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Digital integrated circuits I
If we now consider the transistor with a base current (that is,
we connect point A to logic 1, at 10 V), the transistor turns
on and passes a large collector current, with the effect that
it become a low resistance. The equivalent circuit is shown
in Figure 10.3.
Figure 10.3 Equivalent diagram of a single transistor switch, with point A
connected to logic 1
The output voltage at point B is now:
which is as close to 0 V (logic 0) as we’ll ever get.
So in this circuit the transistor output state is always the
opposite of the input state. Put another way, whatever the
input state, the output is always the inverse.
We call this simple digital circuit — you guessed it — an
inverter.
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