US Patent 7664811 Apparatus using sampling capacitors

A switched capacitor type filter apparatus includes sampling capacitors and has a steep characteristic with a small number of taps. The filter apparatus includes positive polarity selecting switches, negative polarity selecting switches, positive read-out switches, negative polarity read-out switches, and a timing control unit. Thus, it is possible to read out a negative charge by controlling the polarity upon write-in and the polarity upon read-out to be identical or different. Accordingly, it is possible to set a negative coefficient as a filter weighting coefficient. This configuration causes a finite impulse filter (FIR) to have a steep characteristic.