| 摘要 |
PROBLEM TO BE SOLVED: To realize a subscriber circuit by which a test result high in accuracy can be obtained even with a circuit configuration to which a medium test function is added. SOLUTION: This subscriber circuit 203 that tests a subscriber line 202 connected to a subscriber terminal 201 is provided with a power voltage monitor circuit 216, which outputs a monitor output 218, in response to the change of a power voltage VBB when it is fluctuated, to a current source 219. The current source 219 supplies a current to a line 212 when a 1st transistor(TR) switch 221 is closed and the current flows into the input side of a current mirror circuit 223 via a resistor 222. Since the current mirror circuit 223 has an output resistor at its output side and a voltage at one end of the resistor 225 is given to a DSP circuit 226 and calculated therein, the fluctuation component of the power supply VBB to discriminate the test result of an insulation resistance of a subscriber line 202 or the like is eliminated. A clamp current source 233 keeps the line voltage at a prescribed voltage even when AC induction is present and connects a 2nd output to the output resistor 225 to restore an induced AC voltage. |
