| 摘要 |
PURPOSE:To simplify the constitution of a portable device of a radio transmitter by receiving the information transmitted from the switch side by means of an induction electric field to process the information by a microcomputer and producing a signal which modulates the signal transmitted to the switch side from a clock of the computer. CONSTITUTION:The transmission request signal sent from a controller at the car body side is converted into an electric signal by a loop antenna 3 of a portable device and then fetched to a microcomputer 26 via a transmission request receiving circuit 7. The computer 26 uses a miniature crystal oscillator 27 for wristwatch as a clock oscillator. An output port P21 delivers a clock signal, and a frequency multiplying circuit consists of a PLL oscillation circuit 31 and a frequency dividing circuit 32. Then a specific code signal is supplied to a modulation input terminal IN of the circuit 31. The carrier modulated by the specific code signal is supplied to the antenna 3 via an output circuit 4 and transmitted to a controller at the car body side via an induction magnetic field. Thus it is possible to simplify the constitution of the portable device and secures the optimum transmission of signals with a controller at the switch side.
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