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Original question:

ADS1256: Maximum data output rate on one SE Channel

ADS1256: Weird impulse response of ADS1256's digital filter

Felix Beu
Prodigy 40 points
Part Number: ADS1256
Other Parts Discussed in Thread: DAC8532

Hi,

when I'm using the ADS1256 in the continuous mode at 30SPS my first conversion result should appear after about 5 conversions periods.

To test that behavior I gave the ADS1256 an impulse of one sample after 15000 samples. The impulse is coming from a DAC8532.

The result is a bit confusing, because the impulse response appears already after 3 samples. Where are the 5 samples delay?

I compared the response to the original impulse signal which is created with Matlab.

I hope you understand what I want and someone can help me with that problem. :)

Thanks in advanced

Felix

  • 0
    TI__Mastermind 44550 points

    Hi Felix,

    The ADS1256 digital filter implementation is a SINC5 filter in series with as SINC1 filter with a programmable decimation. At lower decimation (higher data rates, you see the SINC5 settling time, but at the lower data rats the SINC5  filter's settling time gets "masked" by the lower data rate of the SINC1 filter.

    I haven't looked at the impulse response before since typically this type of (high-frequency) signal gets heavily attenuated. However, I would recommend that you try applying a step-input and seeing if it doesn't correspond to the response show in Figure 2 of this E2E blog post: