Introduction:
The term digital is derived from the way operations are performed, by counting digits. For many years, applications of digital electronics were confined to computer systems. Today, digital technology is applied in a wide range of areas in addition to computers. Such applications as television, communications systems, radar, navigation and guidance systems, military systems, medical instrumentation, industrial process control, and consumer electronics use digital techniques. Over the years digital technology has progressed from vacuum-tube circuits to discrete transistors to complex integrated circuits, many of which contain millions of transistors, and many of which are programmable. This article introduces you to digital electronics and provides a broad overview of many important concepts, components, and tools.
What Is Digital And Analog Electronics:
Electronic circuits can be divided into two broad categories, digital and analog. Digital electronics involves quantities with discrete values, and analog electronics involves quantities with continuous values.
An analog* quantity is one having continuous values. A digital quantity is one having a discrete set of values. Most things that can be measured quantitatively occur in nature in analog form. For example, the air temperature changes over a continuous range of values. During a given day, the temperature does not go from, say, 70 to 71 instantaneously; it takes on all the infinite values in between. If you graphed the temperature on a typical summer day, you would have a smooth, continuous curve similar to the curve in Figure 1. Other examples of analog quantities are time, pressure, distance, and sound.
Rather than graphing the temperature on a continuous basis, suppose you just take a temperature reading every hour. Now you have sampled values representing the temperature at discrete points in time (every hour) over a 24-hour period, as indicated in Figure 2. You have effectively converted an analog quantity to a form that can now be digitized by representing each sampled value by a digital code. It is important to realize that Figure 2 itself is not the digital representation of the analog quantity.
Digital Electronics Advantage :
Digital representation has certain advantages over analog representation in electronics applications. For one thing, digital data can be processed and transmitted more efficiently and reliably than analog data. Also, digital data has a great advantage when storage is necessary. For example, music when converted to digital form can be stored more compactly and reproduced with greater accuracy and clarity than is possible when it is in analog form. Noise (unwanted voltage fluctuations) does not affect digital data nearly as much as it does analog signals
Analog System:
A public address system, used to amplify sound so that it can be heard by a large audience, is one simple example of an application of analog electronics. The basic diagram in Figure 3 illustrates that sound waves, which are analog in nature, are picked up by a microphone and converted to a small analog voltage called the audio signal. This voltage varies continuously as the volume and frequency of the sound changes and is applied to the input of a linear amplifier. The output of the amplifier, which is an increased reproduction of input voltage, goes to the speaker(s). The speaker changes the amplified audio signal back to sound waves that have a much greater volume than the original sound waves picked up by the microphone.
Binary Digit:
Digital electronics involves circuits and systems in which there are only two possible states. These states are represented by two different voltage levels: A HIGH and a LOW. The two states can also be represented by current levels, bits and bumps on a CD or DVD, etc. In digital systems such as computers, combinations of the two states, called codes, are used to represent numbers, symbols, alphabetic characters, and other types of information.
The two-state number system is called binary, and its two digits are 0 and 1. A binary digit is called a bit
Bit, Nibble, Byte, Word, Double Word:
An important basic idea in digital electronics and computing is represented, manipulation of data used bit (a binary element), byte, word, double-word.
- The bit is represented 0 and 1 .
- The nibble have 4 bits.
- The byte have 8 bits .
- The word have 16 bits. (2 bytes).
- The double word have 32 bits (2 words).
Number System:
The binary number system and digital codes are fundamental to computers and to digital electronics in general. the binary number system and its relationship to other number systems such as decimal, hexadecimal, and octal are presented.
Decimal Number:
You are familiar with the decimal number system because you use decimal numbers every day. In the decimal number system each of the ten digits, 0 through 9, represents a certain quantity. As you know, the ten symbols (digits) do not limit you to expressing only ten different quantities because you use the various digits in appropriate positions within a number to indicate the magnitude of the quantity. You can express quantities up through
nine before running out of digits; if you wish to express a quantity greater than nine, you use two or more digits, and the position of each digit within the number tells you the magnitude it represents.
Binary Numbers:
The binary number system is another way to represent quantities. It is less complicated than the decimal system because the binary system has only two digits. The decimal system with its ten digits is a base-ten system; the binary system with its two digits is a base-two system. The two binary digits (bits) are 1 and 0. The position of a 1 or 0 in a binary number indicates its weight, or value within the number, just as the position of a decimal digit determines the
value of that digit. The weights in a binary number are based on powers of two.
Hexadecimal Numbers:
The hexadecimal number system has sixteen characters; it is used primarily as a compact way of displaying or writing binary numbers because it is very easy to convert between binary and hexadecimal. As you are probably aware, long binary numbers are difficult to read and write because it is easy to drop or transpose a bit. Since computers and microprocessors understand only 1s and 0s, it is necessary to use these digits when you program in “machine language.” Imagine writing a sixteen bit instruction for a microprocessor system in 1s and 0s. It is much more efficient to use hexadecimal or octal.
Octal Numbers:
The octal number system is composed of eight digits Like the hexadecimal number system, the octal number system provides a convenient way to express binary numbers and codes. However, it is used less frequently than hexadecimal in conjunction with computers and microprocessors to express binary quantities for input
and output purposes.
Logic Gates:
troubleshooting of logic gates. The relationship of input and output waveforms of a gate using timing diagrams is thoroughly covered. Logic symbols used to represent the logic gates are in accordance with ANSI/IEEE Standard 91-1984/ Std. 91a-1991. This standard has been adopted by private industry and the military for use in internal documentation as well as published literature.
The AND Gate:
The AND gate is one of the basic gates that can be combined to form any logic function. An AND gate can have two or more inputs and performs what is known as logical multiplication. An AND gate produces a HIGH output only when all of the inputs are HIGH. When any of the inputs is LOW, the output is LOW. Therefore, the basic purpose of an AND gate is to determine when certain conditions are simultaneously true, as indicated by HIGH levels on
all of its inputs, and to produce a HIGH on its output to indicate that all these conditions are true.
The OR Gate:
The OR gate is another of the basic gates from which all logic functions are constructed. An OR gate has two or more inputs and one output, An OR gate produces a HIGH on the output when any of the inputs is HIGH. The output is
LOW only when all of the inputs are LOW. Therefore, an OR gate determines when one or more of its inputs are HIGH and produces a HIGH on its output to indicate this condition. The inputs of the 2-input OR gate in Figure are labeled A and B, and the output is labeled X.
The Not Gate:
A NOT gate accepts one input value and produces one output value. By definition, if the input value for a NOT gate is 0, the output value is 1, and if the input value is 1, the output is 0. A NOT gate is sometimes referred to as an inverter because it inverts the input value.
Nand And Nor Gate:
The NAND and NOR gates are essentially the opposite of the AND and OR gates, respectively. They are also called universal gates.
XOR Gate:
XOR, or exclusive OR, gate An XOR gate produces 0 if its two inputs are the same, and a 1 otherwise
XNOR Gate:
XOR gate, an XNOR has only two inputs. The bubble on the output of the XNOR symbol indicates that its output is opposite that of the XOR gate. When the two input logic levels are opposite, the output of the exclusive-NOR gate is LOW.
The four possible input combinations and the resulting outputs for an XNOR gate are shown in Figure
Advantage of Digital Electronics:
Application Of Analog Electronics:
