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How to calculate the ADS1281 Group delay

Chen pochi
Prodigy 60 points
Other Parts Discussed in Thread: ADS1281

Hi all~

How to calculate the ads1281 group delay true time?

My config is PIN MODE

MOD = 0

PHS = 0

HPF = 0

DR1 = 0

DR0 = 1

DATA RATE = 500Hz

Signal 1 is the source,signal 4 is the receive trigger.

I get the delay almost 64.30ms, whether as the formula 31/500 = 62ms ?

How much time it takes for the data to begin transitioning to completion?

Thanks for the reply.

  • 0
    TI__Mastermind 44680 points
    Hi Chen,

    Welcome to the TI E2E Forums!

    The group delay is calculated from the digital filter's response. However, in practice it is difficult to verify this timing because your input signal step must occur exactly at the same time when the ADC begins a new conversion. If the step occurs during a conversion, you will likely need to wait an additional conversion cycle to see the step in the ADC's output....In your case, since you're running the ADS1281 at 500 SPS, the conversion cycle is about 2 ms, which may explain this difference.

    NOTE: The ADC clock directly affects the data rate, so clock frequency error may also show up in this time difference.

    Also, keep in mind that the the group delay is different from the settling time...the group delay is how long it takes (+/- 1 conversion cycle, as explained above) for a step input to be seen in the output (when measured from the 50% cross over points). However, the digital filter will still not be fully settled at this time - the settling time is about twice the group delay.

    Best Regards,
    Chris