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[FAQ] ADC Noise: How do you calculate the amount of reference noise passing into your system?

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How do you calculate the amount of reference noise passing into your system when using Delta-Sigma ADCs?

Regards,
Collin Wells
Precision ADC Applications

  • One of the most interesting characteristics of reference noise is that it changes linearly with how much of the ADC’s FSR that you use. If you have a very small input signal, you won’t see much reference noise – and can potentially use a noisier reference as a result. Or if your input signals are greater than mid-scale, you can expect the reference noise to dominate. In this case, always make sure that the ADC noise and reference noise are comparable. Figure 7 qualitatively plots reference noise, ADC noise and total noise as a function of FSR utilization.

    Figure 7: Reference noise, ADC noise and total noise as a function of FSR utilization

    What do the key points – A, B and C – on this plot represent? And how does changing your input signal vs. changing your system gain affect reference noise? Find the answers to these questions in part 8.

    Regards,
    Collin Wells
    Precision ADC Applications

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