Connect with us

BJT vs MOSFET for logic gates help

Discussion in 'General Electronics Discussion' started by Tristan369, Nov 19, 2020.

Scroll to continue with content
  1. ratstar

    ratstar

    270
    11
    Aug 20, 2018
    Ive got a slightly different route than this for my project. > : )

    Having a good computer is nice, but you can get a second hand 2.5ghz 4gb ram computer for only 5 quid down the pawn shop, so that fact makes me head off towards a more custom hardware / analogue computer / fpga route than making an ordinary computer, and then I budgetted I can already equal a (latest) GPU's power with only a megahert clock, as long as the program instructions are all in physically.

    Then i've actually gained performance out of a DIY computer. Actually did something decent for myself.
     
    Last edited: Nov 22, 2020
  2. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    Why are you guys trying to re-invent digital logic when there is already a history of logic types:
    1) RTL resistor-transistor logic.
    2) DTL: Diode-transistor logic.
    3) TTL: Transistor-transistor logic.
    4) CMOS: Complementary MOSfets logic.

    Here is a very odd Cmos circuit posted by Tristan in one of the posts here:
     

    Attached Files:

  3. ratstar

    ratstar

    270
    11
    Aug 20, 2018
    I can do logic with just resistor- resistor logic, and capacitor- capacitor logic, and inductor logic, they dont seem to be the usual list, but its true you can.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,591
    2,360
    Nov 17, 2011
    I have my doubts. You've been promoting this idea across several threads but haven't come up with any proof so far.
     
  5. ratstar

    ratstar

    270
    11
    Aug 20, 2018
    I cant proove it to you, it seems that you'll have to work it out yourself in your own time, but I promise u it is possible!!

    I could draw up the circuits, its not complicated. The logic is the easy thing, the engine that runs it (the oscillator) is harder in my opinion.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    10,591
    2,360
    Nov 17, 2011
    As long as you can't prove it, it's pure fantasy in my opinion.
    If you had a working circuit, you could show it to us.
     
  7. ratstar

    ratstar

    270
    11
    Aug 20, 2018
    But showing you the circuit would do me no good, (Im thinking your not going to like it.) youll have to think of it yourself.
     
  8. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    I listed 4 types of logic circuits that worked perfectly and have been used in many circuits over the years.
    But you are listing impossible logic that will not work.
    The circuit types I listed were made into ICs and computer processor chips. You are not even using any ICs that are readily available and are very inexpensive..
     
  9. bertus

    bertus Moderator

    1,158
    439
    Nov 8, 2019
    Hello,
    What is wrong with the symbols that Tristan is using:
    Mosfet symbols.gif

    Bertus
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    10,591
    2,360
    Nov 17, 2011
    Nothing.
    The oddity is mentioned in the image:
    [​IMG]
    But caption 1) is wrong: P is indicated by the little circle on the gate.
    As for caption 2) : admitted, S and D are not discernible. I think these symbols are simplified to show the logic, not the physical setup. Plus one can swap S and D on a MOSFET if one accepts more or less drastically altered parameters - not that I recommend doing this ;)
     
  11. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    The symbol for a Mosfet should be standardized. I have never seen a datasheet of a Mosfet that has a circle on the gate like an inverter and that is drawn completely symmetrical so you cannot easily see the Source pin.
    I have also never seen the arrows backwards.

    Hee, hee. Just now I looked at the datasheets for two Jfets and they did not show a symbol.
     
  12. Harald Kapp

    Harald Kapp Moderator Moderator

    10,591
    2,360
    Nov 17, 2011
    The direction of the arrows depends on where they are drawn for a reason:
    • When drawn on the source pin they pretty much resemble the arrows of a bipolar transistor indicating the polarity of the source (arrow to source = N doped, arrow from source = P doped).
    • When drawn on the backgate or substrate pin (although this connection is rarely if ever made available as a separate pin, hence the direct connection to the source in the symbol) the arrow indicates the polarity of the backgate vs. the channel. Thus it looks backwards to the arrow on the source but there's actually logic behind this. Take for example an N-MOSFET, then the backgate/substrate would be P doped and the channel, once brought into conduction is N with respect to the backgate. The arrow makes sense now?
    Neither have I. I think this symbol is for illustrating the operating principle of CMOS gates only.
     
  13. Nanren888

    Nanren888

    346
    90
    Nov 8, 2015
  14. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    A symbol should not need a label on it to what is what.
     

    Attached Files:

    Nanren888 likes this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-