Extensions of the weighted-sample method for digitizing continuous-time filters

Methods continue to improve for taking the transfer function of a stable, c ontinuous-time, single-input single-output system or filter and converting it to an "equivalent" discrete-time filter, The weighted-sample (WS) method of carrying out the digitizing process, described in recent literature, is one such method. It is a higher order method, compared with the first-orde r Tustin's method, so it usually achieves a smaller error for a given syste m, input, and sample time. Like the Tustin method, but unlike some recent, higher order digitization methods, it allows the sample time to be selected without being constrained by stability considerations. This paper describe s two extensions to the weighted-sample method. The first provides the abil ity to handle cases in which the continuous filter contains one or more ser ies integrators. The second extension modifies the WS filter to a new form, termed the WS' filter, which turns out to be the same as the MSRP filter r ecently described. Several examples are given, and accuracy is assessed.