# Tricky problem regarding CMOS

by Carl   Last Updated October 09, 2019 19:25 PM

My lecturer gave us the following problem today:

"A CMOS gate consists of a pull-up network with 0 or more PMOS transistors, and a pull-down network with 0 or more NMOS transistors. The output is $$\ f(A,B,C)\$$. The truth table for $$\ f(A,B,C) \$$ has both 0's and 1's as outputs.

What is $$\ f(1,1,1) \$$?"

My initial thought was that $$\ f(1,1,1) = 0 \$$ since the PMOS transistors would be open (so that current can't run through) while the NMOS transistors would be closed and allowed a current through to GND resulting in a low output.

But since I don't know the actual boolean expression of $$\ f(A,B,C) \$$ can I really be sure this is the case?

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