Method and apparatus for eliminating interference caused by spurious signals in a communication device

• US 5,745,848 A
• Filed: 03/04/1996
• Issued: 04/28/1998
• Est. Priority Date: 03/04/1996
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Robin, John F.
• Primary Examiner(s): EISENZOPF, REINHARD
• Assistant Examiner(s): Arthur, G.
• Application Number:
  US08/610,028
• Time in Patent Office: 785 Days
• Field of Search: 455/75, 455/76, 455/77, 455/87, 455/133, 455/165.1, 455/183.1, 455/186.1, 455/260, 455/296, 455/310, 455/316, 455/317
• US Class Current: 455/296
• CPC Class Codes: H03J 7/065 the counter or frequency divider being used in a phase locked loop
• CPC Class Codes: H04B 15/04 the interference being caused by substantially sinusoidal oscillations, e.g. in a receiver or in a tape-recorder
• CPC Class Codes: H04B 2215/064 Reduction of clock or synthesizer reference frequency harmonics

Abstract

An apparatus for eliminating interference caused by spurious signals includes a reference oscillator (127) and a controller (114). Circuitry (500) in a communication device (104) incorporating the apparatus operates at a rate set by a system clock signal (CLOCK). The communication device (104) communicates on any one of a plurality of different channels. The reference oscillator (127) outputs the system clock signal (CLOCK) at a first frequency which generates spurious signals on at least one of the plurality of different channels. The controller (114) shifts the system clock signal (CLOCK) by a first predetermined amount to a second frequency when the communication device (104) is to be tuned to the at least one of the plurality of different channels so as to remove the spurious signals from the at least one of the plurality of different channels.

Claims

1. A method for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the method comprising the steps of:

generating the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels;

shifting the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels;

tuning the communication device to said at least one of the plurality of different channels; and

compensating the rate of the communication device when the communication device has been tuned to said at least one of the plurality of different channels to prevent timing error.

2. A method according to claim 1 further comprising the step of:

shifting the system clock signal back to the first frequency after the communication device is tuned to said at least one of the plurality of different channels.

3. A method according to claim 1 wherein the step of compensating comprises the substep of:

shifting the system clock signal a second predetermined amount to a third frequency after the step of tuning, the second predetermined amount being a negative equivalent of the first predetermined amount.

4. A method according to claim 1 wherein the step of shifting comprises the substeps of:

calculating a first signal having a shift value corresponding to each channel of the plurality of different channels; and

programming a clock circuit of the communication device with the first signal, the clock circuit shifting the system clock signal according to the shift value.

5. A method for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the method comprising the steps of:

generating the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels;

shifting the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels;

tuning the communication device to said at least one of the plurality of different channels; and

compensating the rate of the communication device when the communication device has been tuned to said at least one of the plurality of different channels to prevent timing error, the step of compensating comprising the substeps of;

generating a master timing signal from the system clock signal; and

delaying the master timing signal for a compensating interval.

6. A method for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the method comprising the steps of:

generating the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels;

shifting the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels;

tuning the communication device to said at least one of the plurality of different channels; and

compensating the rate of the communication device when the communication device has been tuned to said at least one of the plurality of different channels to prevent timing error, the step of compensating comprising the substeps of;

generating a master timing signal from the system clock signal; and

advancing the master timing signal for a compensating interval.

7. A method for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the method comprising the steps of:

generating the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels, the spurious signals including at least one harmonic of the system clock signal;

shifting the system clock signal a predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the at least one harmonic from said at least one of the plurality of different channels;

shifting the system clock signal back to the first frequency when the communication device is no longer to be tuned to said at least one of the plurality of different channels including the spurious signals; and

compensating the communication device for said step of shifting to the second frequency so as to prevent accumulation of timing error.

8. An apparatus for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the apparatus comprising:

a reference oscillator to output the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels; and

a controller coupled to shift the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels, and to compensate the rate when the communication device has been tuned to said at least one of the plurality of different channels so as to prevent timing error.

9. An apparatus according to claim 8 wherein the controller shifts the system clock signal back to the first frequency when said at least one of the plurality of different channels is no longer to be tuned.

10. An apparatus according to claim 8 wherein the controller compensates the rate by shifting the system clock signal by a second predetermined amount to a third frequency, the second predetermined amount being a negative equivalent of the first predetermined amount.

11. An apparatus for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the apparatus comprising:

a reference oscillator to output the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels; and

a controller comprising logic circuitry, a divider, and a master timing reference, the divider coupled to receive the system clock signal, the divider coupling a divided down system clock signal to the master timing reference, the master timing reference outputting a master timing signal to the logic circuitry, the controller coupled to shift the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels.

12. An apparatus according to claim 11 wherein the controller further comprises an adder coupled between the master timing reference and the logic circuitry, the logic circuitry compensating for timing error resulting from the shift of the system clock signal to the second frequency by delaying or advancing the master timing reference for a compensating interval.

13. An apparatus for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the apparatus comprising:

a reference oscillator to output the system clock signal at a first frequency, the first frequency generating spurious signals on at least one of the plurality of different channels;

a controller coupled to shift the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels; and

a clock circuit coupled to the reference oscillator and the controller, the clock circuit, responsive to an automatic frequency control (AFC) signal from the controller, outputting the system clock signal at the first frequency or the second frequency.

14. An apparatus according to claim 13 wherein the clock circuit includes a programmable divider coupled to the reference oscillator and the controller, the programmable divider dividing down the system clock signal to a low frequency signal.

15. An apparatus according to claim 14 wherein the clock circuit further comprises a phase-locked loop coupled to the programmable divider, the phase-locked loop, responsive to the low frequency signal from the programmable divider, outputting the system clock signal at the first frequency or the second frequency.

16. An apparatus for eliminating interference caused by spurious signals in communication signals communicated via a communication device on any one of a plurality of different channels, the communication device operating at a rate set by a system clock signal, the apparatus comprising:

reference oscillator to output the system clock signal at a first frequency the first frequency generating spurious signals on at least one of the plurality of different channels;

a controller coupled to shift the system clock signal by a first predetermined amount to a second frequency when the communication device is to be tuned to said at least one of the plurality of different channels so as to remove the spurious signals from said at least one of the plurality of different channels; and

a tuning circuit coupled to the reference oscillator and the controller, the tuning circuit, responsive to a programming signal from the controller, tuning the communication device to any one of the plurality of different channels.

17. A radiotelephone comprising circuitry for eliminating interference caused by spurious signals in communication signals communicated via the radiotelephone, the radiotelephone operating at a rate set by a system clock signal, the radiotelephone comprising:

a receiver to receive the communication signals on any one of a plurality of different channels;

a tuning circuit coupled to the receiver to tune the receiver to any one of the plurality of different channels;

a reference oscillator circuit to generate a reference signal approximately equal to the system clock signal;

a clock circuit coupled to the reference oscillator circuit to adjust the reference signal and output the system clock signal at a first frequency or a second frequency, the first frequency generating spurious signals on at least one of the plurality of different channels; and

a controller coupled to the clock circuit to remove the spurious signals, the controller, when the receiver is to be tuned to said at least one of the plurality of different channels, shifting the clock circuit to output the system clock signal at the second frequency, programming the tuning circuit to tune the receiver to said at least one of the plurality of different channels, shifting back the clock circuit to output the system clock signal at a second frequency, and compensating for timing error resulting from the shifting of the clock circuit.