Design of sigma-delta modulation converters for telecommunication applications

Sigma-delta modulation can provide a highly accurate signal digitisation process with appropriate system design. For telecommunication purposes the two most important performance parameters are output signal to noise ratio and frequency response. Speech channels have standard performance specifications and the properties of the signals are well documented. With the development of the Integrated Services Data Network (ISDN) there is a growing demand for a general message signal interface to the network. The problem arising for the designer of signal digitisers is that a vast variety of potential message signals exist that have either undocumented or poorly documented properties. Performance requirements are vague. At the current time non-speech applications appear to be restricted to purely linear digitisers which are required to have as wide a bandwidth as possible and peak signal to noise ratios equivalent to resolutions of up to 16 binary digits. Resolutions of 10, 12 and 14 binary digits are very commonly used in industry