Application of amplitude transformation for compensation of comb decimation filters

Abstract

The design of compensation filters for comb decimators using amplitude transformation is introduced. It is shown that the transformation of cosine-squared filters provides good compensation characteristics. For a first-degree polynomial, the slope of the transformation line is explicitly set as the unique compensator's multiplierless coefficient. This coefficient changes proportionally with the increase of the comb passband droop. Thus, the proposed approach provides an intuitive and easy way of designing compensation filters.

Wide-band CIC compensators based on amplitude transformation

“…The amplitude transformation approach [13] for CIC compensators consists in modifying the amplitude response of a cosine-squared filter with transfer function F(z) and frequency response F(e jω ) = F(ω)e -jω , where…”

“…Methods [2]- [4] are based on the sharpening technique [5] and, among them, [4] has a wide-band passband characteristic. In methods [6]- [13] the attenuation is improved by increasing K, whereas the passband droop is corrected by using an expanded-by-M compensation filter. Using multirate identities, the compensator can be moved after the downsampler by M so as to have it work at lower rate.…”

“…The framework hinges on the amplitude transformation method recently introduced in [13]. A simple method to obtain the coefficients of CIC compensators is provided, which makes the design of these filters straightforward.…”

“…Section II presents the basics of the amplitude transformation method from [13]. Section III introduces the proposed method.…”

Zero-rotation-based nonrecursive comb structure

“…Many works have been done to improve the magnitude characteristic of the comb filter. The methods [6]- [8] use compensation filters to improve the passband comb characteristic. In [9] the rotation of zeros of recursive comb filter is introduced to increase the alias rejection in the folding bands.…”