# US 11,309,855 B2 · Charge amplifier circuit for high-temperature piezoelectric transducers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,309,855 B2 - Document ID: US11309855B2 - Status: Granted - Kind: B2 - Application number: 16/798,383 - Filed: 2020-02-23 - Published: 2021-08-12 - Granted: 2022-04-19 - Earliest claimed: 2020-02-10 - Assignees: Meggitt (Orange County), Inc. - Applicants: Meggitt (Orange County), Inc. - Inventors: Felix A. Levinzon; Margie Mattingly - Web page: https://patentgrep.com/patent/US11309855B2 ## CPC - H03F 3/70: Charge amplifiers - B06B 1/06: operating with piezoelectric effect or with electrostriction (piezoelectric or electrostrictive devices per se H10N30/00) - G01H 11/08: using piezoelectric devices - G01P 15/09: by piezoelectric pick-up - H03F 3/1855: {with junction-FET devices} - H03F 3/187: in integrated circuits - H03F 3/347: in integrated circuits - H03F 3/45071: {with semiconductor devices only} - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03F 2200/93: Two or more transistors are coupled in a Darlington composite transistor configuration, all transistors being of the same type - H03F: AMPLIFIERS - B06B: METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, {e.g.} FOR PERFORMING MECHANICAL WORK IN GENERAL (for particular applications, see the relevant subclasses, e.g. B07B1/40, B23Q17/12, B24B31/06; measurement of mechanical vibrations G01H; in direction finding, locating, distance or velocity measuring G01S; {generating seismic energy G01V1/02}; control of mechanical vibrations in general G05D; sound-producing devices, e.g. bells, sirens, whistles G10K, {e.g. methods or devices for transmitting, conducting, or directing sound in general G10K11/00}; generation of electrical oscillations H03B; electromechanical resonators in general H03H; electromechanical transducers {for communication techniques, e.g. microphones, speakers} H04R) - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) ## Abstract A circuit has an input and a two-wire output. The circuit is designed for use with HTPE transducers and comprised of four stages. The first stage is a charge amplifier based on operational amplifier, the second stage is a 1-pole passive low-pass filter, the third stage is an active 2-pole low-pass filter based on two JFETs, and the fourth stage is an emitter follower comprising two bipolar junction transistors connected to each other in Darlington configuration. ## Claims ### Claim 1 A charge amplifier circuit comprising: an input and a two-wire output; a charge amplifier comprising an operational amplifier and a feedback capacitor; a first low-pass filter directly coupled to an output of the charge amplifier; a second low-pass filter coupled to an output of the first low-pass filter by a decoupling capacitor; a constant current source located between a positive power supply input of the operational amplifier and a first output of the two-wire output wherein the first output of the two-wire output carries signal and power for the charge amplifier circuit; and a first feedback circuit that provides direct current bias for a non-inverting input of the operational amplifier. ### Claim 2 (depends on 1) The charge amplifier circuit of claim 1 further comprising an emitter follower directly coupled to an output of the second low-pass filter. ### Claim 3 (depends on 1) The charge amplifier circuit of claim 1, wherein the first low-pass filter is a passive 1-pole low-pass filter. ### Claim 4 (depends on 3) The charge amplifier circuit of claim 3, wherein the first low-pass filter comprises a resistor and a capacitor. ### Claim 5 (depends on 1) The charge amplifier circuit of claim 1, wherein the second low-pass filter is an active 2-pole low-pass filter. ### Claim 6 (depends on 5) The charge amplifier circuit of claim 5, wherein the second low-pass filter comprises two junction field effect transistors (JFET) connected in series with each other, three resistors, and two capacitors. ### Claim 7 (depends on 1) The charge amplifier circuit of claim 1, further comprising a second feedback circuit that provides direct current bias for an inverting input of the operational amplifier. ### Claim 8 (depends on 1) The charge amplifier circuit of claim 1, wherein a piezoelectric transducer is in electrical communication with the input of the charge amplifier circuit. ### Claim 9 A charge amplifier circuit comprising: an input and a two-wire output; a charge amplifier comprising an operational amplifier and a feedback capacitor; a first low-pass filter in electrical communication with an output of the charge amplifier; a second low-pass filter in electrical communication with an output of the first low-pass filter; an emitter follower in electrical communication with an output of the second low-pass filter; and a constant current source located between a positive power supply input of the operational amplifier and a first output of the two-wire output wherein the first output of the two-wire output carries signal and power for the charge amplifier circuit. ### Claim 10 (depends on 9) The charge amplifier circuit of claim 9, wherein the first low-pass filter is a passive 1-pole low-pass filter. ### Claim 11 (depends on 10) The charge amplifier circuit of claim 10, wherein the first low-pass filter comprises a resistor and a capacitor. ### Claim 12 (depends on 9) The charge amplifier circuit of claim 9, wherein the second low-pass filter is an active 2-pole low-pass filter. ### Claim 13 (depends on 12) The charge amplifier circuit of claim 12, wherein the second low-pass filter comprises two junction field effect transistors (JFET) connected in series with each other, three resistors, and two capacitors. ### Claim 14 (depends on 9) The charge amplifier circuit of claim 9, further comprising a first feedback circuit that provides direct current bias for a non-inverting input of the operational amplifier. ### Claim 15 (depends on 14) The charge amplifier circuit of claim 14, further comprising a second feedback circuit that provides direct current bias for an inverting input of the operational amplifier. ### Claim 16 (depends on 9) The charge amplifier circuit of claim 9, wherein a piezoelectric transducer is in electrical communication with the input of the charge amplifier circuit. ### Claim 17 A charge amplifier circuit comprising: an input and a two-wire output; a charge amplifier comprising an operational amplifier and a feedback capacitor; a first low-pass filter directly coupled to an output of the charge amplifier wherein the first low-pass filter is a 1-pole passive low-pass filter; a second low-pass filter coupled to an output of the first low-pass filter by a decoupling capacitor wherein the second low pass filter is a 2-pole active low-pass filter; an emitter follower directly coupled to an output of the second low-pass filter; and a constant current source located between a positive power supply input of the operational amplifier and a first output of the two-wire output wherein the first output of the two-wire output carries signal and power for the charge amplifier circuit. ### Claim 18 (depends on 17) The charge amplifier circuit of claim 17, wherein a piezoelectric transducer is in electrical communication with the input of the charge amplifier circuit. ### Claim 19 (depends on 17) The charge amplifier circuit of claim 17, further comprising a first feedback circuit that provides direct current bias for a non-inverting input of the operational amplifier and a second feedback circuit that provides direct current bias for an inverting input of the operational amplifier.