Definitions Of A/D Conversion Accuracy - Hitachi SH7032 Hardware Manual

14.6

Definitions of A/D Conversion Accuracy

The A/D converter compares an analog value input from an analog input channel to its analog
reference value and converts it into 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 using figure 14.7. In the figure, the 10 bits of the
A/D converter have been simplified to 3 bits.
Offset error is the deviation between actual and ideal A/D conversion characteristics when the
digital output value changes from the minimum (zero voltage) 0000000000 (000 in the figure) to
000000001 (001 in the figure)(figure 14.7, item (1)). Full-scale error is the deviation between
actual and ideal A/D conversion characteristics when the digital output value changes from
1111111110 (110 in the figure) to the maximum 1111111111 (111 in the figure)(figure 14.7, item
(2)). Quantization error is the intrinsic error of the A/D converter and is expressed as 1/2 LSB
(figure 14.7, item (3)). Nonlinearity error is the deviation between actual and ideal A/D conversion
characteristics between zero voltage and full-scale voltage (figure 14.7, item (4)). Note that it does
not include offset, full-scale, or quantization error.
Digital output
111
110
101
100
011
010
001
000
0 1/8 2/8 3/8 4/8 5/8 6/8 7/8 FS
FS: Full-scale voltage
422
Ideal A/D
conversion
characteristic
(3) Quantization
error
Analog input
voltage
Figure 14.7 Definitions of A/D Conversion Accuracy
Digital output
Ideal A/D
conversion
characteristic
Actual A/D
convertion
characteristic
(1) Offset error
(2) Full-scale error
(4) Nonlinearity
error
FS
Analog input
voltage