4.5 CMOS Logic Family

CMOS logic has undergone a constant growth in the MSI area because of its offered advantages of faster operation and low power consumption plus the greater packing density reducing the cost per function. There are several series in the CMOS family of digital ICs depicted in the table below.

Table 1. Summary of CMOS Subfamilies

CMOS Series	Prefix	Example IC
Metal-gate CMOS	40 or 140	4001 or 14001 (quad NOR gate)
Metal-gate, pin compatible w/ TTL	74C	74C02 (quad NOR gate)
Silicon-gate, pin compatible w/ TTL, high-speed	74HC	74HC02 (quad NOR gate)
Silicon-gate, high-speed, electrically compatible w/ TTL	74HCT	74HCT02 (quad NOR gate)

4000/14000 series

· 4000 the first CMOS series introduced by RCA (14000 by Motorola). Still widely used despite the emergence of new CMOS series; has higher current capabilities compared to its successors.

74C series

· This is compatible pin-to-pin and function for function with TTL devices having the same number.

74HC series (High-Speed CMOS)

· This is an improved version of the 74C series; with a tenfold increase in switching speed and higher output current capability.

74HCT series

· Also high-speed but designed to be voltage-compatible with TTL devices for it can be directly driven by a TTL output.