CN113727266B

CN113727266B - MEMS microphone control circuit and electronic equipment

Info

Publication number: CN113727266B
Application number: CN202111027696.3A
Authority: CN
Inventors: 陈奇辉; 张治安
Original assignee: Suzhou Novosense Microelectronics Co ltd
Current assignee: Suzhou Novosense Microelectronics Co ltd
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2022-11-01
Anticipated expiration: 2041-09-02
Also published as: CN113727266A

Abstract

The application provides MEMS microphone control circuit and electronic equipment, includes: the signal reading circuit is provided with an input port and an output port and is used for reading or amplifying an output signal of the MEMS microphone circuit; the feedback control circuit is provided with an input port and an output port, the input port of the feedback control circuit is connected with the output port of the signal reading circuit, and the feedback control circuit is used for sampling the output signal of the signal reading circuit; the output port of the MEMS microphone control circuit is connected with the input port of the signal reading circuit, the feedback control circuit can feed back a sampling signal, so that the DC working point of the MEMS microphone circuit can be quickly recovered when the DC working point deviates. Meanwhile, the negative feedback loop control method does not need to reduce, and even can improve the magnitude of the bias impedance, thereby being beneficial to improving the linearity of the circuit.

Description

MEMS microphone control circuit and electronic equipment

Technical Field

The invention relates to the technical field of MEMS microphones and provides an MEMS microphone control circuit and electronic equipment.

Background

Circuits for reading or amplifying signals of capacitive sensors such as MEMS microphones typically comprise very high impedance input terminals. In such circuits, a bias may also be required to define a dc quiescent operating point of the MEMS microphone, including an input dc quiescent operating point and an output dc quiescent operating point. The impedance values typically designed for these bias circuits exceed 1Gohm, and even exceed 100Gohm, which often presents the problem that the dc quiescent operating point takes a long time to settle or recover.

For the problem of establishing a direct current steady state, a method of simply reducing bias impedance at the initial power-on stage is usually adopted, so that a direct current static operating point is quickly established, but for the situation that the direct current operating point is shifted due to the input of large signals or environmental interference such as wind noise and the like when power supply voltage is continuously supplied, the direct current static operating point usually needs a long time to be restored to a steady state value, and thus, part of application occasions of the MEMS microphone are limited.

In order to reduce the time for restoring the dc quiescent operating point, the conventional design idea is to reduce the RC time constant required for dc set-up by reducing the bias impedance.

Fig. 1 and fig. 2 show two optimization schemes of a common microphone control circuit, and the reduction of bias impedance can be achieved by reducing the area of a diode in fig. 1, or reducing the width-to-length ratio of a MOS transistor in fig. 2, or by biasing the MOS transistor to operate in a sub-threshold region.

The disadvantages of fig. 1 and 2 are: although the method of reducing the bias impedance can reduce the dc recovery time, it can affect the performance of the MEMS microphone, such as noise, linearity, lower-3 dB frequency point, etc.

Therefore, there is a need for an improvement to existing MEMS microphone control circuits.

Disclosure of Invention

In view of the above technical problems in the prior art, the present application provides a high performance MEMS microphone control circuit capable of quickly restoring a dc quiescent operating point.

The application provides MEMS microphone control circuit includes: the signal reading circuit is provided with an input port and an output port and is used for reading or amplifying an output signal of the MEMS microphone circuit; the feedback control circuit is provided with an input port and an output port, the input port of the feedback control circuit is connected with the output port of the signal reading circuit, and the feedback control circuit is used for sampling the output signal of the signal reading circuit; the output port of the MEMS microphone circuit is connected with the input port of the signal reading circuit, and the feedback control circuit can feed back a sampling signal, so that the direct current working point of the MEMS microphone circuit can be quickly recovered when the direct current working point deviates.

Optionally, the signal reading circuit comprises: the operational amplifier circuit is used for outputting or amplifying signals and is provided with an input end and an output end, wherein the input end is connected with the MEMS microphone circuit and can acquire the output signals of the MEMS microphone circuit.

Optionally, the method further comprises: and the bias voltage providing circuit is used for rapidly responding to a changing direct current working point, the input end of the bias voltage providing circuit is connected with the output end of the MEMS microphone circuit, and the output end of the bias voltage providing circuit is connected with the output end of the feedback control circuit.

Optionally, the feedback control circuit comprises: the input end of the input filter circuit is connected with the output end of the operational amplifier circuit; the input end of the inverting operational amplifier circuit is connected with the input filter circuit; and the input end of the output filter circuit is connected with the inverting operational amplification circuit, and the output end of the output filter circuit is connected with the input end of the bias voltage supply circuit.

Optionally, the output filter circuit includes a first resistor and a first capacitor, a first end of the first resistor is connected to the output end of the inverting operational amplifier circuit, and a second end of the first resistor is connected to the bias voltage supply circuit; and two ends of the first capacitor are respectively connected with the second end of the first resistor and the ground.

Optionally, the inverting operational amplifier circuit includes: an inverting operational amplifier having an inverting input connected to the output of the input filter circuit, a non-inverting output configured to receive the voltage VBIAS, and an output connected to the input of the output filter circuit.

Optionally, the method further comprises: and the direct current offset module is connected between the inverting input end of the inverting operational amplifier and the output end of the input filter circuit.

Optionally, the method further comprises: and the follower is connected between the inverting input end of the inverting operational amplifier and the output end of the input filter circuit.

Optionally, the bias voltage providing circuit includes a first diode and a second diode, and a cathode of the first diode is connected to an anode of the second diode to form an output terminal of the bias voltage providing circuit; and the anode of the first diode is connected with the cathode of the second diode to form the input end of the bias voltage supply circuit.

In order to achieve the above object, the present application also provides an electronic device characterized by applying the MEMS microphone control circuit according to any one of claims 1 to 9.

To sum up, the application provides a high performance MEMS microphone signal control circuit that can resume the static operating point of direct current fast. The fast recovery of the DC working point after the drift occurs is improved through the negative feedback loop control, and simultaneously, the bias impedance can be improved, and the circuit linearity is favorably improved.

Drawings

FIG. 1 is a schematic diagram of a control circuit of a MEMS microphone shown in the prior art;

FIG. 2 is a second schematic diagram of a control circuit of a MEMS microphone shown in the prior art;

FIG. 3 is a schematic diagram of a MEMS microphone control circuit shown in an embodiment of the present application;

fig. 4 is one of the schematic structural diagrams of the control circuit showing other feedback operational amplifier forms in the embodiment of the present application;

FIG. 5 is a schematic diagram of an optimized structure of the MEMS microphone control circuit shown in FIG. 3 according to an embodiment of the present application;

fig. 6 is a second schematic diagram of an optimized structure of the MEMS microphone control circuit shown in the embodiment of the present application.

Detailed Description

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. However, the present application is not limited to the following embodiments, but includes various changes, substitutions, and alterations within the technical scope of the present disclosure. The terms "first," "second," and the like may be used to explain various elements, the number of elements is not limited by such terms. These terms are only used to distinguish one element from another. Thus, an element referred to as a first element in one embodiment may be referred to as a second element in another embodiment. The singular forms do not exclude the plural forms unless the context requires otherwise.

In the following description, the terms "comprises" or "comprising" are used to indicate features, numerals, steps, operations, elements, parts, or combinations thereof, and do not exclude other features, numerals, steps, operations, elements, parts, or combinations thereof.

The embodiment provides a high-performance MEMS microphone control circuit capable of rapidly restoring a dc quiescent operating point, as shown in fig. 3, including: a signal reading circuit 1 having an input port and an output port, the input port being configured for reading or amplifying a signal of a capacitive sensor such as a MEMS microphone, the input port being used for reading or amplifying a signal of the MEMS microphone circuit 4 as an example hereinafter; and the feedback control circuit 2 is provided with an input port and an output port, the input port of the feedback control circuit 2 is connected with the output port of the signal reading circuit 1 and is used for sampling the output signal of the signal reading circuit 1, and the output port of the feedback control circuit 2 is connected with the input port of the signal reading circuit 1 and can output a feedback signal based on the output signal of the signal reading circuit 1, so that the quick recovery performance of the direct-current working point is improved.

With continued reference to fig. 3, in particular, the signal reading circuit includes 1: the operational amplifier circuit AMP is used for outputting or amplifying signals and is provided with an input end and an output end, wherein the input end is connected with the MEMS microphone circuit and can acquire the output signals of the MEMS microphone circuit.

Optionally, the MEMS microphone control circuit further comprises a bias voltage providing circuit 3 for providing a bias voltage, an output of the bias voltage providing circuit 3 is connected to an output of the MEMS microphone circuit 4, and an input of the bias voltage providing circuit 3 is connected to an output of the feedback control circuit 2.

Specifically, the bias voltage providing circuit 3 includes a first diode D1 and a second diode D2, a cathode of the first diode D1 is connected to an anode of the second diode D2 to form an output terminal of the bias voltage providing circuit 3; the anode of the first diode D1 is connected to the cathode of the second diode D2 to form an input terminal of the bias voltage providing circuit 3, which is equivalent to a resistor with a large resistance value, and the bias voltage can be designed through the resistance value setting of the resistor.

Optionally, the feedback control circuit 2 further comprises: the input filter circuit 21 includes a resistor R and a capacitor C, and a positive terminal of the resistor R is an input terminal of the feedback control circuit 2 and is connected to an output terminal of the operational amplifier circuit AMP. The negative end of the resistor R is connected with the positive end of the capacitor C and is connected with the inverting input end of the inverting operational amplifier circuit 22; the negative end of the capacitor C is connected with the ground;

an inverting operational amplifier circuit 22, an inverting input terminal of which is connected to the output terminal of the input filter circuit 21, a non-inverting output terminal of which is configured to receive a voltage VBIAS (which may be provided by a dc operating point bias circuit), and an output terminal of which is connected to the input terminal of the output filter circuit 23; and

an output filter circuit 23, including a first resistor R01 and a first capacitor C01, wherein a first end of the first resistor R01 is connected to an output end of the inverting operational amplifier circuit 22, and a second end of the first resistor C01 is connected to the bias voltage supply circuit 3; two ends of the first capacitor C01 are respectively connected with the second end of the first resistor R01 and the ground.

Specifically, the inverting operational amplifier circuit 22 includes an inverting operational amplifier, and the output terminal is connected to the output filter circuit 23; a resistor R1 connected between the input filter circuit 21 and the inverting input terminal of the inverting operational amplifier; and the resistor R2 is connected between the output filter circuit 21 and the inverting input end of the inverting operational amplifier, and the amplification factor of the inverting operational amplifier can be adjusted by adjusting the resistance relation between the resistor R1 and the resistor R2.

Alternatively, in some embodiments, for a general MEMS microphone circuit, where there may be a certain difference between the input dc bias voltage and the output dc bias voltage, this embodiment shows a method to make the output dc operation negative feedback loop control circuit operate normally. A dc offset module is added in the feedback loop, and the dc offset is equal to the difference between the negative input dc offset voltage and the output dc voltage, so that each module in the whole loop is in a correct dc working state, specifically, as shown in fig. 5, in order to attenuate the high-frequency noise and provide the feedback voltage corresponding to the correct working point, a dc offset module 5 is disposed between the input filter circuit 21 and the inverting input terminal of the inverting operational amplifier circuit 22.

Optionally, in some embodiments, when there is a difference between the input dc offset and the output dc offset, the dc offset module 5 may provide a difference between the input dc operating point and the output dc operating point, and make the feedback control circuit 2 operate at a normal dc operating point. When the input dc bias and the output dc bias are the same, as shown in fig. 3, a follower x1 is connected between the inverting operational amplifier circuit 22 and the input filter circuit 21, and is used to detect the output dc operating point of the signal reading circuit 1.

The working principle of the feedback control circuit 2 shown in fig. 3 is explained below:

the charge pump provides a supply voltage for the MEMS microphone circuit 4, and the MEMS microphone circuit 4 samples and processes the effective signal to generate a MEMS _ IN signal, which is transmitted to the operational amplifier circuit AMP to obtain an output signal OUT.

When the MEMS microphone control circuit is initially powered on, the potential of the non-inverting input terminal of the inverting operational amplifier circuit 22 is equal to the potential of the inverting input terminal due to the virtual short characteristic of the inverting operational amplifier circuit 22, which are VBIAS. Meanwhile, because of the virtual interruption characteristic of the inverting operational amplifier circuit 22, the current flowing into the inverting input terminal of the inverting operational amplifier circuit 22 is zero, and the current passing through the resistor R2 is equal to the current passing through the resistor R1, so that when the whole loop reaches a stable state, the output voltage of the inverting operational amplifier is equal to the voltage of the non-inverting terminal and equal to the voltage of the inverting terminal and equal to VBIAS.

Because of the nature of the voltage limiting circuit, MEMS _ IN will be quickly set to near the stable operating point voltage of the output, VBIAS. Therefore, the method has the advantages of quick response and greatly shortening the establishment time of the direct-current static working point in the starting process.

When the power supply voltage is continuously supplied, the direct current working point of the signal reading circuit is deviated due to the input large signal or the environmental interference such as wind noise. It is assumed at this time that the output signal OUT rises due to the MEMS _ IN signal at the input terminal of the operational amplifier circuit AMP being affected by a large signal or noise. After passing through the input filter circuit 21 of the feedback control circuit 2, the signal is transmitted to the inverting input terminal of the inverting operational amplifier circuit 22. Therefore, the output of the inverting operational amplifier circuit 22 decreases with the increase of the input signal, and the decrease is determined by the ratio of the feedback resistors R1 and R2. The output signal is connected to the input terminal of the bias voltage supply circuit 3 through the output filter circuit 23 of the feedback control circuit. Because of this reduction IN the output voltage, the diode impedance IN the bias voltage supply circuit 3 is lowered, thereby controlling the quick response of the MEMS _ IN signal.

When the input of large signals or interference is finished, the direct current working points of the MEMS _ IN and the MEMS _ OUT are quickly recovered to be within a range with small difference from a steady state value.

Alternatively, in some other applications, it is desirable to have the output dc voltage recover quickly to within a small error range, which requires a large amplification of the negative feedback loop, but this may cause loop stability problems. As shown in fig. 6, this embodiment shows a method to improve the loop stability, and a feed-forward capacitor CF is connected in parallel across the first resistor R01 by adding a zero point in the feedback loop. Although the zero point formed by the capacitor and the resistor effectively improves the loop stability, the introduction of the capacitor may reduce the linearity of the system, so that a reasonable compromise needs to be made in the final circuit design.

The inverting operational amplifier circuit 22 includes, but is not limited to: single-ended input single-ended output, single-ended input differential output, differential input single-ended output, differential input differential output, and the like.

Optionally, the following describes the operation principle of the feedback control circuit for differential input and differential output with reference to fig. 4:

the output end of the MEMS microphone circuit 4 is connected with the input buffer 6 on one hand and the bias voltage providing circuit 3 on the other hand, the signal reading circuit 1 comprises an operational amplifier circuit AMP, a capacitor C2 is connected between a differential in-phase input end and the input buffer 6, a capacitor C3 is connected between a differential anti-phase input end and the ground, a differential in-phase output end outputs a signal OUTP, a differential anti-phase output end outputs a signal OUTN, a capacitor C1 is connected between the differential in-phase input end and the differential anti-phase output end, and two ends of the capacitor C1 are connected with a resistor R3 in parallel; the differential in-phase output end is connected with the first end of the capacitor C4, and the other end of the capacitor C4 is connected with one end, far away from the ground, of the capacitor C3 on the one hand and connected with the first end of the resistor R4 on the other hand.

The input filter circuit 21 comprises a resistor R6, a resistor R5, a capacitor C6 and a capacitor C5, wherein a first end of the resistor R6 is connected to OUTN, a second end of the resistor R6 is connected to an inverting input terminal of the inverting operational amplifier circuit 22, and is connected to a first end of the capacitor C6, and a second end of the capacitor C6 is grounded; the first end of the resistor R5 is connected to OUTP, the second end is connected to the non-inverting input terminal of the inverting operational amplifier circuit 22, and the first end of the capacitor C5, and the second end of the capacitor C5 is grounded.

The output end of the inverting operational amplifier circuit 22 is connected to the output filter circuit 23, and the output end of the output filter circuit 23 is connected to the second end of the resistor R4.

As shown in fig. 4, this embodiment shows an operation mode of the operational amplifier circuit AMP with differential input and differential output, since the output signals are the differential outputs OUTN and OUTP. Accordingly, the feedback control loop 2 also needs to adopt a differential operational amplifier form for feedback control.

The output signals OUTP and OUTN are connected to the non-inverting input terminal and the inverting input terminal of the inverting operational amplification circuit 22, respectively, through input filter circuits. Meanwhile, the output terminal of the inverting operational amplifier circuit 22 is connected to the inverting differential input terminal of the operational amplifier circuit AMP through the output filter circuit 23. Thereby forming a negative feedback control loop.

When the MEMS _ IN signal rises due to a large signal or noise, the output differential mode signal OUTP-OUTN will also rise accordingly. The output signal of the inverting operational amplifier circuit 22 will also rise as the input signal becomes larger. And because the output signal of the inverting operational amplifier circuit 22 is connected to the inverting terminal of the operational amplifier circuit AMP. The now rising inverted signal will inhibit the continued change in the output signals OUTN and OUTP. Thereby ensuring that the direct current working point can be quickly recovered after the drift occurs.

To sum up, the MEMS microphone control circuit provided by the present application can rapidly recover the dc operating point after drift occurs by means of a negative feedback control loop. Meanwhile, the negative feedback loop control method does not need to reduce, and even can improve the magnitude of the bias impedance, thereby being beneficial to improving the linearity of the circuit.

Therefore, the scope of the invention is not limited to the disclosure of the embodiments, and includes various alternatives and modifications without departing from the invention, which are covered by the claims of this patent application.

Claims

1. A MEMS microphone control circuit, comprising:

the signal reading circuit is provided with an input port and an output port and is used for reading or amplifying an output signal of the MEMS microphone circuit;

the feedback control circuit is provided with an input port and an output port, the input port of the feedback control circuit is connected with the output port of the signal reading circuit, and the feedback control circuit is used for sampling the output signal of the signal reading circuit; the output port of the MEMS microphone circuit is connected with the input port of the signal reading circuit, and the feedback control circuit can feed back a sampling signal, so that the MEMS microphone circuit can be quickly recovered when the direct current working point deviates;

the signal reading circuit includes: the operational amplifier circuit is used for outputting or amplifying signals and is provided with an input end and an output end, wherein the input end is connected with the MEMS microphone circuit and can acquire the output signals of the MEMS microphone circuit;

the feedback control circuit includes: the input end of the input filter circuit is connected with the output end of the operational amplifier circuit; the input end of the inverting operational amplifier circuit is connected with the input filter circuit; the input end of the output filter circuit is connected with the inverting operational amplification circuit, and the output end of the output filter circuit is connected to the input end of the operational amplification circuit;

the operational amplifier circuit and the inverting operational amplifier circuit are configured to receive a stable operating point voltage and adjust an output signal of an output end of the operational amplifier circuit to the stable operating point voltage.

2. The MEMS microphone control circuit of claim 1, further comprising: and the bias voltage providing circuit is used for providing bias voltage, the input end of the bias voltage providing circuit is connected with the output end of the MEMS microphone circuit, and the output end of the bias voltage providing circuit is connected with the output end of the feedback control circuit.

3. The MEMS microphone control circuit of claim 2, wherein an output of the output filter circuit is connected to an input of the bias voltage providing circuit.

4. The MEMS microphone control circuit according to claim 3, wherein the output filter circuit comprises a first resistor and a first capacitor, a first end of the first resistor is connected to the output end of the inverting operational amplifier circuit, and a second end of the first resistor is connected to the bias voltage supply circuit; and two ends of the first capacitor are respectively connected with the second end of the first resistor and the ground.

5. The MEMS microphone control circuit of claim 3, wherein the inverting operational amplification circuit comprises:

an inverting operational amplifier having an inverting input connected to the output of the input filter circuit, a non-inverting output configured to receive the voltage VBIAS, and an output connected to the input of the output filter circuit.

6. The MEMS microphone control circuit of claim 5, further comprising: and the direct current offset module is connected between the inverting input end of the inverting operational amplifier and the output end of the input filter circuit.

7. The MEMS microphone control circuit of claim 5, further comprising: and the follower is connected between the inverting input end of the inverting operational amplifier and the output end of the input filter circuit.

8. The MEMS microphone control circuit of claim 2, wherein the bias voltage providing circuit comprises a first diode and a second diode, wherein a cathode of the first diode is connected to an anode of the second diode to form an output of the bias voltage providing circuit; and the anode of the first diode is connected with the cathode of the second diode to form the input end of the bias voltage supply circuit.

9. An electronic device, characterized in that the MEMS microphone control circuit according to any one of claims 1 to 8 is applied.