WO2013102499A1 - Differential microphone and method for driving a differential microphone - Google Patents

Differential microphone and method for driving a differential microphone Download PDF

Info

Publication number
WO2013102499A1
WO2013102499A1 PCT/EP2012/050154 EP2012050154W WO2013102499A1 WO 2013102499 A1 WO2013102499 A1 WO 2013102499A1 EP 2012050154 W EP2012050154 W EP 2012050154W WO 2013102499 A1 WO2013102499 A1 WO 2013102499A1
Authority
WO
WIPO (PCT)
Prior art keywords
transistor
microphone
differential
port
terminal
Prior art date
Application number
PCT/EP2012/050154
Other languages
French (fr)
Inventor
Jelena Citakovic HAAS-CHRISTENSEN
Tomasz Hanzlik
Ivan Riis NIELSEN
Daifi Haoues SASSENE
Tomasz Marczak
Original Assignee
Epcos Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Epcos Ag filed Critical Epcos Ag
Priority to US14/370,720 priority Critical patent/US9693135B2/en
Priority to DE112012005578.0T priority patent/DE112012005578B4/en
Priority to PCT/EP2012/050154 priority patent/WO2013102499A1/en
Priority to JP2014550651A priority patent/JP5986221B2/en
Publication of WO2013102499A1 publication Critical patent/WO2013102499A1/en

Links

Classifications

    • 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
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/08—Mouthpieces; Microphones; Attachments therefor
    • 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
    • H04R19/01—Electrostatic transducers characterised by the use of electrets
    • H04R19/016—Electrostatic transducers characterised by the use of electrets for microphones

Definitions

  • the present invention refers to differential microphones and methods for driving such microphones.
  • ECM electret condenser microphone
  • Microphones such as MEMS microphones comprise a perforated backplate and a flexible membrane.
  • the backplate and the mem ⁇ brane establish electrodes of a capacitor.
  • Received sound signals induce oscillations of the membrane. Due to corre ⁇ sponding induced oscillations of the capacity, acoustic sig ⁇ nals can be converted into electrical signals.
  • double back ⁇ plate microphones or double membrane microphones can be cre- ated.
  • the membrane is ar ⁇ ranged between two perforated backplates; in double membrane microphones, a perforated backplate is arranged between two flexible membranes.
  • a microphone that comprises two capacitors and provides a differential output port.
  • a differential port comprises two terminals where each terminal mainly provides the same absolute value of a voltage or a current but with opposite polarity.
  • microphones with differential ports provide a better signal quality
  • their use contrary to simpler microphones with a single capacitor as an acusto-electrical transducer, has not yet been commercialized, thus not much work has been devoted yet to methods to interface such microphones.
  • Microphones providing differential signals are known from US 4,757,545, US 2008/0310655 Al or US 2010/254544 A.
  • the signal quality depends on the quality of the acoustic ca- pacitors' bias voltage. Further, the signal quality depends on the quality of the common mode output voltage. What is needed is a differential microphone with an improved bias voltage of the microphones acoustic capacitors and a better defined common mode output voltage and a method for driving such a microphone.
  • an object of the present invention to provide a differential microphone that can process differential signals from the microphone's acoustic capacitors, that provide a stable and well-defined bias voltage for the capacitor's electrodes and that is able to provide well defined common mode output voltage. It is also an object of the present in- vention to provide amplification of the differential micro ⁇ phone signal with well defined gain, i.e. a well defined am ⁇ plification factor.
  • the present invention provides a differential mi- crophone and a method for driving such a microphone according to the independent claims.
  • Dependent claims provide preferred embodiments thereof.
  • a differential microphone comprises a first microphone elec- trode, a central microphone electrode and a second microphone electrode.
  • the microphone further comprises a differential output port and a differential amplifier stage.
  • the amplifier stage has a differential input port and a differential output port being connected to the output port of the microphone.
  • the microphone further comprises a common mode feedback cir ⁇ cuit having a differential output port being connected to the output port of the microphone.
  • the common mode feedback circuit provides a well defined com- mon mode output voltage.
  • Such a microphone provides means for interfacing a differential microphone by the presented electrical circuitry.
  • the microphone solves existing problems connected with receiving and amplification of a differential microphone signal such as differential microphone biasing, amplifier gain definition, influence of the parasitic capacitances at the interface nodes, differential microphone capacitances impedance conver- sion, obtaining low noise and low cut-off frequency of the amplifier response.
  • the microphone has an amplifier connected to the micro- phone electrodes providing a bias voltage for the capacitors and a common mode output voltage for further circuits proc ⁇ essing the amplified electrical signals encoding the received acoustical signals.
  • a connection denotes an electrical connec ⁇ tion between circuit elements.
  • a first terminal of the amplifier's differ ⁇ ential input port is connected to the first microphone elec- trode and a second terminal of the amplifiers differential input port is connected to the second microphone electrode.
  • This solution of an improved microphone can be based on a as ⁇ sembly where the microphone electrodes are electrically cou- pled to a MOS (metal-oxide-semiconductor) integrated circuit.
  • MOS metal-oxide-semiconductor
  • the amplifier stage has a control port and the common mode feedback circuit is connected to the ampli ⁇ bomb stage's control port.
  • the differential microphone further com ⁇ prises a first resistance element and a second resistance element.
  • the first resistance element is connected between a first terminal of the output port and a first terminal of the input port.
  • the second resistance element is connected be ⁇ tween a second terminal of the output port and a second ter ⁇ minal of the input port.
  • the first and the second resistance elements are part of an amplifier feedback circuit.
  • a first and a second capacitive element may be connected in parallel with the feedback resistance elements.
  • the feedback circuit is connected to the acoustic ca- pacitors and the microphone comprises a capacitive feedback as the microphone capacitors can be regarded as part of the feedback circuit.
  • the resistance elements comprise a first diode and a second diode being connected in parallel to and in the opposite direction of the first diode.
  • the second di ⁇ ode's direction may be opposite to the first diode's.
  • the resistance elements have a resistance R F greater than 10 GO. This requirement is needed because the resistor should not degrade the noise performance of the microphone preampli ⁇ bomb. Additionally to provide that the amplifier is opera ⁇ tional in the whole audio band the cut-off frequency of a mi ⁇ crophone amplifier (inversely proportional to the size of this resistor) should be rather low, e.g. ⁇ 20 Hz.
  • This resistance element can be also a se- ries of diode RE elements or can be implemented in different ways as a series or parallel connection of transistor or di ⁇ ode elements.
  • the common mode feedback circuit comprises a common mode voltage port for setting and adjusting the common mode voltage at the amplifier stage's output.
  • Differential microphone comprise a differential signal port connected to its double backplates or double membranes in the case of a double membrane microphone.
  • the central electrode thereof is kept at a constant voltage representing signal ground.
  • the bias voltage is generated by the electronic cir ⁇ cuitry of the microphone's amplifier.
  • a Dickson voltage mul- tiplier followed by a low pass filter might be used for MEMS microphones, ECM microphones do not need this high bias volt ⁇ age .
  • the amplifier stage can comprise a fully differential opera- tional amp lifier (opamp) .
  • the first and the second acoustic electrodes are connected to the input ports of the opamp.
  • the differential gain of the opamp is typically greater than 1000.
  • the amplifier stage may be a standard MOS topology such as folded cascode amplifier.
  • the DC voltage at the output of the amplifier is determined by the common mode voltage port by the amplifier's common-mode feedback circuit. Normally the DC voltage at the output of the amplifier determined by the common mode voltage port is set to half of a power supply voltage of the microphone.
  • the DC bias voltage of the acoustic capacitors may be gener ⁇ ated on the same integrated circuit chip. Via the common mode control port, the DC voltage of the output of the amplifier stage and the microphone's differential output port is set to a value defined by the common mode control port. The same DC voltage will appear at the microphone's capacitors, i.e. the voltage drop on RE is close to zero. In this way, the DC voltage of the microphone capacitor is well defined and fur- ther more can be adjusted.
  • the amplifier stage's differential input port is connected to gates of a MOS transistors differential pair. Noise of these transistors, connected to the microphone electrodes should be low. Often a P-MOS input stage is used for better noise performance.
  • the microphone comprises a first capaci ⁇ tance element and a second capacitance element.
  • the first ca ⁇ pacitance element is connected between a first terminal of the output port and a first terminal of the amplifier stage's input port.
  • the second capacitance element is connected be- tween a second terminal of the output port and a second ter ⁇ minal of the amplifier stage's input port.
  • the first and the second capacitance elements are part of an amplifier feedback circuit .
  • the capacitance elements may have a capacitance C F between 0.05 pF and 10 pF.
  • the amplification factor is mainly proportional to (V OUT+ - V out - ) / ( V M i - V M2 ) * C M /C F (eqn. 1)
  • the microphone's gain is independent of parasitic ca ⁇ pacitances of the capacitor.
  • V ou t+ and V ou t- are the out ⁇ put voltages at the differential output terminals.
  • V M i - V M2 is the voltage applied to the combination of the capacitors built up by two backplates and a membrane in between.
  • C M is the capacitance of each single capacitor comprising the membrane and one backplate.
  • a desired property of the microphone described is that the gain can be adjusted through the first and second capacitance elements as feedback capacitors having a capacity C F . In that case C F may be connected with some kind of switch arrangement by which the value of C F can be changed i.e. programmed to give variable gain.
  • C F is the capacitance of the first or the second ca- pacitance element
  • R F is the resistance of the first or the second resistance element.
  • the cut-off frequency o cut can be 20 Hz or lower.
  • a low cut-off frequency o cut is obtained.
  • the first terminal and the second terminal establish the two terminals of a differential signal port of the operational amplifier.
  • the operational amplifier is con ⁇ nected in a feedback configuration where the feedback network between the operational amplifier's (opamp's) output and the opamp's input comprises a resistance element having a very large resistance in parallel with feedback capacitor.
  • a purpose of the large resistance is to provide a DC path from the operational amplifier input to the output. At the same time this resistance element provides a DC path from the microphone electrodes through the output of the amplifier to ground.
  • the amplifier's DC output volt ⁇ age is set by its common-mode feedback circuitry, a micro ⁇ phone amplifier is provided in which an amplifier stage and a common mode feedback circuit are combined to improve the sig ⁇ nal quality of a microphone.
  • Such a combination enables a stable and well-defined DC bias voltage for a microphone's capacitor. The bias voltage is applied to the capacitor via the input port of the amplifier stage.
  • the common mode feedback circuit provides a stable and well-defined com ⁇ mon mode output voltage to improve further processing of the electric signals.
  • such a microphone amplifier provides impedance con ⁇ version of capacitive impedances of the microphone's capaci ⁇ tor.
  • a fully differential topology has been used, a low THD (total harmonic distortion) and a good power supply re- jection, i.e. a good immunity against common mode distur ⁇ sayes from the power supply can be achieved.
  • the first microphone electrode, the central microphone electrode and the second microphone electrode are elements of the acoustically active part of a MEMS microphone or a electret condenser microphone.
  • ASIC Applica ⁇ tion-Specific Integrated Circuit
  • the two chips are packaged together.
  • the MEMS microphone and the CMOS inte ⁇ grated circuitry can also be produced on the same silicon substrate i.e. as a single chip.
  • Separate CMOS chip with cir- cuits described can also be connected to an electret con ⁇ denser microphone to form the amplifier described.
  • the amplifier with the feedback described can provide an amplification factor from 1 to 20.
  • the differential microphone can have one membrane and two backplates or one backplate and two membranes.
  • the microphone further comprises a third capacitance element being connected between a first terminal of the amplifier stage's input port and the first microphone electrode and a fourth capacitance element being connected between a second terminal of the amplifier stage's input port and the second microphone electrode (E2) .
  • the third and the fourth capacitance element can have capacitances between 1 pF and 100 pF.
  • a third resistance element is connected between the first microphone electrode and a high bias voltage generated by an integrated circuit.
  • the first micro ⁇ phone electrode and the second microphone electrode are elec ⁇ trically connected.
  • the acoustical capacitor's elec ⁇ trodes are connected to a bias voltage which may be on-chip generated .
  • the amplifier stage is a folded-cascode amplifier comprising a first, a second, a third, a fourth, a fifth, a sixth, a seventh, an eighth, a ninth, a tenth and an eleventh transistor, where the first, the second and the third transistor are connected to a power supply.
  • the fourth transistor is connected between the second and the sixth transistor and the fifth transistor is connected between the third transistor and the seventh transistor.
  • the eighth transistor is connected between the sixth transistor and ground and the ninth transistor is connected between the seventh transistor and ground.
  • the tenth transistor is connected between the first transistor and the eighth transistor and the eleventh transistor is connected between the first transistor and the ninth transistor.
  • the eighth transistor and the ninth transistor are connected to a control port.
  • the amplifier stage can be designed to have the optimal low noise performance when connected together with the microphone.
  • the amplifier is usually designed to be op ⁇ erational under low-voltage and with low current consumption.
  • the amplifier stage comprises a first, a second, a third, a fourth, a fifth, a sixth, a seventh, an eighth, a ninth, a tenth, an eleventh and a twelvth transistor.
  • the first transistor and the second transistor are connected to a power supply.
  • the third transistor is connected between the first transistor and the seventh transistor and the fourth transistor is connected between the second transistor and the ninth transistor.
  • the fifth transistor is connected between the first transistor and the eighth transistor and the sixth transistor is connected between the second transistor and the eighth transistor.
  • the seventh transistor is connected between the third transistor and the tenth transistor and the ninth transistor is connected between the fourth transistor and the twelvth transistor.
  • the eighth transistor is connected to the eleventh transistor.
  • the tenth transistor, the eleventh transistor and the twelvth transistor are connected to ground.
  • the tenth transistor, the eleventh transistor and the twelvth transistor are connected to a control port.
  • the common mode feedback circuit comprises a first, a second, a third, a fourth, a fifth, a sixth, a seventh and an eighth transistor.
  • the first and the second transistor are connected to a power supply.
  • the third tran ⁇ sistor is connected between the first transistor and the seventh transistor.
  • the fourth transistor is connected between the second transistor and the seventh transistor.
  • the fifth transistor is connected between the first transistor and the eighth transistor.
  • the sixth transistor is connected between the second transistor and the eighth transistor.
  • the seventh transistor and the eighth transistor are connected to ground.
  • CMOS circuit chip is assembled together with the MEMS mi- crophone chip in a package either by soldering to a PCB
  • the amplifier and the microphone can be produced starting from the same silicon substrate forming a single chip solution.
  • a method for driving differential microphone e.g. one of the above mentioned microphones, comprising the steps
  • the electrical signal is amplified with a adjustable and well defined gain insensitive to parasitic capacitances.
  • FIG. 4A shows an equivalent circuit diagram of a common
  • FIG. 4B shows an equivalent circuit diagram of another com ⁇ mon mode feedback circuit that may be in use with the amplifier stage shown in FIG. 3B
  • FIG. 5 shows an equivalent circuit diagram of a micro ⁇ phone
  • FIG. 6 shows a cross section of a microphone.
  • FIG. 1 shows an equivalent circuit diagram of a differential microphone MIC comprising an amplifier stage AS being connected to the mechanical elements, i.e. the acoustical elec- trodes, of a MEMS microphone MEM.
  • the mechanical elements MEM comprise a first electrode El and a second electrode E2.
  • a central electrode EC is arranged between the first electrode El and the second electrode E2.
  • the first electrode El and the second electrode E2 can be established by perforated backplates of a double backplate or by membranes of a double membrane microphone.
  • the amplifier stage AS comprises a dif ⁇ ferential input port DIP.
  • the differential output of the am ⁇ plifier stage AS is connected to the differential output DOP of the microphone MIC.
  • the differential input port DIP com- prises two terminals, each terminal receiving a signal of mainly the same absolute value but of different polarity com ⁇ pared to the respective other terminal's signal.
  • a first re ⁇ sistance element RE1 is connected between an input terminal and an output terminal.
  • a second resistance element RE2 is connected between the respective other input terminal and the respective other output terminal.
  • the electric potential of the input terminal and the output terminal connected to one resistance element have an opposite polarity, i.e. the ampli- fier stage is in a negative feedback configuration.
  • the first and second capacitance elements and the first and second re ⁇ sistance elements establish, thus, an amplifier feedback cir ⁇ cuit AFC .
  • first capacitance element CE1 is connected between the first output terminal and the first input terminal.
  • a second capacitance element CE2 is connected between the sec ⁇ ond output terminal and the second input terminal.
  • Embodiments of amplifier stages are shown in FIGs. 3A and 3B.
  • Embodiments of common mode feedback circuits are shown in FIGs. 4A and 4B.
  • FIG. 2 shows an embodiment of a resistance element RE com- prising diodes being connected in parallel but with opposite polarity with respect to each other. Thus, a large resistance for low voltages can be obtained.
  • FIG. 3A shows a more detailed circuit equivalent diagram of an amplifier stage AS comprising 11 transistors Tl - Til.
  • a power supply PS is connected to the respective source of a first transistor Tl, of a second transistor T2, and of a third transistor T3.
  • the gate of first transistor Tl is connected to the gate of the second transistor T2 and the third transistor T3.
  • the drain of the first transistor Tl is connected to the sources of the tenth transistor T10 and the eleventh transistor Til.
  • the gates of the tenth transistor T10 and the eleventh transistor Til establish the respective input terminals of the differential input port DIP.
  • the drains of the second transistor T2 and of the third transis ⁇ tor T3 are connected to the sources of the fourth transistor T4 and the fifth transistor T5.
  • the gate of the fourth transistor T4 is connected to the gate of the fifth transistor T5.
  • the drains of the fourth transistor T4 and the fifth transistor T5 are connected to the differential output port DOP of the common mode feedback circuit.
  • the ports' respec ⁇ tive terminals are connected to the drains of the sixth tran- sistor T6 and the seventh transistor T7 both the gates of which are connected to each other.
  • the drains of the tenth transistor T10 and the eleventh transistor Til are connected to the drains of the eighth transistor T8 and the ninth transistor T9, respectively.
  • the sources of the eighth transistor T8 and the ninth transistor T9 are connected to ground GND.
  • the gates of the eighth transistor T8 and the ninth transis ⁇ tor T9 are connected to a control port VCNT .
  • FIG. 3B shows an equivalent circuit diagram of another embodiment of an amplifier stage AS comprising 12 transistors Tl - T12.
  • a power supply PS is connected to the sources of the first transistor Tl and of the second transistor T2.
  • the gates of the first transistor Tl and of the second transistor T2 are electrically connected to each other.
  • the drains of the first transistor Tl and of the second transistor T2 are connected to the sources of the third transistor T3 and of the fourth transistor T4, respectively. Further, the drains are con ⁇ nected to drains of the fifth transistor T5 and of the sixth transistor T6, respectively.
  • the gates of the fifth transis- tor T5 and of the sixth transistor T6 establish the respective first and second input terminals TIN1, TIN2 of the am ⁇ plifier stage.
  • the sources of the fifth transistor T5 and of the sixth transistor T6 are connected to the drain of the eighth transistor T8. Further, the drains of the third tran- sistor T3 and of the fourth transistor T4 are connected to drains of the seventh transistor T7 and of the ninth transistor T9 respectively and are connected to the output termi ⁇ nals TOUT1, TOUT2 of the output port.
  • the gate of the third transistor T3 is connected to the gate of the fourth transis ⁇ tor T4.
  • the gate of the seventh transistor T7 is connected to the gate of the eighth transistor T8 and to the gate of the ninth transistor T9.
  • the sources of the seventh transistor T7 and of the ninth transistor T9 are connected to the drains of the tenth transistor T10 and of the twelvth transistor T12.
  • the sources of the tenth transistor T10 and of the twelvth transistor T12 are connected to ground GND, as is the source of the eleventh transistor Til.
  • transistor T10 is connected to the gate of the eleventh transistor Til and to the gate of the twelvth transistor T12 and to a control port VCNT .
  • the gate of the seventh transistor T7 is connected to the gate of the ninth transistor T9.
  • the first transistor Tl and the second transistor T2 are connected to a bias terminal and the third transistor T3 and the fourth transistor are connected to a bias terminal.
  • FIG. 4A shows a detailed circuit equivalent diagram of a com- mon mode feedback circuit CMFBC comprising 8 transistors Tl - T8.
  • a power supply PS is connected to the sources of the first transistor Tl and the second transistor T2, the gates of which are connected to each other.
  • the drains of the first transistor Tl and of the second transistor T2 are connected to the sources of a third transistor T3 and of a fifth tran ⁇ sistor T5 and to the sources of a fourth transistor T4 and a sixth transistor T6, respectively.
  • the gates of the fifth transistor T5 and of the sixth transistor T6 establish the terminals of the common mode feedback circuit's output port DOP .
  • the drains of the third transistor T3 and of the fourth transistor T4 are connected to the gate of a sev ⁇ enth transistor T7 and to the drain of the seventh transistor T7.
  • the gate of the seventh transistor T7 is further connected to a control port VCNT .
  • the source of the seventh transistor T7 is connected to ground and to the source of an eighth transistor T8.
  • the drains of the fifth transistor T5 and of the sixth transistor T6 are connected to the gate and to the drain of the eighth transistor T8.
  • Gates of the third transistor T3 and the forth transistor t4 are connected together and connected to a port VCOM.
  • FIG. 4B shows an equivalent circuit diagram of another em- bodiment of a common mode feedback circuit CMFBC .
  • the common mode feedback circuit CMFBC comprises four capacitance ele ⁇ ments CE where each two capacitance elements are connected in series and two series of capacitance elements are connected in parallel. Switches SW can be utilized to electrically connect or disconnect capacitance elements.
  • the common mode feedback circuit CMFBC comprises a first output terminal TOUT1 and a second output terminal TOUT2 forming a differential output port, control port VCNT, and a common mode volt ⁇ age port VCOM.
  • FIG. 5 shows an equivalent circuit diagram of a microphone MIC comprising a third capacitance element CE3 and a fourth capacitance element CE4 and a third resistance element RE3.
  • the third capacitance element CE3 is connected to an input terminal of the differential input port DIP.
  • the fourth ca ⁇ pacitance element CE4 is connected to the respective other input terminal of the differential input port DIP.
  • the third resistance element RE3 is connected between the mi ⁇ crophone electrodes (or membranes) and an on-chip generated bias voltage source. The other side of the resistance element is connected to the third and fourth capacitance element which are also connected to the terminals of the amplifier stage AS.
  • FIG. 1 shows an equivalent circuit diagram of a microphone MIC comprising a third capacitance element CE3 and a fourth capacitance element CE4 and a third resistance element RE3.
  • the third capacitance element CE3 is connected to an input terminal of the differential input port DIP.
  • the fourth ca ⁇ pacitance element CE4 is connected to the respective other input
  • FIG. 6 shows a cross section of a microphone assembly MIC comprising a MEMS chip MC containing the microphone's acous ⁇ tical elements and an ASIC chip AC containing the circuit elements.
  • the microphone chip MC and the ASIC chip AC are arranged on a substrate SU. It is, however, possible that the acoustical and the electrical elements of a microphone are integrated in a single chip, e.g. a silicon chip.
  • a differential microphone is not limited to the embodiments described in the specification or shown in the figures.
  • Amplifiers comprising further elements, e.g. such as
  • CE1, CE2 first, second capacitance element
  • CE3, CE4 third, fourth capacitance element
  • DIP differential input port of the amplifier stage
  • DOP differential output port of the microphone
  • MEM mechanical elements of a MEMS microphone
  • RE1, RE2 first, second resistance element
  • T1-T12 transistors
  • TIN1, TIN2 first, second terminal of a differential input port
  • TOUT1, TOUT2 first, second output terminal of a differential output port

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Amplifiers (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)

Abstract

A differential microphone with improved biasing and a well defined common mode output voltage is connected to an amplifier comprising a differential amplifier stage and a common mode feedback circuit. The amplifier is in a feedback configuration.

Description

Description
Differential Microphone and Method for Driving a Differential Microphone
The present invention refers to differential microphones and methods for driving such microphones. The invention further refers to means for interfacing differential condenser microphones, e.g. MEMS (MEMS = Micro-Electro-Mechanical
Systems) or ECM' s (ECM = electret condenser microphone) .
Microphones such as MEMS microphones comprise a perforated backplate and a flexible membrane. The backplate and the mem¬ brane establish electrodes of a capacitor. Received sound signals induce oscillations of the membrane. Due to corre¬ sponding induced oscillations of the capacity, acoustic sig¬ nals can be converted into electrical signals. In order to improve the signal quality of MEMS microphones, double back¬ plate microphones or double membrane microphones can be cre- ated. In double backplate microphones, the membrane is ar¬ ranged between two perforated backplates; in double membrane microphones, a perforated backplate is arranged between two flexible membranes. In each case, a microphone is obtained that comprises two capacitors and provides a differential output port. A differential port comprises two terminals where each terminal mainly provides the same absolute value of a voltage or a current but with opposite polarity. When signals propagate via differential signal ports or signal paths, common mode disturbances can easily be eliminated.
Although microphones with differential ports provide a better signal quality, their use, contrary to simpler microphones with a single capacitor as an acusto-electrical transducer, has not yet been commercialized, thus not much work has been devoted yet to methods to interface such microphones. There¬ fore, unsolved problems exist related to receiving and ampli¬ fication of the signal from a differential microphone.
Microphones providing differential signals are known from US 4,757,545, US 2008/0310655 Al or US 2010/254544 A.
As a differential MEMS microphone electrically presents two capacitors, its electrodes have to be biased. Accompanying interface circuitry connected to the electrodes of the ca¬ pacitor may provide a bias voltage for the capacitor. In pre¬ vious works biasing is done by connecting a resistance ele¬ ment having a large resistance between the electrodes and ground.
Problems connected with receiving and amplifying a differential microphone signal such as differential microphone bias¬ ing, amplifier gain definition, influence of the parasitic capacitances at the interface nodes, differential microphone capacitances impedance conversion, obtaining low noise and low cut-off frequency of the amplifier response exist.
The signal quality depends on the quality of the acoustic ca- pacitors' bias voltage. Further, the signal quality depends on the quality of the common mode output voltage. What is needed is a differential microphone with an improved bias voltage of the microphones acoustic capacitors and a better defined common mode output voltage and a method for driving such a microphone.
It is, thus, an object of the present invention to provide a differential microphone that can process differential signals from the microphone's acoustic capacitors, that provide a stable and well-defined bias voltage for the capacitor's electrodes and that is able to provide well defined common mode output voltage. It is also an object of the present in- vention to provide amplification of the differential micro¬ phone signal with well defined gain, i.e. a well defined am¬ plification factor.
Therefore, the present invention provides a differential mi- crophone and a method for driving such a microphone according to the independent claims. Dependent claims provide preferred embodiments thereof.
A differential microphone comprises a first microphone elec- trode, a central microphone electrode and a second microphone electrode. The microphone further comprises a differential output port and a differential amplifier stage. The amplifier stage has a differential input port and a differential output port being connected to the output port of the microphone. The microphone further comprises a common mode feedback cir¬ cuit having a differential output port being connected to the output port of the microphone.
The common mode feedback circuit provides a well defined com- mon mode output voltage.
Such a microphone provides means for interfacing a differential microphone by the presented electrical circuitry. The microphone solves existing problems connected with receiving and amplification of a differential microphone signal such as differential microphone biasing, amplifier gain definition, influence of the parasitic capacitances at the interface nodes, differential microphone capacitances impedance conver- sion, obtaining low noise and low cut-off frequency of the amplifier response.
Thus, the microphone has an amplifier connected to the micro- phone electrodes providing a bias voltage for the capacitors and a common mode output voltage for further circuits proc¬ essing the amplified electrical signals encoding the received acoustical signals. In this context, a connection denotes an electrical connec¬ tion between circuit elements.
In one embodiment a first terminal of the amplifier's differ¬ ential input port is connected to the first microphone elec- trode and a second terminal of the amplifiers differential input port is connected to the second microphone electrode.
This solution of an improved microphone can be based on a as¬ sembly where the microphone electrodes are electrically cou- pled to a MOS (metal-oxide-semiconductor) integrated circuit.
In one embodiment the amplifier stage has a control port and the common mode feedback circuit is connected to the ampli¬ fier stage's control port.
In one embodiment the differential microphone further com¬ prises a first resistance element and a second resistance element. The first resistance element is connected between a first terminal of the output port and a first terminal of the input port. The second resistance element is connected be¬ tween a second terminal of the output port and a second ter¬ minal of the input port. The first and the second resistance elements are part of an amplifier feedback circuit. Further, a first and a second capacitive element may be connected in parallel with the feedback resistance elements. Thus, the feedback circuit is connected to the acoustic ca- pacitors and the microphone comprises a capacitive feedback as the microphone capacitors can be regarded as part of the feedback circuit.
In one embodiment the resistance elements comprise a first diode and a second diode being connected in parallel to and in the opposite direction of the first diode. The second di¬ ode's direction may be opposite to the first diode's.
The resistance elements have a resistance RF greater than 10 GO. This requirement is needed because the resistor should not degrade the noise performance of the microphone preampli¬ fier. Additionally to provide that the amplifier is opera¬ tional in the whole audio band the cut-off frequency of a mi¬ crophone amplifier (inversely proportional to the size of this resistor) should be rather low, e.g. < 20 Hz.
Voltage drop across diodes connected in this way is close to zero and a resistance element is obtained that has a very large resistance. This resistance element can be also a se- ries of diode RE elements or can be implemented in different ways as a series or parallel connection of transistor or di¬ ode elements.
In one embodiment the common mode feedback circuit comprises a common mode voltage port for setting and adjusting the common mode voltage at the amplifier stage's output.
Differential microphone comprise a differential signal port connected to its double backplates or double membranes in the case of a double membrane microphone. The central electrode thereof is kept at a constant voltage representing signal ground. The bias voltage is generated by the electronic cir¬ cuitry of the microphone's amplifier. A Dickson voltage mul- tiplier followed by a low pass filter might be used for MEMS microphones, ECM microphones do not need this high bias volt¬ age .
The amplifier stage can comprise a fully differential opera- tional amp lifier (opamp) . The first and the second acoustic electrodes are connected to the input ports of the opamp. The differential gain of the opamp is typically greater than 1000. The amplifier stage may be a standard MOS topology such as folded cascode amplifier.
The DC voltage at the output of the amplifier is determined by the common mode voltage port by the amplifier's common- mode feedback circuit. Normally the DC voltage at the output of the amplifier determined by the common mode voltage port is set to half of a power supply voltage of the microphone.
The DC bias voltage of the acoustic capacitors may be gener¬ ated on the same integrated circuit chip. Via the common mode control port, the DC voltage of the output of the amplifier stage and the microphone's differential output port is set to a value defined by the common mode control port. The same DC voltage will appear at the microphone's capacitors, i.e. the voltage drop on RE is close to zero. In this way, the DC voltage of the microphone capacitor is well defined and fur- ther more can be adjusted.
In one embodiment the amplifier stage's differential input port is connected to gates of a MOS transistors differential pair. Noise of these transistors, connected to the microphone electrodes should be low. Often a P-MOS input stage is used for better noise performance. In one embodiment the microphone comprises a first capaci¬ tance element and a second capacitance element. The first ca¬ pacitance element is connected between a first terminal of the output port and a first terminal of the amplifier stage's input port. The second capacitance element is connected be- tween a second terminal of the output port and a second ter¬ minal of the amplifier stage's input port. The first and the second capacitance elements are part of an amplifier feedback circuit . The capacitance elements may have a capacitance CF between 0.05 pF and 10 pF.
Further, the amplification factor is mainly proportional to (VOUT+ - Vout- ) / ( VMi - VM2) * CM/CF (eqn. 1)
Thus, the microphone's gain is independent of parasitic ca¬ pacitances of the capacitor. Here, Vout+ and Vout- are the out¬ put voltages at the differential output terminals. VMi - VM2 is the voltage applied to the combination of the capacitors built up by two backplates and a membrane in between. CM is the capacitance of each single capacitor comprising the membrane and one backplate. A desired property of the microphone described is that the gain can be adjusted through the first and second capacitance elements as feedback capacitors having a capacity CF. In that case CF may be connected with some kind of switch arrangement by which the value of CF can be changed i.e. programmed to give variable gain.
The cut-off frequency ocut of a microphone amplifier can, then, be denoted as ticut = 1/ (CF RF) (eqn. 2) where CF is the capacitance of the first or the second ca- pacitance element and RF is the resistance of the first or the second resistance element. Thus, with such a feedback configuration, the cut-off frequency ocut can be 20 Hz or lower. Thus, a low cut-off frequency ocut is obtained. The first terminal and the second terminal establish the two terminals of a differential signal port of the operational amplifier. In this case, the operational amplifier is con¬ nected in a feedback configuration where the feedback network between the operational amplifier's (opamp's) output and the opamp's input comprises a resistance element having a very large resistance in parallel with feedback capacitor.
A purpose of the large resistance is to provide a DC path from the operational amplifier input to the output. At the same time this resistance element provides a DC path from the microphone electrodes through the output of the amplifier to ground. Keeping in mind that the amplifier's DC output volt¬ age is set by its common-mode feedback circuitry, a micro¬ phone amplifier is provided in which an amplifier stage and a common mode feedback circuit are combined to improve the sig¬ nal quality of a microphone. Such a combination enables a stable and well-defined DC bias voltage for a microphone's capacitor. The bias voltage is applied to the capacitor via the input port of the amplifier stage. Further, the common mode feedback circuit provides a stable and well-defined com¬ mon mode output voltage to improve further processing of the electric signals.
Further, such a microphone amplifier provides impedance con¬ version of capacitive impedances of the microphone's capaci¬ tor. As a fully differential topology has been used, a low THD (total harmonic distortion) and a good power supply re- jection, i.e. a good immunity against common mode distur¬ bances from the power supply can be achieved.
In one embodiment the first microphone electrode, the central microphone electrode and the second microphone electrode are elements of the acoustically active part of a MEMS microphone or a electret condenser microphone.
The microphone can be produced in MEMS technology on a sili¬ con chip and comprise circuit elements being fully integrated in an IC chip in CMOS process, e.g. an ASIC (ASIC = Applica¬ tion-Specific Integrated Circuit) chip. The two chips are packaged together. The MEMS microphone and the CMOS inte¬ grated circuitry can also be produced on the same silicon substrate i.e. as a single chip. Separate CMOS chip with cir- cuits described can also be connected to an electret con¬ denser microphone to form the amplifier described. In all cases the amplifier with the feedback described can provide an amplification factor from 1 to 20. In all cases the differential microphone can have one membrane and two backplates or one backplate and two membranes.
In one embodiment the microphone further comprises a third capacitance element being connected between a first terminal of the amplifier stage's input port and the first microphone electrode and a fourth capacitance element being connected between a second terminal of the amplifier stage's input port and the second microphone electrode (E2) . The third and the fourth capacitance element can have capacitances between 1 pF and 100 pF.
Thus, it is possible to separate, by these DC blocking ca¬ pacitors, sensitive circuit elements of the input port of the amplifier from the electrodes of the microphone's capacitor. Especially during manufacturing steps, and when applying high bias voltage on the microphone, the amplifier is protected against high DC voltages at its input nodes which might dam¬ age the gate oxide of the input transistors.
In one embodiment a third resistance element is connected between the first microphone electrode and a high bias voltage generated by an integrated circuit. The first micro¬ phone electrode and the second microphone electrode are elec¬ trically connected. Thus, the acoustical capacitor's elec¬ trodes are connected to a bias voltage which may be on-chip generated .
In one embodiment the amplifier stage is a folded-cascode amplifier comprising a first, a second, a third, a fourth, a fifth, a sixth, a seventh, an eighth, a ninth, a tenth and an eleventh transistor, where the first, the second and the third transistor are connected to a power supply. The fourth transistor is connected between the second and the sixth transistor and the fifth transistor is connected between the third transistor and the seventh transistor. The eighth transistor is connected between the sixth transistor and ground and the ninth transistor is connected between the seventh transistor and ground. The tenth transistor is connected between the first transistor and the eighth transistor and the eleventh transistor is connected between the first transistor and the ninth transistor. The eighth transistor and the ninth transistor are connected to a control port.
This circuit is presented as an example, whereas it is possi¬ ble to use many other high-gain amplifier stage implementations that can be found in the literature describing the field of art. The amplifier stage can be designed to have the optimal low noise performance when connected together with the microphone. The amplifier is usually designed to be op¬ erational under low-voltage and with low current consumption. In one embodiment the amplifier stage comprises a first, a second, a third, a fourth, a fifth, a sixth, a seventh, an eighth, a ninth, a tenth, an eleventh and a twelvth transistor. The first transistor and the second transistor are connected to a power supply. The third transistor is connected between the first transistor and the seventh transistor and the fourth transistor is connected between the second transistor and the ninth transistor. The fifth transistor is connected between the first transistor and the eighth transistor and the sixth transistor is connected between the second transistor and the eighth transistor. The seventh transistor is connected between the third transistor and the tenth transistor and the ninth transistor is connected between the fourth transistor and the twelvth transistor. The eighth transistor is connected to the eleventh transistor. The tenth transistor, the eleventh transistor and the twelvth transistor are connected to ground. The tenth transistor, the eleventh transistor and the twelvth transistor are connected to a control port. In one embodiment the common mode feedback circuit comprises a first, a second, a third, a fourth, a fifth, a sixth, a seventh and an eighth transistor. The first and the second transistor are connected to a power supply. The third tran¬ sistor is connected between the first transistor and the seventh transistor. The fourth transistor is connected between the second transistor and the seventh transistor. The fifth transistor is connected between the first transistor and the eighth transistor. The sixth transistor is connected between the second transistor and the eighth transistor. The seventh transistor and the eighth transistor are connected to ground.
This circuit is presented as an example, whereas it is possi- ble to use many other common-mode feedback implementations that can be found in the literature describing the field of art. Switched capacitor common-mode feedback might be used as well . In one embodiment all circuit elements of the amplifier are fully integrated in a CMOS ASIC chip. The chip may be
manufactured in a standard CMOS process.
The CMOS circuit chip is assembled together with the MEMS mi- crophone chip in a package either by soldering to a PCB
(printed circuit board) like substrate (ceramic or similar) or by wire bonding the two chips together.
Further, the amplifier and the microphone can be produced starting from the same silicon substrate forming a single chip solution. A method for driving differential microphone, e.g. one of the above mentioned microphones, comprising the steps
- receiving an acoustical signal,
- converting the acoustical signal into an electrical signal, - adjusting the bias voltage of the first and second micro¬ phone electrode by adjusting a common mode voltage via a com¬ mon mode voltage port (VCOM) of the common mode feedback cir¬ cuit .
In one embodiment of the method the electrical signal is amplified with a adjustable and well defined gain insensitive to parasitic capacitances.
The basic principles and exemplary embodiments thereof are shown in the schematic figures.
Short description of the figures shows an equivalent circuit diagram of a differen tial microphone, shows an embodiment of a resistance element, shows an equivalent circuit diagram of an ampl stage, shows an equivalent circuit diagram of another amplifier stage,
FIG. 4A shows an equivalent circuit diagram of a common
mode feedback circuit that may be in use with the amplifier stage shown in FIG. 3A, FIG. 4B shows an equivalent circuit diagram of another com¬ mon mode feedback circuit that may be in use with the amplifier stage shown in FIG. 3B, FIG. 5 shows an equivalent circuit diagram of a micro¬ phone,
FIG. 6 shows a cross section of a microphone. Detailed description
FIG. 1 shows an equivalent circuit diagram of a differential microphone MIC comprising an amplifier stage AS being connected to the mechanical elements, i.e. the acoustical elec- trodes, of a MEMS microphone MEM. The mechanical elements MEM comprise a first electrode El and a second electrode E2. A central electrode EC is arranged between the first electrode El and the second electrode E2. The first electrode El and the second electrode E2 can be established by perforated backplates of a double backplate or by membranes of a double membrane microphone. The amplifier stage AS comprises a dif¬ ferential input port DIP. The differential output of the am¬ plifier stage AS is connected to the differential output DOP of the microphone MIC. The differential input port DIP com- prises two terminals, each terminal receiving a signal of mainly the same absolute value but of different polarity com¬ pared to the respective other terminal's signal. A first re¬ sistance element RE1 is connected between an input terminal and an output terminal. A second resistance element RE2 is connected between the respective other input terminal and the respective other output terminal. The electric potential of the input terminal and the output terminal connected to one resistance element have an opposite polarity, i.e. the ampli- fier stage is in a negative feedback configuration. The first and second capacitance elements and the first and second re¬ sistance elements establish, thus, an amplifier feedback cir¬ cuit AFC .
Further, a first capacitance element CE1 is connected between the first output terminal and the first input terminal. A second capacitance element CE2 is connected between the sec¬ ond output terminal and the second input terminal.
Embodiments of amplifier stages are shown in FIGs. 3A and 3B. Embodiments of common mode feedback circuits are shown in FIGs. 4A and 4B.
FIG. 2 shows an embodiment of a resistance element RE com- prising diodes being connected in parallel but with opposite polarity with respect to each other. Thus, a large resistance for low voltages can be obtained.
FIG. 3A shows a more detailed circuit equivalent diagram of an amplifier stage AS comprising 11 transistors Tl - Til. A power supply PS is connected to the respective source of a first transistor Tl, of a second transistor T2, and of a third transistor T3. The gate of first transistor Tl is connected to the gate of the second transistor T2 and the third transistor T3. The drain of the first transistor Tl is connected to the sources of the tenth transistor T10 and the eleventh transistor Til. The gates of the tenth transistor T10 and the eleventh transistor Til establish the respective input terminals of the differential input port DIP. The drains of the second transistor T2 and of the third transis¬ tor T3 are connected to the sources of the fourth transistor T4 and the fifth transistor T5. The gate of the fourth transistor T4 is connected to the gate of the fifth transistor T5. The drains of the fourth transistor T4 and the fifth transistor T5 are connected to the differential output port DOP of the common mode feedback circuit. The ports' respec¬ tive terminals are connected to the drains of the sixth tran- sistor T6 and the seventh transistor T7 both the gates of which are connected to each other. The drains of the tenth transistor T10 and the eleventh transistor Til are connected to the drains of the eighth transistor T8 and the ninth transistor T9, respectively. The sources of the eighth transistor T8 and the ninth transistor T9 are connected to ground GND. The gates of the eighth transistor T8 and the ninth transis¬ tor T9 are connected to a control port VCNT .
3B shows an equivalent circuit diagram of another embodiment of an amplifier stage AS comprising 12 transistors Tl - T12. A power supply PS is connected to the sources of the first transistor Tl and of the second transistor T2. The gates of the first transistor Tl and of the second transistor T2 are electrically connected to each other. The drains of the first transistor Tl and of the second transistor T2 are connected to the sources of the third transistor T3 and of the fourth transistor T4, respectively. Further, the drains are con¬ nected to drains of the fifth transistor T5 and of the sixth transistor T6, respectively. The gates of the fifth transis- tor T5 and of the sixth transistor T6 establish the respective first and second input terminals TIN1, TIN2 of the am¬ plifier stage. The sources of the fifth transistor T5 and of the sixth transistor T6 are connected to the drain of the eighth transistor T8. Further, the drains of the third tran- sistor T3 and of the fourth transistor T4 are connected to drains of the seventh transistor T7 and of the ninth transistor T9 respectively and are connected to the output termi¬ nals TOUT1, TOUT2 of the output port. The gate of the third transistor T3 is connected to the gate of the fourth transis¬ tor T4. The gate of the seventh transistor T7 is connected to the gate of the eighth transistor T8 and to the gate of the ninth transistor T9. The sources of the seventh transistor T7 and of the ninth transistor T9 are connected to the drains of the tenth transistor T10 and of the twelvth transistor T12. The sources of the tenth transistor T10 and of the twelvth transistor T12 are connected to ground GND, as is the source of the eleventh transistor Til. The gate of the tenth
transistor T10 is connected to the gate of the eleventh transistor Til and to the gate of the twelvth transistor T12 and to a control port VCNT . The gate of the seventh transistor T7 is connected to the gate of the ninth transistor T9. The first transistor Tl and the second transistor T2 are connected to a bias terminal and the third transistor T3 and the fourth transistor are connected to a bias terminal.
FIG. 4A shows a detailed circuit equivalent diagram of a com- mon mode feedback circuit CMFBC comprising 8 transistors Tl - T8. A power supply PS is connected to the sources of the first transistor Tl and the second transistor T2, the gates of which are connected to each other. The drains of the first transistor Tl and of the second transistor T2 are connected to the sources of a third transistor T3 and of a fifth tran¬ sistor T5 and to the sources of a fourth transistor T4 and a sixth transistor T6, respectively. The gates of the fifth transistor T5 and of the sixth transistor T6 establish the terminals of the common mode feedback circuit's output port DOP . Further, the drains of the third transistor T3 and of the fourth transistor T4 are connected to the gate of a sev¬ enth transistor T7 and to the drain of the seventh transistor T7. The gate of the seventh transistor T7 is further connected to a control port VCNT . The source of the seventh transistor T7 is connected to ground and to the source of an eighth transistor T8. Further, the drains of the fifth transistor T5 and of the sixth transistor T6 are connected to the gate and to the drain of the eighth transistor T8. Gates of the third transistor T3 and the forth transistor t4 are connected together and connected to a port VCOM.
FIG. 4B shows an equivalent circuit diagram of another em- bodiment of a common mode feedback circuit CMFBC . The common mode feedback circuit CMFBC comprises four capacitance ele¬ ments CE where each two capacitance elements are connected in series and two series of capacitance elements are connected in parallel. Switches SW can be utilized to electrically connect or disconnect capacitance elements. The common mode feedback circuit CMFBC comprises a first output terminal TOUT1 and a second output terminal TOUT2 forming a differential output port, control port VCNT, and a common mode volt¬ age port VCOM.
FIG. 5 shows an equivalent circuit diagram of a microphone MIC comprising a third capacitance element CE3 and a fourth capacitance element CE4 and a third resistance element RE3. The third capacitance element CE3 is connected to an input terminal of the differential input port DIP. The fourth ca¬ pacitance element CE4 is connected to the respective other input terminal of the differential input port DIP. Further the third resistance element RE3 is connected between the mi¬ crophone electrodes (or membranes) and an on-chip generated bias voltage source. The other side of the resistance element is connected to the third and fourth capacitance element which are also connected to the terminals of the amplifier stage AS. FIG. 6 shows a cross section of a microphone assembly MIC comprising a MEMS chip MC containing the microphone's acous¬ tical elements and an ASIC chip AC containing the circuit elements. The microphone chip MC and the ASIC chip AC are arranged on a substrate SU. It is, however, possible that the acoustical and the electrical elements of a microphone are integrated in a single chip, e.g. a silicon chip.
A differential microphone is not limited to the embodiments described in the specification or shown in the figures.
Amplifiers comprising further elements, e.g. such as
capacitance elements, resistance elements, transistors, electrodes, or further input or output ports are also
comprised by the present invention.
List of reference signs:
AC: ASIC chip
AMP: amp1i fier
AS : amplifier stage
CE: capacitance element
CE1, CE2: first, second capacitance element
CE3, CE4: third, fourth capacitance element
CMFBC : common mode feedback circuit
DIP: differential input port of the amplifier stage
DOP: differential output port of the microphone
El, E2: first, second electrode of the microphone's ca¬ pacitor
EC: central electrode of the microphone's capacitor
GND: ground
MEM: mechanical elements of a MEMS microphone
MIC: microphone
PS : power supply
RE : resistance element
RE1, RE2 : first, second resistance element
RE3 : third resistance element
SU: substrate
SW: switch
T1-T12 : transistors
TIN1, TIN2: first, second terminal of a differential input port
TOUT1, TOUT2: first, second output terminal of a differential output port
VCNT : control port
VCOM: common mode voltage port

Claims

Claims
1. A differential microphone (MIC), comprising
- a first microphone electrode (El), a central microphone electrode (EC) and a second microphone electrode (E2),
- a differential output port (DOP) ,
- a differential amplifier stage (AS) having a differential input port (DIP) and a differential output port being
connected to the output port (DOP) of the microphone (MIC) , - a common mode feedback circuit (CMFBC) having a
differential output port being connected to the output port of the microphone (MIC) .
2. The differential microphone of the previous claim, where a first terminal of the amplifier's differential input port
(DIP) is connected to the first microphone electrode (El) and a second terminal of the amplifiers differential input port (DIP) is connected to the second microphone electrode (E2) .
3. The differential microphone of one of the previous claims, where
- the amplifier stage (AS) has a control port (VCNT) ,
- the common mode feedback circuit (CMFBC) is connected to the amplifier stage's control port (VCNT) .
4. The differential microphone of one of the previous claims, further comprising
- a first resistance element (RE1) being connected between a first terminal (TOUT1) of the output port (DOP) and a first terminal (TIN1) of the input port (DIP),
- a second resistance element (RE2) being connected between a second terminal (TOUT2) of the output port (DOP) and a second terminal (TIN2) of the input port (DIP), where - the first (RE1) and the second (RE2) resistance elements are part of an amplifier feedback circuit (AFC) .
5. The differential microphone of the previous claim, where - the resistance elements (RE1, RE2) comprise a first diode and a second diode being connected in parallel to and in the opposite direction of the first diode.
6. The differential microphone of one of the previous claims, where the common mode feedback circuit comprises a common mode voltage port (VCOM) for setting and adjusting the common mode voltage at the amplifier stage's output.
7. The differential microphone of one of the previous claims, further comprising
- a first capacitance element (CE1) and a second capacitance element (CE2), where
- the first capacitance element (CE1) is connected between a first terminal (TOUT1) of the output port (DOP) and a first terminal (TIN1) of the amplifier stage's input port (DIP) and
- the second capacitance element (CE2) is connected between a second terminal (TOUT2) of the output port (DOP) and a second terminal (TIN2) of the amplifier stage's input port (DIP),
- the first (CE1) and the second (CE2) capacitance elements are part of an amplifier feedback circuit (AFC) .
8. The differential microphone of one of the previous claims, where the first microphone electrode, the central microphone electrode and the second microphone electrode are elements of the acoustically active part of a MEMS microphone or a electret condenser microphone.
9. The differential microphone of one of the previous claims, further comprising
- a third capacitance element (CE3) being connected between a first terminal (TIN1) of the amplifier stage's input port (DIP) and the first microphone electrode (El) and
- a fourth capacitance element (CE4) being connected between a second terminal (TIN2) of the amplifier stage's input port (DIP) and the second microphone electrode (E2) .
10. The differential microphone of one of the previous claims, further comprising
- a third resistance element (RE3) being connected between the first microphone electrode and a high bias voltage generated by an integrated circuit, where
- the first microphone electrode (El) and the second
microphone electrode (E2) are electrically connected.
11. The differential microphone of one of the previous claims, where the amplifier stage comprises
- a first (Tl), a second (T2), a third (T3), a fourth (T4), a fifth (T5) , a sixth (T6) , a seventh (T7), an eighth (T8), a ninth (T9) , a tenth (T10) and an eleventh (Til) transistor, where
- the first (Tl), the second (T2) and the third (T3)
transistor are connected to a power supply (PS),
- the fourth transistor (T4) is connected between the second (T2) and the sixth (T6) transistor and the fifth transistor (T5) is connected between the third transistor (T3) and the seventh transistor (T7),
- the eighth transistor (T8) is connected between the sixth transistor (T6) and ground (GND) and the ninth transistor (T9) is connected between the seventh transistor (T7) and ground (GND) , - the tenth transistor (T10) is connected between the first transistor (Tl) and the eighth transistor (T8) and the eleventh transistor (Til) is connected between the first transistor (Tl) and the ninth transistor (T9)
- the eighth transistor (T8) and the ninth transistor (T9) are connected to a control port (VCNT) .
12. The differential microphone of one of claims 1-10, where the amplifier stage (AS) comprises
- a first (Tl), a second (T2), a third (T3), a fourth (T4), a fifth (T5) , a sixth (T6) , a seventh (T7), an eighth (T8), a ninth (T9) , a tenth (T10), an eleventh (Til) and a twelvth (T12) transistor, where
- the first transistor (Tl) and the second transistor (T2) are connected to a power supply (PS),
- the third transistor (T3) is connected between the first transistor (Tl) and the seventh transistor (T7) and the fourth transistor (T4) is connected between the second transistor (T2) and the ninth transistor (T9) ,
- the fifth transistor (T5) is connected between the first transistor (Tl) and the eighth transistor (T8) and the sixth transistor (T6) is connected between the second transistor (T2) and the eighth transistor (T8),
- the seventh transistor (T7) is connected between the third transistor (T3) and the tenth transistor (T10) and the ninth transistor (T9) is connected between the fourth transistor (T4) and the twelvth transistor (T12),
- the eighth transistor (T8) is connected to the eleventh transistor (Til),
- the tenth transistor (T10), the eleventh transistor (Til) and the twelvth transistor (T12) are connected to ground (GND) , and - the tenth transistor (T10), the eleventh transistor (Til) and the twelvth transistor (T12) are connected to a control port (VCNT) .
13. The differential microphone of one of the previous claims, where the common mode feedback circuit (CMFBC) comprises
- a first (Tl), a second (T2), a third (T3), a fourth (T4), a fifth (T5) , a sixth (T6) , a seventh (T7) and an eighth (T8) transistor, where
- the first (Tl) and the second (T2) transistor are connected to a power supply (PS),
- the third transistor (T3) is connected between the first transistor (Tl) and the seventh transistor (T7),
- the fourth transistor (T4) is connected between the second transistor (T2) and the seventh transistor (T7),
- the fifth transistor (T5) is connected between the first transistor (Tl) and the eighth transistor (T8),
- the sixth transistor (T6) is connected between the second transistor (T2) and the eighth transistor (T8),
- the seventh transistor (T7) and the eighth transistor (T8) are connected to ground (GND) ,
- the third transistor (T3), the fourth transistor (T4) and the seventh transistor (T7) are connected to a control port (VCNT) , and
- the third transistor (T3) and the fourth transistor (T4) are connected to a common mode voltage port (VCOM) .
14. The differential microphone of one of the previous claims, where all circuit elements of the amplifier (AMP) are fully integrated in a CMOS ASIC chip (AC) .
15. A method for driving a differential microphone of one of the previous claims, comprising the steps
- receiving an acoustical signal,
- converting the acoustical signal into an electrical signal,
- adjusting the bias voltage of the first and second
microphone electrode by adjusting a common mode voltage via a common mode voltage port (VCOM) of the common mode feedback circuit .
16. The method of the previous claim, where the electrical signal is amplified with a adjustable and well defined gain insensitive to parasitic capacitances.
PCT/EP2012/050154 2012-01-05 2012-01-05 Differential microphone and method for driving a differential microphone WO2013102499A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US14/370,720 US9693135B2 (en) 2012-01-05 2012-01-05 Differential microphone and method for driving a differential microphone
DE112012005578.0T DE112012005578B4 (en) 2012-01-05 2012-01-05 Differential microphone and method for driving a differential microphone
PCT/EP2012/050154 WO2013102499A1 (en) 2012-01-05 2012-01-05 Differential microphone and method for driving a differential microphone
JP2014550651A JP5986221B2 (en) 2012-01-05 2012-01-05 Differential microphone and driving method of differential microphone

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2012/050154 WO2013102499A1 (en) 2012-01-05 2012-01-05 Differential microphone and method for driving a differential microphone

Publications (1)

Publication Number Publication Date
WO2013102499A1 true WO2013102499A1 (en) 2013-07-11

Family

ID=45443128

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2012/050154 WO2013102499A1 (en) 2012-01-05 2012-01-05 Differential microphone and method for driving a differential microphone

Country Status (4)

Country Link
US (1) US9693135B2 (en)
JP (1) JP5986221B2 (en)
DE (1) DE112012005578B4 (en)
WO (1) WO2013102499A1 (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015098893A1 (en) * 2013-12-27 2015-07-02 株式会社村田製作所 Capacitance trimming circuit
JP2015149589A (en) * 2014-02-06 2015-08-20 新日本無線株式会社 differential amplifier circuit
WO2015172809A1 (en) * 2014-05-12 2015-11-19 Epcos Ag Microphone assembly and method of manufacturing a microphone assembly
US20160080879A1 (en) * 2014-09-15 2016-03-17 Infineon Technologies Ag System and Method for a Transducer
CN105530570A (en) * 2014-10-20 2016-04-27 现代自动车株式会社 Analogue signal processing circuit for microphone
CN107371110A (en) * 2016-05-11 2017-11-21 现代自动车株式会社 High sensitivity microphone
WO2019097077A1 (en) * 2017-11-20 2019-05-23 Tdk Electronics Ag Charge pump and microphone circuit arrangement

Families Citing this family (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5986221B2 (en) * 2012-01-05 2016-09-06 エプコス アクチエンゲゼルシャフトＥｐｃｏｓ Ａｇ Differential microphone and driving method of differential microphone
WO2014069363A1 (en) 2012-11-02 2014-05-08 ローム株式会社 Chip condenser, circuit assembly, and electronic device
US9301046B1 (en) * 2013-09-27 2016-03-29 Cirrus Logic, Inc. Systems and methods for minimizing distortion in an audio output stage
WO2017006250A1 (en) * 2015-07-06 2017-01-12 Wizedsp Ltd. An acoustic transmit-receive transducer
US20180206043A1 (en) * 2015-07-12 2018-07-19 Wizedsp Ltd. An ultra-low-power ultra-low-noise microphone
JP6533446B2 (en) * 2015-10-05 2019-06-19 株式会社オーディオテクニカ Impedance conversion circuit of condenser microphone
CN105634323A (en) * 2016-02-29 2016-06-01 杭州电子科技大学 Electret thin film based energy collector
DE102016106015A1 (en) 2016-04-01 2017-10-05 Tdk Corporation Negative charge pump and audio ASIC with a negative charge pump
JP7191598B2 (en) * 2018-09-06 2022-12-19 日清紡マイクロデバイス株式会社 amplifier
IT201900001505A1 (en) 2019-02-01 2020-08-01 St Microelectronics Srl CHARGE AMPLIFIER CIRCUIT WITH HIGH OUTPUT DYNAMICS FOR A MICROELECTROMECHANICAL SENSOR
JP7377077B2 (en) * 2019-11-21 2023-11-09 福司 川上 condenser microphone
US11558695B2 (en) 2020-03-31 2023-01-17 Shure Acquisition Holdings, Inc. Condenser microphone pattern adjustment

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2044583A (en) * 1979-03-08 1980-10-15 Sony Corp Capacitor microphones
EP0065746A2 (en) * 1981-05-22 1982-12-01 Kabushiki Kaisha Toshiba Condenser microphone
US4757545A (en) 1983-02-25 1988-07-12 Rune Rosander Amplifier circuit for a condenser microphone system
US20080310655A1 (en) 2007-06-12 2008-12-18 Winbond Electronics Corporation Programmable integrated microphone interface circuit
US20100254544A1 (en) 2009-04-03 2010-10-07 Sanyo Electric Co., Ltd Amplifier circuit of capacitor microphone
WO2011132240A1 (en) * 2010-04-23 2011-10-27 パナソニック株式会社 Amplification device for capacitor microphone

Family Cites Families (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3721835A (en) * 1972-01-05 1973-03-20 Us Navy Hardlimiter, automatic symmetry circuit
DE2619192A1 (en) * 1976-04-30 1977-11-17 Licentia Gmbh CIRCUIT FOR AUTOMATIC DYNAMIC COMPRESSION OR EXPANSION
US4181818A (en) * 1976-11-05 1980-01-01 Gentex Corporation Personal amplifier system
US4533876A (en) * 1983-10-18 1985-08-06 American Microsystems, Inc. Differential operational amplifier with common mode feedback
ES2042865T3 (en) * 1988-05-03 1993-12-16 Endress Hauser Gmbh Co CIRCUIT DEVICE FOR SELF-EXCITATION OF A MECHANICAL OSCILLATION SYSTEM IN OWN RESONANCE OSCILLATIONS.
IT1239899B (en) * 1990-03-22 1993-11-23 Sgs Thomson Microelectronics LOW NOISE AND HIGH INPUT IMPEDANCE AMPLIFIER, PARTICULARLY FOR MICROPHONES
JPH088987A (en) * 1994-06-23 1996-01-12 Toshiba Corp Phase detector
JPH08181754A (en) * 1994-12-21 1996-07-12 Matsushita Electric Ind Co Ltd Handset for communication equipment
DK172085B1 (en) * 1995-06-23 1997-10-13 Microtronic As Micromechanical Microphone
GB2330709B (en) * 1997-10-24 2001-07-04 Sony Uk Ltd Signal processors
US7233774B2 (en) * 2003-01-30 2007-06-19 Broadcom Corporation RF transceiver with compact stacked mixer design for multiple frequency conversion
US7135928B2 (en) * 2003-01-30 2006-11-14 Broadcom Corporation Method for transconductance linearization for DC-coupled applications
US7124942B2 (en) * 2003-12-05 2006-10-24 Hid Corporation Low voltage signal stripping circuit for an RFID reader
US7317234B2 (en) * 2005-07-20 2008-01-08 Douglas G Marsh Means of integrating a microphone in a standard integrated circuit process
EP1921892A4 (en) * 2005-08-30 2012-04-11 Yamaha Corp Capacitor microphone and method for manufacturing capacitor microphone
GB2452941B (en) * 2007-09-19 2012-04-11 Wolfson Microelectronics Plc Mems device and process
JP4944760B2 (en) * 2007-12-27 2012-06-06 ホシデン株式会社 Electret condenser microphone
US7829366B2 (en) * 2008-02-29 2010-11-09 Freescale Semiconductor, Inc. Microelectromechanical systems component and method of making same
JP2010206237A (en) * 2009-02-27 2010-09-16 Panasonic Corp Amplification device and sensor module
ITTO20090495A1 (en) * 2009-06-30 2011-01-01 St Microelectronics Srl PREAMPLIFIER CIRCUIT FOR A CAPACITIVE MICRO-ELECTROMECHANICAL ACOUSTIC TRANSDUCER
US9083300B2 (en) * 2010-09-01 2015-07-14 Qualcomm Mems Technologies, Inc. Electromechanical systems piezoelectric contour mode differential resonators and filters
KR20120061422A (en) * 2010-12-03 2012-06-13 한국전자통신연구원 Mems microphone
US9236837B2 (en) * 2011-08-25 2016-01-12 Infineon Technologies Ag System and method for low distortion capacitive signal source amplifier
JP5986221B2 (en) * 2012-01-05 2016-09-06 エプコス アクチエンゲゼルシャフトＥｐｃｏｓ Ａｇ Differential microphone and driving method of differential microphone

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2044583A (en) * 1979-03-08 1980-10-15 Sony Corp Capacitor microphones
EP0065746A2 (en) * 1981-05-22 1982-12-01 Kabushiki Kaisha Toshiba Condenser microphone
US4757545A (en) 1983-02-25 1988-07-12 Rune Rosander Amplifier circuit for a condenser microphone system
US20080310655A1 (en) 2007-06-12 2008-12-18 Winbond Electronics Corporation Programmable integrated microphone interface circuit
US20100254544A1 (en) 2009-04-03 2010-10-07 Sanyo Electric Co., Ltd Amplifier circuit of capacitor microphone
WO2011132240A1 (en) * 2010-04-23 2011-10-27 パナソニック株式会社 Amplification device for capacitor microphone

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
CARLEY L R ET AL: "Analysis of switched-capacitor common-mode feedback circuit", IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II: ANALOG AND DIGITALSIGNAL PROCESSING, INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS INC, 345 EAST 47 STREET, NEW YORK, N.Y. 10017, USA, vol. 50, no. 12, 1 December 2003 (2003-12-01), pages 906 - 917, XP011105126, ISSN: 1057-7130, DOI: 10.1109/TCSII.2003.820253 *
LIU ET AL: "Nonlinear model and system identification of a capacitive dual-backplate MEMS microphone", JOURNAL OF SOUND & VIBRATION, LONDON, GB, vol. 309, no. 1-2, 26 October 2007 (2007-10-26), pages 276 - 292, XP022317174, ISSN: 0022-460X, DOI: 10.1016/J.JSV.2007.07.037 *
WEIXUN YAN ET AL: "Continuous-Time Common-Mode Feedback Circuit for Applications with Large Output Swing and High Output Impedance", DESIGN AND DIAGNOSTICS OF ELECTRONIC CIRCUITS AND SYSTEMS, 2008. DDECS 2008. 11TH IEEE WORKSHOP ON, IEEE, PISCATAWAY, NJ, USA, 16 April 2008 (2008-04-16), pages 1 - 5, XP031269811, ISBN: 978-1-4244-2276-0 *

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015098893A1 (en) * 2013-12-27 2015-07-02 株式会社村田製作所 Capacitance trimming circuit
JP2015149589A (en) * 2014-02-06 2015-08-20 新日本無線株式会社 differential amplifier circuit
JP2017522752A (en) * 2014-05-12 2017-08-10 Tdk株式会社 Microphone assembly and method of manufacturing a microphone assembly
WO2015172809A1 (en) * 2014-05-12 2015-11-19 Epcos Ag Microphone assembly and method of manufacturing a microphone assembly
US10165342B2 (en) 2014-05-12 2018-12-25 Tdk Corporation Microphone assembly and method of manufacturing a microphone assembly
KR101845589B1 (en) * 2014-09-15 2018-04-04 인피니언 테크놀로지스 아게 System and method for a transducer
CN105430583A (en) * 2014-09-15 2016-03-23 英飞凌科技股份有限公司 System and Method for a Transducer
US9942677B2 (en) * 2014-09-15 2018-04-10 Infineon Technologies Ag System and method for a transducer
US20160080879A1 (en) * 2014-09-15 2016-03-17 Infineon Technologies Ag System and Method for a Transducer
US10200801B2 (en) 2014-09-15 2019-02-05 Infineon Technologies Ag System and method for a transducer
CN105430583B (en) * 2014-09-15 2019-06-21 英飞凌科技股份有限公司 Transducer system and method
CN105530570A (en) * 2014-10-20 2016-04-27 现代自动车株式会社 Analogue signal processing circuit for microphone
CN105530570B (en) * 2014-10-20 2020-08-14 现代自动车株式会社 Analog signal processing circuit of microphone
CN107371110A (en) * 2016-05-11 2017-11-21 现代自动车株式会社 High sensitivity microphone
WO2019097077A1 (en) * 2017-11-20 2019-05-23 Tdk Electronics Ag Charge pump and microphone circuit arrangement
US11496829B2 (en) 2017-11-20 2022-11-08 Tdk Corporation Charge pump and microphone circuit arrangement

Also Published As

Publication number Publication date
DE112012005578T5 (en) 2015-08-27
JP5986221B2 (en) 2016-09-06
JP2015507877A (en) 2015-03-12
US20150016635A1 (en) 2015-01-15
DE112012005578B4 (en) 2019-11-07
US9693135B2 (en) 2017-06-27

Similar Documents

Publication Publication Date Title
WO2013102499A1 (en) Differential microphone and method for driving a differential microphone
KR101408529B1 (en) System and method for capacitive signal source amplifier
US20200252728A1 (en) Sensor arrangement and method
US10182292B2 (en) Differential amplifier circuit for a capacitive acoustic transducer and corresponding capacitive acoustic transducer
US7756279B2 (en) Microphone preamplifier
KR101871811B1 (en) Mems microphone using noise filter
US9590571B2 (en) Single stage buffer with filter
KR101098047B1 (en) Amplifying circuit of condenser microphone
KR101564145B1 (en) System and method for capacitive signal source amplifier
WO2008100055A2 (en) Microphone amplifier
KR101601449B1 (en) System and method for a microphone amplifier
US10412486B2 (en) Electronic circuit for a microphone and microphone
CN210042121U (en) Microphone input circuit
US10547277B2 (en) MEMS capacitive sensor
JP2008124660A (en) Filter circuit and semiconductor integrated device

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 12700015

Country of ref document: EP

Kind code of ref document: A1

ENP Entry into the national phase

Ref document number: 2014550651

Country of ref document: JP

Kind code of ref document: A

WWE Wipo information: entry into national phase

Ref document number: 112012005578

Country of ref document: DE

Ref document number: 1120120055780

Country of ref document: DE

WWE Wipo information: entry into national phase

Ref document number: 14370720

Country of ref document: US

122 Ep: pct application non-entry in european phase

Ref document number: 12700015

Country of ref document: EP

Kind code of ref document: A1