TRANSFORMERLESS HYBRID CIRCUITS

摘要

The two wires of a symmetrical two-wire line are connected via two halves of a terminal line resistor to respective terminals of a relatively low impedance symmetrical input arm of a return path such as a four-wire line, are each connected via a relatively high value resistor to respective inputs of an operational amplifier which leads to the go path, the inputs of the operational amplifier also being connected cross-wise via respective resistors of a value double that of the terminals of the input arm. A threshold value element comprising a transistor may monitor the output voltage of the operational amplifier and change a d.c. reference voltage so that the output signals of two operational amplifiers located in the go path are substantially mutually equal. Other circuit components may serve to determine current asymmetry and to monitor loop closure.