# US 10,481,121 B2 · MEMS sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,481,121 B2 - Document ID: US10481121B2 - Status: Granted - Kind: B2 - Application number: 15/904,737 - Filed: 2018-02-26 - Published: 2018-08-30 - Granted: 2019-11-19 - Earliest claimed: 2017-02-27 - Assignees: Cirrus Logic, Inc. - Applicants: Cirrus Logic International Semiconductor Ltd. - Inventors: Paul Wilson; Karthikeya Kodur - Web page: https://patentgrep.com/patent/US10481121B2 ## CPC - H03F 3/187: in integrated circuits - G01D 5/24: by varying capacitance - G01D 5/2417: {by varying separation} - G01N 27/228: {Circuits therefor (measuring capacitance per se G01R27/26)} - H03F 3/45179: {using MOSFET transistors as the active amplifying circuit (H03F3/45278 takes precedence)} - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03F 3/45645: {Controlling the input circuit of the differential amplifier} - H03F 3/45941: {Controlling the input circuit of the differential amplifier} - H04R 3/06: of electrostatic transducers - H04R 19/005: {using semiconductor materials} - H03F 2201/3212: Using a control circuit to adjust amplitude and phase of a signal in a signal path - H03F 2203/45418: the CMCL comprising a resistor addition circuit - H03F 2203/45424: the CMCL comprising a comparator circuit - H04R 2499/11: Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's - H03F: AMPLIFIERS - 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 - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract This application relates to methods and apparatus for operating MEMS sensors, in particular MEMS capacitive sensors (CMEMS) such as a microphones. An amplifier apparatus (300) is arranged to amplify an input signal (VINP) received at a sense node (104) from the MEMS capacitive sensor. An antiphase signal generator (201; 304) generates a second signal (VINN) which is in antiphase with the input signal (VINP) and an amplifier arrangement (105; 305) is configured to receive the input signal (VINP) at a first input and the second signal (VINN) at a second input and to output corresponding amplified first and second output signals. This converts a single ended input signal effectively into a differential input signal. ## Claims ### Claim 1 An amplifier apparatus for amplifying an input signal from a MEMS capacitive sensor comprising: a sense node for receiving the input signal; an antiphase signal generator for generating a second signal which is in antiphase with the input signal; and an amplifier arrangement configured to receive the input signal at a first input and the second signal at a second input and to output corresponding first and second output signals, wherein the antiphase signal generator generates the second signal based on a common-mode voltage of the first and second output signals. ### Claim 2 (depends on 1) An amplifier arrangement as claimed in claim 1 further comprising biasing circuitry for generating a bias voltage for biasing the MEMS capacitive sensor at a biasing node wherein the amplifier arrangement is configured to modulate the bias voltage at the bias node with a modulation signal based on the second signal. ### Claim 3 (depends on 2) An amplifier arrangement as claimed in claim 2 comprising a feedback path for feeding the second signal or the second output signal back to the biasing node. ### Claim 4 (depends on 3) An amplifier arrangement as claimed in claim 3 wherein said feedback path comprises a biasing capacitor. ### Claim 5 (depends on 1) An amplifier apparatus as claimed in claim 1 wherein the antiphase signal generator comprises a feedback amplifier configured to receive a common-mode signal indicative of a common mode voltage of the first and second output signals and a common-mode reference voltage and to drive the second signal at the second input of amplifier arrangement to keep the common mode voltage of the first and second output signals to be equal to the common-mode reference voltage. ### Claim 6 (depends on 5) An amplifier apparatus as claimed in claim 5 comprising first and second resistances connected in series between a first output node driven with the first output signal and a second output node driven with the second output signal, wherein the common-mode signal is derived from the midpoint of the first and second resistances. ### Claim 7 (depends on 5) An amplifier apparatus as claimed in claim 5 comprising a common-mode reference generator for generating the common-mode reference voltage based on an input reference voltage, wherein the common-mode reference generator comprises a transistor which is a scaled replica of an input transistor of the amplifier arrangement. ### Claim 8 (depends on 1) An amplifier apparatus as claimed in claim 1 wherein the antiphase signal generator comprises an inverting amplifier configured to receive the input signal from the sense node. ### Claim 9 (depends on 1) An amplifier apparatus as claimed in claim 1 wherein the amplifier arrangement comprises a first single-ended amplifier for amplifying the input signal. ### Claim 10 (depends on 9) An amplifier apparatus as claimed in claim 9 wherein the amplifier arrangement further comprises a second single-ended amplifier for amplifying the second signal. ### Claim 11 (depends on 9) An amplifier apparatus as claimed in claim 9 wherein the first amplifier comprise an input transistor with a gate terminal connected to the sense node and a bootstrap circuit for driving a drain terminal of the input transistor in phase with the first output signal. ### Claim 12 (depends on 1) An amplifier apparatus as claimed in claim 1 comprising an input bypass switch for connecting the first input of the amplifier arrangement to the second input. ### Claim 13 (depends on 12) An amplifier apparatus as claimed in claim 12 further comprising clamp controller for selectively controlling the input bypass switch to clamp the input signal within a defined voltage range. ### Claim 14 (depends on 13) An amplifier apparatus as claimed in claim 13 wherein the clamp controller is configured to monitor at least one of the input signal, the first output signal and the second output signal against a clamp limit. ### Claim 15 (depends on 12) An amplifier arrangement as claimed in claim 12 wherein the apparatus is configured to close said input bypass switch in response to a start-up control signal. ### Claim 16 (depends on 2) An amplifier arrangement as claimed in claim 2 wherein said biasing circuitry comprises a voltage source for outputting the bias voltage and a resistance between the voltage source and the biasing node and comprising a biasing bypass switch for providing a bypass path that bypassing the resistance between the voltage source and the biasing node. ### Claim 17 (depends on 16) An amplifier arrangement as claimed in claim 16 wherein the voltage source is also configured to generate a control voltage, the control voltage being higher than the bias voltage, wherein the biasing circuitry is configured such that, in normal operation the control voltage is applied to a gate terminal of the biasing bypass switch. ### Claim 18 An amplifier apparatus for amplifying an input signal from a MEMS capacitive sensor comprising: an amplifier arrangement having first and second inputs; wherein the first input is configured to receive the input signal and the second input is configured to receive a second signal which is in antiphase with the input signal; a signal generator for generating the second signal at said second input; and a bias source for biasing the MEMS capacitive sensor with a bias voltage; wherein the bias voltage is modulated based on the second signal, wherein the signal generator generates the second signal based on a common-mode voltage of first and second output signals of the amplifier arrangement. ### Claim 19 An amplifier arrangement for amplifying an input signal from a MEMS capacitive sensor comprising: a first single-ended input amplifier configured to receive and amplify the input signal as a first output signal; a second single-ended input amplifier configured to receive and amplify a second signal as a second output signal; wherein the second signal is generated by the amplifier arrangement to be in antiphase to the first signal; and a modulator for modulating a bias voltage applied to the MEMS capacitive sensor based on said second signal, wherein the second signal is generated by the amplifier arrangement based on a common-mode voltage of the first and second output signals. ### Claim 20 An amplifier apparatus for amplifying an input signal from a MEMS capacitive sensor comprising: a sense node for receiving the input signal; an antiphase signal generator for generating a second signal which is in antiphase with the input signal; and an amplifier arrangement configured to receive the input signal at a first input and the second signal at a second input and to output corresponding first and second output signals, wherein the antiphase signal generator comprises a feedback amplifier configured to receive a common-mode signal indicative of a common mode voltage of the first and second output signals and a common-mode reference voltage and to drive the second signal at the second input of the amplifier arrangement to keep the common mode voltage of the first and second output signals to be equal to the common-mode reference voltage. ### Claim 21 (depends on 20) An amplifier apparatus as claimed in claim 20 comprising first and second resistances connected in series between a first output node driven with the first output signal and a second output node driven with the second output signal, wherein the common-mode signal is derived from the midpoint of the first and second resistances. ### Claim 22 (depends on 20) An amplifier apparatus as claimed in claim 20 comprising a common-mode reference generator for generating the common-mode reference voltage based on an input reference voltage, wherein the common-mode reference generator comprises a transistor which is a scaled replica of an input transistor of the amplifier arrangement. ### Claim 23 An amplifier apparatus for amplifying an input signal from a MEMS capacitive sensor comprising: an amplifier arrangement having first and second inputs; wherein the first input is configured to receive the input signal and the second input is configured to receive a second signal which is in antiphase with the input signal; a signal generator for generating the second signal at said second input; and a bias source for biasing the MEMS capacitive sensor with a bias voltage; wherein the bias voltage is modulated based on the second signal, wherein the signal generator comprises a feedback amplifier configured to receive a common-mode signal indicative of a common mode voltage of first and second output signals of the amplifier arrangement and a common-mode reference voltage and to drive the second signal at the second input of the amplifier arrangement to keep the common mode voltage of the first and second output signals to be equal to the common-mode reference voltage. ### Claim 24 (depends on 23) An amplifier apparatus as claimed in claim 23 comprising first and second resistances connected in series between a first output node driven with the first output signal and a second output node driven with the second output signal, wherein the common-mode signal is derived from the midpoint of the first and second resistances. ### Claim 25 (depends on 23) An amplifier apparatus as claimed in claim 23 comprising a common-mode reference generator for generating the common-mode reference voltage based on an input reference voltage, wherein the common-mode reference generator comprises a transistor which is a scaled replica of an input transistor of the amplifier arrangement. ### Claim 26 An amplifier arrangement for amplifying an input signal from a MEMS capacitive sensor comprising: a first single-ended input amplifier configured to receive and amplify the input signal as a first output signal; a second single-ended input amplifier configured to receive and amplify a second signal as a second output signal; wherein the second signal is generated by the amplifier arrangement to be in antiphase to the first signal; and a modulator for modulating a bias voltage applied to the MEMS capacitive sensor based on said second signal, wherein the second single-ended input amplifier comprises a feedback amplifier configured to receive a common-mode signal indicative of a common mode voltage of the first and second output signals and a common-mode reference voltage and to drive the second signal at the second input of the amplifier arrangement to keep the common mode voltage of the first and second output signals to be equal to the common-mode reference voltage. ### Claim 27 (depends on 26) An amplifier apparatus as claimed in claim 26 comprising first and second resistances connected in series between a first output node driven with the first output signal and a second output node driven with the second output signal, wherein the common-mode signal is derived from the midpoint of the first and second resistances. ### Claim 28 (depends on 26) An amplifier apparatus as claimed in claim 26 comprising a common-mode reference generator for generating the common-mode reference voltage based on an input reference voltage, wherein the common-mode reference generator comprises a transistor which is a scaled replica of an input transistor of the amplifier arrangement.