数字基础-全套PPT课件.pptx

Introductory Concepts1 Most natural quantities that we see are analog and vary continuously. Analog systems can generally handle higher power than digital systems. Digital systems can process, store, and transmit data more efficiently but can only assign discrete values to each point.Analog Quantities2 Many systems use a mix of analog and digital electronics to take advantage of each technology. A typical CD player accepts digital data from the CD drive and converts it to an analog signal for amplification.Analog and Digital Systems3 Digital electronics uses circuits that have two states, which are represented by two different voltage levels called HIGH and LOW. The voltages represent numbers in the binary system. Binary Digits and Logic LevelsIn binary, a single number is called a bit (for binary digit). A bit can have the value of either a 0 or a 1, depending on if the voltage is HIGH or LOW.HIGH（binary 0）LOW（binary 0）VH(max)VH(min)VL(max)VL(min)Unacceptable4 Digital waveforms change between the LOW and HIGH levels. A positive going pulse is one that goes from a normally LOW logic level to a HIGH level and then back again. Digital waveforms are made up of a series of pulses.Digital Waveforms5 Actual pulses are not ideal but are described by the rise time, fall time, amplitude, and other characteristics.Pulse Definitions6 Examples of Digital Waveforms7 Periodic pulse waveforms are composed of pulses that repeats in a fixed interval called the period. The frequency is the rate it repeats and is measured in hertz. Periodic Pulse WaveformsThe clock is a basic timing signal that is an example of a periodic wave.What is the period of a repetitive wave if f = 3.2 GHz?313 psExampleSolution8 Pulse DefinitionsIn addition to frequency and period, repetitive pulse waveforms are described by the amplitude (A), pulse width (tW) and duty cycle. Duty cycle is the ratio of tW to T.Amplitude (A)Pulse width (tW)Period, T9 A timing diagram is used to show the relationship between t