A TECHNIQUE FOR THE IMPLEMENTATION OF LOW-FREQUENCY DIGITAL-FILTERS WITH SIMPLE FAD-BASED HARDWARE

The MS2014 device (formerly known as the FAD) is marketed by GEC-Pless ey semiconductors as a fixed architecture processor for the implementa tion of tone filters in telephone systems. A method is presented where by the advantage of FAD-based digital filters, namely simple hardware and extremely simple programming, can be extended below the normal low er sampling limit (64 mu s per second-order section) of the device. It is shown theoretically that the proposed method is correct for the va rious filter configurations which are possible with the FAD, and a sel ection of experimentally obtained frequency responses are presented to demonstrate the efficacy of the technique. The FAD (filter and detect ) device was originally designed by British Telecom Research Laborator ies.