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How is A/D conversion accuracy defined at 8-bit resolution?

Latest Updated:03/01/2005

Question:

(A/D Converter)  How is A/D conversion accuracy defined at 8-bit resolution?  [2005/03/01]

Answer:

A/D conversion accuracy at 8-bit resolution is defined as follows:

(1) Relative Accuracy.
 

  • Zero Transition Voltage
    This means an analog input voltage when the actual A/D conversion output data changes from "0" to "1".

  •  
  • Full-Scale Transition Voltage
    This means an analog input voltage when the actual A/D conversion output data changes from "254" to "255".

  •  
  • Zero Transition Error = {V0-(1/2) X (VREF/256)}/1LSB [LSB]
    This means a deviation of an input voltage from "the ideal A/D conversion characteristics between 0 to VREF" when the A/D conversion output data changes from "0" to "1".

  •  
  • Full-Scale Transition Error = [V254-{VREF-(3/2) X (VREF/256)}]/1LSB [LSB]
    This means a deviation of an input voltage from "the ideal A/D conversion characteristics between 0 to VREF" when the A/D conversion output data changes from "254" to "255".

  •  
  • Linearity Error = {Vn-(1LSB X n+V0)}/1LSB [LSB]
    This means a deviation from "the ideal A/D conversion characteristics between 0 to V254" of actual A/D conversion characteristics.

  •  
  • Differential Non-Linearity Error = {(Vn+1-Vn)-1LSB}/1LSB [LSB]
    This means a deviation from "the ideal A/D conversion characteristics between 0 to V254" of the A/D conversion input voltage required to change output data by 1.

  •  

(2) Absolute Accuracy
 

  • Absolute Accuracy = {Vn-1LSB X (n+1/2)}/1LSB [LSB]
    This means a deviation from "the ideal A/D conversion characteristics between 0 to VREF" of actual A/D conversion characteristics.
  •  

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