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ADS131M08EVM: ADS131M08EVM sampling rate

kwon
Intellectual 920 points
Part Number: ADS131M08EVM

Tool/software:

Hi~

1KHz square wave was applied to ads131m08evm.

If the sampling rate is set to 4k in the ads131m08evm program, it is measured as a triangle wave instead of a square wave.

At 32k sampling rate a square wave shape appears, but it is not the same square wave waveform as the source.

Attached is the 1KHZ SORCE waveform, EK sampling 1K/4K/16K/32K measurement waveform.

Nyquist Theorem says that the sampling rate should be more than twice.

1. When the sampling rate is 4k, why is it measured as a triangle wave and how to obtain the same signal as the original signal?

2. Why is it different from the original signal even when it is 32K?

3. What is the sampling rate to restore the same as the original signal?

Thanks~

  • 0
    TI__Mastermind 45805 points

    Hi kwon,

    Please see my answers below.

    Nyquist Theorem says that the sampling rate should be more than twice.

    DL: Twice sampling rate is the minimum requirement in theory. The higher sampling rate, the more samples in one cycle, then the more information can be recovered.

    1. When the sampling rate is 4k, why is it measured as a triangle wave and how to obtain the same signal as the original signal?

    DL: When you use 4ksps sampling rate to sample a 1kHz periodic signal, you only get 4 samples per cycle, the ADC/GUI/EVM are showing the expected result as I explained above. 

    2. Why is it different from the original signal even when it is 32K?

    DL: The ADC has a internal digital filter, it require some time to settle the signal especially when your input is a square signal (step input). 

    3. What is the sampling rate to restore the same as the original signal?

    A square wave signal (step input) is always critical for data acquisition system design. You can select an ADC which does not have any internal analog or digital filter, and also you will have to make the bandwidth of the external active or passive filter in your signal chain wider, so these filter will not have any impact to your step input signal.

    BR,

    Dale