A Novel Circuit Topology for the Implementation of a 2nd order Chebyshev Type-II Low Pass Filter with Independent Frequency and Gain Tuning

  A novel implementation circuit for a Chebyshev type-II filter transfer function is presented in this brief. Chebyshev type-II filters provide steeper roll-off with a flat passband. Most discrete and IC implementations of filters do not allow for zeroes in the transfer functions and hence cannot implement such a filter transfer function. The mathematical formulation for the proposed circuit is fully developed to show the implementation of a Chebyshev type-II transfer function. The notable features of the proposed circuit include independent tuning of gain and bandwidth by varying a minimal number of passive components. The filter is implemented with discrete components and the functionality with independent bandwidth and gain tuning are demonstrated experimentally. Bandwidth tuning is achieved by varying 2 resistors and gain tuning is achieved by varying 1 resistor. A fully differential implementation for ICs is also developed. The proposed topology easily lends itself for cascading to obtain higher order filters.