A digitally controlled universal second-order filter block for biosignals with CMOS D/A converters

A universal second-order low-pass filter block with a digitally adjustable cutoff frequency is described. The filter section replaces conventional manually adjustable low-pass filters and is suitable for a wide range of biosignals such as EEG, EMG, and the recording of evoked potentials (ERPs). The advantages of digital control of filter parameters are briefly outlined and construction hints are given for a number of applications. The universal state-variable filter section may be programmed by any laboratory computer and does not require a complex installation procedure.