It is well known that the poles, zeros and delay of a system play an important role in determining the associated feedback performance limitations. In this paper, we first derive an approximate transfer function for a modulated and demodulated system of a particular form. We next analyse the behaviour of the poles, zeros and delay of this transfer function when the modulation frequency is varied. Some implications of these results are also briefly discussed. © 2005 Elsevier Ltd. All rights reserved.

We consider feedback performance limitations for modulated and demodulated control systems whose base systems have non-minimum phase (NMP) zeros or unstable poles. We first derive a transfer function for the modulated system and then show how the poles and zeros of this function are related to those of the base system. We next analyse the behaviour of the poles and zeros, when the modulation frequency is varied. Bode and Poisson Integral constraints for the modulated system are then considered. The effect of a base system delay is also discussed. Performance limitations, linear systems, control applications, poles and zeros.