ad.c

DSP内部AD采样有误差

 //     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 - REF_LOW_IDEAL_COUNT;
 
    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;

......

 }