Remote-control access control device and method for operating the same
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United States of America Patent
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Sep 3, 1996
Grant Date -
N/A
app pub date -
Sep 2, 1994
filing date -
Sep 2, 1993
priority date (Note) -
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status (Latency Note)
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Abstract
A remote-control access control device, particularly for motor vehicles, includes a stationary transmitter and receiver unit responding to actuation of tripping means for transmitting a question code signal, receiving an answer code signal, and furnishing an unlocking signal to an unlocking unit if the answer code signal matches a command code signal. A portable transponder has a receiver receiving the question code signal and a transmitter transmitting the answer code signal. The question code signal is repeatedly transmitted if no answer code signal has been received in response to an initial transmission, and a signal parameter is modified upon transmission of the answer code signal as a function of a field intensity of the question code signal or of a battery voltage of the transponder. Alternatively, a signal parameter is modified when the answer code signal is transmitted if an information content of the question code signal indicates an emergency operation state. As another alternative, the transmitter and receiver unit has both a transmission channel for receiving signals of low field intensity and a transmission channel for receiving signals of high field intensity. A method is also provided for operating the access control device.
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