Automatic answering system using transponder

Communications: electrical – Condition responsive indicating system – With particular system function

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34082569, 34082572, 307 103, G08B 2600

Patent

active

058350101

ABSTRACT:
The power feeding efficiency and the communicable range of an automatic answering system are improved in an automatic answering system using a transponder which performs code communication using amplitude modulation of a carrier with an electromagnetic coupling transponder mounted in a key or the like. In a transceiver for performing the code communication with the transponder via an antenna coil, a circuit for driving the antenna coil in a transceiver based on clock is implemented by a bridge-type complementary circuit of transistors. Thereby, driving current is increased. Meanwhile, a circuit for controlling the driving mode based on a write signal is implemented by a parallel circuit of a transistor to which a power-supply voltage is applied and a resistor. Thereby, a current corresponding to a resistance of the resistor flows through the antenna coil even during the minimum driving when the transistor is turned off, thus improving the power feeding efficiency and the communicable range of the system.

REFERENCES:
patent: 4918955 (1990-04-01), Kimura et al.
patent: 5280633 (1994-01-01), Camiade et al.
patent: 5287112 (1994-02-01), Schuermann
patent: 5287113 (1994-02-01), Meier
patent: 5619529 (1997-04-01), Fujioka
"RF Transponder Embedded in Auto Ignition Keys Stymies Car Thieves", Electronic Design 41 Dec. 1993 No. 25.
"Preliminary Device Specification Basestation IC", RF-Basestation IC for Communication with Philips Transponders, Philips Semiconductors, Jul. 1994.
PCF7930XP/030612 Date Sheet, Philips Semiconductors, Jul. 1994.

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