A circuit arrangement for deriving a phantom circuit. In four wire circuits, the two wires associated with the "GO" channel form one "side circuit", and those associated with the "return" channel form another. 用来派生一个幻象电路的电路结构。在四线电路中，与“去程”通道相关联的两线就形成了一个“半边电路”, 而与“回程”通道相关联的两线构成了另一个“半边电路”。
