Low-voltage medium Q-SC filters for high frequency communication applications

In this paper the limitations and possibilities of switched capacitor techniques for low voltage communication applications are demonstrated with the help of an intermediate frequency filter design for a digital satellite radio. In order to minimize the requirements for the circuit a pseudo n-path filter approach has been selected. The advantage of n-path filters over conventional sampled data filters is that the center frequency of the band pass filter is solely defined by the clock frequency and the number of paths. The use of wideband compensated SC amplifiers and integrators reduce the amplifier bandwidth and slew rate requirement. A BiCMOS folded cascode amplifier with minimum parasitic nodes has been selected. Simulations show that the filter works properly even with 1% gain error of the amplifiers