Transcript Document
Chapter 15 Introduction to Digital Electronics Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Chapter Goals • Introduce binary digital logic concepts • Explore the voltage transfer characteristics of ideal and nonideal inverters • Define logic levels and logic states of logic gates • Introduce the concept of noise margin • Present measures of dynamic performance of logic devices • Review of Boolean algebra • Investigate simple transistor, diode, and diode-transistor implementations of the inverter and other logic circuits • Explore basic design techniques of logic circuits 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Brief History of Digital Electronics • Digital electronics can be found in many applications in the form of microprocessors, microcontrollers, PCs, DSPs, and an uncountable number of other systems. • The design of digital circuits has progressed from resistortransistor logic (RTL) and diode-transistor logic (DTL) to transistor-transistor logic (TTL) and emitter-coupled logic (ECL) to complementary MOS (CMOS) • The density and number of transistors in microprocessors has increased from 2300 in the 1971 4-bit 4004 microprocessor to 25 million in the more recent IA-64 chip and it is projected to reach over one billion transistors by 2010 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Ideal Logic Gates • Binary logic gates are the most common style of digital logic • The output will consist of either a 0 (low) or a 1 (high) • The most basic digital building block is the inverter 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl The Ideal Inverter The ideal inverter has the following voltage transfer characteristic (VTC) and is described by the following symbol V+ and V- are the supply rails, and VH and VL describe the high and low logic levels at the output 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Logic Level Definitions An inverter operating with power supplies at V+ and 0 V can be implemented using a switch with a resistive load 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Logic Voltage Level Definitions • VL – The nominal voltage corresponding to a low-logic state at the input of a logic gate for vi = VH • VH – The nominal voltage corresponding to a high-logic state at the output of a logic gate for vi = VL • VIL – The maximum input voltage that will be recognized as a low input logic level • VIH – The maximum input voltage that will be recognized as a high input logic level • VOH – The output voltage corresponding to an input voltage of VIL • VOL – The output voltage corresponding to an input voltage of VIH 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Logic Voltage Level Definitions (cont.) Note that for the VTC of the nonideal inverter, there is now an undefined logic state 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Noise Margins • Noise margins represent “safety margins” that prevent the circuit from producing erroneous outputs in the presence of noisy inputs • Noise margins are defined for low and high input levels using the following equations: NML = VIL – VOL NMH = VOH – VIH 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl Noise Margins (cont.) • Graphical representation of where noise margins are defined Continua… 3 Microelettronica – Elettronica digitale 2/ed Richard C. Jaeger, Travis N. Blalock Copyright © 2005 – The McGraw-Hill Companies srl