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CHAPTER 12 A/D CONVERTER
User
’
s Manual U14701EJ3V0UD
12.5 How to Read the A/D Converter Characteristics Table
Here we will explain the special terms unique to A/D converters.
(1) Resolution
This is the minimum analog input voltage that can be identified. That is, the percentage of the analog input voltage
per 1 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).
When the resolution is 10 bits,
1LSB = 1/2
10
= 1/1,024
= 0.098%FSR
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, differential linearity error and errors which are
combinations of these express overall error.
Note that, quantization error is not included in 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.
Figure 12-9. Overall Error
Figure 12-10. Quantization Error
Ideal line
0
……
0
1
……
1
D
Overall
error
Analog input
AV
REF0
0
0
……
0
1
……
1
D
Quantization error
1/2LSB
1/2LSB
Analog input
AV
REF0
0