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ADS1294: Frequency shift of 1Hz.

MUKUND PIPALAVA1
Prodigy 30 points
Part Number: ADS1294

Hi

We are using the ADS1294 for ECG data acquisition we are facing the below-listed Problem.

1. We are feeding 50Hz Signal to ADC and when we are plot FFT of the signal in MatLab it is showing 51Hz same thing happens with other frequency. All frequency whatever we are feeding is shifting by 1Hz from given Frequency.

ADC Sampling Rate: 500SPS

Vref: 2.4V

Regards,

Mukund

  • 0
    TI__Mastermind 47595 points

    Hi Mukund,

    Thanks for bringing this to our attention! 

    Is there any variation to this or is it always +1Hz? 

    Are you using the PDK or is this part of your own design? 

    It is possible that your signal generator is the source of the error, have you verified the performance of the signal generator using a more precise piece of equipment? 

  • 0 in reply to Alexander Smith
    Prodigy 30 points

    Hi 

    Is there any variation to this or is it always +1Hz? 

    ==>It happens always with all signal

    Are you using the PDK or is this part of your own design? 

    ==>Part of Own design

    It is possible that your signal generator is the source of the error, have you verified the performance of the signal generator using a more precise piece of equipment? 

    ==>We have checked all the parameters of the source from where we are giving the input signal to ADC.

    After long troubleshooting, we found out the internal oscillator is generating the issue we enable the external  2Mhz oscillator and this thing works fine now there is no frequency shift in ADC output.

    Very disappointed with Texas Instruments. We almost waste 3 months to resolve this issue. Please check and verify your ADS1294.

    Regards,

    Mukund

  • 0 in reply to MUKUND PIPALAVA1
    TI__Mastermind 47595 points

    Hi Mukund,

    I greatly appreciate you bringing this to our attention. I will make sure this feedback is known by the design team. 

    I would like to get a little more information from you in regards to this issue. 

    Is the device ID returning correctly, and can you confirm that you are sending a /RESET pulse or command after power-up? 

    Does this issue apply to all data rates, all OSR combinations, and high performance and low power modes? Does the 1Hz difference scale as you change the data rate and OSR combinations, or is it always an absolute 1Hz? 

    How many points are being collected for the FFT? It is possible that the bin size is too small to resolve the correct input frequency.