21-09-2013, 02:51 PM
BASIC ELECTRONICS NOTES
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Introduction:
Electronic circuits and systems are of two kinds namely, analog and digital. The distinction between them is not so much in the types of semiconductor devices used in these circuits as it is in voltage and current variations that occur when each type of circuit performs the function for which it is designed.
Analog circuits are those in which voltages and currents vary continuously through the given range. They can take infinite values within specified range. A digital circuit is one which the voltage levels assume a finite number of distinct values. In all modern digital circuits, there are two discrete voltage levels.
Digital systems use binary number system. Therefore, two state devices are used to represent the two binary digits 1 and 0 by two different voltage levels, called HIGH (+5V) and LOW (0V). If the HIGH voltage level is used to represent 1 and the LOW voltage to represent 0, the system is called positive logic system. If the HIGH voltage level represents 0 and the LOW voltage level represents 1, the system is called negative logic system. Both positive and negative logics are used in digital systems, but the positive logic is more common.
Digital circuits are often called as switching circuits because the voltage levels in a digital circuit are assumed to be switched from one value to another instantaneously. Switching circuits may be combinational switching circuits or sequential switching circuits. In combinational switching circuits, the output depends only on the present inputs whereas in sequential switching circuits, the output depends only on the present inputs as well as on the past inputs. In other words sequential circuits have memory and combinational circuits have no memory.
Decimal to binary conversion:
The given decimal number is repeatedly divided by 2, which is the base number of binary system till quotient becomes ‘0’ and the remainder is collected from bottom to top. To convert the fractional part into binary, fraction part is multiplied by 2 repeatedly and any carry in integer place is recorded. The string of integer obtained from top to bottom gives the equivalent fraction in binary number system.
Boolean algebra:
George Boole in 1854 invented a new kind of algebra known as Boolean algebra. It is sometimes called switching algebra. Boolean algebra is the mathematical frame work on which logic design is based. It is used in synthesis and analysis of binary logical function.
Boolean laws: These have been derived by using Boolean postulates. These laws are used to design and analyse logic circuit mathematically. Table 4.5 summarizes the Boolean laws.
Logic Gates:
It is an electronic circuit, which makes logic decisions. A logic gate is a digital circuit with one or more input signal and only one output signal. All input or output signals are either low voltage or high voltage. A digital circuit is referred to as logic gate for simple reason i.e. it can be analysed based on Boolean algebra.To make logical decisions, three gates are used. They are OR, AND and NOT gate. These logic gates are building blocks, which are available in the form of IC. The input and output of the binary variables for each gate can be represented in a tabular column or truth table.
OR Gate:
The OR gate performs logical additions commonly known as OR function. The OR gate has two or more inputs and only one output. The operation of OR gate is such that a HIGH(logic 1) on the output is produced when any of the input is HIGH. The output is LOW(logic 0) only when all the inputs are LOW. If A and B are the input variables of an OR gate and Y is its output, then Y=A+B. Similarly for more than two variables
[attachment=58186]
Introduction:
Electronic circuits and systems are of two kinds namely, analog and digital. The distinction between them is not so much in the types of semiconductor devices used in these circuits as it is in voltage and current variations that occur when each type of circuit performs the function for which it is designed.
Analog circuits are those in which voltages and currents vary continuously through the given range. They can take infinite values within specified range. A digital circuit is one which the voltage levels assume a finite number of distinct values. In all modern digital circuits, there are two discrete voltage levels.
Digital systems use binary number system. Therefore, two state devices are used to represent the two binary digits 1 and 0 by two different voltage levels, called HIGH (+5V) and LOW (0V). If the HIGH voltage level is used to represent 1 and the LOW voltage to represent 0, the system is called positive logic system. If the HIGH voltage level represents 0 and the LOW voltage level represents 1, the system is called negative logic system. Both positive and negative logics are used in digital systems, but the positive logic is more common.
Digital circuits are often called as switching circuits because the voltage levels in a digital circuit are assumed to be switched from one value to another instantaneously. Switching circuits may be combinational switching circuits or sequential switching circuits. In combinational switching circuits, the output depends only on the present inputs whereas in sequential switching circuits, the output depends only on the present inputs as well as on the past inputs. In other words sequential circuits have memory and combinational circuits have no memory.
Decimal to binary conversion:
The given decimal number is repeatedly divided by 2, which is the base number of binary system till quotient becomes ‘0’ and the remainder is collected from bottom to top. To convert the fractional part into binary, fraction part is multiplied by 2 repeatedly and any carry in integer place is recorded. The string of integer obtained from top to bottom gives the equivalent fraction in binary number system.
Boolean algebra:
George Boole in 1854 invented a new kind of algebra known as Boolean algebra. It is sometimes called switching algebra. Boolean algebra is the mathematical frame work on which logic design is based. It is used in synthesis and analysis of binary logical function.
Boolean laws: These have been derived by using Boolean postulates. These laws are used to design and analyse logic circuit mathematically. Table 4.5 summarizes the Boolean laws.
Logic Gates:
It is an electronic circuit, which makes logic decisions. A logic gate is a digital circuit with one or more input signal and only one output signal. All input or output signals are either low voltage or high voltage. A digital circuit is referred to as logic gate for simple reason i.e. it can be analysed based on Boolean algebra.To make logical decisions, three gates are used. They are OR, AND and NOT gate. These logic gates are building blocks, which are available in the form of IC. The input and output of the binary variables for each gate can be represented in a tabular column or truth table.
OR Gate:
The OR gate performs logical additions commonly known as OR function. The OR gate has two or more inputs and only one output. The operation of OR gate is such that a HIGH(logic 1) on the output is produced when any of the input is HIGH. The output is LOW(logic 0) only when all the inputs are LOW. If A and B are the input variables of an OR gate and Y is its output, then Y=A+B. Similarly for more than two variables