Importance

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Abstract

The object of the invention is to propose a communication system using an electronic choke circuit which has impedance slightly varied with a load variation and is prevented from having negative resistance and can stabilize circuit operation. A terminal device includes an electronic choke circuit separating DC power supplied from a management device and a communication signal from each other. The electronic choke circuit includes a variable impedance element constituted by a transistor having its collector and its emitter respectively connected to a first terminal and a third terminal, and an inductor and a resistor connected in series with the variable impedance element. A series circuit of a first resistor and a first capacitor is interposed between the first terminal and a second terminal, and the first capacitor has its one end connected to a base of the variable impedance element. A second capacitor is interposed between the third terminal and a fourth terminal. A second resistor suppresses a phenomenon that resistance characteristics of a circuit between an input terminal and an output terminal have a negative resistance region within a frequency band including a frequency of the communication signal.

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First Claim