TTL input transistor

Discussion in 'Feedback and Suggestions' started by Ron H, May 13, 2012.

  1. Ron H

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    Apr 14, 2005
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    This may be too advanced to include in the e-book. In the section on TTL internal circuitry, the following statement is made:
    From a DC point of view, this is true. However, if that were all there is to it, DTL would have been just fine, and TTL might never have been invented. In fact, Q1 in the inverter acts to speed up switching when the input goes low. When the input is high, Q2 is saturated. When the input goes low, excess base charge must be removed from Q2 before it can turn off. If Q1 were simply two diodes, this charge would have to leak off through its base-emitter junction, which would be very slow. A resistor from base to ground would help, but is not needed here. This is because Q1 briefly acts as a common-base transistor when the input goes low, and the excess charge is rapidly dumped to ground through Q1 C-E and the collector of the driving stage. Once the charge is dumped, Q2 turns off, and current ceases to flow in the Q1 collector.
    I have attached a simulation of the TTL vs "DTL" circuits. I used 2N2369 for the transistors. 2N2369 is a fast saturating switch with low storage times.
     
  2. Wendy

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    Mar 24, 2008
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    Could I get you to show a is and should be quote for the book? I'll submit this to Dennis, our editor.

    One of the reasons I read that TTL was so popular is there wasn't much difference in current draw between on and off. When dealing with thousands of gates this becomes a real concern, as the poor power supply is dragged all over the place.
     
  3. Ron H

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    I don't understand this:
     
  4. Wendy

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    How would you write it?
     
  5. Ron H

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    OK, now I get it.
    How about
    :)
    I'll try to come up with that.
    Do you think it might be outside the scope of the lesson?
     
  6. Wendy

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    This is supposed to be a college level text book. It is not used within the USA except for hobbiest purposes. If we ever get it finished I suspect you will see other people (colleges) use it, instead of folks in India.

    I would keep it simple, but cover the important issues, as you pointed out.

    If it turns out to be a major change I'll try to make it acceptable for our editor. I'm thinking a minor change at the moment.
     
  7. Ron H

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    After attempting to write an IS/SHOULD BE correction, I believe that, if you are going to include my correction, there will be extensive rewrite required. I can't see a way to drop my correction into the existing text. I also believe additional drawing(s) are required.
    The sections on TTL AND/NAND and OR/NOR might also require rewriting.
    I would be willing to correspond with the author, if needed.
     
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