A Method to Derate the Rate-Dependency in the Pass-Band Droop of Comb Decimators

TL;DR

This paper presents a method to derate the dependency on the decimation factor, M, of the pass-band droop inherent to N-th ordered comb decimators by cascading a symmetric 3-tap FIR filter in the integral stage of the corresponding comb decimer.

Abstract

This paper presents a method to derate the dependency on the decimation factor, $M$, of the pass-band droop inherent to $N$-th ordered comb decimators. It is achieved by cascading a symmetric 3-tap FIR filter in the integral stage of the corresponding comb decimator and choosing the coefficients only as a function of order $N$. The proposed derating method derived from the conventional comb decimator can be readily applied to any recently developed comb decimator and droop-compensation filter design method.

Figures (8)

• Figure 1: Change of $H_{3,M}(z)$, when $M$ is changed from $\infty$ to 4.
• Figure 2: The proposed method to derate the dependency of $N$-th order comb decimator on the change of decimation factor of $M$.
• Figure 3: Curves of the pass-band deviation as a function of $M$ for the conventional comb decimators with the order of $N=2,3,4,6$. The proposed derating method makes the curve flat compared with the corresponding ones.
• Figure 4: Example of the sharpened comb decimators with the derating filter.
• Figure 5: Curves of the pass-band deviation for the sharpened comb decimators.