F2812内部集成了ADC转换模块。该模块是一个12位、具有流水线结构的模数转换器，内置双采样保持器（S/H），可多路选择16通道输入，快速转换时间运行在25 MHz、ADC时钟或12.5 Msps，16个转换结果寄存器可工作于连续自动排序模式或启动/停止模式。在实际使用中，ADC的转换结果误差较大，如果直接将此转换结果用于控制回路，必然会降低控制精度。（最大转换误差可以达到9%左右）

F2812的ADC转换精度较差的主要原因是存在增益误差和失调误差，要提高转换精度就必须对两种误差进行补偿。

对于ADC模块采取了如下方法对其进行校正：

选用ADC的任意两个通道（如A3，A4）作为参考输入通道，并分别提供给它们已知的直流参考电压作为输入（RefHigh和RefLow），通过读取相应的结果寄存器获取转换值，利用两组输入输出值求得ADC模块的校正增益和校正失调，然后利用这两个值对其他通道的转换数据进行补偿，从而提高了ADC模块转换的准确度。

实现校准的硬件电路在本文中不作描述，在有关资料中可以查到。下面是该算法的C语言实现：

//首先计算两个通道的参考电压转换后的理想结果

 //     A4 = RefHigh = 2.5V  ( 2.5*4095/3.0 = 3413 ideal count)

//     A3 = RefLow  = 0.5V  ( 0.5*4095/3.0 = 683 ideal count)

#define     REF_HIGH_IDEAL_COUNT   3413

#define     REF_LOW_IDEAL_COUNT    683

#define  SAMPLES       63

//定义所需的各个变量

Uint16  Avg_RefHighActualCount; 

Uint16  Avg_RefLowActualCount; /  

Uint16  CalGain;                                                 // Calibration Gain    

Uint16  CalOffset;                                              // Calibration Offset

Uint16  SampleCount;

Uint16 RefHighActualCount;

Uint16 RefLowActualCount;

//对各个变量进行初始化

void InitCalib()

{

    Avg_RefLowActualCount = 0;

    Avg_RefLowActualCount  = 0;

    Avg_RefHighActualCount = 0;

    RefHighActualCount = 0;

    RefLowActualCount = 0;

    CalGain   = 0;

    CalOffset = 0;

    SampleCount = 0;

}

//获得校准增益和校准失调

// Algorithm: Calibration formula used is:

//

//  ch(n) = ADCRESULTn*CalGain - CalOffset   

// n = 0 to 15 channels

//  CalGain =   (RefHighIdealCount - RefLowIdealCount)

//                       -----------------------------------------

//                      (Avg_RefHighActualCount  - Avg_RefLowActualCount)

//

//  CalOffset = Avg_RefLowActualCount*CalGain - RefLowIdealCount

//

//  A running weighted average is calculated for the reference inputs:

//

//  Avg_RefHighActualCount = (Avg_RefHighActualCount*SAMPLES

//                            + RefHighActualCount) / (SAMPLES+1)

//

//  Avg_RefLowActualCount  = (Avg_RefLowActualCount*SAMPLES

//                                         + RefLowActualCount) / (SAMPLES+1)

//    

void GetCalibParam()

{

 RefHighActualCount = AdcRegs.ADCRESULT4 >>4;

 RefLowActualCount = AdcRegs.ADCRESULT3 >>4;

 if(SampleCount > SAMPLES)

  SampleCount = SAMPLES;

 Avg_RefHighActualCount = (Avg_RefHighActualCount * SampleCount

         + RefHighActualCount) / (SampleCount+1);

 Avg_RefLowActualCount  = (Avg_RefLowActualCount * SampleCount

                              + RefLowActualCount) / (SampleCount+1);

 CalGain = (REF_HIGH_IDEAL_COUNT - REF_LOW_IDEAL_COUNT)

                        / (Avg_RefHighActualCount  - Avg_RefLowActualCount);

 CalOffset = Avg_RefLowActualCount*CalGain - RefLowIdealCount;

 SampleCount++;

}

 //在ADC_ISR中，对其他各个通道的结果进行修正：

interrupt void  adc_isr(void)

{

GetCalibParam();

......

newResult n= AdcRegs.ADCRESULTn*CalGain - CalOffset;

......

 }

通过上面的代码，配合硬件电路改动，可以大幅实现提高ADC采样的精度，实现更灵敏、更精确的控制。