend to have a limited service life and burn out, requiring their replacement.

    Transistors avoid the problems of using tubes to make computing devices. Unlike tubes, transistors can be miniaturized, can run on a minuscule amount of current, and can function essentially forever, as long as they are not damaged by static electricity.

    Since transistors are made from sand, they are literally "dirt cheap", unlike tubes. By being able to be made so small, millions of transistors can be placed on a tiny sliver of semiconductor material and you don't have to wire all these transistors together, unlike tubes.

    It's not like we're going to run out of sand anytime soon. :wink:
  7. Mar 4, 2015 #6


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  8. Mar 5, 2015 #7


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    Do you really mean ALL logic gates can be made with DL gates?

    I had thought the next step up to DTL was necessary for such gates as NOR and NAND.
  9. Mar 5, 2015 #8
    Amplification of signals and easy control of circuits are the strongest points of modern transistors.
  10. Mar 5, 2015 #9
    The 'transistors' actually used in CPUs are not really the same old transistors you could compare to diodes. Less consumption (mostly only when it's switching), faster switching, lower logic voltages...
    All the better: on the semiconductor (miniaturized) they are not necessarily any more complex than diodes...
  11. Mar 5, 2015 #10


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    Apparently the OP hadn't done much research as to what is required to make the world go around or this question would not have been asked. Just from a digital perspective diode logic won't go very far. Try making a shift register with diodes.
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