Inductive sensing with differential inductance readout

An inductive sensing system, comprising

• differential sense (Lsense) and reference (Lref) resonators, including
• a sense inductor coil LS;
• a reference inductor coil LR;
• and
• a common capacitor Cc coupled to the LS and LR inductor coils;
• an inductance-to-data converter (IDC) coupled to the Lsense and Lref resonators, through LSENSE and LREF outputs coupled respectively to the LS and LR inductor coils, and through an LCOM input coupled to the common capacitor Cc, including
• an Lsense driver with an output coupled through the LSENSE output to the LS inductor coil, and an input coupled to the LCOM input, the Lsense driver selectively enabled by an out enable signal OEsense, and
• an Lref driver with an output coupled through the LREF output to the LR inductor coil, and an input coupled to the LCOM input, the Lref driver selectively enabled by an out enable signal OEref,
• the OEsense and OEref signals controlled to time-multiplex operation of the Lsense and Lref drivers;
• the Lsense driver and the Lsense resonator operable as an Lsense ring oscillator to drive, when enabled by the OEsense signal, time-multiplexed Lsense resonator excitation signals through the LSENSE output to the Lsense resonator, to maintain Lsense resonator oscillation, based on resulting time-multiplexed Lsense resonance measurements acquired from the Lsense resonator through the LCOM input;
• and
• the Lref driver and the Lref resonator operable as an Lref ring oscillator to drive, when enabled by the OEref signal, time-multiplexed Lref resonator excitation signals through the LREF output to the Lref resonator, to maintain Lref resonator oscillation, based on resulting time-multiplexed Lref resonance measurements acquired from the Lref resonator through the LCOM input;
• the IDC including readout circuitry to provide differential readout data based on the time-multiplexed Lsense and Lref resonance measurements, corresponding respectively to the inductances of the LS and LR inductor coils.

A method for inductive sensing suitable for use with sense and reference resonators Lsense and Lref, the Lsense and Lref resonators including respectively a sense inductor coil LS, and a reference inductor coil LR, and including a common resonator capacitor Cc, comprising

• driving the Lsense resonator as a time-multiplexed Lsense ring oscillator, including driving time-multiplexed Lsense resonator excitation signals into the Lsense resonator, to maintain Lsense resonator oscillation, based on resulting time-multiplexed Lsense resonance measurements input to the Lsense ring oscillator from the Lsense resonator;
• and
• driving the Lref resonator as a time-multiplexed Lref ring oscillator, including driving time-multiplexed Lref resonator excitation signals into the Lref resonator, to maintain Lsense resonator oscillation, based on resulting time-multiplexed Lref resonance measurements input to the Lref ring oscillator from the Lref resonator;
• time-multiplexing the operation of the Lsense and Lref ring oscillators to enable sharing the common resonator capacitor Cc by the Lsense and Lref resonators;
• and
• providing differential readout data based on the time-multiplexed Lsense and Lref resonance measurements, corresponding respectively to inductances of the LS and LR inductor coils.