# US 2014/0153746 A1 · Microphone Preamplifier Circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0153746 A1 - Document ID: US20140153746A1 - Status: Published application - Kind: A1 - Application number: 14/129,320 - Filed: 2012-07-13 - Published: 2014-06-05 - Earliest claimed: 2011-07-26 - Assignees: ST-Ericsson SA - Inventors: Germano Nicollini; Andrea Barbieri - Web page: https://patentgrep.com/patent/US20140153746A1 ## CPC - H04R 3/00: Circuits for transducers (arrangements for producing a reverberation or echo sound G10K15/08; amplifiers H03F) - H03F 3/005: {using switched capacitors, e.g. dynamic amplifiers; using switched capacitors as resistors in differential amplifiers (H03F3/45 takes precedence)} - H03F 3/187: in integrated circuits - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03F 3/45928: {using IC blocks as the active amplifying circuit} - H03F 3/45937: {Measuring at the loading circuit of the differential amplifier} - H03F 3/45959: {Controlling the input circuit of the differential amplifier} - H03F 2203/45512: the FBC comprising one or more capacitors, not being switched capacitors, and being coupled between the LC and the IC - H03F 2203/45514: the FBC comprising one or more switched capacitors, and being coupled between the LC and the IC - H03F 2203/45528: the FBC comprising one or more passive resistors and being coupled between the LC and the IC - 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) - H03F: AMPLIFIERS ## Abstract A microphone preamplifier circuit (60) is described, adapted to be connected to a microphone circuit (MCD), the microphone circuit (MCD) comprising a microphone (3) and at least one output node (MO, MO′). The microphone preamplifier circuit (60) comprises a preamplifier (PA) comprising: —at least one input node (10, 10′) adapted to be connected to said output node (MO, MO′); —an operational amplifier (OA) comprising at least one input (20, 20′) and at least one output (21, 21′); —at least one input DC decoupling capacitor (CD, CD′) connected between said input node (10, 10′) and said first input of the operational amplifier (20,20′); at least one feedback capacitor (C2A, C2A′) connected between the input (20,20′) and the output (21, 21′) of the operational amplifier (OA) in order to set together with said input DC decoupling capacitor (CD, CD′) a gain value of the preamplifier circuit (60); —a first (40, 40′) and a second feed node (41, 41′) adapted to be fed by a first (VCIMIN) and a second (VCM) bias voltage respectively. The preamplifier (PA) further comprises at least one switched capacitor (C2B, C2B′) adapted to be selectively and alternatively connected under the control of a clock signal (CK): —between said input (20, 20′) and said output (21, 21′) of the operational amplifier (OA); and—between said first (40, 40′) and said second (41, 41′) feed node. ## Claims ### Claim 1 Microphone preamplifier circuit adapted to be connected to a microphone circuit, the microphone circuit comprising a microphone and at least one output node, the microphone preamplifier circuit (60) comprising a preamplifier comprising: at least one input node adapted to be connected to said output node; an operational amplifier comprising at least one input and at least one output; at least one input DC decoupling capacitor connected between said input node and said first input of the operational amplifier; at least one feedback capacitor connected between the input and the output of the operational amplifier in order to set together with said input DC decoupling capacitor a gain value of the preamplifier circuit; a first and a second feed node adapted to be fed by a first and a second bias voltage respectively; wherein said preamplifier further comprises at least one switched capacitor adapted to be selectively and alternatively connected under the control of a clock signal: between said input and said output of the operational amplifier; and between said first and said second feed node; and wherein said preamplifier further comprises an anti-aliasing filter having an output terminal connected to said input node and an input terminal connected/connectable to said output node of the microphone circuit. ### Claim 2 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said switched capacitor comprises: a first plate adapted to be selectively connected to said input of the operational amplifier and said first feed node; a second plate adapted to be selectively connected to said output of the operational amplifier and said second feed node; and wherein said second feed node is configured to be fed with the common mode voltage of said operational amplifier and said first feed node is configured to be fed with a further voltage appropriate for input operation of said operational amplifier. ### Claim 3 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said operational amplifier is fed with a supply voltage and wherein: said common mode voltage (VCM) is half of said supply voltage; and said further voltage is lower than said common mode voltage if the operational amplifier has a P-type input and higher than said common voltage if the operational amplifier has a N-type input. ### Claim 4 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said clock signal has a frequency such that said switched capacitor is adapted to discharge said feedback capacitor at a relatively low frequency so that the preamplifier is adapted to implement a high pass filtering function which does not interfere with audio signals of interest for the operation of said microphone. ### Claim 5 (depends on 4) Microphone preamplifier circuit according to claim 4, wherein said high pass filtering function has a high pass cut-off frequency of 6 Hz or about 6 Hz. ### Claim 6 (depends on 4) Microphone preamplifier circuit according to claim 4, wherein said clock signal has a frequency of the order of magnitude of 100 kHz. ### Claim 7 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said switched capacitor has a capacitance value significantly lower than a capacitance value of said feedback capacitor. ### Claim 8 (depends on 7) Microphone preamplifier circuit according to claim 7, wherein said switched capacitor has a capacitance value of about three magnitude orders lower the capacitance value of said feedback capacitor. ### Claim 9 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein the operational amplifier is a differential amplifier, said preamplifier circuit having a symmetrical circuital structure having two of said input DC decoupling capacitors, two of said feedback capacitors and two of said switched capacitors. ### Claim 10 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said operational amplifier is arranged in said microphone preamplifier circuit in order to operate in an inverting configuration. ### Claim 11 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said anti-aliasing filter comprises a plurality of RC ladder, or serial, cells. ### Claim 12 (depends on 1) Microphone preamplifier circuit according to claim 1, comprising a multiplexer adapted to selectively connect said input node to one of a plurality of microphone circuits. ### Claim 13 (depends on 1) Microphone preamplifier circuit according to claim 1, wherein said multiplexer, said anti-aliasing filter, said input decoupling capacitor and said preamplifier are integrated in a same chip. ### Claim 14 (depends on 1) Microphone system comprising at least a microphone circuit and the microphone preamplifier circuit according to claim 1. ### Claim 15 (depends on 14) Device provided with audio processing and/or recording and/or communication capabilities, comprising the microphone system according to claim 14.