Method for stabilizing the clock frequency of a microcontroller
A method for stabilizing the clock frequency of a microcontroller associated with a field device of automation technology. The field device as a function of application is exposed to different process conditions, wherein the clock frequency of the microcontroller is ascertained at least two different temperature values, and/or at least two different voltage values. Based on the ascertained values, the dependence of the clock frequency of the microcontroller on temperature over a predetermined temperature- and/or frequency range and/or the dependence of the clock frequency of the microcontroller on voltage over a predetermined voltage- and/or frequency range is ascertained. The ascertained values are stored, and the influence of temperature and/or voltage on the clock frequency of the microcontroller is at least approximately compensated taking into considering the ascertained temperature dependence and/or the ascertained voltage dependence.
1. A method for stabilizing the clock frequency of a microcontroller associated with a field device of automation technology, the field device as a function of application is exposed to different process conditions, comprising the steps of:
ascertaining a dependence of the clock frequency of the microcontroller on temperature over a predetermined temperature-range and a dependence of the clock frequency of the microcontroller on voltage over a predetermined voltage-range, wherein
a constant reference frequency is produced with a frequency generator, which is insulated from the microcontroller;
the reference frequency is fed to the microcontroller and the reference frequency is measured as a test frequency;
different temperature values of the microcontroller are measured at voltage held constant;
the test frequencies belonging to the different temperature values are ascertained;
the ascertained test frequency values are stored in dependency of the measured temperature value; and
the voltage dependence of the microcontroller is ascertained by supplying the microcontroller with different supply voltages;
storing the ascertained temperature dependence and voltage dependence of the clock frequency; and
compensating for an influence of temperature and/or voltage on a clock frequency of the microcontroller, taking into consideration the ascertained temperature dependence and the ascertained voltage dependence in such a way that the frequency is kept stable under varying temperatures and voltages.
2. The method as claimed in claim 1 , wherein:
the temperature dependence and voltage dependence of the clock frequency of the microcontroller are ascertained during manufacturing.
3. The method as claimed in claim 1 , wherein:
the ascertained temperature dependence and the ascertained voltage dependence of the clock frequency of the microcontroller, are stored in form a table, the table storing the measured clock frequencies as a function of the corresponding measured voltages and temperatures.
4. The method as claimed in claim 1 , wherein:
the ascertaining of the temperature dependence and the voltage dependence of the clock frequency of the microcontroller occurs by random sampling; and
the ascertained temperature dependence and the ascertained voltage dependence are used for stabilizing the clock frequency of a plurality of similar microcontrollers.
5. The method as claimed in claim 1 , wherein:
for determining the temperature of the microcontroller, the temperature of the chip, on which the microcontroller is arranged, is measured.
6. The method as claimed in claim 1 , wherein:
the microcontroller is clocked via a tunable digitally controlled oscillator.
7. The method as claimed in claim 1 , wherein:
the ascertained temperature dependence and the ascertained voltage dependence of the clock frequency of the microcontroller are stored in a memory by storing the ascertained temperature and voltage dependences as a matching function of the measured clock frequencies and the corresponding measured voltages and temperatures.
8. The method as claimed in claim 1 , wherein:
the ascertained temperature dependence and the ascertained voltage dependence of the clock frequency of the microcontroller are stored in a memory by storing the ascertained temperature and voltage dependences as a linear relationship of the measured clock frequencies and the corresponding measured voltages and temperatures.