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ADS1298 signals offset

Georgina Ballbe Serra
Prodigy 30 points

Other Parts Discussed in Thread: ADS1298, ADS1298R

Hello,

I am using ADS1298  for ECG acquisition with the following configuration:

AVDD=+2.5V and AVSS=-2.5V,

internal reference of +4V

internal clock

WCT A.B.C on

I've acquired same signal with 3 different samples and the offset is always different. The calculated Vpp of each signal is the same for the  3 samples, but not the de DC. Is that correct. I also compared it with the evaluation kit I’ve got and the offset is also different,

Should them all be equal? Do you know the possible reason for such difference?

 

Thank you for your help.

Gina

  • 0
    TI__Guru 68126 points

    Hi Gina,

    Thanks for your question.

    In general, offset voltage is expected to vary within a certain range from channel to channel. For our ADS1298/R devices, you can typically expect between +/-500 uV of offset error, and about 2 uV/deg(C) of drift, according to the datasheet. 

    I've configured an ADS1298R EVM on my desk using the same +/-2.5 V supplies and examined the output of each channel with the inputs shorted together. The picture below shows the output of each channel, which equals my offset error. You'll notice that the offset error for each channel varies from -525 uV to 232 uV.

     

     

    How much offset are you seeing in your system?

     

    Thanks and regards,

  • 0 in reply to Ryan Andrews
    Prodigy 30 points

    Hi Ryan,

    Thank you for your quick replay.

    So from your explanation, every device will have its characteristic offset error for each channel, to get correct data such offset shall be substracted of each signal, i.e. at power on I measure the offsets with "input short" and then when aquiring data I should correct such offset error.

    Is my understanding  correct? 

    BR,

    Gina

  • 0 in reply to Georgina Ballbe Serra
    TI__Guru 68126 points

    Gina,

    You are exactly right!

     

    Best of luck,

     

  • 0 in reply to Ryan Andrews
    Intellectual 835 points

    Hi, I have a question How can i know the internal operation of the device to know the offset system? I read the datasheet and doaesnt appear any information about that, how the device can measure the offset, I know if you configure the input channel as input shorted I'm going to see the offset, but internally how the device can measure the offset.