求助xmega ADC 无符号转换结果偏大

Cortex_M3

再用xmega32a4 做ADC 无符号AD转换时，测量结果存在误差
具体配置函数如下
void ADC_Port_Configuration_Init(void)
{
  struct adc_config          adc_conf;
  struct adc_channel_config  adcch_conf;
  
        // Clear the configuration structures.
        // 清除配置结构
        memset(&adc_conf, 0, sizeof(struct adc_config));
        memset(&adcch_conf, 0, sizeof(struct adc_channel_config));
  
  /* Configure the ADC module:
        * - unsigned, 12-bit results
        * - VCC/1.6 voltage reference
        * - 200 kHz maximum clock rate
        * - manual conversion triggering
        */
/*
12位无符号模式，基准电压Vcc/1.6=2.06V
200KHz时钟频率
*/
        adc_set_conversion_parameters(&adc_conf, ADC_SIGN_OFF, ADC_RES_12, ADC_REF_VCC);
        adc_set_clock_rate(&adc_conf, 200000UL);
        adc_set_conversion_trigger(&adc_conf, ADC_TRIG_MANUAL, 3, 0);
        adc_write_configuration(&ADCA, &adc_conf);
  
        /* Configure ADC channel 0, 1 and 2:
        * - single-ended measurement from configured input pin
        * - interrupt flag set on completed conversion
        */
        adcch_set_input(&adcch_conf, ADCCH_POS_PIN0, ADCCH_NEG_NONE, 1); // PA0  VU_L
        adcch_set_interrupt_mode(&adcch_conf, ADCCH_MODE_COMPLETE);
        adcch_disable_interrupt(&adcch_conf);
        adcch_write_configuration(&ADCA, 0, &adcch_conf);    // 配置到通道0
       
        adcch_set_input(&adcch_conf, ADCCH_POS_PIN1, ADCCH_NEG_NONE, 1); // PA1  VU_R
        adcch_write_configuration(&ADCA, 1, &adcch_conf);    // 配置到通道1

        adcch_set_input(&adcch_conf, ADCCH_POS_PIN7, ADCCH_NEG_NONE, 1); // PA7  Temp
        adcch_write_configuration(&ADCA, 2, &adcch_conf);    // 配置到通道2

        // Enable the ADC and do one dummy conversion.
        adc_enable(&ADCA);
}

uint16_t Get_ADC_Vol(uint8_t ch)
{
        unt16_t value=0;
        adc_start_conversion(&ADCA, ch);
        adc_wait_for_interrupt_flag(&ADCA, ch);
        value = adcch_get_result(&ADCA, ch);
        return (uint16_t) value ;
}

麻烦各位坛友给看看。
PS:开发环境AVR studio

输入端接地，竟然还有150多的输出

hell-prototypes

In unsigned mode, the negative input is connected to half of the voltage reference (VREF) voltage minus a fixed offset.
The nominal value for the offset is：
_V = Vref x 0.05

楼主这个你减掉没。。

Cortex_M3

hell-prototypes 发表于 2014-6-18 09:43
In unsigned mode, the negative input is connected to half of the voltage reference (VREF) voltage mi ...

这个我知道
Vref = VCC/1.6 =2.06V
换算过去为RES = 204

直接减去会出现负的情况，因为我对地 大概是输出RES = 150

会有50 res 偏差