| 摘要 |
PURPOSE:To make a circuit constitution simple, to minimize the number of parts and to improve a profitability and reliability by installing two pairs of the resistance dividing circuit which divide voltage due to a call electric current and an induced current occurring at both ends of the feeding resistance of a A line and a B line, and a differential amplifier which outputs only a voltage component due to a call electric current. CONSTITUTION:Concerning resistances R1-R6, for example, R1, R2, R3, R4, and RS are made equal and R5, R6 and RG are made equal, and an output voltage of the differential amplifier OP from a power source voltage -VBB side is VOD due to the call electric current ILP, and VOC due to the induced current IAC, and then, judging from the characteristic of an operational amplifier that input resistance is sufficiently large and a gain is sufficiently large, the relation of the output voltage VOD and the call electric current ILP and the relation of the output voltage VOC and the induced current IAC are as shown in Table I. Namely, in a call electric current monitoring circuit, a voltage component due to the call electric current ILP is outputted and the voltage component due to the induced current IAC is deleted and not outputted, and the call electric current can be monitored without influencing the induced current. |
