Microphone sensor with readout circuit

Abstract

A readout circuit for a microphone sensor according to an embodiment of the present invention includes an input terminal for receiving a detection signal from the microphone sensor and an output terminal for outputting the detection signal, comprising: a first transistor, wherein a first gate terminal is connected to the input terminal, a first source terminal is connected to the output terminal and a power supply terminal, and a first drain terminal is connected to ground; a second transistor, wherein a second drain terminal is connected to the output terminal and the first source terminal, the second source terminal is connected to the power supply terminal, and a second gate terminal is connected to a reference terminal; a third transistor, wherein a third drain terminal is connected to the first source terminal, the second drain terminal, and the output terminal, a third gate terminal is connected to the reference terminal, and a third source terminal is connected to ground; a fourth transistor, wherein a fourth drain terminal is connected to the reference terminal and the power supply terminal, a fourth gate terminal is connected to the output terminal and the third drain terminal, and a fourth source terminal is connected to the first drain terminal; and a diode portion connected to the fourth drain terminal, the fourth source terminal, and the first drain terminal.

Description

Technical Field

[0001] This invention relates to readout circuits, and more specifically, to readout circuits for microphone sensors, wherein low output impedance and wide dynamic range can be achieved by forming a feedback circuit in a source follower with low noise characteristics, thereby ensuring cost competitiveness by simplifying the readout circuit and miniaturizing the chip. Background Technology

[0002] Microelectromechanical systems (MEMS) are a technology that integrates ultra-miniature mechanical components and electronic circuits at the micrometer (μm, one millionth of a meter) size using semiconductor manufacturing processes. Compared to existing electret condenser microphones (ECM), microphone chips produced using MEMS processes are widely used in high-end mobile devices such as smartphones, tablets, and headsets due to their smaller size and lower power consumption.

[0003] Microelectromechanical system (MEMS) microphones are broadly classified into capacitive-type and piezoelectric-type. Capacitive-type MEMS microphones mainly consist of a sensor section that converts physical signals into electrical signals in response to external sound pressure, and readout integrated circuits (ROICs) that process the high output impedance signals generated by the acoustic sensor.

[0004] Typically, in the readout circuit of a microphone sensor in a microelectromechanical system (MEMS), a source follower is used as a preamplifier to convert the capacitance change caused by the sound pressure generated by the MEMS sensor into a voltage.

[0005] However, since a source follower circuit alone cannot drive loads from several kΩ to several nF while having a wide dynamic range, an additional buffer with low output impedance is required.

[0006] Therefore, as the chip size of the readout circuit increases, it will be difficult to ensure cost competitiveness.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Korean Patent Publication No. 10-1718079 (March 20, 2017) Summary of the Invention

[0010] Technical problems to be solved

[0011] The object of the present invention is to provide a readout circuit for a microphone sensor that can achieve a wide dynamic range with low output impedance without the need for an additional buffer.

[0012] Another object of the present invention is to provide a readout circuit for a microphone sensor that ensures cost competitiveness by simplifying the readout circuit and miniaturizing the chip.

[0013] Other objectives of the present invention will become clearer based on the following detailed description and drawings.

[0014] Technical solutions to the problem

[0015] A readout circuit for a microphone sensor according to an embodiment of the present invention includes an input terminal IN for receiving a detection signal from the microphone sensor and an output terminal OUT for outputting the detection signal. The circuit comprises: a first transistor M1, with its first gate connected to the input terminal IN, its first source connected to the output terminal OUT and a power supply terminal VDD, and its first drain connected to ground; a second transistor M2, with its second drain connected to the output terminal OUT and the first source connected to the power supply terminal VDD, and its second gate connected to a reference terminal N; a third transistor M3, with its third drain connected to the first source, the second drain, and the output terminal OUT, its third gate connected to the reference terminal N, and its third source connected to ground; a fourth transistor M4, with its fourth drain connected to the reference terminal N and the power supply terminal VDD, its fourth gate connected to the output terminal OUT and the third drain, and its fourth source connected to the first drain; and a diode connected to the fourth drain, the fourth source, and the first drain.

[0016] Preferably, the second transistor M2 is one of an NTR transistor and a PTR transistor, and the third transistor M3 is another of an NTR transistor and a PTR transistor.

[0017] Furthermore, preferably, the diode section uses one of an NTR diode connection section, a PTR diode connection section, and a common junction diode.

[0018] Furthermore, preferably, the first transistor M1 and the second transistor M2 are P-type transistors, and the third transistor M3, the fourth transistor M4 and the diode section are N-type transistors.

[0019] Beneficial effects of the invention

[0020] The readout circuit for the microphone sensor of the present invention has the following effects.

[0021] First, low output impedance can be achieved by forming a feedback circuit in a source follower with low noise characteristics.

[0022] Second, the wide dynamic range characteristic can be obtained based on the characteristics of level AB.

[0023] Third, cost competitiveness can be ensured by simplifying the readout circuitry and miniaturizing the chip. Attached Figure Description

[0024] Figure 1 A diagram of a readout circuit for an existing microphone sensor is shown for brevity.

[0025] Figure 2 This diagram illustrates a readout circuit for a microphone sensor according to an embodiment of the present invention.

[0026] Figure 3 A diagram illustrating the low output impedance characteristics of a readout circuit for a microphone sensor according to an embodiment of the present invention.

[0027] Figure 4 To show Figure 1 Existing microphone sensor with readout circuit and Figure 2 The microphone sensor uses a readout circuit to compare the output dynamic range graph.

[0028] Explanation of reference numerals in the attached figures

[0029] 100: Readout circuit for microphone sensor 110: Buffer section

[0030] 120: Feedback section; 130: Diode section. Detailed Implementation

[0031] This invention can be modified in many ways, and therefore can have various embodiments. Specific embodiments are described in detail below with reference to the accompanying drawings. However, this is not intended to limit the invention to specific implementations, but should be understood to include all modifications, equivalent technical solutions, and alternative technical solutions encompassed by the concept and technical scope of the invention. Similar reference numerals have been used for similar structural elements in the description of the various drawings.

[0032] Although terms such as "first," "second," "A," and "B" can be used to describe various structural elements, the aforementioned structural elements are not limited to these terms. These terms are used only to distinguish one structural element from others. For example, without departing from the scope of this invention, a first structural element may be named a second structural element, and similarly, a second structural element may be named a first structural element. The term "and / or" includes a combination of multiple related descriptions or one of multiple related descriptions.

[0033] When indicating that a structural element is "connected" or "in contact" with other structural elements, although it may be directly connected or in contact with other structural elements, it should also be understood that other structural elements may exist in between. Conversely, when indicating that a structural element is "directly connected" or "directly in contact" with other structural elements, it should be understood that no other structural elements exist in between.

[0034] The terminology used in this specification is for illustrative purposes only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions. It should be understood that terms such as "comprising" or "having" in this specification are used only to specify the presence of features, numbers, steps, operations, structural elements, components, or combinations thereof described in this specification, and do not preclude the presence or additional possibilities of one or more other features, numbers, steps, operations, structural elements, components, or combinations thereof.

[0035] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries should be interpreted as having the same meaning as they have in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense unless explicitly defined in this specification.

[0036] Figure 1 A diagram of a conventional microphone sensor readout circuit is shown below. Figure 1 As shown, the existing microphone sensor readout circuit 1 uses a first transistor T1, a second transistor T2, and a third transistor T3 to form a feedback circuit. The existing microphone sensor readout circuit 1 can reduce the output impedance through the above-mentioned feedback circuit.

[0037] Conversely, when there is a load at the output terminal OUT, a reduction in the output dynamic range will occur. Therefore, the following describes a readout circuit 100 for a microphone sensor used to solve the above problem.

[0038] Figure 2A diagram illustrating a readout circuit for a microphone sensor according to an embodiment of the present invention. (Refer to...) Figure 2 The readout circuit 100 for the microphone sensor according to an embodiment of the present invention will be described.

[0039] First, a microphone sensor (not shown) detects changes in sound pressure and generates a detection signal by means of a bias voltage. For example, the microphone sensor (not shown) can generate a detection signal in response to an input bias voltage and via a built-in sensor. In this case, the bias voltage, as the voltage used to bias the microphone sensor (not shown), can be generated by boosting the power supply voltage VDD using a charge pump.

[0040] A microphone sensor (not shown) can be composed of a sensor that generates a detection signal based on the vibration of received sound waves. For example, a capacitive microphone sensor such as a microelectromechanical system (MEMS) microphone can be used.

[0041] This microphone sensor (not shown) may include electrode layers with spacing that varies with sound pressure. Therefore, it can have variable capacitor characteristics where the capacitance value varies with the spacing of the electrode layers. Consequently, the magnitude of the detected signal can vary with the magnitude of the sound pressure received by the microphone sensor (not shown).

[0042] Reference Figure 2 In the microphone sensor readout circuit 100 of this embodiment, the detection signal transmitted from the microphone sensor (not shown) is input to the input terminal IN and output through the output terminal OUT. That is, the output terminal of the microphone sensor (not shown) is connected to the input terminal IN of the readout circuit 100.

[0043] The microphone sensor readout circuit 100 of this embodiment includes a buffer section 110, a feedback section 120, and a diode section 130. The structural elements of the microphone sensor readout circuit 100 can be integrated onto a single chip.

[0044] The buffer unit 110 amplifies the detection signal and transmits it to the output terminal OUT, serving as a voltage buffer for the detection signal provided from the microphone sensor (not shown). In this case, preferably, the phase of the detection signal input to the buffer unit 110 is the same as the phase of the detection signal amplified and output from the buffer unit 110.

[0045] The buffer section 110 is driven by a bias voltage applied from the power supply terminal VDD, and a source follower circuit for performing the buffer function can be used internally. In this case, a first transistor M1 of a PMOSFET structure can be used in the buffer section 110.

[0046] The first gate terminal of the first transistor M1 is connected to the input terminal IN. The first source terminal of the first transistor M1 is connected to the output terminal OUT, the power supply terminal VDD, the second drain terminal of the second transistor M2, and the third drain terminal of the third transistor M3. The first drain terminal of the first transistor M1 is connected to ground. A current source I1 can be connected to the first source terminal of the first transistor M1. A current source I2 can be connected between the first drain terminal of the first transistor M1 and ground.

[0047] The feedback unit 120 can generate a feedback voltage corresponding to the output voltage Vout and apply it to the first drain terminal of the first transistor M1 through a feedback path (not shown).

[0048] In this way, a feedback path can be formed to make the desired output impedance Zin at the output terminal OUT have a relatively low impedance value compared to the load impedance value (several kΩ). Therefore, it can be driven even under load conditions with an impedance value of several kΩ.

[0049] The feedback unit 120 may include a second transistor M2, a third transistor M3, and a fourth transistor M4.

[0050] The second transistor M2 and the third transistor M3 can be transistors with different dynamic ranges. For example, the second transistor M2 can be either an NTR transistor or a PTR transistor. Preferably, the third transistor M3 can be either an NTR transistor or a PTR transistor. In this embodiment, a PMOS is used as the second transistor M2 and an NMOS is used as the third transistor M3. This improves the (amplified) output dynamic range.

[0051] The second source terminal of the second transistor M2 is connected to the power supply terminal VDD. The second drain terminal of the second transistor M2 is connected to the output terminal OUT, the first source terminal of the first transistor M1, and the third drain terminal of the third transistor M3. The second gate terminal of the second transistor M2 is connected to the reference terminal N.

[0052] The third drain terminal of the third transistor M3 is connected to the first source terminal of the first transistor M1, the second drain terminal of the second transistor M2, and the output terminal OUT. The third gate terminal of the third transistor M3 is connected to the reference terminal N. The third source terminal of the third transistor M3 is connected to ground.

[0053] The fourth drain terminal of the fourth transistor M4 is connected to the reference terminal N, the power supply terminal VDD, and the fifth drain terminal of the fifth transistor M5. The fourth gate terminal of the fourth transistor M4 is connected to the output terminal OUT and the third drain terminal of the third transistor M3. The fourth source terminal of the fourth transistor M4 is connected to the first drain terminal of the first transistor M1 and the fifth source terminal of the fifth transistor M5. A current source I3 can be connected between the fourth drain terminal of the fourth transistor M4 and the power supply voltage.

[0054] The diode section 130 maintains the operation of the feedback circuit and is independent of the output voltage level of the fourth transistor M4. That is, because a third transistor M3 is additionally provided to achieve the CLASS AB characteristic and expand the dynamic range, when the output voltage drops to a low level due to the application of a negative voltage to the input, a problem may arise where the output remains fixed at 0 because the feedback structure composed of the fifth transistor M5 is not working. In this case, the fourth transistor M4 can be additionally provided to maintain the feedback structure to ensure a wide dynamic range, regardless of the output voltage.

[0055] In this case, an NTR diode connection, a PTR diode connection, and a normal junction diode can be used as diode section 130. In this embodiment, NMOS transistors can be used as the fourth transistor M4 and the fifth transistor M5.

[0056] Figure 3 This diagram illustrates the low output impedance characteristics of a readout circuit for a microphone sensor according to an embodiment of the present invention. The output impedance was measured with a 100 kΩ impedance and a 1 μF capacitor connected in series to the output terminal OUT of the readout circuit for the microphone sensor in this embodiment.

[0057] Reference Figure 3 The microphone sensor readout circuit of this embodiment has an output impedance of approximately 12 [Ω], thus it can adequately drive loads of several [kΩ].

[0058] Figure 4 To show Figure 1 Existing microphone sensor with readout circuit and Figure 2 The microphone sensor uses a readout circuit to compare the output dynamic range graph.

[0059] In this embodiment, the dynamic range is measured with the output terminal OUT of the microphone sensor readout circuit connected in series with an impedance of 100 kΩ and a capacitor of 1 uF.

[0060] In this case, such as Figure 4 As shown, the dark black line below indicates Figure 2 The output dynamic range of the microphone sensor readout circuit 100 is shown in the figure. The light gray line above indicates the output dynamic range of the existing microphone sensor readout circuit 1.

[0061] Reference Figure 4 Compared to the existing microphone sensor readout circuit 1, the output dynamic range of the microphone sensor readout circuit 100 in this embodiment is about twice as wide.

[0062] As a result, without the need for an additional buffer, the readout circuit for the microphone sensor of this invention exhibits low noise, low output impedance, and a wide dynamic range. Therefore, cost competitiveness can be ensured by simplifying the readout circuit and miniaturizing the chip.

[0063] While the present invention has been described in detail above through preferred embodiments, it may also be implemented through different embodiments. Therefore, the technical concept and scope of the claims described below are not limited to the preferred embodiments.

Claims

1. A readout circuit for a microphone sensor, provided with an input terminal (IN) for receiving a detection signal from a microphone sensor and an output terminal (OUT) for outputting the detection signal, characterized in that, include: The first transistor (M1) has its first gate terminal connected to the input terminal (IN), its first source terminal connected to the output terminal (OUT) and the power supply terminal (VDD), and its first drain terminal connected to ground. The second transistor (M2) has its second drain terminal connected to the output terminal (OUT) and the first source terminal, its second source terminal connected to the power supply terminal (VDD), and its second gate terminal connected to the reference terminal (N). The third transistor (M3) has its third drain terminal connected to the first source terminal, the second drain terminal, and the output terminal (OUT), its third gate terminal connected to the reference terminal (N), and its third source terminal connected to ground. The fourth transistor (M4) has its fourth drain terminal connected to the reference terminal (N) and the power supply terminal (VDD), its fourth gate terminal connected to the output terminal (OUT) and the third drain terminal, and its fourth source terminal connected to the first drain terminal. as well as The diode section is connected to the fourth drain terminal, the fourth source terminal, and the first drain terminal.

2. The readout circuit for a microphone sensor according to claim 1, characterized in that, The second transistor (M2) is one of an NTR transistor and a PTR transistor, and the third transistor (M3) is another of an NTR transistor and a PTR transistor.

3. The readout circuit for a microphone sensor according to claim 1, characterized in that, The diode section uses one of the following: an NTR diode connector, a PTR diode connector, and a standard junction diode.

4. The readout circuit for a microphone sensor according to claim 1, characterized in that, The first transistor (M1) and the second transistor (M2) are P-type transistors, and the third transistor (M3), the fourth transistor (M4) and the diode section are N-type transistors.

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