High performance inductive sensing all digital phase locked loop

A system comprising:

• a sensor;
• a first capacitive element;
• and
• an integrated circuit comprising a first terminal and a second terminal, wherein the first capacitive element and the sensor are coupled in parallel across the first terminal and the second terminal, wherein the integrated circuit comprises an inductance-sensing circuit coupled to a sensor, wherein the inductance-sensing circuit comprises:
• a digital phase-frequency detector (PFD) to receive a first signal representing a reference frequency and a second signal representing a second signal representing a sensor frequency;
• the first capacitive element;
• a second capacitive element, wherein:
• the first capacitive element is selectively coupled between the sensor and the digital PFD to make a first adjustment of the sensor frequency,
• the second capacitive element is selectively coupled between the sensor and the digital PFD to make a second adjustment of the sensor frequency, and
• an output of the inductance-sensing circuit represents an inductance change of the sensor;
• a proportional integral (PI) controller coupled to the digital PFD, the PI controller to selectively couple the first capacitive element and the digital PFD to make the first adjustment;
• and
• a digital filter coupled to the PI controller, the digital filter to provide the output representing the inductance change.

A method comprising:

• measuring, using an inductance-sensing circuit having a digital phase-frequency detector (PFD), a first signal having a sensor frequency of a sensor coupled to the inductance-sensing circuit, wherein the digital PFD receives a second signal representing a reference frequency;
• selectively coupling, by a proportional integral (PI) controller coupled to the digital PFD, a first capacitive element between the sensor and the digital PFD to make a first adjustment of the sensor frequency;
• selectively coupling a second capacitive element between the sensor and the digital PFD to make a second adjustment of the sensor frequency;
• and
• providing, by a digital filter coupled to the PI controller, an output representing an inductance change of the sensor.