A power line communication amplifier circuit for providing a signal transmission across a power line medium when operating in a transmit mode, and for providing a relatively high input impedance to the power line when in a receive mode includes a unity gain buffer integrally coupled with a filter. The...http://www.google.co.uk/patents/US5241283?utm_source=gb-gplus-sharePatent US5241283 - Drive amplifier for power line communications
