A concept of IIR filters with time-varying coefficients and equalised group delay response

In some measurement applications, it is required to have digital filters which simultaneously possess a constant group delay in the passband and a narrow transition band. This kind of filters is usually implemented using allpass filter section which compensates the unfavorable run of the group delay response of the original filter. Unfortunately, the process of equalisation affects the time domain characteristics of the (whole) equalised system. This paper presents theoretical concept and simulation results of a new class of low-pass time-varying infinite impulse response (IIR) filters with equalised group delay response and a transient response of short duration. The improvement of the filters in the time domain is achieved by means of temporary change in the value of the filter parameters. Computer simulations verifying the effectiveness of the proposed IIR filters with equalised group delay response and reduced transient response are presented and compared to the performance of traditional filters. (C) 2014 Elsevier Ltd. All rights reserved.