EM3027
4.3 Crystal Thermal Behaviour
The frequency of the crystal is dependent on the
temperature concurring with the following diagram:
The following formula expresses a compensation value
to be used during frequency correction.
0
2
F
COMP_val Qcoef (T To) XtalOffset
[ppm]
FO
– Thermal quadratic coefficient [ppm/°C2]
– Actual temperature [°C]
-100
Qcoef
T
TO
XtalOffset
– Turnover temperature [°C]
– Crystal offset at TO [ppm]
-200
-300
-400
COMP_val
– Compensation value result [ppm]
The oscillator frequency is adjusted according to the
equation above by using coefficients located in the
EEPROM control page and the temperature.
The actual temperature can be obtained from the internal
thermometer or from Temp register updated externally by
an application.
TO-100
TO-50
TO
TO+50
TO+100
T [°C]
Temperature [°C]
The principle of the frequency compensation is based on
adding/removing of pulses.
Figure 1: Crystal thermal behaviour
TO – Turnover temperature [°C]
FO – Crystal frequency when TO [Hz]
Example 1: Qcoef=0.035; TO=25; XtalOffset=–100
Example 2: Qcoef=0.035; TO=25; XtalOffset=+100
400
[ppm]
600
[ppm]
300
200
100
400
200
Temperature
0
Temperature
150
0
-200
-400
-600
-50
0
50
100
150
-50
0
50
100
-100
-200
-300
-400
Compensation Value
Crystal Error
Compensation Value
Crystal Error
7
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Copyright 2013, EM Microelectronic-Marin SA
3027-DS.doc, Version 8.0, 25-Jan-13
EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
