Extended feedback circuit for impedance matching and voltage isolation

摘要

A network interface circuit employs an extended feedback circuit topology for impedance matching across a high voltage boundary between a line side portion and low voltage portion of a network. The network interface circuit includes an operational amplifier-based circuit which is responsive to a signal applied from user equipment on the low voltage portion. Specifically, the present invention includes a transmit path having a first, second, and third amplifier circuit and an impedance element, and a receive path that includes a transfer function implemented as a second order low pass filter for correcting amplifier gain and phase effects in the complex feedback loop of the circuit. The output impedance is remotely set by multiplying the impedance element by a scale factor to match the network impedance. The feedback loop is extended across the high voltage boundary using high voltage interfaces such as linear optical coupling devices (LOCs).