Differential microphone and method for driving a differential microphone

Patent metadata

Field	Value
Publication number	US-9693135-B2
Application number	US-201214370720-A
Country	US
Kind code	B2
Filing date	Jan 5, 2012
Priority date	Jan 5, 2012
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

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

First claim

The invention claimed is:

1. A differential microphone comprising:
a first microphone electrode;
a central microphone electrode;
a second microphone electrode;
an output port configured as a differential port;
a differential amplifier stage having a differential input port and a differential output port that is connected to the output port of the microphone; and
a common mode feedback circuit having a differential port that is connected to the output port of the microphone,
wherein the first microphone electrode and the central microphone electrode establish a first capacitive element and the central microphone electrode and the second microphone electrode establish a second capacitive element, and
wherein the first and second capacitive elements provide a differential capacitor output port.

2. The differential microphone according to claim 1 , wherein a first terminal of the amplifier stage differential input port is connected to the differential capacitor output port and a second terminal of the amplifier stage differential input port is connected to the differential capacitor output port.

3. The differential microphone according to claim 1 , wherein the amplifier stage has a control port and the common mode feedback circuit is connected to the control port.

4. The differential microphone according to claim 1 , further comprising:
a first resistance element connected between a first terminal of the output port and a first terminal of the input port; and
a second resistance element connected between a second terminal of the output port and a second terminal of the input port,
wherein the first and the second resistance elements are part of an amplifier feedback circuit.

5. The differential microphone according to claim 4 , wherein the first and second resistance elements each comprise a first diode and a second diode that is connected in parallel to and in an opposite direction of the first diode.

6. The differential microphone according to claim 1 , wherein the common mode feedback circuit comprises a common mode voltage port for setting and adjusting the common mode voltage at the amplifier stage output port.

7. The differential microphone according to claim 1 , further comprising:
a first capacitance element and a second capacitance element;
wherein the first capacitance element is connected between a first terminal of the output port and a first terminal of the amplifier stage's input port;
wherein the second capacitance element is connected between a second terminal of the output port and a second terminal of the amplifier stage input port; and
wherein the first and the second capacitance elements are part of an amplifier feedback circuit.

8. The differential microphone according to claim 1 , wherein the first microphone electrode, the central microphone electrode and the second microphone electrode are elements of an acoustically active part of a Micro Electro Mechanical System (MEMS) microphone or a electret condenser microphone.

9. The differential microphone according to claim 1 , further comprising:
a third capacitance element connected between a first terminal of the amplifier stage input port and the first microphone electrode; and
a fourth capacitance element connected between a second terminal of the amplifier stage input port and the second microphone electrode.

10. The differential microphone according to claim 1 , further comprising:
a third resistance element connected between the first microphone electrode and a high bias voltage generated by an integrated circuit, wherein the first microphone electrode and the second microphone electrode are electrically connected.

11. The differential microphone according to claim 1 , wherein the amplifier stage comprises:
a first, a second, a third, a fourth, a fifth, a sixth, a seventh, an eighth, a ninth, a tenth and an eleventh transistor, wherein:
the first, the second and the third transistors are connected to a power supply,
the fourth transistor is connected between the second and the sixth transistors 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.

12. The differential microphone according to claim 1 , wherein 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 twelfth transistor, where
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 twelfth transistor,
the eighth transistor is connected to the eleventh transistor,
the tenth transistor, the eleventh transistor and the twelfth transistor are connected to ground, and
the tenth transistor, the eleventh transistor and the twelfth transistor are connected to a control port.

13. The differential microphone according to claim 1 , wherein the common mode feedback circuit comprises:
a first, a second, a third, a fourth, a fifth, a sixth, a seventh and an eighth transistor, where
the first and the second transistors are connected to a power supply,
the third transistor 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,
the third transistor, the fourth transistor and the seventh transistor are connected to a control port, and
the third transistor and the fourth transistor are connected to a common mode voltage port.

14. The differential microphone according to claim 1 , wherein all circuit elements of the differential amplifier stage are fully integrated in a Complementary Metal Oxide Semiconductor (CMOS) Application Specific Integrated Circuit (ASIC) chip.

15. A method for driving a differential microphone according to claim 1 , the method comprising:
receiving an acoustical signal;
converting the acoustical signal into an electrical signal; and
adjusting a bias voltage of the first and second microphone electrode by adjusting a common mode voltage via a common mode voltage port of the common mode feedback circuit.

16. The method according to claim 15 , wherein the electrical signal is amplified with an adjustable and well defined gain insensitive to parasitic capacitances.

17. An apparatus comprising:
the differential microphone according to claim 1 , wherein the first microphone electrode, the central microphone electrode and the second m

Assignees

• Haas-Christensen Jelena Citakovic
• Hanzlik Tomasz
• Nielsen Ivan Riis
• Sassene Daifi Haoues
• Marczak Tomasz
• Tdk Corp

Inventors

• Haas-Christensen Jelena Citakovic
• Hanzlik Tomasz
• Nielsen Ivan Riis
• Sassene Daifi Haoues
• Marczak Tomasz

Classifications

• H04R3/00 Primary

  Circuits for transducers (arrangements for producing a reverberation or echo sound G10K15/08; amplifiers H03F) · CPC title

• H04R19/016

  for microphones · CPC title

• H04R1/08

  Mouthpieces; {Microphones;} Attachments therefor · CPC title