| 摘要 |
PROBLEM TO BE SOLVED: To be immune to the noise of a common node input by providing the same circuit configuration for two speaking current supply parts on a trunk line interface circuit for supplying a speaking current to the side of a station. SOLUTION: A speaking current supply part 5 is composed of the 1st serial circuit of a resistor 5a and an NPN transistor 5b and the 2nd serial circuit of an NPN transistor 5c and a resistor 5d when viewed from the side of the ground. Then, the base of the transistor 5b is connected to the emitter of the transistor 5c and the base of the transistor 5c is connected to the collector of the transistor 5b respectively. Namely, the speaking current supply part 5 has the same configuration as a speaking current supply part 7 and uses the same components respectively for resistors 5a and 7a, NPN transistors 5b and 7b, NPN transistors 5c and 7c and resistors 5d and 7d. Therefore, since the impedances of the respective speaking current supply parts 5 and 7 are equal, balance characteristics to the ground are improved. |
