| 摘要 |
PROBLEM TO BE SOLVED: To miniaturize a power feeding terminal for transmitting the voltage signal of superimposing a base band signal on a DC voltage through a two-wire type signal line. SOLUTION: A power feeding terminal 1 has a control circuit 11 for generating a voltage control signal Vref matched with the waveform of the base band signal and a transmission circuit 15 composed of a DC/DC converter provided with a transistor Q to be switched by a frequency sufficiently higher than that of the base band signal. Concerning the transmission circuit 15, the serial circuit of a switching element Q, inductor L0 and capacitor C0 is connected between both the terminals of a DC power source E. The on-duty of the switching element Q is controlled corresponding to the signal value of the voltage control signal Vref and during a transmission period, a voltage corresponding to the signal value of the voltage control signal Vref is impressed to a signal line 3. During a reception period, the value of a current flowing to the signal line 3 is kept at a fixed value, which is set by a current control signal Iref, by a constant current control circuit 36.
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