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ADS1261: Digital filter when multiplexing 2 signals

Michael Kathan
Prodigy 10 points

Part Number: ADS1261
Other Parts Discussed in Thread: ADS1260,

Hallo,

I have to measure two signals alternating on 2 Inputs of the ADS1260/61. What is the effect of the digital filter, when I toggle the inputs after every conversion?

Michael Kathan

  • 0
    TI__Mastermind 44760 points

    Hi Michael,

    Welcome to the TI E2E Forums!

    The SINCn filter behaves much like a moving average filter, collecting "n" conversion results and averaging them together... Therefore, depending on which filter type you select, switching channels will require the filter to first collect "n" samples before providing a valid output. Therefore, you'll notice that the SINC2, 3, and 4 filters require about 2, 3, or 4 conversion periods until you get the first conversion result.

    Refer to section 9.4.1.3 (Conversion Latency) in the ADS1261 datasheet. If you plan on collecting a single samples from channel 1 and switching to channel 2 (etc...) then the fastest data rate you'll be able to achieve will be given by "1 /  t(STDR)".

    NOTE:

    • The /DRDY signal will remain high until the digital filter has settled. Therefore, you don't need to ignore any conversion results while the filter is settling.
    • The FIR filter is similar to the SINC1 filter, in that it settles in approximately 1 conversion period.
    • Enabling chopping will further reduce the overall data rate as the ADC must collect twice as much data before providing a result.

    Also, there is an Excel Calculator for the ADS1261 that you might find of interest, found here:

    Best regards,
    Chris