Methods, systems, and devices for coupling a modulated voltage signal to a current loop using a variable impedance bridge

A system for coupling a modulated voltage signal onto a current loop between a host device and a field device, comprising:

• a circuit configured to flow current from the field device between two terminals of an input circuit of the host device, wherein the two terminals are included in the current loop;
• and
• an impedance bridge positioned between the two terminals and configured to modulate impedance to convert the current in a field loop produced by the field device into terminal voltage modulation, without introducing a DC voltage burden to the current.

An electronic device for coupling a modulated voltage signal from a host device to a current loop between the host device and a field device, comprising:

• a resistor included in the current loop and configured to form a voltage across its terminals in relation to a current flowing from the field device through the current loop;
• and
• an impedance bridge included in the current loop and configured to modulate the impedance to convert the current in a field loop produced by the field device into terminal voltage modulation, without introducing a DC voltage burden to the current.