| 摘要 |
PURPOSE:To attain easily large scale circuit integration to the entire subscriber circuit by adding a DC voltage level shift circuit and operating a feeding/2-4 wire converting circuit not used excluding the normal polarity depending on the dielectric strength so as to be activated at reverse supply thereby eliminating the need for a hybrid transformer and a DC coupling capacitor. CONSTITUTION:A talking current (DC) flows from a path comprising earth 13, talking current supply, loop supervisory, 2-4 wire converting circuit BSH17, DC voltage level shift circuit SFT15 and subscriber line terminal 1 to a public telephone set (not shown in figure) at normal talking state and is given to a route comprising terminal 2, SFT16, BSH17 and station battery 5. Then a talking current supply/loop supervisory circuit BS4 is operated at the inverting state, only the 2-4 wire circuit part is operated in the BSH17, a talking current flows to the public telephone set through the earth 13, the BS4 and the terminal 2 and flows to the route comprising the terminal 1, the BS4 and the battery 5. Since the BSH17 is operated normally even for normal/reverse supply in this way, the voice signal is transmitted without interruption. |
