In regard to the ADS1282 Sigma-Delta converter, reference Figure 46 on page 21 of the datasheet which purports to show the passband response of the lowpass multi-stage, multirate filter implemented in the ADS1282. I have attempted, without success, to verify the given response by analyzing the cascade of the Sinc + FIR filter using the filter coefficients as documented in Table 23 on pages 45 and 46. I used the coefficients for implementing a linear phase filter. My analysis produces a magnitude for the passband ripple that exceeds the 0.003dB stated in the datasheet. My magnitude approaches 0.010dB near the start of the transition of the passband towards the stop band. The stage 3 filter ripple in my analysis seems to be too large. I have checked my work but cannot find an error---not to imply that my analysis is flawless. But before I continue, I have three questions for the community.
My questions:
(1) Is it possible that the filter coefficients of Table 23 are not in accordance with the plot shown in Figure 46?
(2) Should I be using the coefficients for the minimum phase filter on my analysis?
(3) Are the scaling factors correct for filter stages 3 & 4?
Also, I have assumed that the scaling factor for Stage 3 and Stage 4 of Table 23 is incorrect as shown in Table 23 and should be the reciprocal of the value stated. Please confirm.