3822_03 Datasheet, PDF (220/328 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.6 A-D converter
2.6.5 Measuring various A-D converter standard characteristics
The measuring various A-D converter standard characteristics is described below.
(1) Absolute accuracy
The absolute accuracy is the difference expressed in LSB between an output code obtained by actual
measurement and an expected output code of the A-D converter with ideal characteristics.
The analog input voltage at absolute accuracy measurement is assumed to be a mid-point of the input
voltage width (= 1 LSB) which outputs the same code from the A-D converter with ideal characteristics.
For example, when VREF = 5.12 V, the width of 1 LSB is 20 mV. So 0 mV, 20 mV, 40 mV, 60 mV
......or 5120 mV is selected as an analog input voltage.
When the A-D converter is actually used, the analog input voltage range is AVSS to VREF. But if the
VREF value is lowered, the accuracy degrades. Every output code for voltage of VREF–VCC is “FF16.”
Figure 2.6.11 shows the absolute accuracy of the A-D converter. Absolute accuracy = ±2 LSB indi-
cates that when the analog input voltage is 100 mV, the output code expected from the ideal A-D
converter is “0516” but the actual A-D conversion result is in the range of “0316” to “0716.”
The absolute accuracy includes a zero error and a full-scale error but not a quantization error.
Output code
0916
0816
0716
0616
0516
0416
Absolute accuracy
+ 2LSB
Ideal A-D conversion
characteristics
Limitless resolution A-D
conversion characteristics
0316
0216
– 2LSB
0116
0016
0
20 40
60 80 100 120 140 160 180 200 220
Analog input voltage (mV)
Fig. 2.6.11 Absolute accuracy of A-D converter
2–154
3822 GROUP USER’S MANUAL