STM32F103RET6 ADC输入IO口的电压会上浮200mv左右是为什么？

用单片机采集分压电阻过来的电压值，在调试期间，发现初始化完IO口后，ADC输入IO口的电压会上浮200mv左右，开始ADC采集时，会出现低电平脉冲，频率是ADC的采集频率，即35.7K。同时，采集到的电压值也不准确，不同电压值，ADC输出口上浮的电压不同。采集到的电压值和实际值偏差也不是固定，感觉有一个关系。
程序上是采用ADC+DMA的采集方式，数据是通过半传输完成这中断+传输完成中断里得到的，每次采集100个数据（数组）。一直连续采集500ms后停止，找出这一阶段中采集到的最大值。
程序如下
/* USER CODE END Header *//* Includes ------------------------------------------------------------------*/#include "adc.h"/* USER CODE BEGIN 0 */#include "tim.h"uint16_t adc_data[100]= {0};/* USER CODE END 0 */ADC_HandleTypeDef hadc1;DMA_HandleTypeDef hdma_adc1;/* ADC1 init function */void MX_ADC1_Init(void){  /* USER CODE BEGIN ADC1_Init 0 */  /* USER CODE END ADC1_Init 0 */  ADC_ChannelConfTypeDef sConfig = {0};  /* USER CODE BEGIN ADC1_Init 1 */  /* USER CODE END ADC1_Init 1 */  /** Common config  */  hadc1.Instance = ADC1;  hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;  hadc1.Init.ContinuousConvMode = ENABLE;  hadc1.Init.DiscontinuousConvMode = DISABLE;  hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;  hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;  hadc1.Init.NbrOfConversion = 1;  if (HAL_ADC_Init( hadc1) != HAL_OK)  {    Error_Handler();  }  /** Configure Regular Channel  */  sConfig.Channel = ADC_CHANNEL_14;  sConfig.Rank = ADC_REGULAR_RANK_1;  sConfig.SamplingTime = ADC_SAMPLETIME_239CYCLES_5;  if (HAL_ADC_ConfigChannel( hadc1,  sConfig) != HAL_OK)  {    Error_Handler();  }  /* USER CODE BEGIN ADC1_Init 2 */    //HAL_ADCEx_Calibration_Start( hadc1);  /* USER CODE END ADC1_Init 2 */}void HAL_ADC_MspInit(ADC_HandleTypeDef* adcHandle){  GPIO_InitTypeDef GPIO_InitStruct = {0};  if(adcHandle->Instance==ADC1)  {  /* USER CODE BEGIN ADC1_MspInit 0 */      GPIO_InitStruct.Pull = GPIO_NOPULL;      GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;  /* USER CODE END ADC1_MspInit 0 */    /* ADC1 clock enable */    __HAL_RCC_ADC1_CLK_ENABLE();    __HAL_RCC_GPIOC_CLK_ENABLE();    /**ADC1 GPIO Configuration    PC4     ------> ADC1_IN14    */    GPIO_InitStruct.Pin = GPIO_PIN_4;    GPIO_InitStruct.Mode = GPIO_MODE_ANALOG;    HAL_GPIO_Init(GPIOC,  GPIO_InitStruct);    /* ADC1 DMA Init */    /* ADC1 Init */    hdma_adc1.Instance = DMA1_Channel1;    hdma_adc1.Init.Direction = DMA_PERIPH_TO_MEMORY;    hdma_adc1.Init.PeriphInc = DMA_PINC_DISABLE;    hdma_adc1.Init.MemInc = DMA_MINC_ENABLE;    hdma_adc1.Init.PeriphDataAlignment = DMA_PDATAALIGN_HALFWORD;    hdma_adc1.Init.MemDataAlignment = DMA_MDATAALIGN_HALFWORD;    hdma_adc1.Init.Mode = DMA_CIRCULAR;    hdma_adc1.Init.Priority = DMA_PRIORITY_LOW;    if (HAL_DMA_Init( hdma_adc1) != HAL_OK)    {      Error_Handler();    }    __HAL_LINKDMA(adcHandle,DMA_Handle,hdma_adc1);    /* ADC1 interrupt Init */    HAL_NVIC_SetPriority(ADC1_2_IRQn, 2, 2);    HAL_NVIC_EnableIRQ(ADC1_2_IRQn);  /* USER CODE BEGIN ADC1_MspInit 1 */    __HAL_DMA_DISABLE_IT( hdma_adc1,DMA_IT_TC | DMA_IT_HT);  //  HAL_DMA_RegisterCallback( hdma_adc1, HAL_DMA_XFER_CPLT_CB_ID, ADCDataCollect_DmaCplCb);  //  HAL_DMA_RegisterCallback( hdma_adc1, HAL_DMA_XFER_HALFCPLT_CB_ID, ADCDataCollect_DmaHalfCplCb);  /* USER CODE END ADC1_MspInit 1 */  }}void HAL_ADC_MspDeInit(ADC_HandleTypeDef* adcHandle){  if(adcHandle->Instance==ADC1)  {  /* USER CODE BEGIN ADC1_MspDeInit 0 */  /* USER CODE END ADC1_MspDeInit 0 */    /* Peripheral clock disable */    __HAL_RCC_ADC1_CLK_DISABLE();    /**ADC1 GPIO Configuration    PC4     ------> ADC1_IN14    */    HAL_GPIO_DeInit(GPIOC, GPIO_PIN_4);    /* ADC1 DMA DeInit */    HAL_DMA_DeInit(adcHandle->DMA_Handle);    /* ADC1 interrupt Deinit */    HAL_NVIC_DisableIRQ(ADC1_2_IRQn);  /* USER CODE BEGIN ADC1_MspDeInit 1 */  /* USER CODE END ADC1_MspDeInit 1 */  }}/* USER CODE BEGIN 1 *//**  * @brief 鍚姩ADC+DMA浼犺緭  * @retval None  */void ADC1Star(void){    //HAL_ADCEx_Calibration_Start( hadc1);    //HAL_Delay(100);    HAL_NVIC_EnableIRQ(DMA1_Channel1_IRQn);    HAL_NVIC_EnableIRQ(ADC1_2_IRQn);    __HAL_DMA_ENABLE_IT( hdma_adc1, DMA_IT_TE | DMA_IT_TC);    HAL_ADC_Start_DMA( hadc1,(uint32_t*)adc_data,100);}/**  * @brief 鍏抽棴ADC+DMA浼犺緭  * @retval None  */void ADC1Stop(void){    HAL_NVIC_DisableIRQ(DMA1_Channel1_IRQn);    HAL_NVIC_DisableIRQ(ADC1_2_IRQn);     __HAL_DMA_CLEAR_FLAG( hdma_adc1, __HAL_DMA_GET_HT_FLAG_INDEX( hdma_adc1));     __HAL_DMA_CLEAR_FLAG( hdma_adc1, __HAL_DMA_GET_TC_FLAG_INDEX( hdma_adc1));    __HAL_DMA_DISABLE_IT( hdma_adc1, DMA_IT_TE | DMA_IT_TC);    HAL_ADC_Stop_DMA( hadc1);    //HAL_ADC_MspDeInit( hadc1);}/**  * @brief DMA半传输完成中断  * @retval None  */void HAL_ADC_ConvHalfCpltCallback(ADC_HandleTypeDef* hadc){    uint8_t i;    if(__HAL_TIM_GET_COUNTER( htim1) < 4920)    {        for(i = 0;i<50;i++)        {            if(adc_data[i] > S_GLOBAL_VARIBLE.ultrasonic_ADC_DATA)            {                S_GLOBAL_VARIBLE.ultrasonic_ADC_DATA = adc_data[i];//找出最大值            }        }    }    //__HAL_DMA_ENABLE_IT( hdma_adc1,DMA_IT_TC);    //启动全传输完成中断}/**  * @brief DMA全传输完成中断  * @retval None  */void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc){    uint8_t i;    if(__HAL_TIM_GET_COUNTER( htim1) < 4920)    {        for(i = 50;i<100;i++)        {            if(adc_data[i] > S_GLOBAL_VARIBLE.ultrasonic_ADC_DATA)            {                S_GLOBAL_VARIBLE.ultrasonic_ADC_DATA = adc_data[i];//找到最大值            }        }    }        //__HAL_DMA_ENABLE_IT( hdma_adc1,DMA_IT_HT);//启动半传输完成中断}/* USER CODE END 1 */