Subscriber line circuit having improved AC impedance matching

摘要

An improved AC impedance matching arrangement including a first amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The first amplifier is arranged to supply loop current to the subscriber loop through first and second resistors. Each resistor having a set DC value. A second amplifier connected to the tip and ring conductors is arranged to develop and output a signal responsive to AC signals applied to the tip and ring conductors from the subscriber loop. A feedback circuit connected to the second amplifier is arranged to receive the second amplifier output signal and develop and output to the first amplifier an impedance matching signal. The impedance matching signal raises the impedance seen by the tip and ring conductors above the set DC value of the first and second resistors.