Clock synchronization between wireless devices during cradled time

• US 6,587,694 B1
• Filed: 09/24/1999
• Issued: 07/01/2003
• Est. Priority Date: 09/24/1999
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Wu, Jian, Mooney, Philip D., McDowell, Richard L., Grundvig, Jeffrey P.
• Primary Examiner(s): Le, Thanh Cong
• Assistant Examiner(s): Corsaro, Nick
• Application Number:
  US09/404,807
• Time in Patent Office: 1,376 Days
• Field of Search: 455/502, 455/572, 455/41, 455/462, 455/573, 370/350, 375/354, 375/355, 375/357
• US Class Current: 455/502
• CPC Class Codes: H04M 1/72502 with one base station connected to a single line

Abstract

Clocks between at least two wireless devices are synchronized to reduce the need to transmit synchronization signals over a wireless communication channel therebetween. Two wireless devices synchronize their respective clocks with each other when each are electrically coupled, e.g., during a cradle time when brought into physical contact with each other through charge contacts, e.g., to recharge a remote portable unit. The charge signal appearing at the charge contacts is driven to create a time duration marked by a start transition and an end transition in the charge signal. The number of clock pulses of each of the two wireless devices during the time duration is counted, and compared to determine the difference in clock speeds of the wireless devices. The frequency of the clock of at least one of the wireless devices is adjusted to bring the difference in the clock speeds within a predetermined threshold tolerance level.

Claims

1. A method of synchronizing a clock of a first wireless device with a clock of a second wireless device, comprising:

electrically coupling said first wireless device to said second wireless device;

providing a start transition and an end transition in a charge signal to indicate a start of said time period and an end of said time period, respectively, said charge signal being provided by said second wireless device to charge a power source of said first wireless device while said first wireless device is electrically coupled to said second wireless device;

counting pulses of said clock of said first wireless device and pulses of said clock of said second wireless device during a time period indicated by said start transition and said end transition; and

adjusting a frequency of one of said clock of said first wireless device and said clock of said second wireless device based on said counted pulses of said clock of said first wireless device and said counted pulses of said clock of said second wireless device.

2. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 1, further comprising:

comparing said counted pulses of at least one of said clock of said first wireless device and said second wireless device to an expected number of clock pulses to determine an amount of said adjustment.

3. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 1, wherein said step of adjusting said frequency of said clock of said wireless device comprises:

adjusting said frequency of said clock of said first wireless device to provide said counted pulses of said clock of said first wireless device to be within a predetermined threshold difference level of said counted pulses of said second wireless device.

4. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 1, wherein said step of counting clock pulses comprises:

starting a counter to count said pulses of said first wireless device upon detection of said start transition;

stopping said counter upon detection of said end transition; and

providing an output of said counter as said counted pulses of said clock of said first wireless device.

5. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 1, wherein:

said start transition and said end transition are each marked by a high to low transition in said charge signal.

6. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 1, wherein said time period comprises:

a first duration; and

a second duration.

7. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 6, wherein:

said charge signal is low during said first duration, and said charge signal is high during said second duration.

8. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 7, wherein:

said first duration and said second duration have substantially equal length.

9. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 7, wherein:

said first duration is shorter than said second duration.

10. The method of synchronizing a clock of a first wireless device with a clock of a second wireless device in accordance with claim 3, wherein:

said predetermined threshold difference level is substantially zero.

11. A system for synchronizing a clock of a first wireless device with a clock of a second wireless device, comprising:

means for electrically coupling said first wireless device to said second wireless device;

means for counting pulses of said clock of said first wireless device and pluses of said clock of said second wireless device, said means for counting pulses counts said pulses of said clock of said first wireless device and said pluses of said clock of said second wireless device during a time period, a start of said time period and an end of said time period being indicated by a start transition and an end transition in a charge signal, respectively, said charge signal being provided by said second wireless device to charge a power source of said first wireless device while said first wireless device is electrically coupled to said second wireless device; and

means for adjusting a frequency of one of said clock of said first wireless device and said clock of said second wireless device based on said counted pulses of said clock of said first wireless device and said counted pulses of said clock of said second wireless device.

12. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 11, further comprising:

means for comparing said counted pulses of said clock of said first wireless device to an expected number of clock pulses to determine an amount of said adjustment.

13. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 12, wherein said means for adjusting said frequency of said clock of said first wireless device comprises:

means for adjusting said frequency of said clock of said first wireless device to provide said counted pulses of said clock of said first wireless device to be within a predetermined threshold difference level of said counted pulses of said second wireless device.

14. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 11, wherein said means for counting clock pulses comprises:

means for starting a counter to count said pulses of said first wireless device upon detection of said start transition;

means for stopping said counter upon detection of said end transition; and

means for providing an output of said counter as said counted pulses of said clock of said first wireless device.

15. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 11, wherein:

said start transition and said end transition are each marked by a high to low transition in said charge signal.

16. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 11, wherein said time period comprises:

a first duration; and

a second duration.

17. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 16, wherein:

said charge signal is low during said first duration, and said charge signal is high during said second duration.

18. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 16, wherein:

said first duration and said second duration have substantially equal length.

19. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 17, wherein:

said first duration is shorter than said second duration.

20. The system for synchronizing a clock of a first wireless device with a clock of a second wireless device according to claim 13, wherein:

said predetermined threshold difference level is substantially zero.

21. A wireless device, comprising:

a wireless base unit having a base clock;

at least one remote wireless handset having a handset clock and a rechargeable power source, said remote wireless handset being adapted to receive a charge signal from said wireless base unit when cradled in contact with said wireless base unit to charge said rechargeable power source; and

a control unit adapted to cause an adjustment of a frequency of at least one of said handset clock and said base clock when said frequency of said handset clock measured during a time period indicated by a measurement signal in said charge signal differs from an expected frequency by more than a predetermined threshold difference level.

22. The wireless device according to claim 21, further comprising:

a counter to count pulses of at least one of said handset clock and said base clock during said time period, said time period being marked by a start transition and an end transition in said charge signal.

23. The wireless device according to claim 22, wherein:

said control unit is adapted to compare said counted pulses of at least one of said handset clock and said base clock to an expected number of clock pulses to determine an amount of said adjustment.

24. The wireless device according to claim 23, wherein:

said expected number of clock pulses corresponds to a number of pulses of said base clock during said time period.

25. The wireless device according to claim 23, wherein:

said expected number of clock pulses corresponds to a number of pulses of said handset clock during said time period.

26. The wireless device according to claim 23, wherein:

said control unit is adapted to adjust said frequency of at least one of said handset clock and said base clock to provide said counted pulses of at least one of said handset clock and said base clock to be within a predetermined threshold difference level of said expected number of clock pulses.

27. The wireless device according to claim 26, wherein:

said predetermined threshold difference level is substantially zero.

28. The wireless device according to claim 21, wherein:

said wireless device is a cordless telephone.

29. The wireless device according to claim 21, wherein said time period comprises:

a first duration; and

a second duration.

30. The wireless device according to claim 29, wherein:

said charge signal is inactive during said first duration, and wherein said charge signal is active during said second duration.

31. The wireless device according to claim 29, wherein:

said first duration and said second duration have substantially equal length.

32. The wireless device according to claim 30, wherein:

said first duration is shorter than said second duration.