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Original question:

ADS124S08EVM: ADS124S08 ADC Incorrect Signal Reading with 4.6V Input

ADS124S08EVM: ADS124S08EVM Not Showing Proper Sine Wave Output from Function Generator Sinewave

Vivek Shirsat
Prodigy 20 points
Part Number: ADS124S08EVM
Other Parts Discussed in Thread: ADS124S08

Tool/software:

Setup Details:

Below are my setup details:

  1. Function Generator Configuration:

    • Signal Type: Sine Wave
    • Frequency: 1 kHz
    • Amplitude: 1.10 Vpp (Peak-to-Peak)
    • DC Offset: 1 V

  2. ADS124S08EVM Configuration:

    • MUXP (Positive Input): AIN0
    • MUXN (Negative Input): AINCOM 
    • PGA (Programmable Gain Amplifier): Gain of 1 with bypass
    • Reference Voltage (VREF): 2.5V
    • Data Rate: 2000 SPS
    • Clock Frequency: 4.096 MHz

  3. Expected vs. Observed Output:

    • Expected: A clean sine wave of 1.10 Vpp centered at 1V DC.
    • Observed: The waveform is distorted and does not resemble the input sine wave (attached image).

I have attached an image of my current output for reference. Any guidance on troubleshooting this issue would be greatly appreciated!

  • +1
    TI__Guru 53516 points

    Hi Vivek Shirsat,

    Recall sampling theorem that says the sampling rate needs to be >=2X the measured input frequency or you will get aliasing. Since you are measuring a 1kHz input with a 2kSPS data rate, you are right at that limit. You are not going to be able to recreate a sinewave with these settings. You either need to dramatically reduce the input frequency or increase the sampling frequency

    Also, the ADS124S08 digital filter has a bandwidth of 718 Hz using the low latency filter at 2 kSPS (the sinc3 filter bandwidth will be even lower). So measuring 1kHz signal with this filter is not advised

    Are you just trying to measure this one input signal (1VPP, 1 kHz)? Are there are signals you need to measure? Please tell us what you are trying to accomplish with this ADC, and maybe we can provide a better alternative for measuring AC signals

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 20 points

    Hii Bryan Lizon,

    Thankyou for your guidance now i got output at 10hz (at 500hz with latency filter its generating noisy/clipped sinewave) , 0.55 Vpp
    also i was not only looking for 1VPP, 1 kHz, i was just checking whether it is working or not.
    thankyou again!
    here is my output