# US 2023/0408564 A1 · Low noise readout interface for capacitive sensors with negative capacitance > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2023/0408564 A1 - Document ID: US20230408564A1 - Status: Published application - Kind: A1 - Application number: 18/331,323 - Filed: 2023-06-08 - Published: 2023-12-21 - Earliest claimed: 2022-06-08 - Assignees: InvenSense, Inc. - Applicants: Invensense, Inc. - Inventors: Stefano Valle; Tomasz E. Hanzlik - Web page: https://patentgrep.com/patent/US20230408564A1 ## CPC - G01R 27/2605: {Measuring capacitance (capacitive sensors G01D5/24)} - H03F 1/223: {with MOSFET's} - H03F 1/26: Modifications of amplifiers to reduce influence of noise generated by amplifying elements - H03F 1/3264: {in audio amplifiers} - H03F 3/183: with semiconductor devices only - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03G 3/3005: {in amplifiers suitable for low-frequencies, e.g. audio amplifiers (H03G3/32, H03G3/34 take precedence)} - H04R 3/00: Circuits for transducers (arrangements for producing a reverberation or echo sound G10K15/08; amplifiers H03F) - H03F 2203/45546: the IC comprising one or more capacitors feedback coupled to the IC - H04R 19/04: Microphones (H04R19/01 takes precedence) - H04R 2201/003: Mems transducers or their use - H04R 2410/03: Reduction of intrinsic noise in microphones - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H03F: AMPLIFIERS - H03G: CONTROL OF AMPLIFICATION - 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 Disclosed embodiments provide a self-contained topology that enables a significant noise reduction of capacitive sensor readout interfaces. For example, various embodiments can provide low noise capacitive sensor readout interfaces or analog front ends having a main buffer amplifier in a bootstrap configuration, wherein a bootstrap loop configuration comprises a negative capacitance coupled to an input of the main buffer amplifier with a negative impedance converter. ## Claims ### Claim 1 An apparatus, comprising: a source follower sensor readout interface comprising a main buffer amplifier, wherein the main buffer amplifier is configured in a bootstrap configuration at an output of a capacitive sensor; and a bootstrap loop of the bootstrap configuration comprising a negative capacitance coupled to an input of the main buffer amplifier, wherein the bootstrap configuration comprising a negative capacitance at the input of the main buffer amplifier is configured to reduce noise associated with the source follower sensor readout interface and that is attributable to the main buffer amplifier. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the bootstrap configuration comprising the negative capacitance comprises a negative capacitance converter. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein the negative capacitance converter comprises a negative impedance converter (NIC) buffer amplifier configured to balance noise associated with the NIC buffer amplifier with noise associated the main buffer amplifier to increase signal-to-noise (SNR) of the source follower sensor readout interface. ### Claim 4 (depends on 2) The apparatus of claim 2, wherein the negative capacitance converter is coupled to the main buffer amplifier at the input to the main buffer amplifier. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the negative capacitance converter is coupled to the input of the main buffer amplifier in the bootstrap loop. ### Claim 6 (depends on 4) The apparatus of claim 4, wherein the negative capacitance converter is coupled between the input of the main buffer amplifier and ground. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the bootstrap loop is configured to provide a reduction of source follower sensor readout interface output impedance based at least in part on the negative capacitance. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the bootstrap loop is configured to provide at least one of a signal gain or signal attenuation for an output signal associated with the capacitive sensor. ### Claim 9 (depends on 8) The apparatus of claim 8, further comprising: an automatic gain control (AGC) controller component associated with the source follower sensor readout interface configured to adjust the at least one of the signal gain or signal attenuation of the source follower sensor readout interface for the output signal. ### Claim 10 (depends on 9) The apparatus of claim 9, wherein the AGC controller component is configured to apply at least one of a predetermined set of capacitances in the negative capacitance converter to adjust the at least one of the signal gain or the signal attenuation. ### Claim 11 (depends on 1) The apparatus of claim 1, wherein the bootstrap configuration comprising the negative capacitance at the input of the main buffer amplifier is configured to lower output impedance associated with the source follower sensor readout interface as a result of an additional capacitance located between the negative capacitance and the source follower sensor readout interface. ### Claim 12 (depends on 1) The apparatus of claim 1, source follower sensor readout interface comprises a microelectromechanical systems (MEMS) acoustic sensor readout interface. ### Claim 13 A method, comprising: applying a negative capacitance at an input of a main buffer amplifier in a source follower sensor readout interface associated with a capacitive sensor, wherein the main buffer amplifier is configured in a bootstrap configuration at an output of the capacitive sensor; reducing source follower sensor readout interface noise via a bootstrap loop of the bootstrap configuration, wherein the bootstrap loop coupled to the negative capacitance is configured to reduce noise associated with the source follower sensor readout interface and that is attributable to the main buffer amplifier. ### Claim 14 (depends on 13) The method of claim 13, wherein the applying the negative capacitance at the input of the main buffer amplifier in the source follower sensor readout interface comprises applying the negative capacitance via a negative capacitance converter coupled to the main buffer amplifier at the input to the main buffer amplifier. ### Claim 15 (depends on 14) The method of claim 14, wherein the applying the negative capacitance via the negative capacitance converter comprises applying the negative capacitance via the negative capacitance converter to the input of the main buffer amplifier in the bootstrap loop. ### Claim 16 (depends on 14) The method of claim 14, wherein the applying the negative capacitance via the negative capacitance converter comprises applying the negative capacitance via the negative capacitance converter between the input of the main buffer amplifier and ground. ### Claim 17 (depends on 14) The method of claim 14, wherein the reducing source follower sensor readout interface noise comprises balancing noise associated with a negative impedance converter (NIC) buffer amplifier of the negative capacitance converter with noise associated the main buffer amplifier to increase signal-to-noise (SNR) of the source follower sensor readout interface. ### Claim 18 (depends on 13) The method of claim 13, further comprising: reducing source follower sensor readout interface output impedance based at least in part on the applying the negative capacitance at the input of a main buffer amplifier in the bootstrap loop. ### Claim 19 (depends on 14) The method of claim 14, further comprising: providing, via an automatic gain control (AGC) controller component, at least one of a signal gain or signal attenuation for an output signal associated with the capacitive sensor. ### Claim 20 (depends on 19) The method of claim 19, wherein the providing the at least one of the signal gain or the signal attenuation for the output signal associated with the capacitive sensor comprises applying at least one of a predetermined set of capacitances in the negative capacitance converter to adjust the at least one of the signal gain or the signal attenuation.