SLUSDQ4 April 2019 BQ79606A-Q1
The digital filter used in the BQ79606A-Q1 is a Cascaded Integrating Comb (CIC) filter, often referred to as a SINCx filter, where the "x" represents the order of the filter. The simplified block diagram of the filter is shown in Figure 6 . The BQ79606A-Q1 contains a 3rd order CIC filter, meaning there are three storage elements on both sides of the decimation switch. The Decimation Ratio, or DR, references to the rate of reduction applied to the sample clock of the modulator. The front half of any SINC3 filter, which integrates the modulator output, is run at the same clock rate as the modulator. The back half of the SINC3 filter, which generates the comb, runs at the decimated clock rate, as shown.
The SINC3 filter will result in the frequency response. Note that the decimation ratio, DR, impacts the width of the passband; the higher DR the lower the corner frequency of the filter. The order of the filter also sets the gain, as G = -20ORDER dB/Decade.
Decimation Ratio is also called Over-Sampling Rate, or OSR, in other descriptions of a SINCx filter. The SINCx filter name is historic, as the transfer response, which is beyond the scope of this document to derive, is similar to the classic definition of sinc(x), or sin(x)/x.