How To Read A/D Converter Characteristics Table - NEC mPD780344 Series User Manual

CHAPTER 12 8-BIT A/D CONVERTER ( µ PD780344, 780344Y SUBSERIES)

12.5 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 error, full-scale error, integral linearity error, differential linearity error and errors which are combi-
nations 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 error, full-scale error, integral linearity error, and
differential linearity error in the characteristics table.
Figure 12-9. Overall Error
1 ...... 1
Ideal line
0 ...... 0
0
Analog input
236
1 ...... 1
Overall
error
0 ...... 0
AV
DD
User's Manual U15798EJ2V0UD
Figure 12-10. Quantization Error
1/2LSB Quantization error
1/2LSB
0
Analog input
AV
DD