Anti-theft system for a motor vehicle

Details Anti-theft system for a motor vehicle Anti-theft system for a motor vehicle

1995-08-28

1998-09-08

Elms, Richard T.

Electrical transmission or interconnection systems

Vehicle mounted systems

Automobile

180287, 307 105, B60R 2504

Patent

active

058048880

ABSTRACT:
An anti-theft system for a motor vehicle includes a portable transponder carrying an item of code information. A stationary antenna has a resonant circuit with components and a resonant frequency being determined by the components. An oscillator oscillates at an oscillator frequency and has an output variable being used as an exciter variable with an exciter frequency for compelling an oscillation of the resonant circuit. The oscillation is amplitude-modulated as a function of the code information of the transponder. An evaluation unit receives the oscillation of the resonant circuit. The evaluation unit detects the modulated oscillation and demodulates the code information out of the oscillation. A comparator compares the code information with command code information and supplies an enable signal if a match occurs. A security unit receives the enable signal. The exciter frequency or the resonant frequency of the resonant circuit is varied if initially no code information is recognized by the evaluation unit.

REFERENCES:
patent: 4918955 (1990-04-01), Kimura et al.
patent: 5616966 (1997-04-01), Fischer et al.
"The Pit and Amplitude Demodulation" (Kirchner), AN 94007, Aug. 1994, pp. 3-27.

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