Patent ID: 6907082
Filing Date: 2005-06-14
Classification: G08C

Abstract:
1. A 4-20 mA input interface circuit for communicating with a two-wire loop, the interface circuit including: a power extraction circuit connected to the two-wire loop and operable to generate a DC operating voltage for use in powering the interface circuit and a related device, the power extraction circuit including a DC-to-DC converter that generates the DC operating voltage as a voltage having a smaller magnitude than a voltage between the two wires of the two-wire loop; a current sensor connected to the two-wire loop and operable to generate a measure of an analog current through the two-wire loop, the measure being used in controlling a device associated with the interface circuit; and a digital communications circuit connected to the two-wire loop and operable to inject a digital transmission signal on to the two-wire loop and to extract a digital reception signal from the two-wire loop, the digital communications circuit including an impedance controller having an operational amplifier connected to control an impedance presented to the two-wire loop by the interface circuit.