| 摘要 |
PURPOSE:To realize a miniature integration with reduction of folding loss and thus to ensure the high-quality talking by supplying the output of the subtractor circuit and the signals on the 4-wire line of the reception side and then minimizing the ratio between the output level of the subtractor circuit and the signal level on the 4-wire line. CONSTITUTION:Reception signal A supplied from 4-wire line 4 via amplifier 15 is supplied to 2-wire line 1 via passive element 9 as well as transmitted to the positive input terminal (+) of subtractor circuit 11. While transmission signal B sent from line 1 reaches the positive terminal (+) of circuit 11 via passive adder circuit 8. At this instant, the signal level of the positive terminal (+) of circuit 11 features as Z0.A+Zn.B/Z0+Z1, where the impedance of line 1 and element 9 are Z0 and Z1 respectively. On the other hand, if the transmission property of variable transmission circuit 10 is set to Z0/(Z0+Z1) or its approximate property, the output of circuit 11 becomes nearly Z1.B/(Z0+Z1). Thus the folding loss can be minimized for signal A. |
