INTERFACE ELECTRONIC CIRCUIT FOR A MICROELECTROMECHANICAL ACOUSTIC TRANSDUCER AND CORRESPONDING METHOD

• US 20190326867A1
• Filed: 04/09/2019
• Published: 10/24/2019
• Est. Priority Date: 04/18/2018
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: DANIONI, Alberto, MORCELLI, Alessandro
• Granted Patent: US 10,965,262 B2
• Time in Patent Office: Days
• CPC Class Codes: H03F 1/0211 with control of the supply voltage or current
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/48 the output of the amplifier being coupled out by a capacitor
• CPC Class Codes: H03F 3/181 Low-frequency amplifiers, e.g. audio preamplifiers
• CPC Class Codes: H03F 3/70 Charge amplifiers
• CPC Class Codes: H04R 19/005 using semiconductor materials
• CPC Class Codes: H04R 19/04 Microphones H04R19/01 takes precedence

Abstract

In at least one embodiment, an interface electronic circuit for a capacitive acoustic transducer having a sensing capacitor is provided. The interface electronic circuit includes an amplifier, a voltage regulator, a common-mode control circuit, and a reference generator. The amplifier has an input coupled to an electrode of the sensing capacitor. The voltage regulator is configured to receive a regulator reference voltage, generate a regulated voltage based on the regulator reference voltage, and supply the regulated voltage to a supply input of the amplifier. The common-mode control circuit controls a common-mode voltage present on the input of the amplifier based on a common-mode reference voltage. The reference generator receives a supply voltage and generates the regulator reference voltage and the common-mode reference voltage with respective values that are variable as a function of the supply voltage.

Claims

1. An interface electronic circuit for a capacitive acoustic transducer having a sensing capacitor, comprising:

an amplifier having an input coupled to a first electrode of said sensing capacitor;

a voltage regulator configured to receive a regulator reference voltage, generate a regulated voltage based on the regulator reference voltage, and supply the regulated voltage to a supply input of said amplifier;

a common-mode control circuit configured to control a common-mode voltage present on said input of said amplifier based on a common-mode reference voltage; and

a reference generator configured to receive a supply voltage and generate said regulator reference voltage and said common-mode reference voltage with respective values that are variable as a function of said supply voltage.

2. The circuit according to claim 1, wherein said reference generator is configured to generate said regulator reference voltage and said common-mode reference voltage proportional to said supply voltage, as a product of said supply voltage by a first multiplicative factor and a second multiplicative factor, respectively.

3. The circuit according to claim 1, further comprising a charge pump coupled to a second electrode of said sensing capacitor and configured to generate a boosted voltage based on said supply voltage and on a charge pump reference voltage, wherein said reference generator is configured to generate said charge pump reference voltage with a value that is variable as a function of said supply voltage.

4. The circuit according to claim 3, wherein the reference generator is configured to generate said charge-pump reference voltage as a combination of:

a first component, which is fixed as said supply voltage varies and is generated based on a voltage reference; and

a second component, which is variable as a function of the supply voltage, wherein said second component has a value lower than the first component.

5. The circuit according to claim 4, wherein said second component has a value lower than 1% of said first component.

6. The circuit according to claim 4, wherein said second component is equal to a difference between the supply voltage and the voltage reference multiplied by a respective multiplicative factor.

7. The circuit according to claim 3, further comprising a filter configured to implement a low-pass filtering of said regulator reference voltage, said common-mode reference voltage, and said charge-pump reference voltage generated by the reference generator, wherein said filter includes:

a filtering input;

a filtering output;

a high-impedance circuit connected between said filtering input and said filtering output;

a capacitor connected to said filtering output; and

a switch connected in parallel to said high-impedance circuit and driven by a timing signal into a closed condition for a start-up time interval during a start-up phase of said interface electronic circuit and into an open condition outside said start-up time interval.

8. The circuit according to claim 7, wherein said start-up time interval occurs at start-up or power-on of said interface electronic circuit or upon resumption from a stand-by or power-down condition.

9. The circuit according to claim 3, wherein said reference generator comprises:

a supply input configured to receive the supply voltage; and

a first voltage divider coupled to the supply input, the first voltage divider having a first divider node, coupled to a first output of said reference generator, which outputs said regulator reference voltage, and a second divider node, coupled to a second output of said reference generator, which outputs said common-mode reference voltage.

10. The circuit according to claim 9, wherein said reference generator further comprises:

a reference input configured to receive a voltage reference;

a second voltage divider coupled to the reference input, the second voltage divider having a third divider node, coupled to a third output of said reference generator, which outputs said charge-pump reference voltage; and

transconductance circuitry having a transconductance, a first comparison input coupled to the supply input, a second comparison input coupled to the reference input, and an output coupled to said third output of said reference generator.

11. The circuit according to claim 10, wherein said reference generator is configured to generate two distinct values for said charge-pump reference voltage, of which a first value is lower and a second value is higher than the voltage reference, and the reference generator further comprises:

a selector circuit coupled to the output of said transconductance circuitry; and

a resistor connected to said reference input,

wherein said selector circuit is selectively supply one of the first value or the second value of said charge-pump reference voltage to said third output of said reference generator.

12. The circuit according to claim 11, wherein said selector circuit comprises:

a first switch connected between the output of the transconductance circuitry and the third divider node, the first switch configured to be controlled by a first control signal;

a second switch connected between the third divider node and said third output, the second switch configured to be controlled by said first control signal;

a third switch connected between the output of the transconductance circuitry and an internal node of said selector circuit, the third switch configured to be controlled by a second control signal, the second control signal being inverted with respect to the first control signal; and

a fourth switch connected between the internal node and said third output, the fourth switch configured to be controlled by said second control signal,

wherein said resistor is connected between said reference input and said internal node.

13. An electronic device, comprising:

a MEMS acoustic transducer having a sensing capacitor; and

an interface electronic circuit, the interface electronic circuit including;

an amplifier having an input coupled to a first electrode of the sensing capacitor;

a voltage regulator configured to receive a regulator reference voltage, generate a regulated voltage based on the regulator reference voltage, and supply the regulated voltage to a supply input of the amplifier;

a common-mode control circuit configured to control a common-mode voltage present on the input of the amplifier based on a common-mode reference voltage; and

a reference generator configured to receive a supply voltage and generate the regulator reference voltage and the common-mode reference voltage with respective values that are variable as a function of the supply voltage.

14. The electronic device of claim 13, further comprising:

a microprocessor electrically coupled to the interface electronic circuit; and

a computer-readable memory electrically coupled to the microprocessor.

15. The electronic device of claim 13, wherein the electronic device comprises at least one of:

a mobile phone, a personal digital assistant (PDA), a notebook computer device, a voice recorder, a voice recorder device, a hydrophone, or a hearing-aid device.

16. A method, comprising:

amplifying, by an amplifier, a capacitive variation of a sensing capacitor of a capacitive acoustic transducer;

generating, by a voltage regulator, a regulated voltage based on a regulator reference voltage, and supplying the regulated voltage to a supply input of the amplifier;

controlling, by a common-mode control circuit, a common-mode voltage present on the input of said amplifier based on a common-mode reference voltage; and

generating, by a reference generator, said regulator reference voltage and said common-mode reference voltage with respective values that are variable as a function of a supply voltage of said capacitive acoustic transducer.

17. The method according to claim 16, wherein the generating said regulator reference voltage and said common-mode reference voltage includes generating said regulator reference voltage and said common-mode reference voltage proportional to said supply voltage, as a product of said supply voltage by a first multiplicative factor and by a second multiplicative factor, respectively.

18. The method according to claim 16, further comprising:

generating, by a charge pump coupled to an electrode of said sensing capacitor, a boosted voltage based on said supply voltage and on a charge-pump reference voltage; and

generating, by the reference generator, said charge-pump reference voltage with a value that is variable as a function of said supply voltage.

19. The method according to claim 18, wherein generating said charge-pump reference voltage includes generating said charge-pump reference voltage as a combination of:

a first component, which is fixed as said supply voltage varies and is generated on based on a voltage reference; and

a second component, which is variable as a function of the supply voltage and has a value lower than the first component.

20. The method according to claim 16, further comprising:

low-pass filtering said regulator reference voltage, said common-mode reference voltage, and said charge-pump reference voltage, wherein said low-pass filtering is de-activated during a start-up time interval of an interface electronic circuit coupled to said capacitive acoustic transducer.