| 摘要 |
PURPOSE:To convert a large-current, high-voltage call signal to a small-current, low-voltage signal level by using a simple current source circuit consisting of a common base grounding type transistor (TR). CONSTITUTION:The value of a resistance 11 is set far larger than the value of a resistance 4 and a call signal current from a call signal source 1 flows through the loop of a subscriber line 6, telephone set 7, subscriber line 5, resistance 3, DC power source 2, and call signal source 1 to send out the call signal. A signal converting circuit 10 operates a P-N-P TR 12 in a positive half cycle by a current i1 to transfer an emitter current to the collector and operates an N-P-N TR 13 in a negative half cycle to transfer a collector current to the emitter; and a current i2 proportional to the current i1 flows through a resistance 16, so a voltage drop is caused and the signal current (i1+i2) is converted into a voltage v2 eventually. |
