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Transistors can also be used in OR and AND gates with the
advantage of gain as well if that is needed. Another facility provided
by transistors and much used in logic circuits is inversion,.which
changes 'signal' to 'no signal' and vice versa. Although any
common-emitter amplifier inverts, so hardly qualifies as a gate, in
the context of electronic logic it is called a NOT gate. Most often
however it combines the NOT function with being an OR or AND
gate,
the combination being termed a NOR or NAND gate.
A simple n-p-n-transistor gate is shown in Fig. 25.24 with the
relevant waveforms. With both A and Β at zero volts the base is
ία) (b> ...