TABLE OF CONTENTS Sigma-Delta analog-to-digital converters are commonly used when high resolution is required, this is because of the sigma-delta modulator s ability to shape noise away from the desired band. Moreover, sigma-delta modulators require a two-level (one-bit) quantizer to achieve a high-resolution Nyquist rate sampled stream.
Figure 7.31 shows a block diagram of the Sigma-Delta analog-to-digital converter. It consists of two parts: A Sigma-Delta modulator followed by a decimation filter. The output of the sigma-delta modulator is a one-bit over-sampled stream. A decimation filter converts this over-sampled stream into a Nyquist rate sampled stream having high resolution.
One distinct advantage of the Sigma-Delta technique is that analog signals are digitized using a one-bit quantizer which has a precision much less than the overall resolution of the analog-to-digital converter. The Sigma-Delta analog-to-digital converter is an over-sampling converter. The over-sampled analog signal passes through a Sigma-Delta modulator that quantizes the signal to one bit, sometimes a two-bit or higher resolution quantizer is used.
The Sigma-Delta modulator shapes the noise away from the desired signal band, such that when the signal is decimated to the Nyquist rate, the in-band quantization noise is small, which in turn leads to a high resolution analog-to-digital converter. The effectiveness of the Sigma-Delta modulator in removing the quantization noise from the desired signal band depends on the order of the Sigma-Delta modulator as well as the over sample factor. The higher the order of the Sigma-Delta modulator and the...
