Fig 4.3 depicts the functional block representations of A/D and D/A converters. As indicated, the A/D converter (also called an ADC) accepts an analog sample VA and produces an N-bit digital word. Conversely, the D/A converter (also called a DAC) accepts an N-bit digital word and produces an analog sample. The output samples of the D/A converters are often fed to a sample-and-hold circuit. At the output of the S/H circuit a staircase waveform, such as that in Fig 4.4, is obtained. The staircase waveform can then be smoothed by a low-pass filter, giving rise to the smooth curve shown in the next figure. In this way an analog output signal is reconstructed. Finally, note that the quantization error of an A/D converter is equivalent to +/- 1/2 least significant bit (bs).
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| Fig 4.4 The analog samples at the output of a D/A converter are usually fed to a sample-and-hold circuit to obtain the staircase waveform shown. This waveform can then be filtered to obtain the smooth waveform. The time delay usually introduced by the filter is not shown. |
