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Section 24 A/D Converter
R01UH0134EJ0400 Rev. 4.00 Page 1281 of 2108
Sep 24, 2014
SH7262 Group, SH7264 Group
24.6 Definitions of A/D Conversion Accuracy
The A/D converter compares an analog value input from an analog input channel with its analog
reference value and converts it to 10-bit digital data. The absolute accuracy of this A/D conversion
is the deviation between the input analog value and the output digital value. It includes the
following errors:
Offset error
Full-scale error
Quantization error
Nonlinearity error
These four error quantities are explained below with reference to figure 24.7. In the figure, the 10-
bit A/D converter is illustrated as the 3-bit A/D converter for explanation. Offset error is the
deviation between actual and ideal A/D conversion characteristics when the digital output value
changes from the minimum (zero voltage) B'0000000000 (000 in the figure) to B'000000001 (001
in the figure)(figure 24.7, item (1)). Full-scale error is the deviation between actual and ideal A/D
conversion characteristics when the digital output value changes from B'1111111110 (110 in the
figure) to the maximum B'1111111111 (111 in the figure)(figure 24.7, item (2)). Quantization
error is the intrinsic error of the A/D converter and is expressed as 1/2 LSB (figure 24.7, item (3)).
Nonlinearity error is the deviation between actual and ideal A/D conversion characteristics
between zero voltage and full-scale voltage (figure 24.7, item (4)). Note that it does not include
offset, full-scale, or quantization error.
0
FS
111
110
101
100
011
010
001
000
Analog input
voltage
(3) Quantization
error
(4) Nonlinearity
error
(2) Full-scale error
Ideal A/D
conversion
characteristic
Digital output
[Legend]
FS: Full-scale voltage
FS
Analog input
voltage
Actual A/D
convertion
characteristic
(1) Offset error
Ideal A/D
conversion
characteristic
Digital output
1024
1
1024
2
1024
1022
1024
1023
Figure 24.7 Definitions of A/D Conversion Accuracy