Applied Electronics - Outcome 3 - Logic

Outcome 3 is logic.  It is not vastly different from Intermediate 2, but they may ask you to design a more complicate circuit and look at NAND or NOR equivalents.

Firstly lets consider this circuit:

The first thing we should be able to do is draw the truth table for it:

A and B are our two inputs, but we could put in points to help us after the AND gate (C) and after the NOT gate (D).

A B   C   D   Z
0 0     0    1   1
0 1     0    0   0
1 0     0    1   1
1 1     1    0   1

We could also draw the NAND and NOR equivalent circuits.  By taking one gate at a time we can draw the equivalent for that gate, and then connect them as the original circuit is.

The benefit of designing a NAND equivalent is that we then only need one type of chip.  This makes it cheaper as we have simplified the circuit to only need one type of IC, and we could get a smaller end product as we need to include less ICs.

Here is the NAND equivalent of the above circuit.  Notice that there are two inverters in a row so they cancel each other out.  Instead of drawing the whole circuit again, you can simply put a line through them.

This has really simplified the circuit!  Instead of needing 3 ICs we now only need one, and we only need to wire in two gates.

This is the NOR equivalent.

This is less effective for this circuit as it has actually given us more logic gates to wire.  But we do only need 1 IC instead of 3.