Clock adjustment for a handheld audio system

• US 20070242780A1
• Filed: 04/18/2006
• Published: 10/18/2007
• Est. Priority Date: 04/18/2006
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Sigmatel LLC (NXP Semiconductors NV)
• Inventors: Ragan, Lawrence, May, Michael
• Granted Patent: US 7,724,843 B2
• Time in Patent Office: Days
• US Class Current: 375/340
• CPC Class Codes: G11B 31/003 with radio receiver
• CPC Class Codes: H04B 1/0007 wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
• CPC Class Codes: H04B 1/1653 Detection of the presence of stereo signals and pilot signal regeneration
• CPC Class Codes: H04B 1/28 the receiver comprising at least one semiconductor device having three or more electrodes
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 27/14 Demodulator circuits; Receiver circuits

Abstract

A handheld audio system having a radio signal decoder that includes a method for adjusting a system clock. Adjusting the system clock includes receiving a signal at a rate of a receive clock, wherein the signal includes data at a transmit rate. An error term is determined between the receive rate and the transmit rate. Based on the receive clock and the error term, where the error term is non-zero, a clock signal is generated.

Claims

1. A method for adjusting a system clock comprises:

receiving a signal at a receive rate corresponding to a receive clock, wherein the signal includes data at a transmit rate;

determining an error term between the receive rate and the transmit rate; and

generating a clock signal based on the receive clock and the error term, wherein the error term is non-zero.

2. The method of claim 1 wherein the generating a clock signal comprises:

determining a fractional error of the receive clock based upon the error term; and

adjusting the clock signal based on the receive clock and the fractional error.

3. The method of claim 1 wherein determining the error term comprises:

recovering a pilot tone from the signal;

generating a simulated pilot tone based on the receive clock;

mixing the simulated pilot tone with the recovered pilot tone to produce a mixed signal;

producing a difference between the simulated pilot tone and the recovered pilot tone based on the mixed signal; and

producing the error term based on the difference.

4. The method of claim 3 wherein generating a clock signal comprises:

tuning a variable capacitor of an oscillator module, wherein the oscillator module produces the receive clock.

5. The method of claim 1 wherein the signal comprises a frequency modulated (“

FM”

) radio signal, which includes an embedded pilot tone that corresponds to the transmit rate.

6. A method for adjusting a receive clock comprises:

receiving a signal at a rate of the receive clock, wherein the signal includes data at a transmit rate;

determining an error term between the rate of the receive clock and the transmit rate;

determining whether the error term is within an error tolerance; and

when the error term is not within the error tolerance,

adjusting the rate of the receive clock based on the error term to produce an adjusted receive clock rate, wherein the error tolerance is substantially non-zero.

7. The method of claim 6 wherein the determining whether the error term is within the error tolerance in response to a state change.

8. The method of claim 7 wherein the state change comprises at least one of:

initializing the receive clock; and

adjusting the receiver clock to tune to a channel of the received signal.

9. The method of claim 6 wherein adjusting the rate of the receive clock comprises:

tuning a variable capacitor of an oscillator module, wherein the oscillator module produces the receive clock.

10. The method of claim 6 wherein determining the error term comprises:

recovering a pilot tone from the signal;

generating a simulated pilot tone based on the receive clock;

mixing the simulated pilot tone with the recovered pilot tone to produce a mixed signal;

producing a difference of the simulated pilot tone and the recovered pilot tone based on the mixed signal; and

producing the error term based on the difference.

11. The method of claim 6 wherein the signal comprises a frequency modulated (“

FM”

) radio signal, which includes an embedded pilot tone that corresponds to the transmit rate.

12. A radio signal decoder comprises:

a front-end module operably coupled to, when enabled, convert a received radio signal into digital data in accordance with a rate of a receive clock, wherein the received radio signal includes data at a transmit rate; and

a baseband processing module operably coupled to process the digital data and to produce therefrom output digital data, wherein the baseband processing module includes;

a processing module; and

memory operably coupled to the processing module, wherein the memory stores operational instructions that cause the processing module to;

determine an error term between the rate of the receive clock and the transmit rate;

determine whether the error term is within an error tolerance; and

when the error term is not within the error tolerance,

adjust the rate of the receive clock based on the error term to produce an adjusted receive clock rate.

13. The radio signal decoder of claim 12 wherein the memory further stores operational instructions that cause the processing module to adjust the rate of the receive clock by:

tuning a variable capacitor of an oscillator module, wherein the oscillator module produces the rate of the receive clock.

14. The radio signal decoder of claim 12 wherein the memory further stores operational instructions that cause the processing module to determine the error term by:

recovering a pilot tone from the received signal;

generating a simulated pilot tone based on the receive clock;

mixing the simulated pilot tone with the recovered pilot tone to produce a mixed signal;

producing a difference of the simulated pilot tone and the recovered pilot tone based on the mixed signal; and

producing the error term based on the difference.

15. The radio signal decoder of claim 12 wherein the signal comprises a frequency modulated (“

FM”

) radio signal, which includes an embedded pilot tone that corresponds to the transmit rate.

16. A radio signal decoder comprises:

a front-end module operably coupled to, when enabled, convert a received radio signal into digital data in accordance with a rate of a receive clock, wherein the received radio signal includes data at a transmit rate; and

a baseband processing module operably coupled to process the digital data and to produce therefrom output digital data, wherein the baseband processing module includes;

a processing module; and

memory operably coupled to the processing module, wherein the memory stores operational instructions that cause the processing module to;

determine an error term between the receive rate and the transmit rate; and

generate a clock signal based on the receive clock and the error term, wherein the error term is non-zero.

17. The radio signal decoder of claim 16, wherein the memory further stores operational instructions that cause the processing module to generate the clock signal by:

tuning a variable capacitor of an oscillator module, wherein the oscillator module produces the receive clock.

18. The radio signal decoder of claim 16, wherein the memory further stores operational instructions that cause the processing module to generate the clock signal by:

determining a fractional error of the receive clock based upon the error term; and

adjusting the clock signal based on the receive clock and the fractional error.

19. The radio signal decoder of claim 16 wherein the memory further stores operational instructions that cause the processing module to determine the error term by:

recovering a pilot tone from the signal;

generating a simulated pilot tone based on the receive clock;

mixing the simulated pilot tone with the recovered pilot tone to produce a mixed signal;

producing a difference between the simulated pilot tone and the recovered pilot tone based on the mixed signal; and

producing the error term based on the difference.

20. The radio signal decoder of claim 16 wherein the signal comprises a frequency modulated (“

FM”

) radio signal, which includes an embedded pilot tone that corresponds to the transmit rate.

21. A method for correcting a local time base of a handheld media device comprises:

searching for a continuous-time radio signal that includes a suitable timing reference; and

when the continuous-time radio signal is located,

receiving the continuous-time radio signal from the RF front end;

extracting timing information from the continuous-time radio signal; and

correcting the local time base with the timing information.

22. The method of claim 21 wherein the searching for the continuous-time radio signal comprises searching for the continuous-time radio signal upon a priori knowledge of the continuous-time radio signal.

23. The method of claim 21 wherein the search for the continuous-time radio signal comprises:

scanning a RF band for the continuous-time radio signal.

24. The method of claim 21 wherein correcting the local time base comprises:

adjusting a crystal that generates the local time base.

25. The method of claim 21 wherein the local time base comprises a clock adjust module, wherein correcting the local time base includes:

producing an adjusted clock reference with the clock adjust module.

26. The method of claim 21 wherein the continuous-time signal comprises a frequency modulated signal, which includes an embedded pilot tone for the suitable timing reference.