A-D Converter Errors; Absolute Accuracy - Renesas M16C Series User Manual

M30240 Group

2.6.5 A-D Converter Errors

2.6.5.1 Absolute accuracy

Absolute accuracy is the difference between output code based on the theoretical A-D conversion
characteristics, and actual A-D conversion result. When measuring absolute accuracy, the voltage at
the middle point of the width of analog input voltage (1-LSB width), that can meet the expectation of
outputting an equal code based on the theoretical A-D conversion characteristics, is used as an analog
input voltage. For example, if 10-bit resolution is used and if VREF (reference voltage) = 5.12 V, then 1-
LSB width becomes 5 mV, and 0 mV, 5 mV, 10 mV, 15 mV, 20 mV, etc. are used as analog input
voltages. See Figure 2.96. If analog input voltage is 25 mV, "absolute accuracy = ± 3LSB" refers to the
fact that actual A-D conversion falls on a range from 002
be expected from the theoretical A-D conversion characteristics. Zero error and full-scale error are
included in absolute accuracy.
Also, all the output codes for analog input voltage between V
Output code
(result of A-D conversion)
00B
16
00A
16
009
16
008
16
007
16
006
16
005
16
004
16
003
16
002
16
001
16
000
16
0
Figure 2.96: Absolute accuracy (10-bit resolution)
Rev.1.00 Sep 24, 2003 Page 250 of 360
+3LSB
–3LSB
5 10 15 20 25 30
Analog input voltage (mV)
to 008 though an output code, 005
16 16
and AVcc becomes "3FF
REF
Theoretical A-D conversion
characteristic
35 40 45 50 55
A-D Converter
, can
16
".
16