Precise frequency generation for low duty cycle transceivers using a single crystal oscillator

• US 7,421,251 B2
• Filed: 03/31/2005
• Issued: 09/02/2008
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Westwick, Alan L., Holberg, Douglas R.
• Primary Examiner(s): Anderson; Matthew
• Assistant Examiner(s): Dao; Minh D
• Application Number:
  US11/095,229
• Publication Number:
  US 20060223454A1
• Time in Patent Office: 1,251 Days
• Field of Search: 455/85, 455/574, 455/86, 455/141, 455/146, 455/147, 455/196.1, 455/255, 343/16, 343/17
• US Class Current: 455/85
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation

Abstract

An apparatus and method for calibrating a non-crystal oscillator in a transceiver unit using a crystal-oscillator includes the step of establishing a time base based upon oscillations of the crystal oscillator. A comparison of the number of oscillations for the non-crystal oscillator and the crystal oscillator is made during a known time period is made. An adjustment is determined based upon the established time base and the compared number of oscillations. The transceiving of the transceiver unit is then controlled based upon this adjustment.

Claims

1. A method for calibrating a non-crystal oscillator in a transceiver unit using a crystal controlled oscillator, comprising the steps of:

establishing a time base based upon oscillations of the crystal controlled oscillator;

determining a number of oscillations of the crystal controlled oscillator during at least one period of the non-crystal oscillator;

calculating a frequency of the non-crystal oscillator based upon the determined number of oscillations;

changing the frequency of the non-crystal oscillator to approximately equal a target frequency responsive to the calculated frequency;

controlling operation of the transceiver unit responsive to the changed frequency of the non-crystal oscillator.

2. The method of claim 1, wherein the step of determining further comprises the step of determining a frequency for the non-crystal oscillator in the transceiver unit based upon the established time base and the compared number of oscillations.

3. The method of claim 1, wherein step of changing further comprises the step of altering a stepped capacitance within the transceiver unit to change the frequency.

4. The method of claim 1, farther including the step of detecting an occurrence of a triggering event to initiate the calibration process.

5. A transceiver unit, comprising:

a first oscillator circuit for providing a first clock signal;

a second oscillator circuit for providing a second clock signal;

a crystal associated with the second oscillator circuit for controlling the provision of the second clock signal;

a transceiver for transceiving data from the transceiving unit; and

a controller configured to;

establish a time base based upon oscillations of the crystal;

determine a number of oscillations of the crystal controlled oscillator during at least one period of the non-crystal oscillator;

calculate a frequency of the non-crystal oscillator based upon the determined number of oscillations;

change the frequency of the non-crystal oscillator to approximately equal a target frequency responsive to the calculated frequency;

control operation of the transceiver responsive to the changed frequency of the non-crystal oscillator.

6. The transceiver unit of claim 5, wherein the controller is further configured to determine a frequency for the first oscillator circuit in the transceiving unit based upon the established time base and the compared number of oscillations.

7. The transceiver unit of claim 6, further including:

a CDAC for changing the frequency of the first oscillator circuit to approximately equal a target frequency based upon an oscillator frequency of the crystal, the CDAC controlled by the adjustment determined by the controller.

8. The transceiver unit of claim 7, wherein the adjustment alters a total capacitance provided by the CDAC to change the frequency.

9. The transceiver unit of claim 5, wherein the controller is further configured to initiate the calibration process responsive to detecting an occurrence of a triggering event.

10. A method for calibrating a non-crystal oscillator in a transceiver unit using a crystal controlled oscillator, comprising the steps of:

establishing a time base based upon the oscillations of the crystal controlled oscillator;

counting a number of pulses of the crystal controlled oscillator during at least one period of the non-crystal oscillator;

determining an amount of time in a period of the non-crystal oscillator responsive to the counted number of pulses; and

controlling operation of the transceiver unit responsive to the non-crystal oscillator operating with the period having the determined period of time.

11. A method for calibrating a non-crystal oscillator in a transceiver unit using a crystal controlled oscillator, comprising the steps of:

establishing a time base based upon oscillations of the crystal controlled oscillator;

determining a number of oscillations of the crystal controlled oscillator during at least one period of the non-crystal oscillator;

calculating a frequency of the non-crystal oscillator based upon the determined number of oscillations;

changing the frequency of the non-crystal oscillator to approximately equal a target frequency responsive to the calculated frequency;

controlling operation of the transceiver unit responsive to the changed frequency of the non-crystal oscillator;

counting a number of pulses of the crystal controlled oscillator during at least one period of the non-crystal oscillator;

determining an amount of time in a period of the non-crystal oscillator responsive to the counted number of pulses; and

controlling operation of the transceiver unit responsive to the non-crystal oscillator operating with the period having the determined period of time.

12. The method of claim 11, wherein step of changing the frequency farther comprises the step of altering a stepped capacitance within the transceiver unit to change the frequency.

13. The method of claim 11, farther including the step of detecting an occurrence of a triggering event to initiate the calibration process.