Two-wire signal transmitter and method for maintaining integrity of

Abstract

Two-wire signal transmitter and method in which a very low-level Alternating Circuit (AC) input signal sensed at a remote circuit at a first end of a signal path is added to a low-level Direct Current (DC) bias signal provided by a local circuit that is located at a second end of the signal path. In a preferred embodiment, the remote circuit is electrically coupled to and powered by the local circuit through a two-wire path interconnection, typically a shielded twisted-pair cable. The DC bias signal has sufficient level to overcome minimum ratings of electrical contacts, thereby to pass the sensed very low-level AC input signal reliably through the poor electrical contacts that are used, for instance, for connecting electronic circuits that run the length of a railway train. In a preferred embodiment, the use of a unity gain current amplifier as a part of the remote circuit reduces the signal degrading effects of long signal paths, but does not amplify the AC input signal, thereby retaining known pre-determined railroad vitality requirements. An output signal is provided that is an AC coupled, isolated, non-amplified representation of the AC input signal. An alternate preferred embodiment utilizes no active amplifier as a part of the remote circuit, thereby providing a signal transmitter and method that is less complex, has lower cost, requires smaller packaging, and has somewhat better long-term reliability than the preferred embodiment utilizing the active amplifier in the remote circuit.