WO2023122044A1 - Charge ou capacité constante pour capteurs capacitifs de système micro-électrique-mécanique - Google Patents

Charge ou capacité constante pour capteurs capacitifs de système micro-électrique-mécanique Download PDF

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Publication number
WO2023122044A1
WO2023122044A1 PCT/US2022/053420 US2022053420W WO2023122044A1 WO 2023122044 A1 WO2023122044 A1 WO 2023122044A1 US 2022053420 W US2022053420 W US 2022053420W WO 2023122044 A1 WO2023122044 A1 WO 2023122044A1
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Prior art keywords
capacitance
input
sense element
electrically coupled
capacitive sense
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PCT/US2022/053420
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English (en)
Inventor
Joseph Seeger
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Invensense, Inc.
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Priority claimed from US18/066,802 external-priority patent/US20230192479A1/en
Application filed by Invensense, Inc. filed Critical Invensense, Inc.
Publication of WO2023122044A1 publication Critical patent/WO2023122044A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/005—Electrostatic transducers using semiconductor materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
    • B81B7/008—MEMS characterised by an electronic circuit specially adapted for controlling or driving the same
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—Microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2410/00—Microphones
    • H04R2410/03—Reduction of intrinsic noise in microphones

Definitions

  • the subject disclosure generally relates to embodiments for constant charge or capacitance for capacitive micro-electro-mechanical system (MEMS) sensors.
  • MEMS micro-electro-mechanical system
  • FIG. 1 illustrates a block diagram of a MEMS device that applies a nominally constant charge to a capacitive sense element of the MEMS device, or facilitates maintenance of a nominally constant capacitance value of a sense capacitance of the capacitive sense element, in accordance with various example embodiments;
  • FIGs. 2-3 illustrates block diagrams of respective MEMS device circuits that apply respective nominally constant charges to capacitive sense elements of the respective MEMS device circuits, in accordance with various example embodiments;
  • FIGs. 4-5 illustrates block diagrams of respective MEMS device circuits that include respective amplifiers electrically coupled to respective test capacitances - the respective MEMS devices applying respective nominally constant charges to capacitive sense elements of the respective MEMS device circuits, in accordance with various example embodiments;
  • FIGs. 6-7 illustrates block diagrams of respective MEMS device circuits that include respective summing amplifiers electrically coupled to respective test capacitances - the respective MEMS devices applying respective nominally constant charges to capacitive sense elements of the respective MEMS device circuits, in accordance with various example embodiments;
  • FIG. 8 illustrates a block diagram of a MEMS device circuit including a differential output - the MEMS device applying a nominally constant charge to a capacitive sense element of the MEMS device, in accordance with various example embodiments;
  • FIG. 9 illustrates a block diagram of a MEMS device circuit that facilitates maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • FIG. 10 illustrates a block diagram of a MEMS device circuit that includes an amplifier electrically coupled to a test capacitance - the MEMS device facilitating maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • FIG. 11 illustrates a block diagram of a MEMS device circuit that includes a summing amplifier electrically coupled to a test capacitance - the MEMS device facilitating maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • FIG. 12 illustrates a plot of normalized charge versus normalized bias voltage of a MEMS device, in accordance with various example embodiments;
  • FIG. 13 illustrates a small-signal model of a MEMS device, in accordance with various example embodiments
  • FIG. 14 illustrates a bode diagram of a constant capacitance filter of a MEMS device, in which the MEMS device facilitates maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, in accordance with various example embodiments;
  • FIG. 15 illustrates a process performed by a MEMS device with respect to applying a nominally constant charge to a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • Various embodiments disclosed herein can enable biasing a membrane of a MEMS device closer to, or beyond, the pull-in voltage by applying a nominally constant charge to a capacitive sense element of the MEMS device, or by maintaining a nominally constant capacitance value of a sense capacitance of the capacitive sense element.
  • a MEMS device e.g., microphone, accelerometer, pressure sensor, ultrasonic receiver, gyroscope, or other type of vibration sensing device, comprises a capacitive sense element circuit (114) comprising a bias resistance (220) comprising a resistance input and a resistance output, a charge-pump (210) comprising a charge pump input and a charge pump output, and a capacitive sense element (230) comprising an electrode (222) and a sense capacitance, in which the charge-pump output generates a bias voltage at the resistance input, the resistance output is electrically coupled to the electrode of the capacitive sense element, and the bias voltage is proportional to an inverse of a capacitance value comprising the value of the sense capacitance to facilitate maintenance of a nominally constant charge on the electrode of the capacitive sense element.
  • the MEMS device further comprises a capacitance sensing circuit (112) comprising: a gain circuit (270); a demodulator (260) that modulates a first demodulator input and a second demodulator input to obtain a demodulator output that is electrically coupled, via the gain circuit, to the charge pump input; an alternating current (AC) signal source (240) that generates an AC signal (e.g., an analog voltage; a digital waveform) at a defined frequency, in which the AC signal is electrically coupled to the first demodulator input; and a test capacitance (250) comprising a test capacitance input and a test capacitance output.
  • a capacitance sensing circuit comprising: a gain circuit (270); a demodulator (260) that modulates a first demodulator input and a second demodulator input to obtain a demodulator output that is electrically coupled, via the gain circuit, to the charge pump input; an alternating current (AC) signal source (240) that generates an AC signal (e
  • the capacitance sensing circuit generates, based on the AC signal at the defined frequency, an AC test voltage at the test capacitance input.
  • the test capacitance output is electrically coupled to the electrode of the capacitive sense element.
  • the capacitive sense element circuit generates, based on the AC test voltage at the defined frequency, an output signal that is electrically coupled to the second demodulator input and that represents a value of the sense capacitance.
  • the defined frequency is greater than a resonant frequency of the capacitive sense element. In other embodiment(s), the defined frequency is in a range of about 50 kHz to about 1 MHz.
  • a first portion of the output signal of the capacitive sense element circuit represents an external force that has been applied to a membrane of the capacitive sense element, and a second portion of the output signal of the capacitive sense element circuit represents a measurement of the value of the sense capacitance.
  • an amplifier (410) is electrically coupled between the AC signal source and the test capacitance, and generates, based on the AC signal, the AC test voltage at the test capacitance input.
  • the amplifier comprises a summing amplifier (610) comprising a first amplifier input, a second amplifier input, and an amplifier output, in which the first amplifier input is electrically coupled to the AC signal, the second amplifier input is electrically coupled to the output signal of the capacitive sense element circuit, and the amplifier output is electrically coupled to the test capacitance input - the summing amplifier generating, via the amplifier output based on the AC signal, the AC test voltage at the test capacitance input.
  • a summing amplifier (610) comprising a first amplifier input, a second amplifier input, and an amplifier output, in which the first amplifier input is electrically coupled to the AC signal, the second amplifier input is electrically coupled to the output signal of the capacitive sense element circuit, and the amplifier output is electrically coupled to the test capacitance input - the summing amplifier generating, via the amplifier output based on the AC signal, the AC test voltage at the test capacitance input.
  • an amplitude of the second portion of the output signal of the capacitive sense element circuit is inversely proportional to the value of the sense capacitance.
  • the capacitive sense element circuit further comprises an inverting buffer (820) that generates an inverted output signal that is based on the output signal of the capacitance sense element circuit, in which a differential output signal of the capacitive sense element circuit is represented by the output signal and the inverted output signal.
  • the capacitance sensing circuit further comprises a difference circuit (810) that comprises a first difference circuit input, a second difference circuit input, and a difference circuit output. The first difference circuit input is electrically coupled to the output signal of the capacitive sense element circuit, the second difference circuit input is electrically coupled to the inverted output signal, and the difference circuit output is electrically coupled to the second demodulator input of the demodulator.
  • the gain circuit comprises a low-pass filter (272) electrically coupled to a gain stage (274) comprising a defined gain, in which the nominally constant charge is proportional to the defined gain; and.
  • the MEMS device further comprises a bootstrap capacitance (336) that is electrically coupled between the electrode of the capacitive sense element and the output signal of the capacitive sense element circuit.
  • the bootstrap capacitance facilitates reducing noise of the output signal of the capacitive sense element circuit in response to the capacitive sense element being biased in a negative capacitance region.
  • a MEMS device e.g., microphone, accelerometer, pressure sensor, ultrasonic receiver, gyroscope, or other type of vibration sensing device, comprises: a capacitive sense element circuit (114) comprising a bias resistance (220) comprising a resistance input and a resistance output, a charge-pump (210) comprising a charge pump input and a charge pump output, and a capacitive sense element (230) comprising an electrode (222) and a sense capacitance, in which the charge-pump output generates a bias voltage at the resistance input, and the resistance output is electrically coupled to the electrode of the capacitive sense element.
  • a capacitive sense element circuit 114 comprising a bias resistance (220) comprising a resistance input and a resistance output
  • a charge-pump (210) comprising a charge pump input and a charge pump output
  • a capacitive sense element 230
  • the charge-pump output generates a bias voltage at the resistance input
  • the resistance output is electrically coupled to
  • the MEMS device further comprises a capacitance sensing circuit (112) comprising: a gain circuit (970) that comprises a difference circuit (910) and a filter (920); a demodulator (260) that modulates a first demodulator input and a second demodulator input to obtain a demodulator output that is electrically coupled, via the gain circuit, to the charge pump input; an AC signal source (240) that generates an AC signal (e.g., an analog voltage; a digital waveform) at a defined frequency, in which the AC signal is electrically coupled to the first demodulator input; and a test capacitance (250) comprising a test capacitance input and a test capacitance output.
  • a capacitance sensing circuit (112) comprising: a gain circuit (970) that comprises a difference circuit (910) and a filter (920); a demodulator (260) that modulates a first demodulator input and a second demodulator input to obtain a demodulator output that is electrically coupled, via the gain
  • the capacitance sensing circuit generates, based on the AC signal at the defined frequency, an AC test voltage at the test capacitance input.
  • the test capacitance output is electrically coupled to the electrode of the capacitive sense element.
  • the capacitive sense element circuit generates, based on the AC test voltage at the defined frequency, an output signal that is electrically coupled to the second demodulator input and that represents a value of the sense capacitance.
  • the demodulator output is electrically coupled to a first input of the difference circuit, a reference signal is electrically coupled to a second input of the difference circuit, a difference output of the difference circuit is electrically coupled, via the filter, to the chargepump input, and the demodulator output nominally equals the reference signal to facilitate maintenance of a nominally constant value of the sense capacitance.
  • the defined frequency is greater than a resonant frequency of the capacitive sense element. In embodiment(s), the defined frequency is in a range of about 50 kHz to about 1 MHz.
  • a first portion of the output signal of the capacitive sense element circuit represents an external force that has been applied to a membrane of the capacitive sense element, and a second portion of the output signal of the capacitive sense element circuit represents a measurement of the value of the sense capacitance.
  • a first magnitude of a sum of respective DC component values of the sense capacitance and the test capacitance is inversely proportional to a second magnitude of a second DC component of the reference signal.
  • an amplifier (410) is electrically coupled between the AC signal source and the test capacitance, and generates, based on the AC signal, the AC test voltage at the test capacitance input.
  • the amplifier comprises a summing amplifier (610) comprising a first amplifier input, a second amplifier input, and an amplifier output, in which the first amplifier input is electrically coupled to the AC signal, the second amplifier input is electrically coupled to the output signal of the capacitive sense element circuit, and the amplifier output is electrically coupled to the test capacitance input - the summing amplifier generating, via the amplifier output based on the AC signal, the AC test voltage at the test capacitance input.
  • a summing amplifier (610) comprising a first amplifier input, a second amplifier input, and an amplifier output, in which the first amplifier input is electrically coupled to the AC signal, the second amplifier input is electrically coupled to the output signal of the capacitive sense element circuit, and the amplifier output is electrically coupled to the test capacitance input - the summing amplifier generating, via the amplifier output based on the AC signal, the AC test voltage at the test capacitance input.
  • an amplitude of the second portion of the output signal of the capacitive sense element circuit is inversely proportional to the value of the sense capacitance.
  • the MEMS device further comprises a bootstrap capacitance (336) that is electrically coupled between the electrode of the capacitive sense element and the output signal of the capacitive sense element circuit.
  • the bootstrap capacitance facilitates reducing noise of the output signal of the capacitive sense element circuit in response to the capacitive sense element being biased in a negative capacitance region.
  • a method comprises detecting a value of a sense capacitance of a capacitive sense element of a MEMS device; generating a continuous time bias voltage that is inversely proportional to a capacitance value comprising the value of the sense capacitance; and in response to applying the continuous time bias voltage to the capacitive sense element, generating a nominally constant charge on the capacitive sense element.
  • the detecting of the value of the sense capacitance comprises applying an AC test voltage at a defined frequency to a test capacitance input of a test capacitance, in which a test capacitance output of the test capacitance is electrically coupled to the capacitive sense element, and an output signal of the MEMS device represents, based on the AC test voltage at the defined frequency, the value of the sense capacitance.
  • the applying of the AC test voltage to the test capacitance input further comprises applying the AC test voltage to the test capacitance input in a frequency range of about 50 kHz to about 1 MHz.
  • the method further comprises in response to biasing the capacitance of the capacitive sense element in a negative capacitance region, reducing, via a bootstrap capacitance that is electrically coupled to an output signal of the MEMS device, a noise of the output signal of the MEMS device.
  • CMEMS capacitance of the capacitive sense element depends on an electrode area (A) of an electrode of the capacitive sense element and a gap (g) between the electrode and a backplate of the capacitive sense element:
  • the gap depends on initial gap (g 0 ), external force (F, i.e., sound pressure), charge (q), and membrane stiffness (k):
  • the gap decreases with charge; and the capacitance increases with charge.
  • the voltage across the capacitive sense element changes due to charge, q, and due to changes in an external force (F), e.g., sound pressure, which has been applied to the capacitive sense element.
  • F an external force
  • FIG. 12 a plot (1200) of normalized charge versus normalized bias voltage (at zero force) of a conventional MEMS device, e.g., microphone, is illustrated, in accordance with various example embodiments.
  • the maximum bias voltage that can be applied, via conventional technologies, to the conventional MEMS device is a pull-in voltage of “Vpi”, e.g., represented by a ratio of 1 on the plot.
  • Point “A” represents a typical bias point of a conventional MEMS device, which is approximately 70% of the pull-in voltage.
  • Point “B” represents a higher bias voltage and charge, which has been applied to the conventional MEMS device, than bias voltage and charge that has been applied to the conventional MEMS device at point A; therefore, point B represents a higher capacitance and higher sensitivity of the conventional MEMS device than capacitance and sensitivity of the conventional MEMS device corresponding to point A.
  • the conventional MEMS device is stable with an applied bias voltage corresponding to point B ; however, because such bias voltage is near the pull-in voltage, the conventional MEMS device is likely to be unstable in practice due to parameter variation(s) of the conventional MEMS device that occur over process and temperature changes.
  • Point “C” represents a bias point corresponding to a charge, a sensitivity, and a capacitance that are higher than respective charges, sensitivities, and capacitances represented by bias points A and B ; however, point C it is beyond the pull-in voltage, and therefore the conventional MEMS device is unstable with a constant bias voltage being applied at point C.
  • FIG. 12 illustrates that such technologies are limited in an amount of charge that can be applied to the capacitive sense element, and thus in an amount of sensitivity that can be achieved - due to instability corresponding to the pull-in voltage.
  • various embodiments disclosed herein can enable improved biasing of a membrane of a MEMS device, e.g., beyond a pull-in voltage of the MEMS device, by facilitating maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, or by facilitating maintenance of a nominally constant capacitance value of the sense capacitance - enabling stable operation of the MEMS device at points A, B, and C illustrated in FIG. 12. Further, such embodiments facilitate improvement of a signal-to-noise ratio (SNR) of the MEMS device by biasing the MEMS device beyond the pull-in voltage/point.
  • SNR signal-to-noise ratio
  • FIGs. 2-3 block diagrams of respective MEMS device (110) circuits (200 and 300) that apply respective nominally constant charges to capacitive sense elements of the respective MEMS device circuits are illustrated, in accordance with various example embodiments.
  • the MEMS device (110) e.g., microphone, accelerometer, pressure sensor, ultrasonic receiver, gyroscope, or other type of vibration sensing device, comprises a capacitive sense element circuit (114) comprising a bias resistance (“Rb”) (220) comprising a resistance input and a resistance output, a charge-pump (“CP”) (210) comprising a charge pump input and a charge pump output, and a capacitive sense element (230) comprising an electrode (222) and a sense capacitance (“CMEMS”), in which the charge-pump output generates a bias voltage (“Vb”) at the resistance input, and the resistance output is electrically coupled to the electrode of the capacitive sense element.
  • Rb bias resistance
  • CP charge-pump
  • CMEMS sense capacitance
  • the electrode is electrically coupled to the membrane of the capacitive sense element. In yet other embodiment(s), the electrode is electrically coupled to a backplate of the capacitive sense element.
  • the electrode is electrically coupled to a high-pass filter (HPF) (232) that comprises a HPF resistance (“RHPF”) and a HPF capacitance (”CHPF”); and the HPF is electrically coupled to a unity gain buffer (234), which generates an output signal (“Vo”) of the capacitive sense element circuit.
  • HPF high-pass filter
  • RHPF HPF resistance
  • CHPF HPF capacitance
  • the output of the test capacitance and an input of a bootstrap capacitance (336) are electrically coupled between the HPF and the unity gain buffer.
  • a first portion of the output signal of the capacitive sense element circuit represents an external force (e.g., audio signal) that has been applied to a membrane of the capacitive sense element, and a second portion of the output signal of the capacitive sense element circuit represents a measurement of the value of the sense capacitance.
  • the bias resistance ranges from about 1 giga-ohm to about 1 tera-ohm. In other embodiment(s), the bias voltage ranges from about 5 volts to about 20 volts.
  • the MEMS device further comprises a capacitance sensing circuit (112) comprising: a gain circuit (270); an AC signal source (240) that generates an AC signal (e.g., analog voltage; a digital waveform) at a defined frequency (e.g., being greater than a resonant frequency of the capacitive sense element; being in a range of about 50 kHz to about 1 MHz); a demodulator (260) that modulates a first demodulator input and a second demodulator input to obtain a demodulator output that is electrically coupled, via the gain circuit, to the charge pump input; and a test capacitance (“Ct”) (250) comprising a test capacitance input and a test capacitance output.
  • a capacitance sensing circuit comprising: a gain circuit (270); an AC signal source (240) that generates an AC signal (e.g., analog voltage; a digital waveform) at a defined frequency (e.g., being greater than a resonant frequency of
  • the AC signal is electrically coupled to the first demodulator input and the test capacitance.
  • the capacitance sensing circuit generates, based on the AC signal at the defined frequency, an AC test voltage (“Vt”) at the test capacitance input; and the test capacitance output is electrically coupled to the electrode of the capacitive sense element.
  • Vt AC test voltage
  • the capacitive sense element circuit generates, based on the AC test voltage at the defined frequency, the output signal - the output signal representing a value of the sense capacitance as follows:
  • Vo Vt*Ct/(C ME Ms + C t ) .
  • the demodulator rectifies V o ,e.g., multiplies V o by a square wave at the same phase and frequency as Vt), resulting in a DC component of the demodulator output being equal to
  • the gain circuit comprises a low-pass filter (“LPF”)
  • the demodulator, LPF, and gain stage provide a feedback signal to the chargepump, in which the bias voltage is equal to
  • MEMS device is ideally, or nominally, constant, being equal to
  • the nominally constant charge (C[MEMS + ct) i s proportional to the defined gain G.
  • the charge on CMEMS can be considered nominally constant.
  • the MEMS device further comprises a bootstrap capacitance (“Cmatch”) (336) that is electrically coupled between the electrode of the capacitive sense element and the output signal of the capacitive sense element circuit.
  • the bootstrap capacitance is used to bootstrap Ct , e.g., to prevent, account for, improve upon, etc. reduced sensitivity and/or increased distortion.
  • FIG. 13 a block diagram (1300) of a small-signal model of a MEMS device, e.g., microphone, comprising a capacitive sense element is illustrated, in accordance with various example embodiments.
  • a MEMS device e.g., microphone
  • Css represents a small-signal capacitance of the MEMS device.
  • Cbs is a capacitance that is bootstrapped by a unity gain buffer (“+1”).
  • V n is a voltage source representing noise of the unity gain buffer.
  • V on ( 1 + — ) V n , in which larger values of Css represent lower values of Css' output signal noise.
  • the slope of the line representing the plot of normalized charge versus normalized bias voltage is the small signal capacitance representing the change in charge versus small changes in voltage given by
  • point A has a positive slope and positive value of C ss .
  • Point B has a larger slope than point A; and as the value of C ss at point B is larger than the value of C ss at point A, point B will have lower noise than point A.
  • Point C has a negative slope and therefore has a negative value of C ss .
  • FIGs. 4-5 illustrate block diagrams of respective MEMS device circuits (400 and 500) that include respective amplifiers (410) electrically coupled to respective test capacitances (250) - the respective MEMS devices applying respective nominally constant charges to capacitive sense elements of the respective MEMS device circuits, in accordance with various example embodiments.
  • an amplifier (410) is electrically coupled between the AC signal source and the test capacitance (250), and the amplifier generates, based on the AC signal at the defined frequency, the test voltage (Vt).
  • FIGs. 6-7 illustrates block diagrams of respective MEMS device circuits (600 and 700) that include respective summing amplifiers (610) electrically coupled to respective test capacitances (250) - the respective MEMS devices applying respective nominally constant charges to capacitive sense elements of the respective MEMS device circuits, in accordance with various example embodiments.
  • the demodulator rectifies V o , e.g., multiplies V o by a square wave at the same phase and frequency as Vt, resulting in a DC component of the demodulator output being equal to
  • the demodulator, LPF, and gain stage provide a feedback signal to the charge-pump, in which the bias voltage is equal to
  • the summing amplifier (610) comprises a first amplifier input, a second amplifier input, and an amplifier output.
  • the first amplifier input is electrically coupled to the AC signal
  • the second amplifier input is electrically coupled to the output signal of the capacitive sense element circuit
  • the amplifier output is electrically coupled to the test capacitance input.
  • FIG. 8 illustrates a block diagram of a MEMS device circuit (800) including a differential output - the MEMS device applying a nominally constant charge to a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • the capacitive sense element circuit comprises an inverting buffer (820) that generates an inverted output signal that is based on the output signal of the capacitance sense element circuit - a differential output signal, e.g., V o , represented by the output signal and the inverted output signal.
  • the capacitance sensing circuit comprises a difference circuit (810) that comprises a first difference circuit input, a second difference circuit input, and a difference circuit output - the difference circuit facilitating subtraction of the first difference input and the second difference input.
  • the first difference circuit input is electrically coupled to the output signal of the capacitive sense element circuit
  • the second difference circuit input is electrically coupled to the inverted output signal
  • the difference circuit output is electrically coupled to the second demodulator input of the demodulator.
  • FIG. 9 illustrates a block diagram of a MEMS device circuit (900) that facilitates maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • the MEMS device (110) e.g., microphone, accelerometer, pressure sensor, ultrasonic receiver, gyroscope, or other type of vibration sensing device, comprises a capacitive sense element circuit (114) comprising a bias resistance (“Rb”) (220) comprising a resistance input and a resistance output, a charge-pump (“CP”) (210) comprising a charge pump input and a charge pump output, and a capacitive sense element (230) comprising an electrode (222) and a sense capacitance (“CMEMS”).
  • the charge-pump output generates a bias voltage (“Vb”) at the resistance input, and the resistance output is electrically coupled to the electrode of the capacitive sense element.
  • the electrode is electrically coupled to the membrane of the capacitive sense element. In yet other embodiment(s), the electrode is electrically coupled to a backplate of the capacitive sense element.
  • the electrode is electrically coupled to a high-pass filter (HPF) (232) that comprises a HPF resistance (“RHPF”) and a HPF capacitance (”CHPF”); and the HPF is electrically coupled to a unity gain buffer (234), which generates an output signal (“Vo”) of the capacitive sense element circuit.
  • HPF high-pass filter
  • RHPF HPF resistance
  • CHPF HPF capacitance
  • test capacitance output and an input of the bootstrap capacitance are electrically coupled between the HPF and the unity gain buffer.
  • a first portion of the output signal of the capacitive sense element circuit represents an external force (e.g., audio signal) that has been applied to a membrane of the capacitive sense element
  • a second portion of the output signal of the capacitive sense element circuit represents a measurement of the value of the sense capacitance
  • the bias resistance ranges from about 1 giga-ohm to about 1 tera-ohm. In other embodiment(s), the bias voltage ranges from about 5 volts to about 20 volts.
  • the MEMS device further comprises a capacitance sensing circuit (112) comprising: a gain circuit (970) comprising a difference circuit (910) and a filter (920); an AC signal source (240) that generates an AC signal (e.g., analog voltage; a digital waveform) at a defined frequency (e.g., being greater than a resonant frequency of the capacitive sense element; being in a range of about 50 kHz to about 1 MHz); a demodulator (260) that modulates a first demodulator input and a second demodulator input to obtain a demodulator output (“Vdemod”) that is electrically coupled, via the gain circuit, to the charge pump input; and a test capacitance (“Ct”) (250) comprising a test capacitance input and a test capacitance output.
  • a capacitance sensing circuit comprising: a gain circuit (970) comprising a difference circuit (910) and a filter (920); an AC signal source (240) that generates an AC signal (e
  • the AC signal is electrically coupled to the first demodulator input and the test capacitance.
  • the capacitance sensing circuit generates, based on the AC signal at the defined frequency, an AC test voltage (“V”) at the test capacitance input; and the test capacitance output is electrically coupled to the electrode of the capacitive sense element.
  • V AC test voltage
  • the capacitive sense element circuit generates, based on the AC test voltage at the defined frequency, the output signal - the output signal being electrically coupled to the second demodulator input and representing a value of the sense capacitance as follows:
  • Vo Vt*Ct/(C M EMs + Ct) .
  • the demodulator rectifies V o ,e.g., multiplies V o by a square wave at the same phase and frequency as Vt), resulting in a DC component of the demodulator output being equal to
  • the demodulator output is electrically coupled to a first input of the difference circuit, and a reference signal (“V re f”) is electrically coupled to a second input of the difference circuit.
  • V re f a reference signal
  • a difference output of the difference circuit is electrically coupled, via the filter, to the charge-pump input.
  • a first magnitude of a sum of respective DC component values of the sense capacitance and the test capacitance is inversely proportional to a second magnitude of a second DC component of the reference signal.
  • the defined frequency is greater than a resonant frequency of the capacitive sense element. In other embodiment(s), the defined frequency is in a range of about 50 kHz to about 1 MHz.
  • a first portion of the output signal of the capacitive sense element circuit represents an external force that has been applied to a membrane of the capacitive sense element, and a second portion of the output signal of the capacitive sense element circuit represents a measurement of the value of the sense capacitance.
  • FIG. 10 illustrates a block diagram of a MEMS device circuit (1000) that includes an amplifier (410) electrically coupled to a test capacitance (250) - the MEMS device facilitating maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element (230) of the MEMS device, in accordance with various example embodiments.
  • An amplifier (410) is electrically coupled between the AC signal source (240) and the test capacitance (250); and the amplifier generates, based on the AC signal source, the test voltage (Vt).
  • FIG. 11 illustrates a block diagram of a MEMS device circuit (1100) that includes a summing amplifier (610) that is electrically coupled to a test capacitance (250) - the MEMS device circuit facilitating maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element (230) of the MEMS device, in accordance with various example embodiments.
  • a summing amplifier (610) that is electrically coupled to a test capacitance (250) - the MEMS device circuit facilitating maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element (230) of the MEMS device, in accordance with various example embodiments.
  • the summing amplifier (610) comprises a first amplifier input, a second amplifier input, and an amplifier output.
  • the first amplifier input is electrically coupled to the AC signal
  • the second amplifier input is electrically coupled to the output signal of the capacitive sense element circuit
  • the amplifier output is electrically coupled to the test capacitance input.
  • FIG. 14 illustrates a bode diagram (1400) of a constant capacitance filter (920) of a MEMS device (110), in which the MEMS device facilitates maintenance of a nominally constant capacitance value of a sense capacitance of a capacitive sense element of the MEMS device, in accordance with various example embodiments.
  • the constant capacitance filter includes an integrator (not shown) to provide high gain at DC summed with and LPF (not shown) to provide a defined phase margin with respect to maintaining closed- loop stability.
  • a unity gain frequency of the integrator and a bandwidth of the LPF are typically low frequency, e.g., less than 100 Hz; below a low- frequency corner, e.g., -3 dB cutoff point, of a frequency response of the MEMS device.
  • the low frequency corner, or other defined frequency points of the frequency response are adjusted during startup or overload recovery of the MEMS device, e.g., to enable the MEMS device to settle to a steady state condition within a defined period of time.
  • portion(s) of the constant capacitance filter are digital filters corresponding to discrete-time signals associated with a continuous-time analog signals of the constant capacitance filter, e.g., to satisfy low-frequency time constants corresponding to implementation of the continuous-time analog signals.
  • FIG. 15 illustrates a process/methodology in accordance with the disclosed subject matter.
  • the process/methodology is depicted and described as a series of acts. It is to be understood and appreciated that various embodiments disclosed herein are not limited by the acts illustrated and/or by the order of acts. For example, acts can occur in various orders and/or concurrently, and with other acts not presented or described herein. Furthermore, not all illustrated acts may be required to implement the process/methodology in accordance with the disclosed subject matter. In addition, those skilled in the art will understand and appreciate that the process/methodology could alternatively be represented as a series of interrelated states via a state diagram or events.
  • a process (1500) performed by a MEMS device e.g., microphone, accelerometer, pressure sensor, ultrasonic receiver, gyroscope, or other type of vibration sensing device, with respect to applying a nominally constant charge to a capacitive sense element of the MEMS device is illustrated, in accordance with various example embodiments.
  • a value of a sense capacitance of a capacitive sense element of the MEMS device is detected.
  • a continuous time bias voltage that is inversely proportional to a capacitance value comprising the value of the sense capacitance is generated.
  • a nominally constant charge on the capacitive sense element is generated in response to the continuous time bias voltage being applied to the capacitive sense element.
  • the value of the sense capacitance is detected by applying an AC test voltage at a defined frequency to a test capacitance input of a test capacitance, in which a test capacitance output of the test capacitance is electrically coupled to the capacitive sense element, and an output signal of the MEMS device represents, based on the AC test voltage at the defined frequency, the value of the sense capacitance.
  • the applying of the AC test voltage to the test capacitance input further comprises applying the AC test voltage to the test capacitance input in a frequency range of about 50 kHz to about 1 MHz.
  • the method further comprises reducing, via a bootstrap capacitance that is electrically coupled to an output signal of the MEMS device, a noise of the output signal of the MEMS device in response to biasing the capacitance of the capacitive sense element in a negative capacitance region.
  • circuit and “device” refer to substantially any analog and/or digital based device(s), circuit(s), etc. comprising, e.g., a micro-electro-mechanical structure, a resistor, a capacitor, a transistor, a diode, an inductor, a memory, a programmable device, e.g., fuse, field programmable gate array (FPGA), complex programmable logic device (CPLD), etc. relevant to performing operations and/or functions of circuit(s), device(s), system(s), etc. disclosed herein.
  • programmable device e.g., fuse, field programmable gate array (FPGA), complex programmable logic device (CPLD), etc. relevant to performing operations and/or functions of circuit(s), device(s), system(s), etc. disclosed herein.
  • exemplary and/or “demonstrative” is used herein to mean serving as an example, instance, or illustration.
  • the subject matter disclosed herein is not limited by such examples.
  • any aspect or design described herein as “exemplary” and/or “demonstrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it meant to preclude equivalent exemplary structures and techniques known to those of ordinary skill in the art having the benefit of the instant disclosure.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
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Abstract

L'invention concerne des modes de réalisation pour une charge ou une capacité constante pour des capteurs capacitifs de système micro-électromécanique (MEMS). Un dispositif MEMS comprend un circuit d'élément de détection comprenant une résistance de polarisation, une pompe de charge et un élément de détection capacitif comprenant une électrode et une capacité de détection. La pompe de charge génère, au niveau d'une résistance de polarisation couplée électriquement à l'électrode, une tension de polarisation qui est inversement proportionnelle à une valeur de capacité comprenant une valeur de la capacité de détection pour faciliter la maintenance d'une charge nominalement constante sur l'électrode. Un circuit de détection comprend une source de signal de courant alternatif (CA) qui génère un signal CA à une fréquence définie ; et génère, sur la base du signal CA, une tension de test CA à une capacité de test qui est électriquement couplée à l'électrode. Le circuit d'élément de détection génère, sur la base de la tension de test CA à la fréquence définie, un signal de sortie représentant la valeur de la capacité de détection.
PCT/US2022/053420 2021-12-20 2022-12-19 Charge ou capacité constante pour capteurs capacitifs de système micro-électrique-mécanique WO2023122044A1 (fr)

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US63/291,604 2021-12-20
US18/066,802 US20230192479A1 (en) 2021-12-20 2022-12-15 Constant charge or capacitance for capacitive micro-electrical-mechanical system sensors
US18/066,802 2022-12-15

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070160234A1 (en) * 2003-12-01 2007-07-12 Audioasics A/S Microphone with voltage pump
US20130279717A1 (en) * 2012-04-18 2013-10-24 Nxp B.V. Sensor circuit and calibration method
US20160157017A1 (en) * 2013-04-26 2016-06-02 Cirrus Logic International Semiconductor Limited Signal processing for mems capacitive transducers

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070160234A1 (en) * 2003-12-01 2007-07-12 Audioasics A/S Microphone with voltage pump
US20130279717A1 (en) * 2012-04-18 2013-10-24 Nxp B.V. Sensor circuit and calibration method
US20160157017A1 (en) * 2013-04-26 2016-06-02 Cirrus Logic International Semiconductor Limited Signal processing for mems capacitive transducers

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