ESP32-S3 ADC2电压偏差是什么原因导致的？

1. 使用ESP32-S3 ADC2 CH7(GPIO18)，读取校准后的电压偏低。实际是2V左右，log打印只有1.8V多。没有打开wifi，请问可能是什么问题？
2. 另外如果直接计算adc_raw/4095*Vref，这个Vref是多少
I (100531) bat_adc: adc_raw= 2238 cali_data= 1803mVI (102531) bat_adc: adc_raw= 2238 cali_data= 1803mVI (104531) bat_adc: adc_raw= 2236 cali_data= 1800mVI (106531) bat_adc: adc_raw= 2236 cali_data= 1800mVI (108531) bat_adc: adc_raw= 2238 cali_data= 1803mVI (110531) bat_adc: adc_raw= 2237 cali_data= 1802mVI (112531) bat_adc: adc_raw= 2237 cali_data= 1802mVI (114531) bat_adc: adc_raw= 2237 cali_data= 1802mVI (116531) bat_adc: adc_raw= 2237 cali_data= 1802mVI (118531) bat_adc: adc_raw= 2237 cali_data= 1802mVI (120531) bat_adc: adc_raw= 2235 cali_data= 1800mVI (122531) bat_adc: adc_raw= 2239 cali_data= 1803mV
附上ADC2读取函数：
//ADC Channels#define ADC_EXAMPLE_CHAN0    ADC2_CHANNEL_7   // GPIO18//ADC Attenuation#define ADC_EXAMPLE_ATTEN    ADC_ATTEN_DB_11//ADC Calibration#if CONFIG_IDF_TARGET_ESP32#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_VREF#elif CONFIG_IDF_TARGET_ESP32S2#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_TP#elif CONFIG_IDF_TARGET_ESP32C3#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_TP#elif CONFIG_IDF_TARGET_ESP32S3#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_TP_FIT#endifstatic esp_adc_cal_characteristics_t adc_chars;static bool adc_calibration_init(void){    esp_err_t ret;    bool cali_enable = false;    ret = esp_adc_cal_check_efuse(ADC_EXAMPLE_CALI_SCHEME);    if (ret == ESP_ERR_NOT_SUPPORTED)    {        ESP_LOGW(TAG, "Calibration scheme not supported, skip software calibration");    }    else if (ret == ESP_ERR_INVALID_VERSION)    {        ESP_LOGW(TAG, "eFuse not burnt, skip software calibration");    }    else if (ret == ESP_OK)    {        cali_enable = true;        esp_adc_cal_characterize(ADC_UNIT_2, ADC_EXAMPLE_ATTEN, ADC_WIDTH_BIT_DEFAULT, 0, &adc_chars);    }    else    {        ESP_LOGE(TAG, "Invalid arg");    }    return cali_enable;}esp_err_t adc_init(void){    bool cali_enable = adc_calibration_init();    if (true != cali_enable)    {        ESP_LOGI(TAG, "adc init fail!!!");        return ESP_FAIL;    }        //ADC2 config    ESP_ERROR_CHECK(adc2_config_channel_atten(ADC_EXAMPLE_CHAN0, ADC_EXAMPLE_ATTEN));    ESP_LOGI(TAG, "adc init ok");    return ESP_OK;}uint16_t adc_get_voltage(void){    uint16_t adc_raw;    uint16_t voltage = 0;    adc2_get_raw(ADC_EXAMPLE_CHAN0, ADC_WIDTH_BIT_DEFAULT, &adc_raw);    voltage = esp_adc_cal_raw_to_voltage(adc_raw, &adc_chars);    ESP_LOGI(TAG, "adc_raw= %d cali_data= %dmV", adc_raw, voltage);    return voltage;}