Efficient design of adaptive complex narrowband IIR filters

In this paper a new adaptive complex digital filter structure is proposed. First, a very low sensitivity second-order complex bandpass (BP) filter section with independent tuning of the central frequency and the bandwidth (BW) is developed (the low sensitivity of the narrow-band realization is ensuring a higher BW-tuning accuracy or better precision in a severe coefficient quantization). Then, a BP/Bandstop (BS) adaptive filter structure is formed around this section, using LMS algorithm to adapt the central frequency. The developed filter circuit is providing a low computational complexity and a very fast convergence, and is convenient for cancellation/enhancement of complex sinusoids or narrowband signals. All theoretical results in the work are verified experimentally.