Modeling, analysis and design tools for dual-rate systems

This paper is concerned with dual-rate sampled-data systems modeled as dual-rate discrete systems. We assume that the continuous-time system has been already designed in order to meet continuous time-domain and frequency-domain specifications. Based on the lifting technique, dual-rate high-order-holds and discrete equivalent models are obtained. Dual-rate models are computed based on dual-rate high-order-holds and dual-rate samplers. The dual-rate equivalent model of controllers, filters, estimators, etc. are encountered in the indirect design of digital controllers. From a dual-rate point-of-view, two different situations can arise: (a) the output is sampled every NT instants and the input is updated at T (N-times faster); (b) the input is updated at NT and the output is sampled at T (N-times faster). The effectiveness of the dual-rate sampling can be studied a priori at single-rate low frequency (constrained frequency) by analyzing its effects on the system when the ratio between frequencies goes to infinity.