FAQ - Switch Design

Q1: Should I use a signal's true or complemented value?

Q2: When should I simplify a Boolean expression for switch-level
implemention?

Q1:
In working switch design problems, I'm not sure how to figure out if
the variable (A, B, C...) is complemented or not, on the drawing. Do
we look at the expression corresponding to the drawing and complement
the variable?

Remember that the pull high network is implemented with active low
P-type transistors. This necessitates complementing the controlling
signal as needed.

Q2:
I've noticed on your practice tests that there are times when you have
given a Boolean expression and want us to draw a transistor-level
design of said expression. However, the instructions say not to
simplify. I'm particularly thinking of one I saw that was "out = -(A
+ B + C)" Now, most of the transistor level stuff we've done has been
much easier to draw if the output expression is high. So, what exactly
do the instructions mean in cases like these? If I simplified this to
be -A * -B * -C and then drew it high (just because it's easier for me
to think of it that way) then is that in violation with the
instructions?

Generally, one can only directly implement a Boolean expression as a
transistor-level design if the only bars in the expression are over
individual inputs (literals). If an expression is given in this
format, there would be no reason to modify the format.

One except is the case where a bar covers the entire Boolean
expression. In this case, the expression under the bar indicates when
the output is low, rather than high. In this case, the pull down
network can be directly implemented using N-type switches, taking care
to note that their active high behavior does not require complementing
the inputs as in the case of P-type switches.