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problem of F28335 ADC:the adc value is not same each time

ww wang
Prodigy 20 points

I have used one channel of f28335 adc to measure voltage. I connect the DC power GND to ADCLO and '+' to ADCINA0,I set DC power to 2.708V. I measured 512 times  each time and calculated the average value of 512 ADC as measurement result.But I found that I got different value each time: 3715,3683,3691,3730...The value varied each time,and the delta value is not same .The So what is the reason of this,have any solutions to solve this?

  • 0
    TI__Expert 4595 points
    You state that the average value is correct result. Sounds like it is exactly right.

    Keep in mind that the ADC has tolerances, as listed in the device datasheet in the electrical specs section. I would expect each individual ADC reading is within those tolerances.
  • 0
    Guru 192875 points
    Hi,

    As Jeff has stated ADC values will vary but should be within the tolerance values. Apart from that if your supply is noisy, it might introduce some additional noise thus increasing the variation. Yes, averaging is one of the techniques to reduce this variation and apart from this you should use a RC filter at the ADC input too.

    Regards,
    Gautam
  • 0 in reply to Gautam Iyer
    Prodigy 20 points
    Hi,Guru
    Thanks for your reply.The RC filter can reduce the noise of input.I just measure the power supply of F28335.I found that there is some noise of VDD 3.3v power supply,does this affect the ADC result.If it did affected the ADC result, can RC filter at the ADC input reduce it too.

    Thanks a lot.
  • 0 in reply to ww wang
    Guru 192875 points
    RC filter should surely improve any noise but your ADC Vref should also be very stable. Hence if your 3.3v is noisy and if you're using internal reference generator for ADC then this would be affected too. Hence device supply has to be very stable and noise free.

    Regards,
    Gautam