MOS switched-capacitor filters with reduced number of operational amplifiers

Using voltage inverter switches, exact analog sampled-data equivalents of Rs, Ls and Cs, as well as unit elements, can be designed with MOS capacitors and switches. Due to the underlying bilinear transformation, no limitation other than the Nyquist limit is imposed on the ratio of corner to sampling frequency. For an nth order filter, the number of voltage inverter switches is (n+1)/4 to (n+1)/2. A 3.4 kHz third-order Chebyshev low-pass CMOS circuit is described in detail. It uses only one voltage inverter switch implemented by a switched op amp integrator. The sampling frequency is 24 kHz, the dynamic range exceeds 70 dB and the chip area is 1.2 mm/SUP 2/. A CMOS voltage inverter switch, which has zero DC power and occupies only 0.09 mm/SUP 2/ is presented, whose dynamic range exceeds 85 dB. This allows low power switched capacitor filters without operational amplifiers and with a frequency capability approaching the megahertz range.