Digital Electronics: Principles, Devices and Applications

172 Digital Electronics+VDDAQ 1Q 3Q2Q5Q8Y=A.BBQ 4Q6Q 9Q 7Figure 5.56BiCMOS two-input NAND.constitute a two-input NAND in CMOS. Also note the similarity of this circuit to the one shown inFig. 5.55. The CMOS inverter stage of Fig. 5.55 is replaced by CMOS NAND in Fig. 5.56. N-channelMOSFET Q 3 in Fig. 5.55 is replaced by a series connection of N-channel MOSFETs Q 5 and Q 6 toaccommodate the two inputs. The HIGH-state and LOW-state output voltage levels of this circuit aregiven by the equationsV OH = V DD − 07 (5.9)V OL = 07 (5.10)5.7 NMOS and PMOS LogicLogic families discussed so far are the ones that are commonly used for implementing discrete logicfunctions such as logic gates, flip-flops, counters, multiplexers, demultiplexers, etc., in relatively lesscomplex digital ICs belonging to the small-scale integration (SSI) and medium-scale integration (MSI)level of inner circuit complexities. The TTL, the CMOS and the ECL logic families are not suitablefor implementing digital ICs that have a large-scale integration (LSI) level of inner circuit complexityand above. The competitors for LSI-class digital ICs are the PMOS, the NMOS and the integratedinjection logic (I 2 L). The first two are briefly discussed in this section, and the third is discussed inSection 5.8.