Method and apparatus to provide digitally controlled crystal oscillators

• US 7,808,327 B2
• Filed: 08/07/2006
• Issued: 10/05/2010
• Est. Priority Date: 08/07/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Muhammad, Khurram, Lee, Meng-Chang, Hung, Chih-Ming, Feygin, Gennady
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US11/500,083
• Publication Number:
  US 20080042755A1
• Time in Patent Office: 1,520 Days
• Field of Search: 331/46, 331/47, 331/49, 331/74
• US Class Current: 331/46
• CPC Class Codes: H03L 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence
• CPC Class Codes: H03L 3/00 Starting of generators
• CPC Class Codes: H03L 7/0995 the oscillator comprising a ring oscillator
• CPC Class Codes: H03L 7/24 using a reference signal directly applied to the generator

Abstract

Methods and systems to provide digitally controlled crystal oscillators are disclosed. One example method includes determining a state of an oscillator system and selecting a first output of a digitally controlled crystal oscillator or a second output of a second oscillator based on the determination. In an example implementation, the second oscillator is a ring oscillator.

Claims

1. A system comprising:

a digitally controlled crystal oscillator;

a second oscillator, wherein the digitally controlled crystal oscillator is injection-locked to the second oscillator; and

a controller to selectively couple an output terminal to one of a first output of the digitally controlled crystal oscillator or a second output of the second oscillator, wherein a first switch couples an output of the second oscillator to the digitally controlled crystal oscillator, and a second switch couples an output of the digitally controlled crystal oscillator to the second oscillator.

2. A system as defined in claim 1, wherein the second oscillator is locked to the digitally controlled crystal oscillator.

3. A system as defined in claim 1, wherein the controller is a state machine.

4. A system as defined in claim 1, further comprising a multiplexer that receives the first output and the second output.

5. A system as defined in claim 4, wherein selecting between a first output associated with the digitally controlled crystal oscillator and a second output associated with the second oscillator comprises instructing the multiplexer to select one of the first output or the second output.

6. A system as defined in claim 1, wherein the digitally controlled crystal oscillator comprises:

an oscillator;

an adjustable reactive load coupled to the oscillator; and

a signal source.

7. A system as defined in claim 6, wherein the digitally controlled crystal oscillator further comprises a digitally controlled crystal oscillator controller to control the adjustable reactive load.

8. A system as defined in claim 1, wherein the second oscillator is at least one of a ring oscillator a phase-locked oscillator, or a frequency-locked oscillator.

9. A system as defined in claim 1, wherein the output of the second oscillator is injected into the digitally controlled crystal oscillator.

10. A method comprising:

determining a state of an oscillator system;

selecting a first output of a first oscillator or a second output of a digitally controlled crystal oscillator based on the determination;

the digitally controlled crystal oscillator is injection locked to the first oscillator;

opening or closing a first switch based on the determination; and

opening or closing a second switch different than the first switch based on the determination.

11. A method comprising:

determining a state of an oscillator system;

selecting a first output of a first oscillator or a second output of a digitally controlled crystal oscillator based on the determination;

the digitally controlled crystal oscillator is injection locked to the first oscillator;

opening or closing a first switch based on the determination; and

opening or closing a second switch different than the first switch based on the determination, wherein the second switch couples the second output to the first oscillator.

12. A non-transitory machine-accessible medium having a plurality of machine accessible instructions that, when executed, cause a machine to:

determine a state of an oscillator system;

select a first output of a first oscillator or a second output of a digitally controlled crystal oscillator based on the determination;

the digitally controlled crystal oscillator is injection locked to the first oscillator;

cause the machine to open or close a first switch based on the determination; and

open or close a second switch different than the first switch based on the determination.

13. A system comprising:

a digitally controlled crystal oscillator;

a second oscillator, wherein the digitally controlled crystal oscillator is injection-locked to the second oscillator;

a controller to select between a first output associated with the digitally controlled crystal oscillator and a second output associated with the second oscillator; and

a multiplexer that receives the first output and the second output, wherein a first switch couples an output of the second oscillator to the digitally controlled crystal oscillator, and a second switch couples an output of the digitally controlled crystal oscillator to the second oscillator.

14. A system as defined in claim 13, wherein selecting between a first output associated with the digitally controlled crystal oscillator and a second output associated with the second oscillator comprises instructing the multiplexer to select one of the first output or the second output.

15. A method comprising:

determining a state of an oscillator system;

selecting a first output of a first oscillator or a second output of a digitally controlled crystal oscillator injection-locked to the first oscillator based on the determination by causing a multiplexer to output the first output if the oscillator system is in a first state or to output the second output if the oscillator system is in a second state, wherein a first switch couples an output of the first oscillator to the digitally controlled crystal oscillator, and a second switch couples an output of the digitally controlled crystal oscillator to the first oscillator.

16. A method as defined in claim 15, wherein the first state is associated with initialization of the oscillator system.

17. A method as defined in claim 15, wherein the second state is associated with a post-initialization state.

18. A method as defined in claim 15, wherein the first state is associated with a frequency change of the digitally controlled crystal oscillator.

19. A non-transitory machine-accessible medium having a plurality of machine accessible instructions that, when executed, cause a machine to:

determine a state of an oscillator system;

select a first output of a first oscillator or a second output of a digitally controlled crystal oscillator injection-locked to the first oscillator based on the determination by causing a multiplexer to output the first output if the oscillator system is in a first state or output the second output if the oscillator system is in a second state, wherein a first switch couples an output of the first oscillator to the digitally controlled crystal oscillator, and a second switch couples an output of the digitally controlled crystal oscillator to the first oscillator.

20. A non-transitory machine-accessible medium as defined by claim 19, wherein the first state is associated with initialization of the oscillator system.

21. A non-transitory machine-accessible medium as defined by claim 19, wherein the second state is associated with a post-initialization state.

22. A method comprising:

determining a state of an oscillator system;

selecting a first output of a first oscillator or a second output of a digitally controlled crystal oscillator based on the determination;

opening or closing a first switch based on the determination, wherein the first switch causes the digitally controlled crystal oscillator to be injection-locked to the first oscillator opening and closing a second switch based on the determination, wherein the second switch couples an output of the digitally controlled crystal oscillator to the first oscillator.

23. A non-transitory machine-accessible medium having a plurality of machine accessible instructions that, when executed, cause a machine to:

determine a state of an oscillator system;

select a first output of a first oscillator or a second output of a digitally controlled crystal oscillator based on the determination;

cause the machine to open or close a first switch based on the determination, wherein the first switch causes the digitally controlled crystal oscillator to be injection-locked to the first oscillator and further cause the machine to open or close a second switch based on the determination, wherein the second switch couples the output of the digitally controlled crystal oscillator to the first oscillator.