| 摘要 |
<p>PURPOSE:To eliminate an A line ground detecting circuit and to unify its function to current supply circuits by forming electronically the current supply circuit and adopting a high resistance to the ground-side current supply circuit. CONSTITUTION:Current supply circuits consisting of current supply transistors TRs 107 and 108, operational amplifiers 109 and 110, resistances 111 and 112 for current supply, etc. are connected to a subscribers' line to which an A line ground resistance 101 and a terminal resistance 102 are connected, and a terminal C1 is controlled at a loop current detection time to set the operational amplifier 110 to the operation state, and the loop current passing the TR108, the subscriber's line 103, and the TR107 is detected by monitoring the resistance 111; and when the A line ground is detected, the terminal C1 is controlled to stop the operation of the operational amplifier 110, and the current detection threshold value of a loop detecting circuit is reduced, and the current flowed from the A line side is detected by monitor of the resistance 111.</p> |
