FIR filters are strictly not analog or even mixed signal in nature. They are in fact, digital circuits. However, it seems that more and more of these filters are being used in mixed signal designs, specially in fine line semiconductor processes, where analog processing is used to convert to digital and then circuit blocks such as FIR filters, Comb filters, multipliers etc take on the task of further signal processing within a chip. A perfect example is a sigma delta A/D converter. Here there is a minimum of analog circuitry, followed by significant amounts of digital ciruitry. Among these are digital filters. ( Usually sinc filters). A brief note on the practicalities of FIR filter design are presented and can be found in the engineering pages of the our website: www.signalpro.biz.