Modeling and control of digital transducers

The control system aspects of digital transducers, based upon the application of sigma-delta modulation to a closed-loop structure, is discussed. Such a system is a nonlinear, discrete data, control system and consequently presents a challenging task for the design engineer. In this paper the authors consider the use of describing function techniques in the s and w-domains to predict limit cycling conditions and closed loop performance. Simple examples of an electric current transducer and an accelerometer are used to illustrate the approach. It is also shown that the design of accelerometer compensation is to be carefully considered if the resultant transducer is to behave as a true sigma delta modulator.