
52
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER for VOLTAGE SYNTHESIZER
with ON-SCREEN DISPLAY CONTROLLER
M37225M6–XXXSP, M37225M8–XXXSP
M37225ECSP
MITSUBISHI MICROCOMPUTERS
Rev. 1.0
[LSB]
[LSB]
8.8.8 Definition of A-D Conversion Accuracy
The definition of A-D conversion accuracy is described below (refer
to Figure 8.8.4).
(1) Relative Accuracy
Zero transition error (V
0T
)
The deviation of the input voltage at which A-D conversion output
data changes from “0” to “1,” from the corresponding ideal A-D
conversion characteristics between 0 and V
REF
.
(V
0
– 1/2
V
REF
/256)
V
0T
=
Non-linearity error
The deviation of the actual A-D conversion characteristics, from the
ideal A-D conversion characteristics between V
0
and V
254
.
1LSB
(V
REF
– 3/2
V
REF
/256) – V
254
1LSB
V
FST
=
Non-linearity error =
[LSB]
[LSB]
EDifferential non-linearity error
The deviation of the input voltage required to change output data
by “1,” from the corresponding ideal A-D conversion characteris-
tics between 0 and V
REF
.
(2) Absolute Accuracy
EAbsolute accuracy error
The deviation of the actual A-D conversion characteristics, from the
ideal A-D conversion characteristics between 0 and V
REF
.
V
n
– (1LSB
n + V
0
)
1LSB
[LSB]
Differential non-linearity error =
(V
n+1
– V
n
) – 1LSB
1LSB
Absolute accuracy error =
1LSB
A
with respect to absolute accuracy =
1LSB with respect to relative accuracy =
Note:
The analog input voltage “Vn” at which A-D conversion output data
changes from “n” to “n + 1” (n ; 0 to 254) is as follows (refer to Figure
8.8.4) :
V
254
– V
0
254
V
REF
256
[V]
[V]
Fig. 8.8.4 Definition of A-D Conversion Accuracy
Full-scale transition error (V
FST
)
The deviation of the input voltage at which A-D conversion output
data changes from “255” to “254,” from the corresponding ideal A-
D conversion characteristics between 0 and V
REF
.
V
n
– 1LSB
A
(n + 1/2)
1LSB
A
Output code
0
Analog input voltage (mV)
20
40
80
100
120
140
160
180
200
220
00
16
01
16
02
16
03
16
04
16
05
16
06
16
07
16
08
16
09
16
+ 2LSB
– 2LSB
60
Absolute accuracy
Limitless resolution A-D
conversion characteristics
Ideal A-D conversion
characteristics