# Logic Circuit

Logic circuit is a kind of discrete signal transmission and processing, based on the principle of binary, the realization of digital signal logic operation and operation of the circuit. It is divided into combinational logic circuit and sequential logic circuit. The former is composed of the most basic “AND gate” circuit, “OR gate” circuit and “NOT gate” circuit. Its output value depends only on the current value of its input variable and has nothing to do with the past value of the input variable—that is, it has no memory and storage. Function; the latter is also composed of the above-mentioned basic logic gate circuit, but there is a feedback loop-its output value depends not only on the current value of the input variable, but also on the past value of the input variable. Since it is only divided into high and low levels, it has strong anti-interference ability and good accuracy and confidentiality. It is widely used in computer, digital control, communication, automation and instrumentation. The most basic ones are AND circuit, OR circuit and NOT circuit.

Logic circuit refers to a circuit that completes logic operations. This kind of circuit generally has several input terminals and one or several output terminals. When the input signals meet a certain logical relationship, the circuit is opened and there is output; otherwise, the circuit is closed and there is no output. Therefore, this kind of circuit is also called logic gate circuit, or gate circuit for short.
It mainly includes digital electronic technology (several logic circuits), basic gate circuits (semiconductor characteristics, discrete components, TTL integrated circuits, CMOS integrated gate circuits), combinational logic circuits (adders, encoders, decoders and other integrated logic functions) ) Sequential logic circuits (counters, registers) and digital-to-analog and analog-to-digital conversion.

Basic logic circuit-gate circuit
A simple logic circuit is usually composed of a gate circuit, or it can be made with a transistor. For example, the collector of an NPN transistor is connected to the emitter of another NPN transistor. This can be regarded as a simple AND gate circuit, namely : When the bases of the two transistors are connected to high level, the circuit is turned on, and as long as one is not connected to high level, the circuit is not turned on.