TTL Inverter question...

Discussion in 'Homework Help' started by wanderer, Nov 21, 2009.

  1. wanderer

    Thread Starter New Member

    Nov 21, 2009
    5
    0
    Hello Everyone,

    I believe that for the most part I know how the TTL works, but I still have a couple of doubts that I would love if someone could clarify!

    Most of the configurations that I see all have the following resistors:

    [​IMG]

    But I have yet to read why do they select those specifics resistors, does anyone knows why those specific values are chosen?!

    I believe I know how to do it but... How would you compare the delay times between the input and the output?


    Thanks in advance!
     
  2. Thav

    Member

    Oct 13, 2009
    82
    0
    The resistors are there probably to make sure the inverter can switch quickly without being overdriven. I can't say much about that particular configuration, but I assume it was a choice to get either better speed, noise immunity or to meet some input requirements.

    To calculate the delay I imagined you'd have to have some model for the transistors which would include junction capacitances, gains, Vbe, Vce_sat and some assumption of input drive and output load. If you've got a way to estimate that, it's probably more than I know. I would think the best way to figure it out is empirically or by trusting the datasheet waveforms/specs.
     
  3. wanderer

    Thread Starter New Member

    Nov 21, 2009
    5
    0
    I figured that I had something to do with how to saturate the transistors and because of that the switching speeds but I wanted to make sure that I was not missing something...


    Thanks for the reply!
     
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