INDUCTIVE SENSING WITH DIFFERENTIAL INDUCTANCE READOUT BASED ON SENSE/REFERENCE LC-RING OSCILLATORS WITH A SHARED CAPACITOR

摘要

For inductive sensing (such as for proximity switching), differential inductance readout is based on Sense/Reference resonators implemented as LC-ring oscillators, with LS/LR inductor coils and a shared (time-multiplexed) resonator capacitor. The ring oscillators include matched Lsense/Lref drivers time-multiplexed (by out enable signals), to provide Lsense/Lref resonator excitation signals to the Lsense/Lref resonators, based on resulting Lsense/Lref resonance measurements (such as of resonance state) acquired by the ring oscillators from the Lsense/Lref resonators. Differential readout data is based on the time-multiplexed Lsense/Lref resonance measurements, corresponding respectively to LS/LR coil inductances (such as based on Lsense/Lref resonator oscillation frequency). The ring oscillators can be implemented with a Schmitt trigger, converting analog resonance measurements into digital input to the Lsense/Lref drivers. Driver matching and layout matching can be used to improve accuracy. Effects of parasitic capacitance at the driver outputs can be suppressed by shorting or bootstrapping across the inactive LS/LR coil inductances.