ADS1262: 9.3.10.2 FIR filter achieves 50/60Hz rejection

您好

Aotian Long 说：

1. As shown in the figure, why is it necessary to pass through a configurable SINC filter again to extract the required output rate after passing through the SINC5 filter, instead of directly extracting the output rate at SINC5?

A pure sinc 5 filter takes longer to settle compared to a sinc1 through sinc4, so this is to speed up the first conversion latency

Aotian Long 说：

2. On the basis of question one, I think that directly extracting to a lower output rate may incur significant hardware overhead, so cascading a sinc filter is necessary. However, I have seen in other products that only one SINC1 needs to be cascaded, but ADS1262 cascades a configurable SINC filter. Why is this?

A sinc1 filter has the lowest latency but the highest noise, while a sinc4 has the longest latency but the lowest noise. A configurable filter allows the user to choose which parameter they want to optimize

Aotian Long 说：

3.On the basis of the previous question, I speculate that using configurable high-order filters can produce better notch effects when suppressing 50/60Hz, but I am not sure if it is correct. Secondly, when the data output rate is 2.5/5/10Hz, using high-order SINC filters can also produce good suppression effects at the beginning of 50/60Hz. Why do we still provide FIR filters for 50/60Hz suppression? Is it because FIR filters only require a single cycle stabilization time?

Yes this is correct. The FIR filters are there for combined 50/60Hz rejection at higher data rates, specifically at 20SPS. Since 20SPS is not an integer factor of 50Hz, a pure sinc filter would not offer good rejection at 50Hz when it is operating at 20SPS. The FIR filter provides good rejection at both frequencies at higher data rates

Aotian Long 说：

4. I haven't seen the transfer function or implementation principle of the FIR filter on ADS1262, so I'm not sure how to extract FIR from 600SPS to 20SPS while achieving 50/60Hz suppression.

We do not provide the frequency response of the FIR filter, the design - and specifically the filter coefficients - are proprietary

Hello, thank you very much for your reply. It has been very helpful for me to understand and use ADS1262.