| 摘要 |
PURPOSE:To adjust the signal level, reaching the exchanger to almost a given level, by increasing the output level of amplifier more when the power supply fed from the telephone line is smaller so that the loss of telephone line increased by longer telephone line can compensated. CONSTITUTION:When the power supply voltage is small and the voltage across the capacitor C1 is lowe, since no current is flowed in the resistor R5, TrQ1 and Q2 are OFF and diodes D1,D2, D3 and D4 are OFF, and the output level of the OP amplifier I1 is great and that appeared at the terminals 1 and 2 is great. When the power supply voltage is great and the voltage across the capacitor C1 is increased, current starts flowing to R5, TrQ1 and Q2 are conductive, the current inproportional to that flowing to R5 is fed to the analog switch, and the both ends of the microphone M is terminated with the operation resistance inversely proportional to the current flowing to the diodes D1,D2,D3 and D4 constituting the said analog switch, and the output level of M is decreased. |
