STM32H755 Nucleo board ADC noise

[mosamasa]

Hi,

I'm using STM32H755 Nucleo board and I'm evaluating ADC. I'm using 1.92MSPS per ADC sample rate for ADC1 and ADC2. I'm using A0 and A5 pins from CN9. I'm using ethernet to transfer data. My input to A0 (I channel) is 100kHz sine and A5 (Q channel) input is constant 1.6V.

 

The problem is periodic noise around 320kHz.What might cause that and is it possible to get rid of that? I have read that it might be caused by ethernet connection. I would need ethernet in final application, so would need to solve the issue somehow.

[KDJEM.1]

Hello @mosamasa;

What is the Ethernet reference clock and the frequency?

As mentioned in this ADC value affected by ETH PHY 50 MHz from RMII interface, that  the Ethernet reference clock (ETH_REF_CLK) has been observed to introduce noise into ADC (analog-to-digital converter) measurements.

The issue primarily arises in STM32 microcontrollers where the Ethernet reference clock operates at high frequencies, such as 50 MHz. This high-speed clock can interfere with the ADC's performance, leading to increased noise in the ADC readings.

For that I recommend you to look at this FAQ and check the proposed solution.

I hope this help you.

Kaouthar

[Andrew Neil]

---

@mosamasa wrote:

I'm using STM32H755 Nucleo board and I'm evaluating ADC.

---

Note that Nucleo boards aren't optimised for analogue performance.

And having an ADC on the same die as loads of high-speed digital stuff is always a compromise anyhow...

[EZHON.1]

I'm not clear for your description. it seems all pictures show the frequency and time domain from input. How do you use the ADC for data converting? 

For the 320KHz noise, please double confirm if it's not related to the input 100kHz signals?

[mosamasa]

Here is my ADC configuration:

static void MX_ADC1_Init(void)
{

  /* USER CODE BEGIN ADC1_Init 0 */

  /* USER CODE END ADC1_Init 0 */

  ADC_MultiModeTypeDef multimode = {0};
  ADC_ChannelConfTypeDef sConfig = {0};

  /* USER CODE BEGIN ADC1_Init 1 */

  /* USER CODE END ADC1_Init 1 */

  /** Common config
  */
  hadc1.Instance = ADC1;
  hadc1.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
  hadc1.Init.Resolution = ADC_RESOLUTION_12B;
  hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
  hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;
  hadc1.Init.LowPowerAutoWait = DISABLE;
  hadc1.Init.ContinuousConvMode = ENABLE;
  hadc1.Init.NbrOfConversion = 1;
  hadc1.Init.DiscontinuousConvMode = DISABLE;
  hadc1.Init.NbrOfDiscConversion = 1;
  hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  hadc1.Init.ConversionDataManagement = ADC_CONVERSIONDATA_DMA_ONESHOT;
  hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;
  hadc1.Init.LeftBitShift = ADC_LEFTBITSHIFT_NONE;
  hadc1.Init.OversamplingMode = DISABLE;
  hadc1.Init.Oversampling.Ratio = 1;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure the ADC multi-mode
  */
  multimode.Mode = ADC_MODE_INDEPENDENT;
  if (HAL_ADCEx_MultiModeConfigChannel(&hadc1, &multimode) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_2;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5;
  sConfig.SingleDiff = ADC_SINGLE_ENDED;
  sConfig.OffsetNumber = ADC_OFFSET_NONE;
  sConfig.Offset = 0;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN ADC1_Init 2 */

  /* USER CODE END ADC1_Init 2 */

}

/**
  * @brief ADC2 Initialization Function
  * @PAram None
  * @retval None
  */
static void MX_ADC2_Init(void)
{

  /* USER CODE BEGIN ADC2_Init 0 */

  /* USER CODE END ADC2_Init 0 */

  ADC_ChannelConfTypeDef sConfig = {0};

  /* USER CODE BEGIN ADC2_Init 1 */

  /* USER CODE END ADC2_Init 1 */

  /** Common config
  */
  hadc2.Instance = ADC2;
  hadc2.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
  hadc2.Init.Resolution = ADC_RESOLUTION_12B;
  hadc2.Init.ScanConvMode = ADC_SCAN_DISABLE;
  hadc2.Init.EOCSelection = ADC_EOC_SEQ_CONV;
  hadc2.Init.LowPowerAutoWait = DISABLE;
  hadc2.Init.ContinuousConvMode = ENABLE;
  hadc2.Init.NbrOfConversion = 1;
  hadc2.Init.DiscontinuousConvMode = DISABLE;
  hadc2.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc2.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  hadc2.Init.ConversionDataManagement = ADC_CONVERSIONDATA_DMA_ONESHOT;
  hadc2.Init.Overrun = ADC_OVR_DATA_PRESERVED;
  hadc2.Init.LeftBitShift = ADC_LEFTBITSHIFT_NONE;
  hadc2.Init.OversamplingMode = DISABLE;
  hadc2.Init.Oversampling.Ratio = 1;
  if (HAL_ADC_Init(&hadc2) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_15;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5;
  sConfig.SingleDiff = ADC_SINGLE_ENDED;
  sConfig.OffsetNumber = ADC_OFFSET_NONE;
  sConfig.Offset = 0;
  sConfig.OffsetSignedSaturation = DISABLE;
  if (HAL_ADC_ConfigChannel(&hadc2, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN ADC2_Init 2 */

  /* USER CODE END ADC2_Init 2 */

}

I can see this 320kHz noise even though both inputs are connected to ground, so it is unlikely caused by the signal source.

[mosamasa]

My Ethernet reference clock is 50Mhz. Recommended solutions are not ideal. Maybe changing L2 600R@100MHz might improve the situation.