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Digital integrated circuits I
Figure 10.31
A transistor switch, with three inputs A, B and C
If you look at it carefully, you should be able to figure out
how it works. When all three of the three inputs, A, B, or C
are connected to logic 0, the transistor is off, hence the transistor
is a very high resistance, which means that the output
is at logic 1. However, when any one of the three inputs is
connected to logic 1 the transistor turns on, hence becoming
a low resistance, and the output becomes logic 0. The truth
table of Figure 10.32 shows this, and if you compare this to
the truth table in Figure 10.25 you’ll see they are the same.
Yes, the three input transistor switch of Figure 10.31 (which
is merely an adapted inverter) is a NOR gate!
Figure 10.32 Truth table for the transistor switch circuit of Figure 10.31
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