How To Read A/D Converter Characteristics Table - NEC 78K0S/KA1+ Preliminary User's Manual

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10.5 How to Read A/D Converter Characteristics Table

Here, special terms unique to the A/D converter are explained.
(1) Resolution
This is the minimum analog input voltage that can be identified. That is, the percentage of the analog input
voltage per bit of digital output is called 1LSB (Least Significant Bit). The percentage of 1LSB with respect to the
full scale is expressed by %FSR (Full Scale Range).
1LSB is as follows when the resolution is 10 bits.
1LSB = 1/2
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Accuracy has no relation to resolution, but is determined by overall error.
(2) Overall error
This shows the maximum error value between the actual measured value and the theoretical value.
Zero-scale error, full-scale error, integral linearity error, and differential linearity errors that are combinations of
these express the overall error.
Note that the quantization error is not included in the overall error in the characteristics table.
(3) Quantization error
When analog values are converted to digital values, a ±1/2LSB error naturally occurs. In an A/D converter, an
analog input voltage in a range of ±1/2LSB is converted to the same digital code, so a quantization error cannot
be avoided.
Note that the quantization error is not included in the overall error, zero-scale error, full-scale error, integral
linearity error, and differential linearity error in the characteristics table.
(4) Zero-scale error
This shows the difference between the actual measurement value of the analog input voltage and the theoretical
value (1/2LSB) when the digital output changes from 0......000 to 0......001.
If the actual measurement value is greater than the theoretical value, it shows the difference between the actual
measurement value of the analog input voltage and the theoretical value (3/2LSB) when the digital output
changes from 0......001 to 0......010.
10
= 1/1024
= 0.098%FSR
Figure 10-14. Overall Error
1 ...... 1
Ideal line
0 ...... 0
0
Analog input
CHAPTER 10 A/D CONVERTER
Figure 10-15. Quantization Error
1 ...... 1
Overall
error
0 ...... 0
AV
REF
Preliminary User's Manual U16898EJ1V0UD
1/2LSB Quantization error
1/2LSB
0
AV
Analog input
REF
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