Chapter2-1

Chapter2-1 - Spring 2009 ELEC001 Electronic &...

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P.1 Chapter 02 -- Foundation of Digital Systems Binary Number, Logic, Computer and IC Spring 2009 ELEC001 Electronic & Information Technology
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P.2 Analog Signals An analog signal represents a physical phenomena that varies continuously with time and in amplitude. Examples: the sound we hear, the visual signal we see, the current generated by the mouthpiece of a conventional telephone, etc. A continuous quantity is not countable – for any two possible distinct values of the quantity, there will be at least one other possible value in between. A continuous quantity takes on an infinite number of values. In the classical world model, many physical quantities in nature are continuous and varies continuously with time: distance, mass, velocity, force, etc. m t f dt t dv / ) ( ) ( = Example: consider Newton’s 2nd Law (force = acceleration x mass)
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P.3 Analog Systems )) ( ( 2 sin ) ( 2 sin ) ( ) ( t t x f t s t f t x t s c FM c AM βπ π + = = A system is analog when the signal is manipulated (e.g. filtered, modulated, amplified, transmitted, received) as a continually changing quantity. Examples: - The suspension system for your car - The telephone invented by Bell in 1876 - AM/FM modulation for signal transmission over radio - A World-War II fire control system before the digital computer
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P.4 Alexander Graham Bell and his Telephone time current In 1876, Bell invented the telephone. At the mouth piece, the moving of a diaphragm compresses the carbon grains and changes their electrical resistance, causing changes in the electrical current flowing through the telephone circuit. At the receiver, the current drives a magnet which moves a diaphragm to recreate the speech signal.
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P.5 Digital Signals and Systems A digital signal is a quantity that is measured in discrete values at discrete time/space instances. Examples: the gender of one or a group of students in this class, a .bmp computer file, the 8,000 × 8 bits per second telephone signal in the modern telephone network. A true analog signal can have an infinite number of values. Any finite system must inherently be digital/discrete While human touch and feel analog signals, we process information in digital terms – we make yes/no decision; we can deal with physical quantities only with finite accuracies Consider your age. Is this a continuous or discrete quantity? (The quantity is supposedly continuous but any answer that you can give me is discrete!)
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P.6 Example - Digital Telephony Since the 1970s, the core of the telephone network has been converted into a digital network. Each voice signal is converted into a digital signal of 64 kbps – each analog voice signal is sampled 8,000 times per second, and 8 bits are used to represent the amplitude of each sample, meaning that each sample can be represented by only one of 256 values.
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Chapter2-1 - Spring 2009 ELEC001 Electronic &...

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