Noise problem with ADC

[Pablito Parseval]

Good morning,

I have a problem with the adc converter of the microcontroller stm32L053. I am in the prototype state and am using the Discovery Board.

I only have the analog AN0 pin connected to ground. When I execute the reading the converter does not return 0 and I have ./- 5LSB of noise. Is there something I'm wrong about?

Below the ADC Configuration:

/* ADC init function */

static void MX_ADC_Init(void)

{

 ADC_ChannelConfTypeDef sConfig;

  /**Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion) 

  */

 hadc.Instance = ADC1;

 hadc.Init.OversamplingMode = DISABLE;

 hadc.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV16;

 hadc.Init.Resolution = ADC_RESOLUTION_12B;

 hadc.Init.SamplingTime = ADC_SAMPLETIME_39CYCLES_5;

 hadc.Init.ScanConvMode = ADC_SCAN_DIRECTION_FORWARD;

 hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc.Init.ContinuousConvMode = DISABLE;

 hadc.Init.DiscontinuousConvMode = DISABLE;

 hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;

 hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;

 hadc.Init.DMAContinuousRequests = DISABLE;

 hadc.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

 hadc.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 hadc.Init.LowPowerAutoWait = DISABLE;

 hadc.Init.LowPowerFrequencyMode = DISABLE;

 hadc.Init.LowPowerAutoPowerOff = DISABLE;

 if (HAL_ADC_Init(&hadc) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

  /**Configure for the selected ADC regular channel to be converted. 

  */

 sConfig.Channel = ADC_CHANNEL_0;

 sConfig.Rank = ADC_RANK_CHANNEL_NUMBER;

 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

  /**Configure for the selected ADC regular channel to be converted. 

  */

 sConfig.Channel = ADC_CHANNEL_VREFINT;

 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

}

[Uwe Bonnes]

Do not look at the translated values. Look at the digits. If the steps in tour diagramm translate to digit and are not by some calculation clipping that is +/- 4 LSB max. That does not sound to bad.

[RomainR.]

You should do an ADC Calibration (on time) before start a conversion​. This will remove ADC Offset Error.

Take a look in your STM32Cube Repository ADC example.

/* ### - 2 - Start calibration ############################################ */
  if (HAL_ADCEx_Calibration_Start(&hadc, ADC_SINGLE_ENDED) != HAL_OK)
  {
    Error_Handler();
  }

Also, if you use STM32L0538DISCOVERY kit, note thay WakeUp Blue user button is shared with PA0 pin.

Best regards

rrom

[Pablito Parseval]

I try the calibration and the offset return to 0. The noise is alwais +/-5 digit.

I try to implement a mean to 8 sample, but i don't like this solution.

[RomainR.]

Hello Pablito,

I've tried to reproduce by using NucleoL053, and PA0 wired to GND.

My code use the same ADC setup (but without VREF_INT Channel) and perform ADC conversion on PA0 and fill a buffer of 64 samples.

Below my resuts are 0 with +2 lsb max .

Could you share your code please ?

BR

rrom