Electronic – Does the NOT gate count towards the depth of a circuit

circuit analysisdigital-logic

So I was going through some problems for a course that I am taking this semester and I came upon a problem that seemed to imply something. Let me first say that I am not looking for the solution to this problem, but rather it spawned a question that has me in the need for some clarification.

The problem was to write a two-level logic version of the following equation using AND, OR, and NOT gates only.

F = A + (B*\$\bar C\$)

As far as I can tell – that's not possible unless the NOT gate does not count towards the depth. So this raised the question – does a NOT gate not count towards the depth of a circuit?

The definition I typically see is that the depth of a Boolean circuit is the largest number of gates between a given input and output. The textbook for my course also uses this definition. So is this the impossible task? Or am I just not thinking cleverly enough?

Thanks for any insight!

Best Answer

A typical Programmable Array Logic (PAL) chip has only two levels of logic. When squeezing a bunch of logic into some PAL chips, NOT gates on the inputs don't count towards the depth of the circuit.

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