| 摘要 |
<p>An output stage of a subscriber line interface circuit comprising two amplifiers, a first (111) one of which is configured to operate as an inverting amplifier (negative amplification) and a second (110) one as a non-inverting amplifier (positive amplification). Each amplifier has an output connected to a respective wire (a, b) in a subscriber line. A common reference voltage (Vref) and a common control voltage (Vc) are supplied to each amplifier (110, 111). The reference voltage (Vref) is used for setting the average voltage of the subscriber line. The control voltage (Vc) level determines the offset of the amplifier output voltages (Vb, Va) from the average voltage. The difference between the amplifier output voltages is the subscriber line operating voltage. In an on-hook state, the control voltage (Vc) is limited to a level ensuring that the maximum output voltages of the amplifiers (110, 111) are at a predetermined voltage offset from ground and from operating voltage potential, so as to allow an alternating current information signal to be transferred over the subscriber line in the on-hook state.</p> |
