1.2.4 Compound Gate and Multiplexers

Complex Boolean functions of multiple input variables can be realized by simple extension of the circuit structures developed for the basic NAND and NOR gates discussed above.

Consider the boolean function whose CMOS implements is shown in fig 1.7.

The output node attains the logic `1' owing to the pMOS sub-circuit. One can easily see that driving both the gate inputs (labeled A and B ) of the pMOS transistors or driving the inputs (labeled C and D ) of the series pMOS transistors achieves the output `1'. Due to the complementary nature of the pMOS and nMOS transistors, any series combination of transistors in the nMOS tree gets replaced by a parallel connection in the pMOS tree and vice versa.