analog-to-digital converter

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analog-to-digital converter

[¦an·əl‚äg tə ¦dij·ət·əl kən′vərd·ər]
(electronics)
A device which translates continuous analog signals into proportional discrete digital signals.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Analog-to-digital converter

A device for converting the information contained in the value or magnitude of some characteristic of an input signal, compared to a standard or reference, to information in the form of discrete states of a signal, usually with numerical values assigned to the various combinations of discrete states of the signal.

Analog-to-digital (A/D) converters are used to transform analog information, such as audio signals or measurements of physical variables (for example, temperature, force, or shaft rotation) into a form suitable for digital handling, which might involve any of these operations: (1) processing by a computer or by logic circuits, including arithmetical operations, comparison, sorting, ordering, and code conversion, (2) storage until ready for further handling, (3) display in numerical or graphical form, and (4) transmission.

If a wide-range analog signal can be converted, with adequate frequency, to an appropriate number of two-level digits,or bits, the digital representation of the signal can be transmitted through a noisy medium without relative degradation of the fine structure of the original signal. See Computer graphics, Data communications, Digital computer

Conversion involves quantizing and encoding. Quantizing means partitioning the analog signal range into a number of discrete quanta and determining to which quantum the input signal belongs. Encoding means assigning a unique digital code to each quantum and determining the code that corresponds to the input signal. The most common system is binary, in which there are 2n quanta (where n is some whole number), numbered consecutively; the code is a set of n physical two-valued levels or bits (1 or 0) corresponding to the binary number associated with the signal quantum.

The illustration shows a typical three-bit binary representation of a range of input signals, partitioned into eight quanta. For example, a signal in the vicinity of 3/8; full scale (between 5/16 and 7/16) will be coded 011 (binary 3).

A three-bit binary representation of a range of input signalsenlarge picture
A three-bit binary representation of a range of input signals
McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.

A/D converter

(Analog/Digital converter) A device that converts continuously varying analog signals from instruments and sensors that monitor conditions, such as sound, movement and temperature into binary code for the computer. The A/D converter may be contained on a single chip or can be one circuit within a chip. See codec and sampling.

A/D Converters Are Everywhere
Every digital desk phone and cellphone has an A/D converter that turns electronic sound waves into digital PCM code. Every digital camera, camcorder and scanner uses A/D converters to transform the variable charges captured in CCD and CMOS chips into the binary pixel data that make up a digital image. See modem, DSP, CCD sensor, CMOS sensor, PCM and codec. Contrast with D/A converter.


A/D Converter
Widely used in consumer electronics, as well as industrial machinery, the A/D converter can be a chip or a circuit within a chip.
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