Line fault detection system with a differential driver

Abstract

This is a detector system comprised of a differential driver circuit, a driver output stage and splitter circuit and a multiplexor. The driver circuit employs a bridge circuit that converts input logic voltages to lower voltage differential outputs by utilizing a pair of current switch transistors coupled to the bridge circuit. The bridge circuit is comprised of cross coupled transistors whose inputs are coupled to matched true and complement input logic voltages that swing between zero volts and the power supply voltage. The bridge transistors convert the differential logic input voltage swings to smaller values that are compatible with driving the splitter and multiplexor circuits coupled thereto. The driver circuit and the splitter circuit share the driver output transistors which are arranged in parallel pairs. These pairs are coupled to respective output lines whose physical state is to be determined and to the multiplexor which is an emitter coupled switch coupled to emitter follower transistors which are, in turn, connected to respective output lines so that the output voltage of the output transistors can be used to determine if the output lines are open.