Apparatus and method for preventing beat interference

• US 6,345,175 B1
• Filed: 09/05/1996
• Issued: 02/05/2002
• Est. Priority Date: 09/07/1995
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Murakami, Yoshihiro
• Primary Examiner(s): Chang, Vivian
• Assistant Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US08/708,326
• Time in Patent Office: 1,979 Days
• Field of Search: 455/296, 455/310, 455/255, 455/257-258, 455/260, 455/265, 455/317, 455/318, 331/1.A, 331/37, 331/40, 331/42, 331/64, 331/158, 331/116.R, 375/373, 375/376
• US Class Current: 455/296
• CPC Class Codes: H04B 15/06 by local oscillators of receivers

Abstract

Interference in a receiver caused by a beat frequency arising from mutual interference of local oscillation signals from other, proximately located receivers is prevented by changing over between an externally supplied clock signal and internal clock signal. The selected clock signal is used as the local oscillation signal of the receiver, thereby removing a difference between the mutually interfering local oscillation signals and preventing the beat interference from arising.

Claims

1. An apparatus for reconstructing an audio signal from a transmitted radio signal, comprising:

means for receiving the transmitted radio signal;

internal clock signal generating means and including a local oscillator for generating a local clock signal for internally providing timing for reconstructing said audio signal from the received radio signal;

detecting means for detecting whether the received radio signal includes an external clock signal for providing timing for reconstructing said audio signal from said radio signal;

selecting means for selecting as said local oscillation signal used to reconstruct the audio signal said external clock signal when said detecting means detects said external clock signal and for selecting as said local oscillation signal said local clock signal when said external clock signal is not detected; and

means for stopping all of the internal clock signal generating means included within the respective apparatus which do not receive an input clock signal so as to inhibit the generation of the respective local clock signals from within the respective apparatus when said detecting means detects said external clock signal.

2. A receiver for receiving and converting a radio signal transmitted at a radio signal frequency into an audio signal suitable for audio reproduction by mixing said radio signal with a local oscillation signal, wherein said receiver is subject to beat frequency interference which manifests in the reconstructed audio signal as an audible beat caused by erroneous pick-up of another local oscillation signal from another receiver substantially tuned to receive the same said radio signal, comprising:

means for receiving the transmitted radio signal;

internal clock means for generating an internal clock signal for providing timing for reconstructing said audio signal from the received radio signal;

external clock detecting means for detecting whether the received radio signal includes an external clock signal for providing timing for reconstructing said audio signal from said radio signal;

selecting means, responsive to said external clock detecting means, for selecting as said local oscillation signal said external clock signal when said external clock detecting means detects said external clock signal and for selecting as said local oscillation signal said internal clock signal when said external clock signal is not detected; and

means for stopping all of the internal clock means included within the respective receiver which do not receive an input clock signal so as to inhibit the generation of the respective internal clock signals from within the respective receiver when said external clock signal is detected by said detecting means;

wherein both said receiver and said another receiver select said external clock signal as said local oscillation signal with the same said frequency such that said beat frequency interference is suppressed.

3. The receiver according to claim 2, wherein said selecting means comprise switch change-over means for switching between said external clock signal when detected by said detecting means and said internal clock signal when said external clock is not detected.

4. The receiver according claim 2, wherein said receiver includes processor means for processing said radio signal;

and reset means for generating a reset signal for resetting said processor means when said selecting means selects between said external clock signal and said internal clock signal, thereby preventing a disturbance in said processing of said radio signal caused by a transition from said external clock signal to said internal clock signal.

5. The receiver of claim 2, further comprising phase locked loop means coupled to receive said local oscillation signal for generating an oscillating signal phase locked to said local oscillation signal.

6. The receiver according to claim 2, further comprising mixing means for mixing said radio signal with said local oscillation signal to produce therefrom an intermediate frequency signal.

7. The receiver according to claim 6, further comprising an intermediate frequency amplifier for amplifying said intermediate frequency signal.

8. A receiver system having a plurality of proximately situated local receivers for receiving a common radio signal, such that interference signals erroneously transmitted by a local receiver are received by at least one other of said local receivers, and for converting said common radio signal into an audio signal suitable for audio reproduction by frequency mixing said radio signal with a local oscillation signal, wherein each local receiver is subject to beat frequency interference which manifests in the reconstructed audio signal as an audible beat caused by erroneous pick-up of another local oscillation signal of different frequency from another local receiver, each local receiver comprising:

means for receiving the radio signal;

internal clock means for generating an internal clock signal for providing timing for reconstructing said audio signal from the received radio signal;

external clock detecting means for detecting whether the received radio signal includes an external clock signal for providing timing for reconstructing said audio signal from said radio signal;

selecting means, responsive to said external clock detecting means, for selecting as said local oscillation signal said external clock signal when said external clock detecting means detects said external clock signal and for selecting as said local oscillation signal said internal clock signal when said external clock signal is not detected;

means for stopping all of the internal clock means included within the respective local receiver which do not receive an input clock signal so as to inhibit the generation of the respective internal clock signals from within the respective local receiver when said external clock signal is detected by said external clock detecting means;

whereby both a respective local receiver and another local receiver select said external clock signal as said local oscillation signal with the same said frequency such that said beat frequency interference is suppressed.

9. The receiver according to claim 8, wherein said selecting means comprise switch change-over means for switching between said external clock signal when detected by said detecting means and said internal clock signal when said external clock is not detected.

10. The receiver according to claim 9, further comprising phase locked loop means coupled to receive said local oscillation signal for generating an oscillating signal phase locked to said local oscillation signal.

11. The receiver according to claim 9, further comprising mixing means for mixing said radio signal with said local oscillation signal to produce therefrom an intermediate frequency signal.

12. The receiver according to claim 11, further comprising an intermediate frequency amplifier for amplifying said intermediate frequency signal.

13. The receiver according claim 8, wherein each receiver includes processor means for processing said radio signal;

and reset means for generating a reset signal having a predetermined pulse width for resetting said processor means when said selecting means selects between said external clock signal and said internal clock signal, thereby preventing a disturbance in said processing of said radio signal caused by a transition from said external clock signal to said internal clock signal.

14. A method of receiving radio signals by a plurality of proximately situated local receivers for receiving a common radio signal, such that interference signals erroneously transmitted by a local receiver are received by at least one other of said local receivers, and for converting said common radio signal into an audio signal suitable for audio reproduction by frequency mixing said radio signal with a local oscillation signal, wherein each local receiver is subject to beat frequency interference which manifests in the reconstructed audio signal as an audible beat caused by erroneous pick-up of another local oscillation signal of different frequency from another local receiver, comprising the steps of:

receiving the radio signal;

generating an internal clock signal by use of internal clock signal generating means for providing timing for reconstructing said audio signal from the received radio signal;

detecting whether the received radio signal includes an external clock signal for providing timing for reconstructing said audio signal from said radio signal;

selecting said external clock signal as said local oscillation signal when said external clock signal is detected and selecting said internal clock signal as said local oscillation signal when said external clock signal is not detected; and

stopping all of the internal clock signal generating means within the respective local receiver which do not receive an input clock signal so as to inhibit the generation of the respective internal clock signals within the respective local receiver when said external clock signal is detected,

whereby both a respective local receiver and another local receiver select said external clock signal as said local oscillation signal with the same said frequency such that said beat frequency interference is suppressed.

15. The method according to claim 14, wherein said step of selecting switches between said external clock signal when detected and said internal clock signal when said external clock is not detected.

16. The method according to claim 15, wherein each receiver includes a phase locked loop having a controllable oscillator, and further comprising the step of phase-locking said controlled oscillator to said local oscillation signal.

17. The method according to claim 15, further comprising the step of mixing said radio signal with said local oscillation signal to produce therefrom an intermediate frequency signal.

18. The method according to claim 17, further comprising the step of amplifying said intermediate frequency signal.

19. The method according claim 14, wherein each receiver includes processor means for processing said radio signal;

and further comprising the step of generating a reset signal having a predetermined pulse width for resetting said processor means when said local oscillation signal is selected between said external clock signal and said internal clock signal, thereby preventing a disturbance in said processing of said radio signal caused by a transition from said external clock signal to said internal clock signal.