|
|
请教为什么精度不好？？？
小弟使用电池和电阻分压后的0~75mV电压，经过运放放大37倍左右到AD端，现在测量AD端电压与ADC的数字转换的结果，数据如下。
进入ADC前级的RC参数是1K,10nF。ADC使用的是内部的ADC基准。
下面的AD采样值是经过10次求平均得到的。单次转换使用TIME0，20us中断进行SOC触发采样。
就是说实际上ADC的采样周期是200us。使用串口观察，ADC的采样值波动4以内吧，还算稳定。
就是在低电压采样时，精度很差，超出2%了。
备注：我测量3.3V电源，发现电压是3.32V。不过应该和ADC没有关系吧？使用DSP的内部晶振源。
AD采样电压V AD采样值 误差百分比
0.166 223 -7.60%
0.423 543 -3.31%
1.043 1313 -1.40%
1.477 1854 -1.12%
1.773 2221 -0.92%
2.129 2662 -0.73%
2.544 3176 -0.58%
2.836 3537 -0.48%
3.085 3849 -0.52%
ADC的代码
void AD_Config()
{
// Interrupts that are used in this example are re-mapped to
// ISR functions found within this file.
EALLOW; // This is needed to write to EALLOW protected register
PieVectTable.ADCINT1 = &adc_isr;
EDIS; // This is needed to disable write to EALLOW protected registers
InitAdc(); // init the ADC
// Enable ADCINT1 in PIE
PieCtrlRegs.PIEIER1.bit.INTx1 = 1; // Enable INT 1.1 in the PIE
IER |= M_INT1; // Enable CPU Interrupt 1
EINT; // Enable Global interrupt INTM
ERTM; // Enable Global realtime interrupt DBGM
// Configure ADC
EALLOW;
AdcRegs.ADCCTL1.bit.INTPULSEPOS = 1; //ADCINT1 trips after AdcResults latch
AdcRegs.INTSEL1N2.bit.INT1E = 1; //Enabled ADCINT1
AdcRegs.INTSEL1N2.bit.INT1CONT = 0; //Disable ADCINT1 Continuous mode
AdcRegs.INTSEL1N2.bit.INT1SEL = 1; //setup EOC1 to trigger ADCINT1 to fire
AdcRegs.ADCSOC0CTL.bit.CHSEL = 0; //set SOC0 channel select to ADCINA0
AdcRegs.ADCSOC1CTL.bit.CHSEL = 2; //set SOC1 channel select to ADCINA2
AdcRegs.ADCSOC2CTL.bit.CHSEL = 4; //set SOC2 channel select to ADCINA4
AdcRegs.ADCSOC3CTL.bit.CHSEL = 6; //set SOC3 channel select to ADCINA6
AdcRegs.ADCSOC0CTL.bit.TRIGSEL = 1; //set SOC0 start trigger on TIME0, due to round-robin SOC0 converts first then SOC1
AdcRegs.ADCSOC1CTL.bit.TRIGSEL = 1; //set SOC1 start trigger on TIME0, due to round-robin SOC0 converts first then SOC1
AdcRegs.ADCSOC2CTL.bit.TRIGSEL = 1; //set SOC2 start trigger on TIME0, due to round-robin SOC0 converts first then SOC1
AdcRegs.ADCSOC3CTL.bit.TRIGSEL = 1; //set SOC3 start trigger on TIME0, due to round-robin SOC0 converts first then SOC1
AdcRegs.ADCSOC0CTL.bit.ACQPS = 6; //set SOC0 S/H Window to 7 ADC Clock Cycles, (6 ACQPS plus 1)
AdcRegs.ADCSOC1CTL.bit.ACQPS = 6; //set SOC1 S/H Window to 7 ADC Clock Cycles, (6 ACQPS plus 1)
AdcRegs.ADCSOC2CTL.bit.ACQPS = 6; //set SOC1 S/H Window to 7 ADC Clock Cycles, (6 ACQPS plus 1)
AdcRegs.ADCSOC3CTL.bit.ACQPS = 6; //set SOC1 S/H Window to 7 ADC Clock Cycles, (6 ACQPS plus 1)
EDIS;
}
//-------------------------------------------------
//20us sample period;
interrupt void adc_isr(void)
{
Voltage1[ConversionCount] = AdcResult.ADCRESULT0;
Voltage2[ConversionCount] = AdcResult.ADCRESULT1;
Voltage3[ConversionCount] = AdcResult.ADCRESULT2;
Voltage4[ConversionCount] = AdcResult.ADCRESULT3;
// If 10 conversions have been logged, start over
if(ConversionCount == 9)
{
ConversionCount = 0;
}
else ConversionCount++;
AdcRegs.ADCINTFLGCLR.bit.ADCINT1 = 1; //Clear ADCINT1 flag reinitialize for next SOC
PieCtrlRegs.PIEACK.all = PIEACK_GROUP1; // Acknowledge interrupt to PIE
return;
} |
阿莫论坛20周年了！感谢大家的支持与爱护！！
曾经有一段真挚的爱情摆在我的面前，我没有珍惜，现在想起来，还好我没有珍惜……
|
发表于 2014-6-4 08:53:43
楼主
