Digital Logical Circuit（俞鹤伟）chapter3-a.pptVIP

* Digital Logic Chapter 3: Digital Circuits Introdution Digital circuits is the hardware of digital systems. The basis of digital circuits is analog circuits. The purpose of this chapter is to give you a solid working knowledge of the electrical aspects of digital circuits. * 3.1 Logic Signals and Gates Digital logic maps the infinite set of real values for a physical quantity into two subsets corresponding to just two logic values : 0, and 1. * Basic logic elements * Logic Circuit Timing diagram * 3.2 Logic Families ? We can use many kinds of electronic components to design an electronic logic circuit. ? TTL—— Transistor-Transistor Logic ? MOS——Metal-Oxide Semiconductor ? CMOS—— Complementary Metal-Oxide Semiconductor ? CMOS logic is both the most capable and the easiest to understand commercial digital logic technology. lower power consumption and higher levels of integration CMOS circuits now account for the vast majority of the worldwide IC market * 3.3 CMOS logic 3.3.1 CMOS Logic Levels ? Real logic circuits process electrical signals such as voltage levels. ? There is a range of voltages that is interpreted as a logic 0, and another, non-overlapping range that is interpreted as a logic 1. ? A MOS transistor can be modeled as a 3-terminal device that acts like a voltage-controlled resistance. 3.3.2 MOS Transistors * MOS transistors The symbols and characteristics of MOS transistors If Vgs=0, Rds is very high. Increase Vgs, Rds decreases to a very low value. If Vgs=0, Rds is very high. Algebraically decrease Vgs, Rds decreases to a very low value. * 3.3.3 Basic CMOS Inverter Circuit * Another way to visualize CMOS operation Q2 (p-channel) Q2 (p-channel) Q1 (n-channel) Q1 (n-channel) * A way of drawing CMOS circuits inversion bubble More readily apparent * * * 用“If Vgs=0, Rds is very high”解释即可