17.8 UNIVERSAL GATES
AND and OR gates have a larger propagation delay and larger power dissipation when compared to NAND and NOR gates. Universal gates are the gates which can be used for implementing any gate such as AND, OR and NOT or any combination of these basic gates. The basic gates can be implemented by using either NAND gates or NOR gates. Hence, NAND and NOR gates are called universal gates. However, there are some rules that need to be followed when implementing either NAND- or NOR- based gates. Consider the NAND gate, shown in Fig. 17.19(a) and an OR gate with bubbled (inverted) inputs shown in Fig. 17.19(b). The outputs are same in both the cases, which means one can replace one gate by the other. Similarly consider the NOR gate, ...
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