ADuC7061. ADC Offset Calibration Register (ADC0OF, ADC1OF)

Hi,

I saw that you attached an image, but it's not loading on my end.

Have you checked the offset calibration register before initiating the calibration? Is the reading 0 as well?

The ADC offset calibration register is automatically applied to the ADC reading to compensate for the offset error.

Regards,

Karl

Before initiating the calibration value of registers ADC0OF, ADC1OF is about 2..8.

What is the configuration for the ADCFLT register? Is chopping enabled?

Yes, of course:

ADCFLT_CHOP_ENABLE | ADCFLT_RUNNING_AVERAGE | ADCFLT_NOTCH2
+
 SF=9, AF=63 (Data_Rate=12.12Hz, Settling_Time=165ms, 50Hz --> -329dB)

Chopping already corrects the offset error. That is why the offset calibration register (ADC0OF, ADC1OF) reads as 0 after initiating the calibration since the chopping is enabled.

Primary (ADC0/ADC1)/ Auxiliary (ADC2/ADC3) channels are in differential mode, enable, external reference inputs (VREF+, VREF−).

All the iput pins are short-circuited. (ADC0=ADC1=ADC2=ADC3).

"Chop Enable = 1" does not correct the offset error Auxiliary (ADC2/ADC3) channel.

Command ADC self-offset calibration: "ADCMDE  = ADCMDE_OFFSET_CAL | ADCCLKSEL_131KHZ;" does not correct the offset error Auxiliary (ADC2/ADC3) channel too.

The value of offset error Auxiliary (ADC2/ADC3) channel = 1500 ... 3500.

When using an internal reference, self-offset calibration works well. The value of offset error = 0..3.

Is there no difference in ADC output before and after enabling chop or performing ADC self-offset calibration?

Are you using an ADuC7060 evaluation board or your board in testing the ADC?

Can you show the register values and sequence used in configuring both?

   The board is its own. The board does not affect, because the inputs are short-circuited.

Uref = 300 Ohm * 600 uA = 180 mV. Increasing the current to 1000uA (300 mV) has no effect.

    // Excitation Current Sources = 600 uA

    IEXCON  = BIT7 | BIT2 | BIT1; // IEXC1=1, 600uA
    DelayMS(2000);          // Delay 2000 mS



    // ADC0 = (ADC0/ADC1) pins
    // ADC1 = (ADC2/ADC3) pins

    ADCMDE  = ADC_IDLE_MODE;    // ADC idle mode
    // SF=7, AF=59 (Data_Rate=16.128Hz, Settling_Time=124ms, 50Hz --> -329dB)
    ADCFLT  = (ADCFLT_CHOP_ENABLE | (0x07 << 0) | (0x3B << 8));
    // ADC0 Gain=1, ext.ref (VREF+,VREF-), ADC0/ADC1
    ADC0CON = (ADC0CON_REF_EXT | ADC0CON_ADC0EN | ADC0CON_CHANNEL_DIFF_0_1);
    // ADC1 Gain=1, ext.ref (VREF+,VREF-), ADC2/ADC3
    ADC1CON = (ADC1CON_REF_EXT | ADC1CON_ADC0EN | ADC1CON_CHANNEL_2_3_DIFF);
    DelayMS(250);               // Delay 250 mS


    // Get Data ADC
    ADCMDE  = ADCMDE_VALUE;     // Continuous mode, ADCCLK = 512 kHz  
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    ADC1_Dat = ADC1DAT;        // Auxiliary ADC  =  107
    ADC0_Dat = ADC0DAT;        // Primary ADC    =  2564

    // ADC self-gain calibration
    ADCMDE  = ADCMDE_OFFSET_CAL | ADCCLKSEL_131KHZ;
    while(!(ADCSTA & ADCCALSTA)) {} // Wait ADC calibration status

    // Get Data ADC
    ADCMDE  = ADCMDE_VALUE;     // Continuous mode, ADCCLK = 512 kHz  
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    ADC1_Dat = ADC1DAT;        // Auxiliary ADC  =  -27
    ADC0_Dat = ADC0DAT;        // Primary ADC    =  2417









    // ADC0 = ADC1 = (ADC2/ADC3) pins


    ADCMDE  = ADC_IDLE_MODE;    // ADC idle mode
    // SF=7, AF=59 (Data_Rate=16.128Hz, Settling_Time=124ms, 50Hz --> -329dB)
    ADCFLT  = (ADCFLT_CHOP_ENABLE | (0x07 << 0) | (0x3B << 8));
    // ADC0 Gain=1, ext.ref (VREF+,VREF-), ADC2/ADC3
    ADC0CON = (ADC0CON_REF_EXT | ADC0CON_ADC0EN | ADC0CON_CHANNEL_DIFF_2_3);
    // ADC1 Gain=1, ext.ref (VREF+,VREF-), ADC2/ADC3
    ADC1CON = (ADC1CON_REF_EXT | ADC1CON_ADC0EN | ADC1CON_CHANNEL_2_3_DIFF);
    DelayMS(250);               // Delay 250 mS


    // Get Data ADC
    ADCMDE  = ADCMDE_VALUE;     // Continuous mode, ADCCLK = 512 kHz  
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    ADC1_Dat = ADC1DAT;        // Auxiliary ADC  =  2480
    ADC0_Dat = ADC0DAT;        // Primary ADC    =  2488

    // ADC self-gain calibration
    ADCMDE  = ADCMDE_OFFSET_CAL | ADCCLKSEL_131KHZ;
    while(!(ADCSTA & ADCCALSTA)) {} // Wait ADC calibration status

    // Get Data ADC
    ADCMDE  = ADCMDE_VALUE;     // Continuous mode, ADCCLK = 512 kHz  
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    while (!(ADCSTA & (ADC0RDY | ADC1RDY))) {}  // Wait new data
    ADC1_Dat = ADC1DAT;        // Auxiliary ADC  =  2447
    ADC0_Dat = ADC0DAT;        // Primary ADC    =  2478

Can you check the ADC reading before and after calibration if the primary and auxiliary ADC configuration uses the internal reference?

Can you also try performing a system zero-scale calibration using your ADC configurations?

Internal reference, before calibration:  ADC0 = 2730;  ADC1 = 4772

Internal reference, after calibration:  ADC0 = 1;   ADC1 = -3

As an experiment, I tried to use zero-scale calibration. Works well. But to do this,have to short the channel externally. In work it is impossible.