Transmitter having an improved LC oscillator

• US 5,983,084 A
• Filed: 06/06/1997
• Issued: 11/09/1999
• Est. Priority Date: 06/06/1997
• Status: Expired due to Fees

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Lin, Xing Ping
• Primary Examiner(s): Bost, Dwayne D.
• Assistant Examiner(s): Vuong, Quochien B.
• Application Number:
  US08/870,188
• Time in Patent Office: 886 Days
• Field of Search: 455/113, 455/114, 455/118, 455/119, 455/120, 455/127
• US Class Current: 455/114.2
• CPC Class Codes: H03B 2201/0291 and being controlled by a processing device, e.g. a microprocessor
• CPC Class Codes: H03B 5/326 the resonator being an acoustic wave device, e.g. SAW or BAW device
• CPC Class Codes: H04B 2001/0491 with frequency synthesizers, frequency converters or modulators

Abstract

A transmitter for use with a receiver responsive to a function request signal transmitted by said transmitter for performing a requested function. The transmitter includes a controller for providing a function command and an LC oscillator for providing the request signal at a fixed frequency in response to the command from the controller. The oscillator includes a semi-conductor having first, second, and third electrodes and a tank circuit including first, second, and third impedances. A surface acoustic wave resonator is connected from the first electrode to ground. A feedback capacitor is connected from the second electrode to said first electrode for reducing spurious frequency signals.

Claims

1. A transmitter for use with a receiver responsive to a function request signal transmitted by said transmitter for performing a requested function, comprising:

a controller for providing a function command;

a LC oscillator for providing said request signal at a fixed frequency in response to each occurrence of a said command and for the duration of said command from said controller and including a semi-conductor having first, second, and third electrodes and a tank circuit including first and second impedances, said first impedance being connected between the second and third electrodes, said second impedance being connected from the third electrode to ground, and a third impedance being connected from a voltage source to said second electrode;

a surface acoustic wave resonator connected from said first electrode to ground and operative in response to each said command for locking said oscillator to operate at said fixed frequency upon completion of a start up period initiated by the commencement of each said command and during which start up period said oscillator provides spurious frequency signals at frequencies other than said fixed frequency; and

a feedback capacitor connected from said second electrode to said first electrode for reducing said spurious frequency signals during said start up period.

2. A transmitter as set forth in claim 1, including amplifying means for amplifying said request signal provided by said oscillator.

3. A transmitter as set forth in claim 1, including an antenna.

4. A transmitter as set forth in claim 3, including amplifying means interposed between said oscillator and said antenna for amplifying said request signal.

5. A transmitter as set forth in claim 1, wherein said semi-conductor is an NPN transistor and wherein said first, second, and third electrodes are respectfully a collector, an emitter, and a base.

6. A transmitter as set forth in claim 5, including amplifying means for amplifying said request signal provided by said oscillator.

7. A transmitter as set forth in claim 5, including an antenna.

8. A transmitter as set forth in claim 7, including amplifying means interposed between said oscillator and said antenna for amplifying said request signal.

9. A transmitter as set forth in claim 1, wherein said LC oscillator is a Colpitts oscillator.

10. A transmitter as set forth in claim 9, wherein said first and second impedances are first and second capacitors and wherein said third impedance is an inductor.

11. A transmitter as set forth in claim 1, including a function request switch and wherein said controller is responsive to operation of said switch for providing a said function command.

12. A transmitter as set forth in claim 1, for use with a remote keyless entry system having a said receiver responsive to a vehicle function request signal transmitted by said transmitter for performing a requested vehicle function.