Switched-capacitor cosine filter

摘要

A switched-capacitor cosine filter for a sampled-data system functions to reject extraneous frequency components of an incoming analog signal around the sampling frequency, thereby avoiding aliasing. The filter comprises an operational amplifier whose inverting input receives input signals through a switched input capacitor controlled by a four-switch network controlled by alternating clock phases and feedback signals from the amplifier output through a feedback capacitor. The transfer function of the circuit provides a zero of transmission at the sampling frequency, thereby eliminating unwanted frequency components. A self-contained version of the cosine filter is provided by the addition of another grounded switched capacitor with appropriately timed switches in the feedback network.