Chapter 13 - Analog-to-Digital and Vice Versa

Abstract

While some systems operate solely on digital data, others have to interact with the analog world. It may be necessary to convert an analog input into a form that can be manipulated by the digital system, or to transform an output from a digital system into the analog realm. These tasks are performed by Analog-to-Digital (A/D) and Digital-to-Analog (D/A) converters, respectively. A transducer is a device that converts input energy of one form into output energy of another. In order to be processed by a digital system, the analog quantity must be detected and converted into a suitable form by means of an appropriate transducer called a sensor. The output from the sensor typically undergoes some form of signal processing, such as filtering and amplification, before being passed to the A/D converter. The complete range of values that the analog signal can assume is divided into a set of discrete bands or quanta. The main factor governing the accuracy of the conversion is the number of bands used. A D/A converter accepts a digital code and transforms it into a useful corresponding analog current or voltage by means of an appropriate transducer called an actuator. The conversions usually occur at regular time intervals and are triggered by a clock signal from the digital part of the system. Analog signal processing can be very effective for a variety of tasks, but it tends to be limited to things like amplification, filtering, signal conditioning, and similar activities.