Logic Gates
Logic circuits are classified into two major groups, the Decision Making Logic Circuits and the Memory Circuits. The Decision making logic circuits are electronic circuits that perform specific operation on its input/s and become its output. This operation is referred to as the decision perform by these logic circuits. The outputs of these circuits are usually a function of the present state of its input.
There are three major classifications of decision making logic circuits, these are: Basic Logic gates, Universal Logic gates, and the Combinational Logic Circuits. Special logic circuits are usually classified as combinational logic circuits.
Basic Logic gates are logic circuits which perform basic logic function. Basic in the sense that all complex logic circuitry are formed using the basic logic gates. There are three basic logic gates under this group: the Inverter or NOT gate, the OR gate, and the AND gate.
The Inverter of the NOT gate performs complementary operation on its input. The output is simply the complement of its input. If the input is high the output will be low, and if the input is low the output will be high.
The OR gate has two or more inputs and only one output. The output is the logic sum of the inputs. That is, a high output if any one or more than one or all inputs is/are high. We can also describe it as a circuit having low output if all inputs are low. In logic addition: 0+0=0, 0+1=1, 1+0=1, and 1+1=1.
AND gates have two or more inputs and only one output. Its output is the product of its inputs. That is 0*0=0, 0*1=0, 1*0=0, and 1*1=1. A high output occurs if and only if all its input are logic high.
The second groups are called the Universal Logic Gates. These are formed by using two basic logic gates. And there are only two universal logic gates; the NAND gates and the NOR gates.
NAND comes from a contraction of two word “Not” and “AND”. NAND is formed when an inverter or NOT gate is connected or the AND gate output. As a result, the output of the equivalent circuit will be low if and only if all inputs are at logic high, which is the opposite if the AND gate output. The word NOR is also a contraction of two words: “Not” and “OR”. NOR is produced when an inverter or NOT gate is connected to the OR output. In effect, it output will be high if and only if all inputs are at logic low.
Output table of the logic gates
There are three major classifications of decision making logic circuits, these are: Basic Logic gates, Universal Logic gates, and the Combinational Logic Circuits. Special logic circuits are usually classified as combinational logic circuits.
Basic Logic gates are logic circuits which perform basic logic function. Basic in the sense that all complex logic circuitry are formed using the basic logic gates. There are three basic logic gates under this group: the Inverter or NOT gate, the OR gate, and the AND gate.
The Inverter of the NOT gate performs complementary operation on its input. The output is simply the complement of its input. If the input is high the output will be low, and if the input is low the output will be high.
The OR gate has two or more inputs and only one output. The output is the logic sum of the inputs. That is, a high output if any one or more than one or all inputs is/are high. We can also describe it as a circuit having low output if all inputs are low. In logic addition: 0+0=0, 0+1=1, 1+0=1, and 1+1=1.
AND gates have two or more inputs and only one output. Its output is the product of its inputs. That is 0*0=0, 0*1=0, 1*0=0, and 1*1=1. A high output occurs if and only if all its input are logic high.
The second groups are called the Universal Logic Gates. These are formed by using two basic logic gates. And there are only two universal logic gates; the NAND gates and the NOR gates.
NAND comes from a contraction of two word “Not” and “AND”. NAND is formed when an inverter or NOT gate is connected or the AND gate output. As a result, the output of the equivalent circuit will be low if and only if all inputs are at logic high, which is the opposite if the AND gate output. The word NOR is also a contraction of two words: “Not” and “OR”. NOR is produced when an inverter or NOT gate is connected to the OR output. In effect, it output will be high if and only if all inputs are at logic low.
Output table of the logic gates
Figure 1. Inverter and OR Gate
Figure 2. AND Gate
Digital electronics was founded from the most basic of circuits. This builds up into more complex formation of those basics until all the complexities converge to perform one industrial function. Thus the need, to study basics logic gates, their behavior, output characteristics and function is almost equivalent as learning ABC’s. The basic logic gates, (AND, OR, & NOT) can be combined to have more advance logic gates like NOR & NAND, try it.
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