79 Logic Elements 79.1 IC Logic Family Operation and Characteristics Logic Family. ECL Logic Family. Logic Family Circuit Mos C Logic Families and Subfamilies. TTL Logic Family Gregory L. Moss Logic families Purdue University 79.2 Logic Gates (IC Peter graham Gate Specification Parameters. Bipolar Transistor Florida Atlantic University(Retired) Gates. Complementary Metal-Oxide Semiconductor(CMOS) Logic Choosing a Logic Family Richard S. Sandige 79.3 Bistable Devices Basic Latches· Gated Latches·Flip- Flops·ldge- Triggered Flip H. S. Hinton Flops. Special Notes on Usi University of colorado 79.4 Optical Devices All-Optical Devices. Optoelectronic Devices. Limitations 79.1 IC Logic Family Operation and Characteristics Gregory L. Moss Digital logic circuits can be classified as belonging to one of two categories, either combinational (also called combinatorial)or sequential logic circuits. The output logic level of a combinatorial circuit depends only on the current logic levels present at the circuit's inputs Sequential logic circuits, on the other hand, have a memory characteristic so the sequential circuit's output is dependent not only on the current input conditions but also on the current output state of the circuit. The primary building block in combinational circuits is the logic gate. The three simplest logic gate functions are the inverter (or NOT), AND, and OR Other common basic logic functions are derived from these three. Table 79.1 gives truth table definitions of the various types of logic gates. The memory elements used to construct sequential logic circuits are called latches and flip-flops The integrated circuit switching logic used in modern digital systems will generally be from one of three families: transistor-transistor logic(TTL), complementary metal-oxide semiconductor logic(CMOS), or emit ter-coupled logic(ECL). Each of the logic families has its advantages and disadvantages. The three major families are also divided into various subfamilies derived from performance improvements in integrated circuit(IC) design technology. Bipolar transistors provide the switching action in both TTl and ECL families, while enhancement-mode MOS transistors are the basis for the CMOS family. Recent improvements in switching circuit performance are also attained using BiCMOS technology, the merging of bipolar and CMOS technologies on a single chip. a particular logic family is usually selected by digital designers based on such criteria as 1. Switching speec 3. PC board area requirements(levels of integration) 4. Output drive capability(fan-out) 5. Noise immunity characteristics 6. Product breadth 7. Sourcing of components c 2000 by CRC Press LLC© 2000 by CRC Press LLC 79 Logic Elements 79.1 IC Logic Family Operation and Characteristics IC Logic Families and Subfamilies • TTL Logic Family • CMOS Logic Family • ECL Logic Family • Logic Family Circuit Parameters • Interfacing Between Logic Families 79.2 Logic Gates (IC) Gate Specification Parameters • Bipolar Transistor Gates • Complementary Metal-Oxide Semiconductor (CMOS) Logic • Choosing a Logic Family 79.3 Bistable Devices Basic Latches • Gated Latches • Flip-Flops • Edge-Triggered Flip￾Flops • Special Notes on Using Latches and Flip-Flops 79.4 Optical Devices All-Optical Devices • Optoelectronic Devices • Limitations 79.1 IC Logic Family Operation and Characteristics Gregory L. Moss Digital logic circuits can be classified as belonging to one of two categories, either combinational (also called combinatorial) or sequential logic circuits. The output logic level of a combinatorial circuit depends only on the current logic levels present at the circuit’s inputs. Sequential logic circuits, on the other hand, have a memory characteristic so the sequential circuit’s output is dependent not only on the current input conditions but also on the current output state of the circuit. The primary building block in combinational circuits is the logic gate. The three simplest logic gate functions are the inverter (or NOT), AND, and OR. Other common basic logic functions are derived from these three. Table 79.1 gives truth table definitions of the various types of logic gates. The memory elements used to construct sequential logic circuits are called latches and flip-flops. The integrated circuit switching logic used in modern digital systems will generally be from one of three families: transistor-transistor logic (TTL), complementary metal-oxide semiconductor logic (CMOS), or emit￾ter-coupled logic (ECL). Each of the logic families has its advantages and disadvantages. The three major families are also divided into various subfamilies derived from performance improvements in integrated circuit (IC) design technology. Bipolar transistors provide the switching action in both TTL and ECL families, while enhancement-mode MOS transistors are the basis for the CMOS family. Recent improvements in switching circuit performance are also attained using BiCMOS technology, the merging of bipolar and CMOS technologies on a single chip. A particular logic family is usually selected by digital designers based on such criteria as 1. Switching speed 2. Power dissipation 3. PC board area requirements (levels of integration) 4. Output drive capability (fan-out) 5. Noise immunity characteristics 6. Product breadth 7. Sourcing of components Gregory L. Moss Purdue University Peter Graham Florida Atlantic University (Retired) Richard S. Sandige University of Wyoming H. S. Hinton University of Colorado