A/D and D/A Converters:
An A/D converter (ADC) converts analog data into its equivalent digital data (binary data). The A/D converter and D/A converter are also called data converters and they are also available as monolithic integrated circuits. D/A converter (DAC) converts digital data into its equivalent analog data. The analog data is required to drive motors and other analog devices.
The above diagram shows a typical application in which A/D and D/A conversions are employed. An analog input signal from a transducer is band-limited by an anti-aliasing filter. The signal is then sampled at a frequency rate higher than twice the maximum frequency of the band-limited input signal.
Analog and Digital Data Conversions:
In the application of signal processing, the measurement and analysis of signals are very important to discover their characteristics. If the signal is unknown, the process of analysis begins with the acquisition of the signal. The most common technique of acquiring signals is sampling.
A sampling of a signal is the process of acquiring its values only at discrete points in time. The definitions related to the process of sampling and the subsequent analog and digital conversion processes are:
1. An analog signal is a signal that is defined over a continuous period of time and in which the amplitude may assume a continuous range of values.
2. The term quantization refers to the process of representing a variable by a finite set of discrete values.
3. A quantized variable is the signal variable that can assume only finite distinct values.
4. A discrete-time signal is defined at particular points of time only. Therefore, the independent time variable is quantized. When the amplitude of a discrete-time signal is allowed to assume a continuous range of values, the function is called a sampled-data signal. A sampled data signal could result from sampling an analog signal at discrete points in time.