A review of sigma-delta modulation structures

The increasing availability of high capacity data communication networks has generated a demand for accurate, fast and low power dissipation analogue to digital signal converters. Such converters are now required to convert a wide range of signals to binary weighted pulse code modulated format. The use of sigma-delta modulation for the primary data conversion is very attractive, since it uses a one bit quantizer and requires no sample and hold. The sampling rate employed is much faster than the highest frequency in the message signal (oversampling). The high accuracy conversion is achieved as a result of the modulator operating as a self adaptive, fast limit cycling system. The digital output data from the modulator, containing quantization noise principally out of the signal band, is subsequently filtered and code converted digitally. A complete converter may be realised in integrated form using a combination of CMOS linear and digital circuitry