PRODUCING A DESIRED FREQUENCY USING A CONTROLLED OSCILLATOR WITH KNOWN TEMPERATURE SENSITIVITY

• US 20110187462A1
• Filed: 05/05/2010
• Published: 08/04/2011
• Est. Priority Date: 02/01/2010
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Sonntag, Jeffrey L.
• Granted Patent: US 8,975,970 B2
• Time in Patent Office: Days
• US Class Current: 331/34
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop

Abstract

A controlled oscillator is tuned to produce a desired, temperature independent frequency. A first frequency ratio is determined between a first frequency of the output signal generated by the controlled oscillator and a frequency of an output signal from another oscillator. The first frequency is determined based on a sensed temperature. A desired frequency of the output signal of the controlled oscillator is used to determine a desired frequency ratio between the desired frequency and the frequency of the output signal from the other oscillator. The controlled oscillator is tuned and the frequency ratio measured until the tuning has caused the desired frequency ratio to be achieved, thereby causing the controlled oscillator to provide the desired frequency.

Claims

1. A method of producing an output signal having a desired frequency from a controlled oscillator comprising:

determining a first frequency ratio between a first frequency of the output signal generated by the controlled oscillator and a second frequency of another output signal from another oscillator;

determining a desired frequency ratio between the desired frequency of the output signal generated by the controlled oscillator and the second frequency of the other output signal from the other oscillator; and

tuning the controlled oscillator to substantially achieve the desired frequency ratio and thereby produce the output signal having the desired frequency.

2. The method as recited in claim 1 further comprising determining the first frequency ratio in a frequency ratio measuring circuit.

3. The method as recited in claim 2 further comprising after determining the first frequency ratio, determining one or more additional frequency ratios in the frequency ratio measuring circuit responsive to the tuning of the controlled oscillator, until the desired frequency ratio is substantially reached.

4. The method as recited in claim 3 wherein determining the one or more additional frequency ratios further comprises adjusting tuning controls of the controlled oscillator.

5. The method as recited in claim 4 wherein adjusting the tuning controls of the controlled oscillator comprises employing a search algorithm to determine tuning control values.

6. The method as recited in claim 2 further comprising:

after determining the first frequency ratio, determining one or more additional frequency ratios in the frequency ratio measuring circuit using a first measurement interval; and

after measuring the one or more additional ratios, using a second measurement interval longer than the first, to determine at least one additional frequency ratio.

7. The method as recited in claim 2 further comprising specifying a time period over which the first frequency ratio is determined.

8. The method as recited in claim 2 wherein measuring the first frequency ratio comprises:

counting a predetermined value in a first counter clocked using the other output signal from the other oscillator; and

counting in a second counter clocked using the output signal from the controlled oscillator and stopping counting when the predetermined value has been counted by the first counter, a value in the second counter upon stopping corresponding to the first ratio.

9. The method as recited in claim 8 wherein the predetermined value is fixed.

10. The method as recited in claim 1 further comprising:

after achieving the desired frequency ratio, adjusting tuning of the controlled oscillator in response to a temperature change.

11. The method as recited claim 1 further comprising determining the first frequency of the output signal generated by the controlled oscillator.

12. The method as recited claim 11 wherein determining the first frequency further comprises measuring a temperature associated with the controlled oscillator and using the measured temperature to calculate to the first frequency.

13. The method as recited in claim 1 wherein the desired frequency ratio (R_desired) can be calculated as R_desired=R_{predetermined}×

F<sub>out—

desired</sub>/F<sub>out—

predetermined</sub>, wherein R_{predetermined} is the first frequency ratio and F<sub>out—

predetermined</sub> is the first frequency and F<sub>out—

desired</sub> is the desired frequency.

14. An apparatus comprising:

a controlled oscillator coupled to supply a controlled oscillator output signal;

a second oscillator coupled to supply a second oscillator output signal;

a frequency ratio measurement circuit coupled to receive the controlled oscillator output signal and the second oscillator output signal, and to generate and to supply an indication of a frequency ratio between the controlled oscillator output signal and the second oscillator output signal; and

a control circuit coupled to receive the indication of the frequency ratio and to adjust tuning of the controlled oscillator according to the ratio indication.

15. The apparatus as recited in claim 14 further comprising a temperature sensor coupled to supply a temperature measurement to the control circuit.

16. The apparatus as recited in claim 14 wherein the frequency ratio measurement circuit further comprises:

a first counter coupled to count the controlled oscillator output signal; and

a second counter coupled to count the second oscillator output signal;

wherein the first counter is configured to begin counting when the second counter begins counting and to stop counting when the second counter has counted a predetermined value.

17. The apparatus as recited in claim 16 wherein after the first counter stops counting, a count value in the first counter corresponds to the indication of the frequency ratio.

18. The apparatus as recited in claim 14 further configured to:

determine a predetermined ratio between a first frequency of the controllable oscillator output signal and the frequency of the second oscillator output signal,

wherein the control circuit is responsive to adjust tuning of the controlled oscillator responsive to a desired ratio, the desired ratio being a ratio between a desired frequency of the controllable oscillator output signal and the frequency of the second oscillator output signal.

19. The apparatus as recited in claim 18 wherein the control circuit is responsive to the desired frequency ratio to adjust tuning of the controlled oscillator, evaluate each measured frequency ratio, until the measured frequency ratio is substantially the desired ratio.

20. The apparatus as recited in claim 18 wherein the control circuit is configured to employ a search algorithm to adjust tuning of the controlled oscillator, until the measured frequency ratio is substantially the same as the desired ratio.

21. The apparatus as recited in claim 14 wherein the control circuit controls a duration during which each measured frequency ratio is determined.

22. The apparatus as recited in claim 14 wherein the control circuit controls the duration during which the frequency ratio is determined to be different during different frequency ratio measurements.

23. A computer program stored on computer readable storage media, operable when executed on a processor:

to determine a first frequency of a controlled oscillator output signal according to a measured temperature;

responsive to a first frequency ratio between the first frequency of controlled oscillator output signal and a frequency of a second oscillator output signal from a second oscillator, to determine a desired frequency ratio according to a desired frequency of the controlled oscillator output signal and the frequency of the second oscillator output signal; and

to iteratively provide control values to tune the controller oscillator output signal until a measured frequency ratio is substantially equal to the desired frequency ratio.

24. The computer program stored as recited in claim 23 wherein the desired frequency ratio (R_desired) is