an fsk demodulator is disclosed suitable for use in a cmos ic using switched capacitor circuits . the mark and space filters are each modified to produce sine and cosine outputs . these outputs are rectified separately and the result summed . the summed outputs are passed through low pass filters and applied to a comparator which determines which of the mark and space signals is dominant . the invention substantially reduces the size of the demodulator filter capacitors and improves the demodulation signal to noise ratio .