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ADS1292: How to reduce the clock accuracy range of ADS1292

Grady Lee
Genius 4165 points
Part Number: ADS1292

Tool/software:

Hi, TI expert

I have a question from a customer about ADS1292IPBS.

The customer is developing a Holter ECG using the internal clock (512kHz) of ADS1292.

The internal clock accuracy is expressed as below on the datasheet (0.5%), but the error of the actual measured data is larger than the customer's specification (0.03%), which is causing a problem.

Q1) Can the error range be reduced by using an external clock?

Q2) Is there a way to reduce the error range when using an internal clock? (The relevant AFE circuit diagram is attached below.)

Q3) Can you recommend a crystal that can reduce the error of the external clock?

Please check. Thanks

  • 0
    TI__Guru 66186 points

    Hi Grady,

    Thank you for your post.

    It is possible to improve ADC accuracy with an external oscillator. The specification highlighted in the data sheet is only for the frequency tolerance of the internal clock and does not reflect clock jitter or other important parameters.

    Note: the ADCs in the ADS1292R do not sample directly at the internal oscillator frequency. Instead, the delta-sigma modulators sample at fCLK / 4 = 128 kHz. This clock division makes the absolute accuracy of the internal clock much less important. The ADS1292R typically measures low frequency input signals (i.e. < 5 kHz, approximately). Clock accuracy is usually not a dominate source of error.

    Grady Lee said:
    the error of the actual measured data is larger than the customer's specification (0.03%)

    Can you describe this test in more detail?

    • What are the input voltages applied to INP and INN? Is it DC or AC? What is the amplitude range?
    • What is the input source?
    • Is the customer measuring back the applied signal with a high-resolution DMM or scope at the input of the signal chain?
    • How many samples are collected for each measurement point?
    • How is the ADS1292R configured? Please provide complete register settings.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Genius 4165 points

    Hi, Ryan

    Thank you for reply.

    We will check with the customer and provide feedback on the additional inquiries you have made.

    Thanks.