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Abstract

An N-path filter has a number N of parallel resistive-capacitive filter sections. A switching arrangement connects each filter section periodically into an input signal path through the filter. The switching arrangement also triggers a sample and hold network to sample the filtered input signal for a portion of the time each filter section is connected into the input signal path through the filter and then hold the sampled, filtered input signal. The sampling time is preferably selected to be an initial portion of the time each filter section is connected as the signal path through the filter when variations in the charging rates of the capacitors in the filter sections have the least effect. The sampled N-path filter technique thus reduces the need to match the filter section components. With the addition of a further low-pass filter to suppress harmonics, the sampled N-path filter is particularly suited for use in frequency-responsive medical diagnostic equipment such as electrocardiographs and electroencephalographs.

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