Oki ML63611, User Manual

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ML63611 User’s Manual
Chapter 16 A/D Converter (ADC)
16 – 12
OPTION B (D): 1.5 V (3.0 V), With regulator
circuit for LCD bias
OPTION A (C): 1.5 V (3.0 V), Without regulator
circuit for LCD bias
Consequently, by performing conversion processing corresponding to the characteristics shown by Figure 16-9 to
nT0, it is possible to express temperatures by digital values.
The conversion method from an analog value of RT0 to a digital value of nT0 is now explained.
To convert RT0 to a digital value, the ratio of oscillation frequencies of RT0 to RS0 (ideal if independent of
temperature) is used. This is to cancel the error factors of the oscillation characteristics.
As shown in Figures 16-9 and 16-11, RT0 depends on temperature T and RS0 is always constant regardless of
temperature T. The oscillation characteristics, f
OSC
-T, using these resistances is ideal if the solid lines of Figures
16-12 and 16-13 can be realized. However, in reality, the dotted lines are obtained due to error factors of the
temperature characteristics of the IC and others. Since the conditions of f
OSC
(RT0) and f
OSC
(RS0) are about the
same except the resistance, their error should be similar with each other and consequently, if the ratio of one to the
other is taken, the error should be canceled.
The ratio of f
OSC
(RT0) to f
OSC
(RS0) corresponds to the A/D conversion value of nT0 which, ideally, depends
solely on RT0.
R
e
fer
e
n
c
e r
e
si
sta
n
ce
v
a
lue R
S
0
Temperature T Temperature T
With error due to factors
other than RT0
Ideal
f
OSC
(RS0) =
1
k
OSCCLK
• CS0 • RT0
f
OSC
(RT0)
Figure 16-11 Temperature Characteristics Figure 16-12 Oscillation Characteristics
of Thermistor of Thermistor
Temperature T
With error due to factors other than RS0
(RS0)
f
OSC
(RS0) =
1
k
OSCCLK
• CS0 • RS0
Ideal
f
OSC
Figure 16-13 Oscillation Characteristics of Reference Resistance