Method and apparatus for calibration of a low frequency oscillator in a processor based system

• US 7,250,825 B2
• Filed: 06/10/2004
• Issued: 07/31/2007
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Labs CP, Inc. (Silicon Laboratories Incorporated)
• Inventors: Wilson, Brent, Fernald, Kenneth W., Highley, Paul
• Primary Examiner(s): Pascal; Robert
• Assistant Examiner(s): GOODLEY, JAMES E
• Application Number:
  US10/865,110
• Publication Number:
  US 20050270108A1
• Time in Patent Office: 1,146 Days
• Field of Search: 331/44, 331/74, 331/175
• US Class Current: 331/44
• CPC Class Codes: H03L 1/02 against variations of temperature only
• CPC Class Codes: H03L 7/08 Details of the phase-locked loop

Abstract

Method and apparatus for calibration of a low frequency oscillator in a processor based system. A method for calibrating an on-chip non-precision oscillator. An on-chip precision oscillator is provided having a known frequency of operation that is within an acceptable operating tolerance. The on-chip precision oscillator is used as a time base and then the period of the on-chip oscillator is measured as a function of the time base. The difference between the measured frequency of the on-chip non-precision oscillator and a desired operating frequency of the on-chip non-precision oscillator is then determined. After the difference is determined, the frequency of the on-chip non-precision oscillator is adjusted to minimize the determined difference.

Claims

1. A method for calibrating an on-chip non-precision oscillator, comprising the steps of:

providing an on-chip precision oscillator having a known frequency of operation that is within an acceptable operating tolerance;

using the on-chip precision oscillator as a time base;

measuring the period of the on-chip non-precision oscillator as a function of the time base;

determining from the measured period relative to the frequency of the on-chip precision oscillator the frequency of the non-precision oscillator;

determining the difference between the determined frequency of the on-chip non-precision oscillator and a desired operating frequency of the on-chip non-precision oscillator;

adjusting the frequency of the on-chip non-precision oscillator via a control input to said non-precision oscillator to minimize the determined difference; and

when minimized, fixing the frequency of the non-precision oscillator to operate independent of the on-chip precision oscillator.

2. The method of claim 1, wherein the on-chip non-precision oscillator normally operates in an operating mode and the steps of measuring, determining and adjusting are carried out in a calibration mode different from the operating mode and further comprising the step of changing from the operating mode to the calibration mode in response to generation of a calibration signal.

3. The method of claim 2, wherein the on-chip precision oscillator is disabled when the on-chip non-precision oscillator is in the operating mode and is enabled when the operational mode is changed to the calibration mode.

4. The method of claim 2, wherein the on-chip non-precision oscillator operates in conjunction with a processing circuit and provides the time base therefor.

5. The method of claim 4, wherein the processing circuit operates in a first mode with the non-precision on-chip-oscillator providing the time base therefor when the on-chip non-precision oscillator is in the operating mode therefor, and the processing circuits in a second mode with the precision on-chip oscillator providing the time base therefor.

6. The method of claim 5, wherein the on-chip precision oscillator is disabled when the on-chip non-precision oscillator is in the operating mode and is enabled when the operational mode is changed to the calibration mode.

7. The method of claim 5, wherein the non-precision on-chip oscillator has a lower frequency than the precision on-chip oscillator.