WO2014138059A1 - Resonant impedance sensing based on controlled negative impedance - Google Patents

Resonant impedance sensing based on controlled negative impedance Download PDF

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Publication number
WO2014138059A1
WO2014138059A1 PCT/US2014/020305 US2014020305W WO2014138059A1 WO 2014138059 A1 WO2014138059 A1 WO 2014138059A1 US 2014020305 W US2014020305 W US 2014020305W WO 2014138059 A1 WO2014138059 A1 WO 2014138059A1
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Prior art keywords
sensor
negative impedance
resonator
resonant
impedance
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PCT/US2014/020305
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English (en)
French (fr)
Inventor
George P. REITSMA
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Texas Instruments Japan Ltd
Texas Instruments Inc
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Texas Instruments Japan Ltd
Texas Instruments Inc
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Priority to CN201480012097.6A priority Critical patent/CN105190325B/zh
Priority to JP2015561543A priority patent/JP6410740B2/ja
Publication of WO2014138059A1 publication Critical patent/WO2014138059A1/en
Anticipated expiration legal-status Critical
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
    • G01D5/2006—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils
    • G01D5/202—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils by movable a non-ferromagnetic conductive element
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H2/00—Networks using elements or techniques not provided for in groups H03H3/00 - H03H21/00
    • H03H2/005—Coupling circuits between transmission lines or antennas and transmitters, receivers or amplifiers

Definitions

  • This relates generally to sensors and sensing, such as may be used in measuring or detecting the response of a sensor to a target, for example, based on position, proximity or physical state or condition.
  • a resonant sensor includes a resonator configured for steady-state (non- sensing) operation at a resonant frequency and amplitude.
  • Resonant sensing is based on changes in sensor resonance state as manifested by, for example, changes in resonator oscillation amplitude and frequency resulting from changes in sensor/resonator resonant impedance in response to a target.
  • Sensor response to a target can be caused, for example, by proximity or position of the target relative to the sensor, or some sensed physical state of the target.
  • sensor (resonator) impedance is affected by a storage or loss in magnetic flux energy output from the inductive sensing coil of an LC resonator, such as may be caused by the eddy current effect associated with a conductive target.
  • resonator impedance is affected by the storage or loss of electric field energy.
  • sensor resonance is affected by a change in mechanical stress on the piezo-crystal.
  • Apparatus and methods are provided for resonant impedance sensing using a resonant sensor that includes a resonator characterized by a resonant impedance and resonant frequency, and a resonance state that corresponds to resonator oscillation amplitude and resonator frequency, including a resonance state corresponding to steady-state oscillation (steady-state resonance), where both resonant impedance and resonance state change in response to the target.
  • Various described embodiments of a resonant impedance sensing methodology may include: (a) generating a controlled negative impedance which is presented to 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.
  • An embodiment of an apparatus configured to implement the resonance impedance sensing methodology may include: (a) negative impedance circuitry configured to couple to the sensor, and configured to present to the sensor a negative impedance controlled in response to a negative impedance control signal; and (b) impedance control circuitry configured to generate the negative impedance control signal based on a detected sensor resonance state, such that the controlled negative impedance substantially cancels the sensor resonant impedance so that the sensor resonance state corresponds to steady-state oscillation.
  • a negative impedance control loop includes the sensor resonator as a loop filter, and controls negative impedance such that the negative impedance control signal corresponds to sensor response data that represents the response of the sensor to the target.
  • FIG. 1A is an example functional illustration of resonant impedance sensing with controlled negative impedance, including a resonant sensor (represented by a resonator in parallel with a resonant impedance), and a sensor data converter that includes a negative impedance stage and a negative impedance control stage that establish a negative impedance control loop in which a controlled negative impedance is presented to the sensor to maintain steady-state oscillation, according to aspects of the invention.
  • a resonant sensor represented by a resonator in parallel with a resonant impedance
  • sensor data converter that includes a negative impedance stage and a negative impedance control stage that establish a negative impedance control loop in which a controlled negative impedance is presented to the sensor to maintain steady-state oscillation, according to aspects of the invention.
  • FIG. 1 B illustrates an example resonant sensor for inductive sensing based on an LC resonator, with resonant impedance represented (a) by a series resistance Rs, and (b) an equivalent circuit representation with parallel resistance Rp.
  • FIG. 2 illustrates an example functional embodiment of resonant impedance sensing with controlled negative impedance, using an inductive resonant sensor (LC resonator), coupled to a sensor data converter that includes a negative impedance stage and a negative impedance control stage, where the negative impedance stage is implemented by a trans-admittance amplifier with variable (controllable) trans-admittance (gm), and the impedance (admittance) control stage provides a gm control signal to modulate/tune gm (admittance), and thereby control negative impedance.
  • LC resonator inductive resonant sensor
  • FIG. 3 illustrates an example functional embodiment of resonant impedance sensing with controlled negative impedance using an inductive resonant sensor (LC resonator) coupled to a sensor data converter that includes a negative impedance stage and a negative impedance control stage, where the negative impedance stage is implemented by a trans-admittance amplifier configured to switch between two discrete trans-admittance levels (such as gmjow/high), and the negative impedance control stage is configured to provide a corresponding gmjow/high control signal.
  • LC resonator inductive resonant sensor
  • FIG. 4 illustrates an example embodiment of resonant impedance sensing with controlled negative impedance in which the negative impedance stage is implemented with a trans-admittance amplifier based on a Class A or AB amplifier configuration.
  • FIG. 5 illustrates an example embodiment of resonant impedance sensing with controlled negative impedance in which the negative impedance stage is implemented with a trans-admittance amplifier based on a Class D amplifier configuration interfaced to the resonant sensor with a ground-referenced H-Bridge.
  • FIG. 6 illustrates an example embodiment of resonant sensor system with controlled negative impedance, including an inductance-to-digital converter (LDC) implemented with a Class D negative impedance stage based on a ground- referenced H-bridge Class D trans-admittance amplifier.
  • LDC inductance-to-digital converter
  • FIGS. 7A and 7B illustrate example applications for resonant impedance sensing according to aspects of the invention, including (7A) axial position sensing in which the response of the sensor to the target corresponds to an axial (z axis) position and/or orientation of the sensor relative to the target, and (7B) lateral position sensing in which the sensor response corresponds to a relative lateral (xy) position of the sensor and a target, and depends on a fraction of target area that is exposed to the magnetic flux generated by the sensor.
  • Example embodiments are given generally in the context of inductive sensing in which an inductive resonant sensor (LC resonator) is used in connection with conductive targets, such that the response of the resonant sensor to a target corresponds to a storage or loss in magnetic flux energy output from the inductive resonant sensor.
  • the embodiments are not limited in applicability to inductive sensing, but rather is applicable to resonant impedance sensing in general (including, for example, capacitive and mechanical resonant impedance sensing).
  • FIG. 1A is an example functional illustration of resonant impedance sensing with controlled negative impedance.
  • a resonant impedance sensing system 10 includes a resonant sensor 50 and a sensor data converter 100.
  • Resonant sensor 50 includes a resonator 51 that can be characterized by a resonant impedance 53 and a resonance state which is characterized by resonator oscillation amplitude and frequency. Resonant sensor 50 can be operated in a resonance state corresponding to steady-state oscillation by injecting energy into resonator 51 sufficient to overcome the losses of resonant impedance 53.
  • the presence of (interaction with) a target is reflected in changes in sensor/resonant impedance and frequency, causing changes in resonance state.
  • the response of the resonant sensor 50 (resonator 51 ) to a target is captured and converted to sensor response data by presenting to the resonant sensor a controlled negative impedance required to maintain resonator 51 at steady-state oscillation. That is, the sensor response data quantifies the negative impedance required to maintain steady-state oscillation.
  • This sensor response data can be provided, for example, to a processor or controller for detection, measurement or other processing.
  • FIG. 1 C illustrates a resonant sensor 50 with an LC resonator 51 and a parallel resonant impedance 53 represented by resistance Rp.
  • sensor data converter 100 is configured to convert/capture the response of resonant sensor 50 to a target.
  • the sensor data converter 100 implements resonant impedance sensing according to aspects of the invention by presenting a controlled negative impedance 55 to resonant sensor 50, substantially canceling resonant impedance 53 to maintain a resonance state corresponding to steady-state oscillation.
  • the controlled negative impedance required to maintain steady-state oscillation can be quantified as sensor response data.
  • the sensor data converter can be configured to present the controlled negative impedance either in parallel with resonant impedance, as illustrated in FIG. 1A, or in series with resonant impedance.
  • Sensor data converter 100 is coupled to the resonant sensor 50.
  • Converter 100 includes a negative impedance stage 120 followed by a negative impedance control stage 130.
  • the negative impedance stage 120 is configured to present to the resonant sensor a negative impedance that is controlled in response to changes in resonance state (resonator oscillation amplitude and frequency) resulting from the presence of or interaction with a sensed target.
  • the resonant impedance sensing system 10 can be configured/optimized for operation at a specified resonator frequency by connecting additional reactive components to the resonant sensor (resonator 51 ), for example, a capacitor in parallel or in series, or an inductor in parallel or in series, or a combination of both.
  • This system configuration can enable the sensor data converter 100 to be designed/configured independent of the design/configuration of the resonant sensor 50.
  • the resonant impedance sensing system 10 can then be configured/optimized for an existing resonant sensor 50 by incorporating additional reactive component(s), and then coupling the sensor data converter to the resonant sensor with added reactive component(s) used to adjust resonant impedance and frequency range.
  • Negative impedance stage 120 and negative impedance control stage 130 establish a negative impedance control loop that controls the negative impedance 55 presented by the sensor data converter 100 to the resonant sensor 50.
  • the resonant impedance 53 changes, resulting in a corresponding change in resonance state.
  • the negative impedance control loop responds by controlling the negative impedance presented by the negative impedance stage 120 to substantially cancel resonant impedance, and maintain a resonance state corresponding to steady-state oscillation.
  • a change in resonant impedance 53 (resonance state) is represented as a change in the output 121 of the negative impedance stage 120.
  • the negative impedance control stage 130 In response, the negative impedance control stage 130 generates a negative impedance control signal 139 to control the negative impedance presented by the negative impedance stage 130 so as to maintain steady-state oscillation.
  • This negative impedance control signal corresponds to sensor response data quantifying the controlled negative impedance required to maintain steady-state oscillation, and representing the response of the sensor to the target.
  • the bandwidth of the negative impedance control loop will be substantially lower than the resonance frequency.
  • the closed impedance control loop enables control of any non-zero resonance state and maintains a constant oscillation amplitude, which is advantageous for low voltage applications.
  • the negative impedance control loop is illustrated as controlling resonator oscillation amplitude.
  • sensor data converter 100 can be configured to control the negative impedance 55 presented to the resonant sensor 50 based on changes in resonator oscillation amplitude. That is, a change in resonance state of resonator 51 caused by a change in resonant impedance 53 in response to a target is reflected in a change in resonator oscillation amplitude.
  • Sensor data converter 100 and the negative impedance control loop operate to detect changes in resonator oscillation amplitude (resonance state) as a measure of the change in resonant impedance.
  • the negative impedance stage 120 is controlled in response to the changes in resonator oscillation amplitude to adjust the negative impedance 55 presented to the resonator 51 , and thereby adjust resonator oscillation amplitude to maintain steady-state oscillation.
  • the negative impedance control stage 130 can be functionally implemented as a resonator amplitude detection and control block 131 that includes resonator amplitude detection 133 and negative impedance control 135.
  • Resonator amplitude detection 133 detects resonator oscillation amplitude which is represented as the output 121 of the negative impedance stage 120.
  • Negative impedance control 135 generates negative impedance control signal 139 based on a difference between (a) resonator oscillation amplitude as detected by resonator amplitude detection 133, and (b) a reference amplitude signal corresponding to a resonator oscillation amplitude at steady-state oscillation.
  • the output of the resonator amplitude detection and control block 131 provides the negative impedance control signal 139 looped back to negative impedance stage 120 to control the negative impedance, which corresponds to the sensor data output by the sensor converter 100.
  • negative impedance is controlled to substantially cancel resonant impedance as it changes in response to a target, thereby maintaining resonator oscillation amplitude substantially constant to achieve a resonance state corresponding to steady-state oscillation.
  • the controlled negative impedance associated with steady-state oscillation is quantified as sensor response data that represents to the response of the sensor to the target.
  • resonant impedance sensing includes: (a) generating a controlled negative impedance which is presented to 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 with 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.
  • FIG. 2 illustrates an example functional embodiment of resonant impedance sensing in connection with an resonant sensor 50 configured for inductive sensing with an LC resonator 51 and a resonant impedance 53 represented by series resistance Rs.
  • a sensor data converter 200 coupled to resonant sensor 50 includes a negative impedance stage 220 and a negative impedance control stage 230.
  • the negative impedance stage 220 is functionally implemented with a trans-admittance amplifier 223 controlling a current source 225 that provides excitation current drive to the resonant sensor (resonator 51 ).
  • Trans-admittance amplifier 223 is implemented with variable (continuous) controllable gm, and with a positive feedback loop to create negative impedance/resistance.
  • Impedance control stage 230 is configured to provide the negative impedance control signal 239 as a gm control signal that modulates (tunes) trans-admittance gm, thereby controlling negative impedance in the manner described above in connection with FIG. 1A.
  • the gm control signal corresponds to sensor response data that represents the sensor response captured/converted by the sensor data converter 200.
  • the negative impedance stage 220 can be implemented with a trans-admittance amplifier with constant gm, and a variable controllable current source controlled by the negative impedance control signal (positive feedback).
  • FIG. 3 illustrates an example functional embodiment of resonant impedance sensing in connection with an LC resonant sensor including an LC resonator 51 and a resonant impedance 53 represented by series resistance Rs.
  • a sensor data converter 300 coupled to resonant sensor 50 includes a negative impedance stage 320 and a negative impedance control stage 330.
  • the negative impedance stage 320 is implemented with a trans- admittance amplifier 323 and a current source 325 that provides excitation current drive to the resonant sensor (resonator 51 ).
  • Trans-admittance amplifier 323 is configured to switch between two discrete trans-admittance levels (gmjow and gm_high), and with a positive feedback loop to create negative impedance.
  • Impedance control stage 330 is configured to provide the negative impedance control signal 339 as a gmjow/high control signal that modulates (tunes) trans- admittance gm by switching between trans-admittance levels, thereby controlling negative impedance in the manner described above in connection with FIG. 1A.
  • the time average of the gmjow/high control signal constitutes sensor response data that represents the sensor response captured/converted by sensor data converter 300 (quantifying the controlled negative impedance required to maintain steady-state oscillation).
  • the negative impedance stage 320 can be implemented with a trans-admittance amplifier with constant gm, and a discrete excitation current source that provides two or more discrete current drive levels, with switching between the discrete current drive levels controlled by the negative impedance control signal (positive feedback).
  • Example embodiments in which controlled negative impedance is implemented based on discrete current drive are described in connection with FIGS. 5 and 6.
  • the discrete gm control signal 339 can be translated into a digital sensor read-out corresponding to sensor response, such as by digital filtering of the discrete gmjow/high control bit stream. That is, the negative impedance control loop is based on generating a predetermined number of discrete negative impedances applied sequentially in time, based on a negative impedance (gmjow/high) control signal 139, such that sensor response data corresponds to the time average negative impedance presented to the resonant sensor 50.
  • discrete gm control is illustrated with two levels of gm control, gmjow/high, in contrast to the variable gm control in the embodiment illustrated in FIG. 2.
  • discrete gm control can be implemented with a number of levels greater than two, for example to increase accuracy and reduce quantization noise.
  • FIG. 4 illustrates an example embodiment of a negative impedance stage 420 implemented as a trans-admittance amplifier 423 based on a linear Class A or AB amplifier configuration.
  • Trans-admittance amplifier 423 includes discrete gmjow/high control.
  • An advantage of the Class A or AB implementation for a negative impedance stage is its high linearity, avoiding generation of higher harmonics.
  • a design consideration in implementing a negative impedance stage with a linear amplifier is power consumption, given that the amplifiers used in trans- admittance amplifier 423 must have a bandwidth substantially higher than the resonant frequency.
  • Negative impedance stage 520 is implemented as a Class D trans-admittance amplifier 521 interfaced to the resonant sensor 50 by a ground- referenced H-bridge S1/S2.
  • the Class D trans-admittance amplifier 521 includes a comparator 523, and a current source 525 providing current drive to resonant sensor 50 (resonator 51 ).
  • current source 525 provides discrete (Imin/lmax) excitation current drive through the ground-referenced H-bridge S1/S2, with switching between discrete current drive levels (Imin/lmax) controlled by a discrete gmjow/high control signal 539 from the negative impedance control stage 530,.
  • Comparator 523 commutates the H-bridge, connecting the positive side of sensor resonator 51 to the excitation current source 525, and the negative side of the resonator 51 to ground.
  • the comparator correspondingly changes the states of S1/S2 of the H-bridge to maintain the positive side of resonator 51 as the noninverting input to comparator 323 (positive feedback), with the inverting input at ground.
  • the time average of the current pulse output of discrete current source 525 corresponds to the resonator oscillation amplitude output from resonator 51 as applied to the inputs (inverting/noninverting) to the comparator 523.
  • current source 525 outputs Imax current drive, resonator oscillation amplitude increases, and when current source 525 outputs current drive Imin, resonator oscillation amplitude decreases.
  • controlling resonator polarity controls the positive feedback (noninverting input to the comparator 523) that results in a controlled negative impedance being presented to resonator 51 .
  • This controlled negative impedance counters the resonant impedance 53 (Rs) to maintain steady-state oscillation.
  • Imin/lmax represent the gain of the Class D trans-admittance amplifier.
  • FIG. 6 illustrates an example embodiment of a resonant sensor system 60 configured for inductive sensing, including an LC resonant sensor 50 interfaced to an inductance-to-digital converter (LDC) 600.
  • the LC resonant sensor includes an LC resonator 51 and a resonant impedance 53 represented by Rs.
  • LDC 600 implements resonant impedance sensing with controlled negative impedance, capturing/converting the response of resonant sensor 50 to a target as sensor response data.
  • LDC 600 includes a negative impedance stage 620 and a negative impedance control stage 630. As described in connection with FIG. 1A, the negative impedance stage 620, negative impedance control stage 630 and a negative impedance control signal 639 establish a negative impedance control loop that controls the negative impedance presented to the resonant sensor 50 (resonator 51 ). This negative impedance control loop includes the resonant sensor 50 (resonator 51 ).
  • LDC 600 detects the changes in resonant impedance (Rs) resulting from target interaction as changes in resonance state (resonator oscillation amplitude), and effects resonant impedance sensing by controlling the negative impedance presented to the resonant sensor to counteract changes in resonator oscillation amplitude and maintain steady-state oscillation. That is, the controlled negative impedance substantially cancels resonant impedance 53, maintaining a resonance state (resonator oscillation amplitude and resonance frequency) corresponding to steady-state oscillation.
  • the controlled negative impedance that counteracts resonant impedance to maintain steady-state oscillation is quantified as sensor response data that corresponds to the sensor response to the target.
  • LDC 600 is configured to detect changes in the resonator oscillation amplitude component of the resonance state caused by the interaction of resonant sensor 50 with a target.
  • Negative impedance stage 620 is implemented as a Class D H-bridge (ground referenced) amplifier configuration.
  • Class D trans-admittance amplifier 621 that includes comparator 623 and discrete DAC current drive 625.
  • the Class D trans- admittance amplifier 621 including discrete current source DAC 623, is controlled to provide discrete Imin/lmax excitation current drive to the LC resonator 51 .
  • DAC current source 625 provides, in response to the discrete gmjow/high control signal 639 from a quantizer 637 in the negative impedance control stage 630, discrete (Imin/lmax) excitation current drive through the ground-referenced H-bridge S1/S2.
  • Comparator 623 commutates the H-bridge to provide positive feedback, connecting the positive side of the sensor resonator 51 to the DAC current source 625, and the negative side of the resonator 51 to ground.
  • the discrete Imax/lmin current drive from the DAC current source 625 is time averaged by the resonant sensor 50, which acts as a loop filter in the negative impedance control loop. That is, the time average of the current pulse output of the DAC current source 625 corresponds to the resonator oscillation amplitude of the output from resonator 51 as applied to the inputs (inverting/noninverting) to the comparator 623.
  • RPmin and Rpmax can be used to specify a range of operation for resonant sensor 50.
  • quantization of gm control can be increased to more than two levels with a corresponding increase in quantization of the gm control signal 639.
  • Resonant sensor 50 is included in the negative impedance control loop at a summing node, where the positive resonant impedance of the sensor is compared with the negative impedance of the control loop of the LDC 600.
  • Advantages of this configuration include: (a) enables a direct measurement of resonant impedance rather than measuring a parameter correlated to it; (b) nonlinearity from a magnetic core is substantially eliminated, since, for example, a constant resonator oscillation amplitude of the sensor implies a constant amplitude of the magnetic flux generated by the sensor; (c) transient response of the LDC can be optimized for the sensor, since the transient response of the control loop tracks the transient response of the sensor; and (d) quantization noise from the LDC (Class D) is attenuated by the sensor.
  • Class D amplifier 621 can be implemented by a Class D OTA (operational transconductance amplifier), with a ground-referenced H-bridge input interface.
  • a Class D OTA operation transconductance amplifier
  • Implementing the negative impedance stage as a trans-admittance amplifier allows negative impedance to be defined by resistors, which have a low temperature coefficient relative to transistors, thereby mitigating temperature drift.
  • Negative impedance control stage 630 is implemented with an integrator 631 including the integrating Rint/Cint. Integrator 631 provides additional filtering for the resonator current drive supplied by the DAC current source 625. This additional filtering is a design choice, but is advantageous for reducing quantization noise.
  • Resonator oscillation amplitude voltage 632 is input to the negative impedance control stage 630, and integrator 631 , through a buffer 633 to avoid loading resonator 51 .
  • This detected resonator oscillation amplitude voltage is converted to a current by Rint, and subtracted by a reference current 633 (corresponding to Vref in FIG. 1A).
  • the resulting resonator oscillation amplitude current is integrated by the integrator 631 and Rint Cint.
  • a stability control circuit 635 is included to enhance stability by configuring a zero from the resonant amplitude voltage input to the integrator, which is used to compensate for the poles introduced by the resonant sensor capacitor and the integration capacitor Cint.
  • the integration output from integrator 631 is summed 636 with the feed forward output of stability control circuit 635, and the result quantized by quantizer 637 as the gmjow/high (impedance) control signal 639.
  • the quantized gmjow/high control signal is input to the DAC current drive 625 to generate the excitation currents Imin/lmax injected into resonant sensor 50.
  • Quantizer 637 outputs the discrete gmjow/high control signal 639.
  • Quantizer 637 is implemented as a comparator, with comparator output levels corresponding to the gmjow/high admittance levels for which trans-admittance amplifier 621 is configured, i.e. for the Imin/lmax injected resonator current.
  • the impedance (gmjow/high) control signal 639 output from quantizer 637 is generated by the negative impedance control stage 630 based on detected resonator oscillation amplitude, such that the controlled negative impedance of the negative impedance stage 620 substantially cancels the resonant impedance (Rp) 53 of the resonant sensor 50, and maintains the output resonator oscillation amplitude substantially constant.
  • the impedance control signal 639 corresponds to the response of resonant sensor 50 to a target in that it represents the negative impedance required to maintain resonator oscillation amplitude substantially constant (steady-state oscillation amplitude).
  • the output 624 of comparator 623 in the Class D trans-impedance amplifier 621 which is used to commutate the H-bridge S1/S2, corresponds to resonator frequency (resonance frequency at steady-state oscillation). That is, the comparator output 624 provides measurement (open loop) of resonator frequency. And, as noted above, the resonance state of a sensor resonator is characterized by resonator oscillation amplitude and frequency.
  • the controlled negative impedance required to maintain resonance state at steady-state oscillation which is derived from changes in resonator oscillation amplitude resulting from sensor/target interaction, corresponds to sensor response data available from LDC 600 as an output of the negative impedance control loop. That is, the negative impedance control signal 639 that controls the negative impedance presented to the resonant sensor by the negative impedance stage 620 constitutes sensor response data that quantifies the controlled negative impedance .
  • Resonance frequency 624 provides additional sensor response data that can be used in processing and determining resonant sensor response (for example, performing temperature compensation).
  • Applications for embodiments of resonant impedance sensing according to the invention may include: (a) axial position sensing in which the response of the sensor to the target corresponds to an axial position and/or orientation of the target relative to the sensor; (b) lateral position sensing in which the sensor response depends on a fraction of target area that is exposed to the magnetic flux generated by the sensor; and (c) magnetic impedance modulation in which sensor response is based on modulation of magnetic impedance of a magnetic circuit.
  • Advantages of resonant impedance sensing according to the invention include: (a) accuracy - because the sensor/resonator resonant impedance is measured directly, rather than a parameter correlated to it, higher accuracy is achieved; (b) temperature independence -- because the matching negative impedance is temperature independent, only drift of the resonant sensor remains; and (c) integration in high density CMOS - the sensor/resonator impedance sensing methodology can be applied using a low constant resonance amplitude, enabling implementation in high density CMOS, and allowing for advanced signal processing, and temperature correction of the resonant sensor, which is particularly advantageous for inductive (eddy current) sensing applications.
  • FIGS. 7A and 7B illustrate example applications for resonant impedance sensing according to aspects of the claimed invention.
  • FIG. 7A illustrates an example resonant impedance sensing application in which the response of a resonant sensor 50 to a target 701 is based on an axial (z axis) position of the sensor relative to the target.
  • FIG. 7B illustrates an example resonant impedance sensing application in which the response of a resonant sensor 50 with one or more sensors (coils) 50a and 50b to one or more respective targets 703a and 703b is based on a lateral (xy axis) position of a resonant sensor relative to a respective target.
  • the response of the resonant sensor to the target can be captured/converted by a sensor-to-data converter (such as LDC 600 in illustrated in FIG. 6) as sensor response data that corresponds to the controlled negative impedance generated by the converter, and therefore represents sensor response to the target.
  • a sensor-to-data converter such as LDC 600 in illustrated in FIG. 6

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PCT/US2014/020305 2013-03-04 2014-03-04 Resonant impedance sensing based on controlled negative impedance Ceased WO2014138059A1 (en)

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CN201480012097.6A CN105190325B (zh) 2013-03-04 2014-03-04 基于受控负阻抗的谐振阻抗感测
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US201361838084P 2013-06-21 2013-06-21
US61/838,084 2013-06-21
US201361877759P 2013-09-13 2013-09-13
US61/877,759 2013-09-13
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