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RL78/G1A CHAPTER 11 A/D CONVERTER
R01UH0305EJ0200 Rev.2.00 394
Jul 04, 2013
11.9 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 12 bits.
1LSB = 1/2
12
= 1/4096
≈ 0.024%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, 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.
Figure 11-38. Overall Error Figure 11-39. Quantization Error
Ideal line
0
......
0
1
......
1
Digital output
Overall
error
Analog input
AV
REF
0
0......0
1
......
1
Digital output
Quantization error
1/2LSB
1/2LSB
Analog input
0
AV
REF
(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.