Control circuit and control method of communication device

1. A control circuit of a communication device, comprising:

a periodic packet detection circuit, detecting a periodic packet of a data signal to generate a packet indication signal corresponding to the periodic packet;

a frequency synthesis circuit, coupled to the periodic packet detection circuit, generating a working clock according to a reference clock; and

a setting value generating circuit, coupled to the periodic packet detection circuit and the frequency synthesis circuit, generating a setting value according to a relationship between frequencies of the working clock and the packet indication signal;

wherein, the frequency synthesis circuit further adjusts the working clock according to the setting value, such that the frequency of the working clock is substantially a predetermined multiple of the frequency of the packet indication signal.

2. The control circuit according to claim 1 , wherein the frequency of the packet indication signal is a frequency at which the periodic packet occurs in the data signal.

3. The control circuit according to claim 1 , wherein the setting value generating circuit comprises:

a counter, coupled to the periodic packet detection circuit and the frequency synthesis circuit, generating a counter value according to the packet indication signal and the working clock; and

a decision circuit, coupled to the counter, generating the setting value according to the counter value and the predetermined multiple.

4. The control circuit according to claim 1 , further comprising:

a candidate value generating circuit, selecting one of a plurality of candidate values;

wherein, the frequency synthesis circuit generates a candidate clock according to the selected candidate value, and the periodic packet detection circuit detects the periodic packet according to the candidate clock.

5. The control circuit according to claim 4 , further comprising:

a determination circuit, coupled to the periodic packet detection circuit and the candidate value generating circuit, determining an initial value from the candidate values according to the packet indication signal;

wherein, the frequency synthesis circuit generates the working clock according to the initial value and the reference clock.

6. The control circuit according to claim 1 , further comprising:

a frequency offset detection circuit, coupled to the setting value generating circuit, detecting a value of a frequency offset of the working clock to determine whether to instruct the setting value generating circuit to update the setting value.

7. The control circuit according to claim 6 , wherein while the frequency offset detection circuit detects the value of the frequency offset of the working clock, the setting value generating circuit suspends generating the setting value; while the setting value generating circuit generates the setting value, the frequency offset detection circuit suspends detecting the value of the frequency offset of the working clock.

8. The control circuit according to claim 1 , applied to a USB device, wherein the periodic packet detection detects a start of frame (SOF) packet of the data signal to generate the packet indication signal.

9. A control method of a communication device, comprising:

detecting a periodic packet of a data signal to generate a packet indication signal corresponding to the periodic packet;

generating a working clock according to a reference clock; and

adjusting the working clock according to a relationship between frequencies of the working clock and the packet indication signal, such that the frequency of the working clock is substantially a predetermined multiple of the frequency of the packet indication signal.

10. The control method according to claim 9 , wherein the frequency of the packet indication signal is a frequency at which the periodic packet occurs in the data signal.

11. The control method according to claim 9 , wherein the step of adjusting the working clock according to the relationship between the frequencies of the working clock and the packet indication signal comprises:

generating a counter value according to the packet indication signal and the working clock;

generating a setting value according to the counter value and the predetermined multiple; and

adjusting the working clock according to the setting value.

12. The control method according to claim 9 , further comprising:

selecting one of a plurality of candidate values, and generating a candidate clock according to the selected candidate value and the reference clock;

wherein, the step of detecting the periodic packet of the data signal is performed according to the candidate clock.

13. The control method according to claim 12 , further comprising:

determining an initial value from the candidate values according to the packet indication signal;

wherein, the working clock is generated according to the initial value and the reference clock.

14. The control method according to claim 9 , further comprising:

detecting a value of a frequency offset of the working clock to determine whether to again adjust the working clock.

15. The control method according to claim 9 , further comprising:

suspending generating the setting value while the value of the frequency offset of the working clock is detected; and

suspending detecting the value of the frequency offset of the working clock while the setting value is generated.

16. The control method according to claim 9 , applied to a USB device, wherein the step of detecting the periodic packet of the data signal detects a start of frame (SOF) packet of the data signal.