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Designing with transmission gates

Designing with transmission gates

From: Robert Dick <dickrp_at_avoiding.spam>
Date: Tue Oct 14 2008 - 19:20:37 EDT

I think it might be useful to some students to have more guidance on designing
with transmission gates. We should have a solid understanding of two-level
logic gate based design now, but maybe not as solid an understanding of
transmission gate based design. The guidelines I am about to present do not
permit any possible TG-based design but will generally lead to a good design.
Give them a try to see how they work, relative to starting from a truth table
style implementation and looking for redundancy.

1) Minimize the function.

2) Do a MUX-based design, using at most a 2^(n-1):1 MUX, where n is the number
of inputs to the minimized function.

3) Decompose the MUX into multiple 2:1 MUXs.

4) Look for any redundancy, e.g., a 2:1 MUX with 0 on both inputs is a wire to

5) Decompose the 2:1 MUXs to TGs.


Does that help? You should understand how to TG-based design even when not
following this cookie-cutter style, but the style will often work well.

Best Regards,

-Robert Dick-
Received on Tue Oct 14 18:20:37 2008

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