Odd-Order Cascade-Form Bandwidth-Tunable Lowpass Filter With Low Complexity

This paper introduces a stability-guaranteed odd-order bandwidth-tunable lowpass digital filter with low complexity. The filter is comprised of a first-order section and a few biquad sections, and those sections are serially connected. The stability of the odd-order tunable lowpass filter is guaranteed through ensuring the stability of all those sections. This is achieved by adopting a coefficient-transformation scheme to carry out coefficient transformations such that both the first-order and the biquad sections meet the stability condition. To reduce filter complexity, the polynomials of different degrees are employed to express the filter coefficients. An odd-order bandwidth-tunable lowpass filter is included for testifying the guaranteed stability and demonstrating the significant complexity reduction. The simulation results exemplify that 40% complexity reduction can be achieved.