Resonant impedance sensing based on controlled negative impedance

摘要

Resonant impedance sensing with a resonant sensor (such as LC) is based on generating a controlled negative impedance to maintain steady-state oscillation in response to changes in resonance state caused by interaction with a target. Resonant impedance sensing can include: (a) generating a controlled negative impedance at the sensor; (b) controlling the negative impedance based on a detected resonance state to substantially cancel the sensor resonant impedance, such that the sensor resonance state corresponds to steady-state oscillation, where the negative impedance is controlled by a negative impedance control loop that includes the sensor resonator as a loop filter; and (c) providing sensor response data based on the controlled negative impedance, such that the sensor response data represents a response of the sensor to the target. Thus, the response of the sensor to the target corresponds to the negative impedance required for steady-state oscillation.

主权项

1. A circuit operable to capture the response of a resonant sensor to a target where the resonant sensor includes a resonator characterized by a resonant impedance loss factor, and a resonance state (resonator oscillation amplitude and resonator oscillation frequency), including a resonance state corresponding to steady-state oscillation, comprising:
class D negative impedance circuitry configured to drive current into the resonator with a negative impedance, including
a comparator configured to receive a resonator oscillation voltage, and to provide a class D switching output with a frequency synchronized to the resonator oscillation frequency;current drive circuitry configured to output a drive current based on a loop control signal corresponding to a controlled negative impedance magnitude; andH-bridge circuitry configured to interface the drive current source to the resonator;the comparator class D switching output controlling the H-bridge circuitry to maintain positive feedback, such that the resonator is driven with the negative impedance; and loop control circuitry configured to generate the loop control signal based on a detected sensor resonance state, such that a time average of the drive current corresponds to a magnitude of the controlled negative impedance that substantially cancels the sensor resonator losses to maintain steady-state oscillation; thereby establishing a negative impedance control loop that includes the sensor resonator as a loop filter, and that controls negative impedance, such that the loop control signal corresponds to sensor response data that represents the response of the sensor to the target.