CC2650MODA: ADC Accuracy

Hello,

I have a question to the ADC accuracy on the CC2650MODA. I am using the TI project adcsinglechannel_CC2650_LAUNCHXL to measure the Input Voltage on my custom Hardware (with CC2650MODA). 

I measured the Voltage with a failure of -100mV (At a input voltage of 1.6V).
Is there a way to increase the accuracy of the ADC?

I have configured the ADC in the following way:

typedef enum CC2650_LAUNCHXL_ADCName {
    CC2650_LAUNCHXL_ADC0 = 0,
    CC2650_LAUNCHXL_ADC1,
    CC2650_LAUNCHXL_ADC2,
    CC2650_LAUNCHXL_ADC3,
    CC2650_LAUNCHXL_ADC4,
    CC2650_LAUNCHXL_ADC5,
    CC2650_LAUNCHXL_ADC6,
    CC2650_LAUNCHXL_ADC7,
    CC2650_LAUNCHXL_ADCDCOUPL,
    CC2650_LAUNCHXL_ADCVSS,
    CC2650_LAUNCHXL_ADCVDDS,
    CC2650_LAUNCHXL_ADCCOUNT
} CC2650_LAUNCHXL_ADCName;

...

const ADCBufCC26XX_AdcChannelLutEntry ADCBufCC26XX_adcChannelLut[] = {
    {PIN_UNASSIGNED, ADC_COMPB_IN_VDDS},
    {PIN_UNASSIGNED, ADC_COMPB_IN_DCOUPL},
    {PIN_UNASSIGNED, ADC_COMPB_IN_VSS},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO7},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO6},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO5},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO4},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO3},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO2},
    {PIN_UNASSIGNED, ADC_COMPB_IN_AUXIO1},
    {IOID_14, ADC_COMPB_IN_AUXIO0},
};

const ADCCC26XX_HWAttrs adcCC26xxHWAttrs[CC2650_LAUNCHXL_ADCCOUNT] = {
    {
         .adcDIO = IOID_14,
         .adcCompBInput = ADC_COMPB_IN_AUXIO0,
         .refSource = ADCCC26XX_FIXED_REFERENCE,
         .samplingDuration = ADCCC26XX_SAMPLING_DURATION_682_US,
         .inputScalingEnabled = true,
         .triggerSource = ADCCC26XX_TRIGGER_MANUAL
    },
...

Read out the ADC value

    ADC_Params_init(&params);
    adc = ADC_open(CC2650_LAUNCHXL_ADC0, &params);

    if (adc == NULL) {
        System_abort("Error initializing ADC channel 1\n");
    }
    else {
        System_printf("ADC channel 1 initialized\n");
    }

    for (i = 0; i < ADC_SAMPLE_COUNT; i++) {
        res = ADC_convert(adc, &adcValue1[i]);

        if (res == ADC_STATUS_SUCCESS) {
            System_printf("ADC channel 1 convert result (%d): 0x%x\n", i,
                adcValue1[i]);
        }
        else {
            System_printf("ADC channel 1 convert failed (%d)\n", i);
        }

        System_flush();
    }

    ADC_close(adc);