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ADS1298: Synchronization of the ADS1298 with other equipment

Kim Munck
Prodigy 10 points
Part Number: ADS1298

I have designed an equipment where i use the DRDY pulse from the ADS1298 to trigger a sample of other devices.

However, I need to know if the sample that is ready for conversion, when the DRDY is triggered, is from that specific time or if their is a delay between conversion and when data is ready.
Perhaps the delay is specifically related to the t_settle time, Meaning that a sample rate of 1 kHz would have a delay of 4.5 ms relative to the DRDY.

  • 0
    TI__Mastermind 38745 points

    Hey Kim,

    Unfortunately it is not that simple. The ADS1298 is a delta-sigma ADC. The idea behind delta-sigma A-to-D converters is to oversample, filter, and decimate. The ADS1298 actually samples the input signal very fast, 512 kHz or 256 kHz depending on whether the device is in High Resolution or Low Power mode, respectively. The fast samples are then input to the digital low pass filter which the datasheet discussed in section 9.3.2.4. After the data is filtered, it is downsampled (otherwise known as "decimation") to the data rate. For example, for a data rate of 500 SPS in HR mode, the output of the modulator is downsampled by 1024 samples. This behavior is key to the great noise performance of the ADS1298.

    Long story short, any output sample is really an average of thousands of samples that are constantly being taken so it is tough to say what point in time any one sample corresponds to. What I can say is that there is a 4xtclk delay between when the digital filter is ready to output a sample to when DRDY actually asserts, but I'm not sure if that is helpful information given what i discussed above.

    Regards,

    Brian Pisani