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CC2530 ADC offset and gain compensation

Emanuele Tavelli1
Prodigy 150 points
Other Parts Discussed in Thread: CC2530, Z-STACK, REF3325, CC2530EM

Hi all,

I'm doing some test with CC2530 and the internal 12-bit ADC but the results are very poor..

I use a very high precision Vref of 2500mV in P0_7 and I do a 12bit conversion as in the TI-MAC or Z-Stack hal_adc.c file, but the result are very different from the multimeter measure.

I set the input voltage from 0 to 2500mV and I read the ADC value, but the ADC have a drift from -10mV to 10,15mV after 1995mV from the real value!!

Is possibile to do a software compensation to have a more precise value?

Did anybody have the same problem?

thank you

Regards,

Emanuele

  • 0
    TI__Guru**** 317180 points

    The INL in the datasheet should be correct.

    What is your input?

    Could you post a table/ graph with some results for better understanding?

  • 0 in reply to TER
    Prodigy 150 points

    thank you for your answer..

    I do 20 measure every sampling so I think I hope to reduce the effect of INL.

    In input I have a regulated supply voltage and I do a test measure from 0 to 2500mV, I use an Agilent 6dgt multimeter to verify the value. I take the measure with reference P0_7 where I have a TI REF3325.

    I do single ended measure, so with 12bit I have 11bit  ( 0 to 2047), correct? If I consider the 0 I have 2048 levels.

    I post the measure I have done:

    Vinput ADC register ADC register ( expected )
    4,8 0,0 3,9
    15,5 6,0 12,7
    21,5 11,0 17,6
    244,0 194,0 199,9
    311,0 253,0 254,8
    399,0 325,0 326,9
    514,0 421,0 421,1
    601,0 494,0 492,3
    722,0 594,0 591,5
    819,0 674,0 670,9
    912,0 752,0 747,1
    1030,0 850,0 843,8
    1121,0 925,0 918,3
    1229,0 1015,0 1006,8
    1319,0 1089,0 1080,5
    1662,0 1373,0 1361,5
    1700,0 1405,0 1392,6
    1706,0 1410,0 1397,6
    1805,0 1492,0 1478,7
    1928,0 1594,0 1579,4
    2129,0 1761,0 1744,1
    2226,0 1841,0 1823,5
    2350,0 1944,0 1925,1
    2421,0 2003,0 1983,3
    2470,0 2043,0 2023,4
    2475,0 2047,0 2027,5

    The expected value is ADCvalue*2500/2048.

    If you take a look to the results, we have an offset that variable from about 4mV to 20mV.

    With a software compensation from these values I have obtain better results, but I would be sure this is a "normal" behavior.

    thank you

    Regards,

    Emanuele

  • 0 in reply to Emanuele Tavelli1
    TI__Guru**** 317180 points

    Your expected values looks a bit strange, if you follow ADCvalue*2500/2048 you should get something very close to 2500mV in the last value. I played a bit with different values in that equation and found that if I use 2470 instead of 2500 the variation reduses to a few mV offset. Probably it is a IR drop internally that causes the reference internally is slightly lower than what is applied externally. By doing some software compensation you should get an accurate result.

  • 0 in reply to Emanuele Tavelli1
    TI__Guru 71516 points

    Emanuele,

    You did not say if you are using the CC2530EM or Dev Kit for these measurements, or your own pcb design.  Layout, decoupling, GND/PWR planes, will have a direct impact on the conversion readings.  Please describe the test setup.

    Thank you,

    -Leonard