| 摘要 |
<p>PURPOSE:To attain the miniaturization and high density packaging by producing a voltage in proportion to the difference between currents supplied to lines A and B by means of PNP and NPN transistors (TR) and providing means for eliminating influence across respective bases and emitters of both TRs from the voltage. CONSTITUTION:A current 1A is supplied from a battery VB negative electrode to a line A of a subscriber line, while a current 1B is supplied to a line B from a ground, and voltages V1 and V2 are generated at both ends of resistances 1A and 1B. The V1 is inputted to an NPNTR103 through PNP and NPNTRs 101 and 102, and a current 16 flows in a resistance 114. On the other hand, the V2 is inputted to the base of a PNPTR109 through an NPNTR 114, and a current 17 flows in a resistance 115. A difference current between the currents 16 and 17 is inputted to a rectifier circuit 17, and a voltage in proportion to an absolute value of the difference current is produced at both ends of a resistance 18 and inputted to a difference current detector 40. Moreover, the influence of voltages VP and VN across bases and emitters is practically removed from the difference voltage, and the difference voltage detection results with high accuracy can be obtained.</p> |
