AVR教程 ADC.pptVIP

December 2004 ADC Analog to Digital Converter Agenda What is ADC? ADC errors Offset Gain INL DNL Calibration of errors AVR ADC AVR characteristics Increase bit resolution Application example What is ADC? Analog to Digital Converter A device/circuit/IC that converts a continous analogue signal into a discrete binary signal A way to monitor a continously varying signal and be able to manage it in the digital world Sensor readings Temperature, flow, light Digitize Audio information Frequency counting Transfer function, ideal ADC ADC definitions ADC Errors Measured in LSB’s (Least Significant Bit) One LSB is conveying the least amount of precision LSB not equal to ”bit” LSB correspond to one step 10 bit ADC ? 1024 steps = ”1024 LSB’s” ADC resolution Number of bit’s the ADC uses to divide the input signal ADC error definitions Transfer function perfect ADC Quantisation error Always 0.5 LSB ADC error definitions Offset Deviation actual ADC’s transfer function from ideal straight line at zero input voltage ADC error definitions Gain Deviation of the last output step’s midpoint from ideal stragiht line, after removing offset error ADC error definitions DNL, Differential Non-Linearity Maximum and minimum difference between the step width and the perfect width (1LSB) of any output step ADC error definitions INL, Integral Non-Linearity Maximum vertical difference between the actual and the perfect curve INL can be interpreted as a sum of DNLs ADC error definitions Absolute error Maximum deviation from ideal straight line and the actual transfer function, including quantization steps. All errors from analog signal on pin till result in ADC register Absolute err. = Quantisation err. + offset err. + gain err. + INL ADC Calibration Offset Differential channel Connect both input channels to same voltage, reading is correction value Singel ended channel Positive offset, do a GND reading Negative offset, increase input voltage from GND until the first transition i