A-D CONVERTER
12.4 Absolute accuracy and Differential non-linearity error
12.4 Absolute accuracy and Differential non-linearity error
The A-D converter’s accuracy is described below. Refer to section “Appendix 10. 4. A-D converter standard
characteristics,” also.
12.4.1 Absolute accuracy
The absolute accuracy is the difference expressed in the LSB between the actual A-D conversion result
and the output code of an A-D converter with ideal characteristics. (See Figure 12.4.1 for more details.)
The analog input voltage at measurement of the absolute accuracy is assumed to be the mid point of the
analog input voltage width that outputs the same output code from an A-D converter with ideal characteristics.
For example, in the case of the 10-bit resolution mode, when VREF = 5.12 V, 1 LSB width is 5 mV, and 0
mV, 5 mV, 10 mV, 15 mV, 20 mV, ... are selected as the analog input voltages.
The absolute accuracy = ±3 LSB indicates that when the analog input voltage is 25 mV, the output code
expected from an ideal A-D conversion characteristics is “00516,” but the actual A-D conversion result is
between “00216” to “00816.”
The absolute accuracy includes the zero error and the full-scale error.
The absolute accuracy degrades when VREF is lowered. Any of the output codes for analog input voltages
in the range from VREF to Vcc is “3FF16.”
Output code
(A-D conversion result)
00B16
00A16
00916
+3 LSB
00816
Ideal A-D conversion
characteristics
00716
00616
00516
00416
00316
00216
–3 LSB
00116
00016
0
5
10
15
20
25
30
35
40
45
50
55
Analog input voltage (mV)
Fig. 12.4.1 Absolute accuracy of A-D converter (10-bit resolution mode)
7905 Group User’s Manual Rev.1.0
12-19
RENESAS [ RENESAS TECHNOLOGY CORP ]
