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Note for Digital Electronics Circuit - DEC By Srikrishna Thota

  • Digital Electronics Circuit - DEC
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  • Electronics and Communication Engineering
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Digital Electronics Introduction of Digital Techniques and Concepts: All of us are familiar with the impact of Modern Digital Computers, Calculators, Watches, etc.one of the main causes of this revolution is the advent of Integrated Circuits. (IC) There are two basic types of Electronic Signals and techniques of analog and digital. An analog signal is an AC or DC voltage or current that varies smoothly or continuously. The fig shows the type of analog signal a sine wave. A significant number of electronic signals are sinusoidal. A fixed DC voltage is also an analog signal. Digital Signal; Digital signals are essentially a series of pulses or rapidly changing voltage levels that vary in discrete steps. Digital signals are pulses of voltage that switch between two fixed levels. Electronic circuits that process these digital signals are called digital circuits. Why Digital? • • • • • • • • Increased Noise Immunity Reliable Inexpensive Programmable Easy to Compute Nonlinear Functions Reproducible Small Most analog systems were less accurate, and were slow in computation and performance. • Digital system have the ability to work faster than analog equivalents, and can operate on very high frequencies too. • It was much economical than analog methodologies as the performance was faster T.Srikrishna, M.Tech,G.V.P College for Degree and PG Courses ,Vizag

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Digital Electronics Applications of Digital Techniques: 1) Communication: It is used as TDM (Time Division Multiplexing). It converts simple amplitude signal into digital signal. 2) Industry: Using digital machine we can find the error of motor shaft or control system. Computer: Digital computer, digital techniques are used as semiconductor memories, e.g.: RAM, ROM, PROM, EAROM, CAM, etc. INTRODUCTION TO NUMBER SYSTEM: - Many number systems are in use in digital technology. The most common are the decimal, binary, octal, and hexadecimal systems. The decimal system is clearly the most familiar to us because it is a tool that we use every day. Some of other commonly used number systems are Binary, Octal and Hexadecimal number systems. DECIMAL SYSTEM: We are familiar with the number system in which an ordered set often symbols 0 through 9 known as digits. A collection of these digits makes a number which in general has two parts integer and fractional. are used to specify any number this system is popularly known as decimal system. The radix or base of this number system is 10. Any number is collection of these digits. 103 =1000 102 =100 101 =10 100 =1 Most Significant Digit . 10-1 =0.1 10-2 =0.01 Decimal point 10-3 =0.001 Least Significant Digit BINARY NUMBER SYSTEM:The number system with base (radix) 2 is known as the binary number system. Only two symbols are used to represent numbers in this system and these are 0 & 1. These are known as bits. 23 =8 Most Significant Digit 22 =4 21 =2 20 =1 . Binary point 2-1 =0.5 2-2 =0.25 2-3 =0.125 Least Significant Digit . T.Srikrishna, M.Tech,G.V.P College for Degree and PG Courses ,Vizag

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Digital Electronics VOLTAGE ASSIGNMENT: Binary 1: Any voltage between 2V to 5V Binary 0: Any voltage between 0V to 0.8V Not used: Voltage between 0.8V to 2V in 5 Volt CMOS and TTL Logic, this may cause error in a digital circuit. Today's digital circuit’s works at 1.8 volts, so this statement may not hold true for all logic circuits. 0-low, off, false, open 1-high, on, true, close BYTE & NIBBLE: Digital systems work in a binary fashion in which only two digits 0 and 1 known as bits. Are used to specify any number a group of eight bits is known as byte and a group of four bits is known as a nibble. CODING: Since a digital system understand 0’s and 1’s. Any information, which is usually in numerals, alphabetic or alphanumeric form is to be suitably converted into the binary language before it can be processed by digital circuits. This process is known as coding. OCTAL NUMBER SYSTEM:This system is used in many computers and microcomputers for entering data. The number system with base 8 is known as the octal number system. In this eight symbols 0, 1, 2, 3, 4, 5, 6&7 are used to represent numbers. 83 =512 82 =64 81 =8 80 =1 Most Significant Digit . 8-1 =1/8 8-2 =1/64 Octal point 8-3 =1/512 Least Significant Digit HEXADECIMAL NUMBERS:The hexadecimal system uses base 16. Thus, it has 16 possible digit symbols. It uses the digits 0 through 9 plus the letters A, B, C, D, E, and F as the 16 digit symbols 163 162 161 160 16-1 16-2 16-3 T.Srikrishna, M.Tech,G.V.P College for Degree and PG Courses ,Vizag

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Digital Electronics =4096 =256 =16 Most Significant Digit =1 . =1/16 Hexa Decimal point =1/256 =1/4096 Least Significant Digit CODE CONVERSION BINARY-TO-DECIMAL CONVERSION Any binary number can be converted to its decimal equivalent simply by summing together the weights of the various positions in the binary number which contain a 1. Binary 110112 24+23+01+21+20 Result Decimal =16+8+0+2+1 2710 Binary Decimal 101101012 27+06+25+24+03+22+01+20 =128+0+32+16+0+4+0+1 Result 18110 We should have noticed that the method is to find the weights (i.e., powers of 2) for each bit position that contains a 1, and then to add them up. DECIMAL-TO-BINARY CONVERSION Repeat Division-Convert decimal to binary This method uses repeated division by 2. Convert 2510 to binary Division 25/2 12/2 6/2 3/2 1/2 Result Remainder = 12+ remainder of 1 = 6 + remainder of 0 = 3 + remainder of 0 = 1 + remainder of 1 = 0 + remainder of 1 2510 Binary 1 (Least Significant Bit) 0 0 1 1 (Most Significant Bit) = 110012 T.Srikrishna, M.Tech,G.V.P College for Degree and PG Courses ,Vizag

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