how can find the maximum fan-out of the TTL-NAND gate using LTSpice ? i tried to solve problem by hand, but the problem how to find fan-out using ltspice

  • 1
    It depends on the device spec. Read the datasheet. – Long Pham Aug 7 at 9:21
  • 1
    Show how can you use the LTSpice in order to measure the maximum Fanout for the TTL circuit above. Calculate the simulated Fanout. Show the steps you followed. Are the calculated and simulated values the same? What difficulties you have faced? – Hamzeh Hassaan Aug 7 at 9:23
  • 1
    Um, is this a homework question ? – Long Pham Aug 7 at 9:24
  • yes,this is a homework question – Hamzeh Hassaan Aug 7 at 9:28
  • 4
    @HamzehHassaan Then press on "edit" and edit your question. Include your attempt of solving the question and where you got stuck. – Hazem Aug 7 at 9:44

It can be done. Make a simulated circuit using the NAND gate driving some TTL inverters. Keep adding inverters until the NAND gate's low level is no longer low enough to make the inverter outputs high. That's not the right way to find the fanout, though. You would only do so if you're sure you're not misreading an idiotic homework assignment. @Long Pham's comment is correct and all you need to know.

  • Last time I looked, most spice 7400 libraries use behavioural simulations based on controlled voltage sources, not accurate simulations. Unless you find one of the few that accurately simulates the internals of the component, this won't work... – Jules Aug 8 at 0:19
  • My answer was a way to deal with the homework assignment. Note that I said "idiotic." Of course it won't work. – stretch Aug 9 at 1:18

Your Answer


By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.