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ADS131E08 latency

Paul Thomas25
Prodigy 50 points
Other Parts Discussed in Thread: ADS131E08

Hello,

I'm trying to figure out the measurement latency for the ADS131E08 at different data rates. I've been testing it at 64 kSPS, and I still have about 160 μs of unexplained delay, and am wondering if that is all from the converter itself. This is just using a 50 Hz sin wave as an input. Is this information somewhere I'm missing in the datasheet? If not is it something TI can provide?

thanks,

Paul

  • 0
    TI__Mastermind 38745 points

    Hey Paul,

    Check out this white paper I wrote about delay in the ADS131E08 called "Accounting for delay from multiple sources in delta-sigma ADCs". Essentially, the ADS131E08, like all delta-sigma ADCs, has a linear phase, FIR, digital decimation filter what produces group delay for all signals. The PGA also produces delay, but not as much as the digital filter. The calculations are described in the document. There are other sources of delay such as the time it takes for the data to be shifted out of the device. I did not discuss other sources in the document. 

    Brian

  • 0 in reply to Brian Pisani
    Prodigy 50 points
    Thanks Brian,

    That's exactly what I was looking for. So if I'm reading Table 2 correctly it says at 64 kSPS (DR[2:0 = 000) and a gain of 1 the max latency should be 25 μs, and not the ~160 μs I'm seeing. Hmm, I guess I'll have to look at my test setup more more. Should it matter that I'm just setting the rate, but actually reading a a much lower rate, 5kHz using RDATA command?

    -Paul
  • 0 in reply to Paul Thomas25
    TI__Mastermind 38745 points
    Hey Paul,

    It will depend on how you read it. In that paper, the timing I am suggesting corresponds to when the DRDY signal occurs. That means that the data that is ready when the DRDY signal occurs corresponds to a signal that "appeared at the input" x microseconds ago. When your microcontroller actually toggles SCLK, shifts out the data, and interprets it is a different time altogether. Without knowing your setup, I can't be sure when the "delay stopwatch" is being started or stopped.

    Brian