UPD78F0138 NEC, UPD78F0138 Datasheet - Page 265

• Manufacturer Part Number: UPD78F0138
• Description: (UPD78xxxx) 8-Bit Single-Chip Microcontrollers
• Manufacturer: NEC

12.5 How to Read A/D Converter Characteristics Table
(1) Resolution
(2) Overall error
(3) Quantization error
(4) Zero-scale error
Here, special terms unique to the A/D converter are explained.
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
Accuracy has no relation to resolution, but is determined by 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.
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.
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.
1 …… 1
0 …… 0
= 0.098%FSR
Figure 12-12. Overall Error
10
0
= 1/1024
Ideal line
Analog input
CHAPTER 12 A/D CONVERTER
Overall
error
AV
User’s Manual U16228EJ2V0UD
REF
1 …… 1
0 …… 0
Figure 12-13. Quantization Error
0
1/2LSB
Analog input
1/2LSB
Quantization error
AV
REF
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