A is analog, D is digital, A/D conversion, is the conversion of analog signals to digital signals (the device, the process).

　　With the rapid development and popularity of digital technology, especially information technology, in modern control. Communication and detection and other fields, in order to improve the performance indicators of the system, the processing of the signal is widely used digital computer technology. As the actual objects of the system are often some analogue quantities (e.g. temperature. Pressure. Displacement. Image, etc.), in order for the computer or digital instrument to be able to recognise them. To process these signals, these analogue signals must first be converted into digital signals; and by the computer analysis. The digital output after processing also often needs to be converted into a corresponding analogue signal in order to be accepted by the actuator. This requires a circuit that acts as a bridge between analogue and digital signals - an analogue-to-digital and digital-to-analogue converter.

　　The circuit that converts an analogue signal into a digital signal is called an analogue-to-digital converter (a/d converter or adc, analog to digital converter); the circuit that converts a digital signal into an analogue signal is called a digital-to-analogue converter (d/a converter or dac, digital to analog converter); the a/d The a/d converter and the d/a converter have become indispensable in information systems to ensure the accuracy of the system processing results, the a/d converter and the d/a converter must have sufficient conversion accuracy; to achieve real-time control and detection of rapidly changing signals, the a/d and d/a converters also require a high conversion speed. Conversion accuracy and conversion speed are important technical indicators of a/d and d/a converters. With the development of integration technology, many monolithic and hybrid integrated a/d and d/a converters have been developed and produced, which have more and more advanced technical specifications.

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