Communication system interface circuit

Abstract

A communication system includes a mobile station, a plurality of base stations and a central terminal. Each base station converts RF signals from the mobile station to AF signals. The AF signals are carried over a balanced line to the central terminal. Each base station generates a DC voltage signal whose level is representative of the level of its received RF signal. The central terminal includes means to monitor DC current levels, from each base station, on the balanced line and select that base station producing the highest DC current. The unique interface circuit senses the base station generated DC voltage, which is referenced to a fixed ground potential, and produces a corresponding current which is referenced to a floating ground potential. This current is then coupled to the balanced line for transmission to the central terminal. The interface circuitry includes a DC to AC converter which converts the DC signal voltage to an AC signal. This AC signal is capacitively coupled to an AC to DC converter which generates a corresponding DC voltage. The final stage is a transconductance circuit which produces an output current presenting the DC voltage level generated by the AC to DC converter. In this manner, a ground referenced voltage is transformed to a floating ground reference current suitable for transmission down a balanced line.