Configurable interface circuit

A method for operating a configurable interface circuit in any of a plurality of selectable operational modes, including an analog mode and a digital mode, wherein the configurable interface circuit comprises:

• a device terminal couplable to an external field device;
• a digital current path coupled to the device terminal, wherein the digital current path comprises a digital sense resistor having a first terminal coupled to the device terminal;
• an analog current path comprising an analog sense resistor having a first terminal coupled to the first terminal of the digital sense resistor;
• and
• a measurement circuit for use in measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor, the measurement circuit comprising:
• a first input terminal coupled to a second terminal of the digital sense resistor;
• and
• a second input terminal coupled to a second terminal of the analog sense resistor;
• wherein the method comprises:
• when the configurable interface circuit is operating in the analog mode and an analog current can flow through the analog current path:
• measuring an analog signal by measuring a voltage between a second terminal of the digital sense resistor and a second terminal of the analog sense resistor, and
• when the configurable interface circuit is operating in the digital mode and a digital current can flow through the digital current path:
• measuring a digital signal by measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor.

An interface circuit supporting a plurality of selectable operational modes, the

• interface circuit comprising:
• a device terminal couplable to an external field device;
• a first current path coupled to the device terminal, wherein the first current path comprises a first sense resistor having a first terminal coupled to the device terminal;
• a second current path comprising a second sense resistor having a first terminal coupled to the first terminal of the first sense resistor;
• and
• a measurement circuit for use in measuring the voltage between the second terminal of the digital sense resistor and the second terminal of the analog sense resistor, the measurement circuit comprising:
• a first input terminal coupled to a second terminal of the digital sense resistor;
• and
• a second input terminal coupled to a second terminal of the analog sense resistor;
• wherein, when the interface circuit is operating in a first mode where a first current can flow through the first current path, the interface circuit is for use in measuring a first signal by measuring a voltage between a second terminal of the first sense resistor and a second terminal of the second sense resistor, and
• wherein, when the interface circuit is operating in a second mode where a second current can flow through the second current path, the interface circuit is for use in measuring a second signal by measuring the voltage between the second terminal of the first sense resistor and the second terminal of the second sense resistor.