System and method for modulating a frequency signal

• US 6,275,539 B1
• Filed: 07/20/1998
• Issued: 08/14/2001
• Est. Priority Date: 07/20/1998
• Status: Expired due to Fees

• Current Assignee: Lear Automotive Dearborn, Incorporated (Lear Corporation)
• Original Assignee: Lear Automotive Dearborn, Incorporated (Lear Corporation)
• Inventors: Kulha, Steven P.
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/119,365
• Time in Patent Office: 1,121 Days
• Field of Search: 332/100, 332/101, 332/102, 375/272, 375/303, 375/304, 375/306, 455/113, 455/107, 331/167, 331/172
• US Class Current: 375/304
• CPC Class Codes: H04L 27/12 Modulator circuits; Transmitter circuits

Abstract

A radio frequency transmitter circuit including a user input switch for producing an input signal, an oscillator for producing a frequency signal having a first frequency, an antenna connected to the oscillator for broadcasting the frequency signal, a coupling circuit disposed a predetermined distance from the antenna, and a microprocessor for enabling the oscillator and activating the coupling circuit in response to the input signal. When the coupling circuit is activated, a reflected impedance, derived from a change in inductance, is reflected from the coupling circuit upon the antenna thereby shifting the frequency signal to a second frequency. Sequentially activating and deactivating the coupling circuit modulates the frequency signal.

Claims

1. A radio frequency transmitter circuit comprising:

a user input switch for producing an input signal;

an oscillator for producing a frequency signal having a first frequency;

an antenna connected to said oscillator for broadcasting said frequency signal;

a coupling signal disposed a predetermined distance from said antenna; and

a microprocessor for enabling said oscillator and activating said coupling circuit in response to said input signal;

said coupling circuit arranged to produce a reflected impedance when activated to alter an inductance of said antenna, thereby shifting said frequency signal to a second frequency upon activation of said coupling circuit.

2. A transmitter circuit as set forth in claim 1 wherein said coupling circuit includes an activation and said controller selectively closes said activation switch to activate said coupling circuit.

3. A transmitter circuit as set forth in claim 2 wherein said activation switch comprises an open collector transistor.

4. A transmitter circuit as set forth in claim 1 wherein said shifting of said frequencies modulates said signal to carry information.

5. A method of modulating a signal comprising:

a) generating a signal having a first frequency from an oscillator circuit; and

b) producing a reflected impedance to selectively alter an inductance of an antenna in the oscillator circuit to shift the signal to a second frequency.

6. A method of claim 5 wherein producing the reflected impedance comprises disposing a coupling circuit a predetermined distance from the oscillator circuit.

7. The method of claim 6 wherein step b) further includes activating the coupling circuit to produce the reflected impedance and shift the signal to a second frequency.