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Original question:

ADC124S101 results problem

ADC124S101: Result Problem

Melvin Lim
Prodigy 10 points
Part Number: ADC124S101

Hi Tom,

I also encountered the same issue when I read more than one channels sequentially using a FPGA. The results were different when compared to reading any single one channel at a time. My questions are as follows:

1) Does increasing the number of consecutive readings of the same channel (before switching to the next channel) improve the accuracy of the results?

2) Or should I simply reduce the SPI clock during the track phase (the first 3 cycles of the SPI frame) to allow a longer settling time for the internal ADC capacitor?

Hope to hear from you soon. Thank you in advance.

Regards

Melvin

  • 0
    TI__Guru 62035 points

    Hi Melvin,

    Is the customer using an input driver with the design?  If not they may be seeing typical measurement droop associated with driving SAR ADCs without an input amplifier.  Take a look at the theory and system recommendations in the video below:

    https://training.ti.com/ti-precision-labs-driving-sar-without-amplifiers

  • +1
    Prodigy 10 points

    Hi Collin,

    Thank you for your response. I have forwarded the link to my H/W engineer and seen the video myself. The video is very informative & I have learnt much from it. Currently, the H/W is already fabricated without any analog input driver. It is a simple direct connection from the sensor output to the ADC input. As such, I am trying to mitigate the issue of inaccurate ADC readings.

    Question: Should I increase the number of consecutive readings of the same channel (before switching to the next one) or increase the acquisition phase in order for a better ADC reading?

    Hope to hear from you soon. Thanks.

  • 0 in reply to Melvin Lim
    TI__Guru 62035 points

    Hi Melvin,

    Apologies for the delay, I was out of the office for a week.  

    Either approach will likely work, but I believe the simpler would be increasing the acquisition timing as this would likely take less overall time than waiting for the multi-read settling behavior to occur.  The multi-read approach has the benefit of some inherent averaging capabilities if you want to throw away the first unsettled samples and then average the rest once the settling is near the final values.