Portable radio terminal and AFC control method

1. A portable radio terminal for realizing automatic frequency control (AFC) for automatically controlling an oscillation frequency of an oscillator, comprising:

means for intermittently performing AFC operation; and

means for shortening an AFC operation stop period when a frequency shift of the oscillation frequency is greater than a first threshold value;

means for lengthening the AFC operation stop period when the frequency shift of the oscillation frequency is less than a second threshold value; and

means for maintaining the AFC operation stop period at a current value when the frequency shift of the oscillation frequency is a value that is less than the first threshold value and greater than the second threshold value,

wherein the first threshold value is greater than the second threshold value.

2. A terminal according to claim 1 , wherein the intermittent operation includes not only the AFC operation but also operation stop of said portable radio terminal.

3. A terminal according to claim 1 , wherein the AFC operation stop period is lengthened by doubling a current AFC operation stop period to thereby obtain a longer AFC operation stop period to be used in a next cycle.

4. A terminal according to claim 1 , wherein the AFC operation stop period is shortened by halving a current AFC operation stop period to thereby obtain a shorter AFC operation stop period to be used in a next cycle.

5. A terminal according to claim 4 , wherein the AFC operation stop period is shortened by halving a current AFC operation stop period to thereby obtain a shorter AFC operation stop period to be used in a next cycle.

6. A terminal according to claim 1 , further comprising:

means for determining whether a power value (RSSI) of a signal received by the terminal is less than a predetermined value,

wherein, when the RSSI is determined to be less than the predetermined value, the AFC operation stop period is set to a minimum value.

7. An AFC control method of realizing automatic frequency control (AFC) for automatically controlling an oscillation frequency of an oscillator, comprising:

intermittently performing AFC operation,

wherein, when a frequency shift of the oscillation frequency is greater than a first threshold value, shortening an AFC operation stop period,

wherein, when the frequency shift of the oscillation frequency is less than a second threshold value, lengthening the AFC operation stop period, and

wherein, when the oscillation frequency is a value that is less than the first threshold value and greater than the second threshold value, the AFC operation stop period is maintained at a current value,

wherein the first threshold value is greater than the second threshold value.

8. A method according to claim 7 , wherein the intermittent operation includes not only the AFC operation but also operation stop of a portable radio terminal.

9. A method according to claim 7 , wherein the AFC operation is performed at a predetermined short period when decoding fails, no pilot signal is detected, or a step-out state is detected.

10. A method according to claim 7 , wherein the AFC operation stop period is lengthened by doubling a current AFC operation stop period to thereby obtain a longer AFC operation stop period to be used in a next cycle.

11. A method according to claim 10 , wherein the AFC operation stop period is shortened by halving a current AFC operation stop period to thereby obtain a shorter AFC operation stop period to be used in a next cycle.

12. A method according to claim 7 , wherein the AFC operation stop period is shortened by halving a current AFC operation stop period to thereby obtain a shorter AFC operation stop period to be used in a next cycle.

13. A method according to claim 7 , further comprising:

determining whether a power value (RSSI) of a signal received by the terminal is less than a predetermined value,

wherein, when the RSSI is determined to be less than the predetermined value, the AFC operation stop period is set to a minimum value.