Types of Standard Logic ICs

Standard logic ICs are classified into the following types according to their structure (i.e., manufacturing process used), which differ in electrical characteristics. At present, CMOS logic ICs that combine low power consumption and low cost are most commonly used.

■TTL (transistor-transistor logic)

• Bipolar logic that was initially widely used as standard logic ICs
• Provides a higher current drive capability and operating speed but dissipates more power than CMOS logic ICs

■CMOS logic (CMOS: Complementary MOSFET)

• Combines p-channel and n-channel MOSFETs to achieve lower power dissipation than TTL
• Was initially slower than TTL, but now provides higher operating speed than TTL because of fine wafer fabrication processes

■BiCMOS logic (bipolar CMOS)

• Uses a CMOS process for the input stage and logic circuit to reduce power dissipation and bipolar transistors for the output stage to provide a high current drive capability
• High cost incurred by complicated manufacturing processes because of MOS-bipolar combination