How To Read A/D Converter Characteristics Table - NEC mPD780024AS Series Preliminary User's Manual

CHAPTER 11 8-BIT A/D CONVERTER ( µ PD780024AS SUBSERIES)

11.5 How to Read 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 8 bits,
8
1LSB = 1/2 = 1/256
= 0.4%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 offset, full scale offset, integral linearity error, differential linearity error and errors which are
combinations of these express overall error.
Furthermore, quantization error is not included in overall error in the characteristics table.
(3) Quantization error
When analog values are converted to digital values, there naturally occurs a ±1/2LSB error. In an A/D converter,
an analog input voltage in a range of ±1/2LSB are converted to the same digital code, so a quantization error
cannot be avoided.
Furthermore, it is not included in the overall error, zero scale offset, full scale offset, integral linearity error, and
differential linearity error in the characteristics table.
Figure 11-9. Overall Error
1 ...... 1
Ideal line
0 ...... 0
0
Analog input
1 ...... 1
Overall
error
0 ...... 0
AV
DD
Preliminary User's Manual U16035EJ1V0UM
Figure 11-10. Quantization Error
1/2LSB Quantization error
1/2LSB
0
Analog input
AV
DD
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