Audio speaker system using piezoelectric diaphragms

Abstract

An audio speaker system includes: an amplifier wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node; and a piezoelectric diaphragm comprising: a metal plate; a first piezoelectric film attached to the metal plate, where the first piezoelectric film is configured to function as a speaker during operation of the audio speaker system; and a second piezoelectric film attached to the metal plate and spaced apart from the first piezoelectric film, where the second piezoelectric film is configured to function as a microphone during operation of the audio speaker system, where an output terminal of the amplifier is coupled to the first piezoelectric film, and where a negative input terminal of the amplifier is coupled to the second piezoelectric film.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. application No. 18 / 146,718, filed on December 27, 2022 and entitled “Audio Speaker System Using Piezo Diaphragm,” and specifically, this patent application is a continuation of said U.S. application No. 18 / 146,718, which is hereby incorporated by reference as if reproduced in its entirety. Technical Field

[0003] The present disclosure relates generally to audio speaker systems, and in particular to audio speaker systems constructed using piezoelectric diaphragms. Background Art

[0004] Piezoelectric speakers are widely used as speakers, for example, in mobile devices or computers, due to their compact size. Piezoelectric speakers are typically very thin (e.g., 1 mm or less in thickness) and are designed to have an almost flat frequency response within the audio frequency band (e.g., between 1 KHz and 20 KHz), and for some special piezoelectric speakers, between 500 Hz and 20 KHz. In order to achieve an almost flat frequency response, piezoelectric speakers may be designed to have a multilayer structure and / or use special materials. Therefore, piezoelectric speakers are relatively expensive (e.g., currently between $1 and $10 each).

[0005] Piezoelectric diaphragms (also known as piezoelectric buzzers) are widely available on the market and typically cost only a fraction of the price of a piezoelectric speaker (e.g., 1 / 3 or less). Piezoelectric diaphragms are designed for applications where audio quality is not a concern. For example, piezoelectric diaphragms are typically used for alarms, buzzers, and the like, where sounds consisting primarily of tones (e.g., a single frequency) are produced by the piezoelectric diaphragm. When used in a typical circuit configuration (e.g., as an alarm or buzzer), the piezoelectric diaphragm has a non-flat frequency response within the audio frequency band, where there are many peaks and valleys in the frequency response curve. For example, the maximum variation in the frequency response of the piezoelectric diaphragm within the audio frequency band may be as large as, for example, 30 dB or more. This poor frequency response may result in severe distortion of the audio signal and is the reason why piezoelectric diaphragms are currently not usable as speakers for audio signals (such as music, vocals, and the like).

[0006] The present disclosure discloses various embodiments in which a piezoelectric diaphragm is used to form an audio speaker system suitable for playing audio signals. Significant cost reductions can be achieved by using a piezoelectric diaphragm instead of a piezoelectric speaker in an audio speaker system while maintaining a small form factor. Summary of the invention

[0007] According to an embodiment, an audio speaker system includes: an amplifier, wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node; and a piezoelectric diaphragm, which includes: a metal plate; a first piezoelectric film attached to the metal plate, wherein the first piezoelectric film is configured to function as a speaker during operation of the audio speaker system; and a second piezoelectric film attached to the metal plate and spaced apart from the first piezoelectric film, wherein the second piezoelectric film is configured to function as a microphone during operation of the audio speaker system, wherein an output terminal of the amplifier is coupled to the first piezoelectric film, and wherein a negative input terminal of the amplifier is coupled to the second piezoelectric film.

[0008] According to an embodiment, an audio speaker system includes: a piezoelectric diaphragm, which includes: a metal plate; a first piezoelectric film attached to the metal plate; and a second piezoelectric film attached to the metal plate, wherein the second piezoelectric film is at least partially surrounded by the first piezoelectric film and separated from the first piezoelectric film; and an amplifier, wherein an output terminal of the amplifier is coupled to the first piezoelectric film, wherein a negative input terminal of the amplifier is coupled to the second piezoelectric film, and wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node.

[0009] According to an embodiment, a method for playing an audio signal using a piezoelectric diaphragm includes: receiving an audio signal at a positive input terminal of an amplifier or a negative input terminal of the amplifier; supplying a reference voltage to the positive input terminal of the amplifier; sending an output signal of the amplifier to a first piezoelectric film of the piezoelectric diaphragm, wherein the first piezoelectric film is configured to convert the output signal of the amplifier into movement of the first piezoelectric film; dynamically coupling the first piezoelectric film with a second piezoelectric film of the piezoelectric diaphragm, wherein the second piezoelectric film is configured to convert the movement of the second piezoelectric film into an electrical signal; and feeding the electrical signal back to the negative input terminal of the amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0011] Figure 1 shows the frequency response of the piezoelectric membrane in a conventional application of the piezoelectric membrane in an embodiment;

[0012] Figure 2A and Figure 2B Various views showing a piezoelectric membrane in an embodiment;

[0013] Figures 3 to 5 Various embodiments of piezoelectric membranes are shown;

[0014] Figure 6 The symbols of the piezoelectric membranes in the embodiment are shown;

[0015] Figure 7 An audio speaker system constructed using a piezoelectric diaphragm in an embodiment is shown;

[0016] Figure 8 An audio speaker system constructed using a piezoelectric diaphragm in another embodiment is shown;

[0017] Fig. 9 An audio speaker system constructed using a piezoelectric diaphragm in yet another embodiment is shown;

[0018] Fig.10 shows the frequency response of a piezoelectric diaphragm used in an audio speaker system in an embodiment; and

[0019] Fig.11 A flow chart showing a method for playing an audio signal using a piezoelectric diaphragm in some embodiments. DETAILED DESCRIPTION

[0020] The following is a detailed discussion of the conduct and use of the currently disclosed examples. However, it should be understood that the present disclosure provides many applicable inventive concepts that can be implemented in a variety of specific contexts. The specific examples discussed are merely illustrative of specific ways to conduct and use the present disclosure and do not limit the scope of the present disclosure. Throughout the discussion herein, unless otherwise indicated, identical or similar reference numerals or labels in different figures refer to identical or similar components or signals.

[0021] The present disclosure will be described with reference to examples in a specific context, namely, an audio speaker system constructed using a piezoelectric diaphragm.

[0022] Figure 1 The frequency response of a piezoelectric film in a conventional application of a piezoelectric film in an embodiment is shown. In such an application, a piezoelectric film is used to generate a sound (eg, a tone) for use in, for example, an alarm, a buzzer, etc.

[0023] exist Figure 1 In FIG. 1 , curve 11 shows the sound pressure level (SPL) of the piezoelectric diaphragm, and curve 13 shows the impedance of the piezoelectric diaphragm. Figure 1 As shown in , the magnitude of the frequency response (e.g., curve 11) varies significantly within the audio frequency band. Figure 1 Multiple peaks and valleys are observed in the frequency response of the piezoelectric diaphragm. The maximum change in the frequency response can be as large as, for example, 30 dB or more. Such a poor frequency response may cause severe distortion of audio signals (e.g., music, human voice, etc.) including multiple and / or continuous frequency components within the audio frequency band. Therefore, conventional speaker systems constructed using piezoelectric diaphragms are not suitable for playing audio signals.

[0024] Figure 2A and Figure 2BA top view and a cross-sectional view of the piezoelectric film 100A in the embodiment are respectively shown. Figure 2B The piezoelectric film 100A is shown along Figure 2A Cross-sectional view of section D-D' in FIG.

[0025] like Figure 2A and Figure 2B As shown in , the piezoelectric film 100A includes a plate 101, a first piezoelectric film 103 and a second piezoelectric film 105. In some embodiments, the plate 101 is a metal plate such as a brass plate, a nickel alloy plate, etc. In an embodiment, the first piezoelectric film 103 and the second piezoelectric film 105 are formed of the same piezoelectric material. In another embodiment, the first piezoelectric film 103 and the second piezoelectric film 105 are formed of different piezoelectric materials.

[0026] The first piezoelectric film 103 and the second piezoelectric film 105 can be formed by depositing a piezoelectric material layer on the plate 101, and then patterning the deposited piezoelectric material (e.g., etching using an etching mask having a mask pattern) to remove part of the deposited piezoelectric material. After patterning, the remaining part of the deposited piezoelectric material forms the first piezoelectric film 103 and the second piezoelectric film 105. In other embodiments, each of the first piezoelectric film 103 and the second piezoelectric film 105 can be pre-formed as a dielectric material layer having a predetermined shape, and then the pre-formed first piezoelectric film 103 and the pre-formed second piezoelectric film are attached (e.g., glued) to the plate 101.

[0027] exist Figure 2A In the example shown, the plate 101 has a circular shape. The first piezoelectric film 103 has a circular shape with a slit. The inside of the slit has a test tube shape, and the outside of the slit is enlarged and has a curved shape. In the example shown, the second piezoelectric film 105 is disposed within the slit of the first piezoelectric film 103 and may have a similar geometric shape to the slit. For example, the second piezoelectric film 105 may have a test tube shape at one end and an enlarged portion at the other end. Figure 2A As shown in , the second piezoelectric film 105 is at least partially surrounded by the first piezoelectric film 103. Note that the second piezoelectric film 105 is spaced apart from the first piezoelectric film 103, and there is a gap 104 (e.g., an empty space) between the second piezoelectric film 105 and the first piezoelectric film 103. The shapes and relative positions of the first piezoelectric film 103 and the second piezoelectric film 105 allow for good coupling (e.g., dynamic coupling) between the first piezoelectric film 103 and the second piezoelectric film 105. For example, vibration of the first piezoelectric film 103 causes the same or similar vibration of the second piezoelectric film 105.

[0028] Figure 2AAlso shown are three terminals of the piezoelectric film 100A: a terminal A attached to the first piezoelectric film 103, a terminal B attached to the second piezoelectric film 105, and a third terminal C attached to the plate 101. In some embodiments, each of the terminals A, B, and C can be formed by bonding (e.g., soldering) a conductive wiring member (e.g., copper wire, metal connector, etc.) to a corresponding member (e.g., 103, 105, or 101) of the piezoelectric film 100A.

[0029] In the illustrated embodiment, during operation of the piezoelectric diaphragm 100A (e.g., as a speaker in an audio speaker system), terminal C is coupled to a reference voltage such as electrical ground. Terminal A is configured to receive an (amplified) audio signal (e.g., a time-varying voltage carrying audio information). The first piezoelectric film 103 is configured to convert the audio signal (e.g., an electrical signal) into a movement (e.g., a vibration) of the first piezoelectric film 103 to produce an audio sound. In other words, the first piezoelectric film 103 is configured to function as a speaker. The movement (e.g., a vibration) of the first piezoelectric film 103 is picked up (e.g., sensed) by the second piezoelectric film 105 through the dynamic coupling between the first piezoelectric film 103 and the second piezoelectric film 105, and causes the movement (e.g., a vibration) of the second piezoelectric film 105. The second piezoelectric film 105 generates an electrical signal in response to its movement. In other words, the second piezoelectric film 105 functions as a microphone that converts the audio sound generated by the first piezoelectric film 103 into an electrical signal, which is fed back to the negative input terminal of the amplifier of the audio speaker system. The amplifier generates an amplified audio signal which is sent to the first piezoelectric film 103. The details are discussed below.

[0030] Figures 3 to 5 Various embodiments of the piezoelectric film are shown. Specifically, Figure 3 , Figure 4 and Figure 5 The structures and functions of the piezoelectric films 100B, 100C and 100D are similar to those of the piezoelectric film 100A, but have different shapes for the first piezoelectric film 103, the second piezoelectric film 105 and / or the plate 101.

[0031] Figure 3 The piezoelectric film 100B in FIG. 1 is similar to the piezoelectric film 100A, but Figure 3 The first piezoelectric film 103 in FIG. 1 has a circular shape, and a circular portion is removed to form a recessed region. The second piezoelectric film 105 of the piezoelectric film 100B has a (smaller) circular shape, and is disposed in the recessed region.

[0032] Figure 4 The piezoelectric film 100C in FIG. 1 is similar to the piezoelectric film 100A, but Figure 4The slit in the first piezoelectric film 103 has a rectangular shape, and the second piezoelectric film 105 of the piezoelectric film 100C also has a rectangular shape and is arranged Figure 4 The first piezoelectric film 103 is provided with a rectangular slit.

[0033] Figure 5 The piezoelectric film 100D in FIG. 1 is similar to the piezoelectric film 100C in that a rectangular slit is provided in the first piezoelectric film 103 and the second piezoelectric film 105 also has a rectangular shape. However, Figure 5 The plate 101 in FIG. 1 has a rectangular shape, and the first piezoelectric film 103 also has a rectangular shape.

[0034] Figure 2A , Figure 2B as well as Figures 3 to 5 The various embodiments of the piezoelectric diaphragm shown in are illustrative and non-restrictive. Other shapes and / or structures of the piezoelectric diaphragm are also possible and are fully intended to be included within the scope of the present disclosure. Note that the piezoelectric diaphragms described herein (e.g., 100A, 100B, 100C, and 100D) are self-driven type piezoelectric diaphragms, which have three terminals (e.g., A, B, and C), and when used as a buzzer, can be used to form an oscillation circuit to generate a frequency signal (e.g., a tone) internally. The self-driven type piezoelectric diaphragm is different from the external drive type piezoelectric diaphragm, which has two terminals and needs to be supplied with an external frequency signal (e.g., a tone) to produce a sound (e.g., an alarm or a buzzer). The piezoelectric diaphragm for building an audio speaker system discussed herein is a self-driven type piezoelectric diaphragm.

[0035] Figure 6 The symbol of the piezoelectric film 100 in the embodiment is shown. The piezoelectric film 100 may represent any suitable self-driven type piezoelectric film, such as piezoelectric films 100A, 100B, 100C, and 100D. Figure 6 The symbols shown in are used in subsequent figures to represent piezoelectric diaphragms used in audio speaker systems. Figure 6 As shown in FIG. 1 , symbols show a plate 101 , a first piezoelectric film 103 (shown as a speaker icon), and a second piezoelectric film 105 (shown as a microphone icon). Figure 6 The dashed arrows in show coupling (eg, dynamic coupling) between the first piezoelectric film 103 and the second piezoelectric film 105 . Figure 6 The symbols in also show terminals A, B, and C of the piezoelectric film 100 .

[0036] Figure 7An audio speaker system 200A in an embodiment is shown. The audio speaker system 200A is suitable for playing audio signals such as music and speech, and is formed using a piezoelectric diaphragm 100. The piezoelectric diaphragm 100 may be any suitable piezoelectric diaphragm such as piezoelectric diaphragms 100A, 100B, 100C, 100D or a commercially available (e.g., off-the-shelf) self-driven type piezoelectric diaphragm. For simplicity, Figure 7 Not all features of the audio speaker system 200A may be shown.

[0037] like Figure 7 As shown in FIG. 1 , the audio speaker system 200A includes a piezoelectric diaphragm 100 and an amplifier 111. The amplifier 111 may be, for example, an audio amplifier such as an operational amplifier. Figure 7 In the example, the amplifier 111 is coupled to a supply voltage V DD The amplifier 111 is connected between a power supply (e.g., +3V, +5V, etc.) and a reference voltage node 112, which can be, for example, coupled to electrical ground. The output terminal 118 of the amplifier 111 is coupled to the terminal A of the piezoelectric film 100, and provides an amplified audio signal to the first piezoelectric film 103 (which serves as a speaker). The terminal B of the piezoelectric film 100 outputs an electrical signal (e.g., a voltage signal) generated by the second piezoelectric film 105. The terminal C of the piezoelectric film 100 is coupled to the reference voltage node 106, which can be, for example, coupled to electrical ground.

[0038] Still refer to Figure 7 , reference voltage V REF is applied to node 114, which is coupled to positive input terminal 115 of amplifier 111. As an example, reference voltage V REF has a fixed nominal value and may be, for example, the supply voltage V DD half.

[0039] An audio signal (e.g., a time-varying voltage signal carrying audio information) is applied to node 121, which is coupled to negative input terminal 113 of amplifier 111 via capacitor C1 and resistor R3 coupled in series. In some implementations, capacitor C1 functions as a high-pass filter to block (e.g., filter out) low-frequency components (e.g., DC components) of the audio signal.

[0040] like Figure 7 As shown in FIG, resistor R1 and resistor R2 are coupled in series between terminal B of piezoelectric membrane 100 and reference voltage node 117. In the embodiment shown, reference voltage node 117 is coupled to electrical ground. Node 116 between resistors R1 and R2 is also coupled to negative input terminal 113 of amplifier 111.

[0041] During operation of the audio speaker system 200A, an audio signal applied at the node 121 is filtered by the capacitor C1 (e.g., to remove low frequency components such as a DC component). The filtered audio signal is sent to the amplifier 111 and amplified by the amplifier 111. The amplified audio signal at the output terminal 118 of the amplifier 111 drives (e.g., excites) the first piezoelectric film 103 and causes movement (e.g., vibration) of the first piezoelectric film 103 to produce audio sounds (e.g., music or speech). The movement (e.g., vibration) of the first piezoelectric film 103 causes the same or similar movement (e.g., vibration) of the second piezoelectric film 105 through dynamic coupling, which acts as a microphone and converts the audio sound into an electrical signal (e.g., a voltage signal). The electrical signal is fed back to the negative input terminal 113 of the amplifier 111. Figure 7 In the example of , a scaled version of the electrical signal at terminal B is generated by a voltage divider formed by resistors R1 and R2 and is combined (e.g., added together) with the filtered audio signal to form a feedback voltage, which is then applied to the negative input terminal 113 of the amplifier 111.

[0042] Figure 8 An audio speaker system 200B in another embodiment is shown. The audio speaker system 200B is similar to the audio speaker system 200A, but the audio signal is applied to the node 131, which is coupled to the positive input terminal 115 of the amplifier 111 through the capacitor C1. In addition, the reference voltage V REF is applied to node 124, which is coupled to the positive input terminal 115 of the amplifier 111 through resistor R3. The operation of the audio speaker system 200B is similar to that of the audio speaker system 200A, so the details are not discussed here. Note that in both the audio speaker systems 200A and 200B, the electrical signal at terminal B is fed back to the negative input terminal 113 of the amplifier.

[0043] Fig. 9 An audio speaker system 300 is shown in yet another embodiment. The audio speaker system 300 is similar to the audio speaker system 200B (or 200A), but has fewer details in order to illustrate the speaker system at a higher level of abstraction. For example, Fig. 9 The electrical signal at terminal B of the piezoelectric film 100 is shown being fed back to the negative input terminal 113 of the amplifier, which is one of many features that differ from conventional circuit configurations using the piezoelectric film 100 in applications such as sirens or buzzers. Fig. 9 Amplifier 111 and piezoelectric diaphragm 100 in FIG. 1 represent a high-level abstraction of audio speaker systems 200A and 200B.

[0044] In addition, Fig. 9In the embodiment, an audio signal is applied at node 201. The audio signal is then processed (e.g., amplified) by preamplifier 203 (e.g., an audio preamplifier). The output of preamplifier 203 is then processed by tone and volume control circuit 205, which may be, for example, a filter that adjusts the gain and / or phase of the audio signal at different frequencies in the audio frequency band. In some embodiments, one or both of preamplifier 203 and tone and volume control circuit 205 are omitted. In some embodiments, the audio signal at the output of tone and volume control circuit 205 is applied to Figure 7 Node 121 or Figure 8 Node 131 in.

[0045] Modifications and variations of the present disclosure are possible and are fully intended to be included within the scope of the present disclosure. For example, Figure 7 , Figure 8 and Fig. 9 The examples in use single-ended signals as non-limiting examples. Those skilled in the art will readily appreciate that the principles of the present disclosure are applicable to differential signals, and the disclosed embodiments can be readily applied to differential signals. In addition, the disclosed embodiments can be used with different types of amplifiers, such as class A amplifiers, class AB amplifiers, class D amplifiers, class G amplifiers, and class H amplifiers.

[0046] Fig.10 The frequency response of a piezoelectric diaphragm used in an audio speaker system in an embodiment is shown. The audio speaker system may be, for example, the audio speaker system 200A, 200B, or 300.

[0047] exist Fig.10 In FIG. 2 , curve 21 shows the sound pressure level (SPL) of the piezoelectric diaphragm, and curve 23 shows the impedance of the piezoelectric diaphragm. Fig.10 As shown in , the amplitude of the frequency response (e.g., curve 21) remains substantially flat within the audio frequency band (e.g., between 1 KHz and 20 KHz). In some embodiments, within the audio frequency band, the maximum variation of the frequency response relative to the mean of the frequency response is less than 3 dB. For example, the amplitude of the frequency response may be within ±3 dB of the mean of the amplitude of the frequency response within the audio frequency band. Such a substantially flat frequency response allows the use of a piezoelectric diaphragm to produce high-quality audio signals (e.g., music, vocals, etc.).

[0048] Fig.11 1 shows a flow chart of a method for playing an audio signal using a piezoelectric diaphragm in some embodiments. It should be understood that Fig.11The example methods shown in are merely examples of many possible example methods. Those skilled in the art will recognize many variations, alternatives, and modifications. For example, the following may be added, removed, replaced, rearranged, or repeated. Fig.11 The various steps shown in .

[0049] Reference Fig.11 At box 1010, an audio signal is received at a positive input terminal of an amplifier or a negative input terminal of the amplifier. At box 1020, a reference voltage is supplied to the positive input terminal of the amplifier. At box 1030, an output signal of the amplifier is sent to a first piezoelectric film of a piezoelectric film, wherein the first piezoelectric film is configured to convert the output signal of the amplifier into a motion of the first piezoelectric film. At box 1040, the first piezoelectric film is dynamically coupled to a second piezoelectric film of the piezoelectric film, wherein the second piezoelectric film is configured to convert the motion of the second piezoelectric film into an electrical signal. At box 1050, the electrical signal is fed back to the negative input terminal of the amplifier.

[0050] Embodiments can achieve advantages as described below. For example, the audio speaker system disclosed herein is formed using a piezoelectric diaphragm. The circuit configuration of the disclosed audio speaker system allows the audio speaker system to achieve excellent frequency response that was previously not achieved using a piezoelectric diaphragm. Since a piezoelectric diaphragm is much cheaper than a piezoelectric speaker while having approximately the same form factor (e.g., size), the disclosed audio speaker system (which uses a piezoelectric diaphragm) can be used to replace currently used, more expensive speaker systems formed using a piezoelectric speaker.

[0051] Examples of the present disclosure are summarized here. Other examples may also be understood based on the entirety of the specification and claims submitted herein.

[0052] Example 1. According to an embodiment, an audio speaker system includes: an amplifier, wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node; and a piezoelectric film, which includes a metal plate; a first piezoelectric film attached to the metal plate, wherein the first piezoelectric film is configured to function as a speaker during operation of the audio speaker system; and a second piezoelectric film attached to the metal plate and spaced apart from the first piezoelectric film, wherein the second piezoelectric film is configured to function as a microphone during operation of the audio speaker system, wherein an output terminal of the amplifier is coupled to the first piezoelectric film, and wherein a negative input terminal of the amplifier is coupled to the second piezoelectric film.

[0053] Example 2. The audio speaker system according to Example 1, wherein during operation of the audio speaker system, the microphone formed by the second piezoelectric membrane is dynamically coupled to the speaker formed by the first piezoelectric membrane.

[0054] Example 3. The audio speaker system according to Example 1 further includes a first resistor and a second resistor coupled in series between the second piezoelectric film and a second reference voltage node, wherein the negative input terminal of the amplifier is coupled to a first node between the first resistor and the second resistor.

[0055] Example 4 The audio speaker system according to Example 3, further comprising: a capacitor and a third resistor coupled in series between the negative input terminal of the amplifier and the second node, wherein the second node is configured to receive an audio signal.

[0056] Example 5. The audio speaker system of Example 4, wherein the second reference voltage node is configured to be coupled to electrical ground, wherein the first reference voltage node is configured to be coupled to a voltage supply having a voltage higher than electrical ground.

[0057] Example 6. The audio speaker system according to Example 3, further comprising: a capacitor coupled between the second node and a positive input terminal of the amplifier, wherein the second node is configured to receive an audio signal; and a third resistor coupled between the positive input terminal of the amplifier and the first reference voltage node.

[0058] Example 7. The audio speaker system of Example 6, wherein during operation of the audio speaker system, the voltage at the second reference voltage node is equal to electrical ground and the voltage at the first reference voltage node is higher than electrical ground.

[0059] Example 8. The audio speaker system of Example 1, wherein the audio speaker system has a frequency response within a frequency band between 1 KHz and 20 KHz, wherein a magnitude variation of the frequency response within the frequency band is less than 3 dB.

[0060] Example 9. The audio speaker system of Example 1, further comprising an audio preamplifier coupled between the input terminal of the audio speaker system and the positive input terminal of the amplifier.

[0061] Example 10. The audio speaker system of Example 9, further comprising a tone and volume control circuit coupled between the audio preamplifier and the positive input terminal of the amplifier.

[0062] Example 11. According to an embodiment, an audio speaker system includes: a piezoelectric diaphragm including: a metal plate; a first piezoelectric film attached to the metal plate; and a second piezoelectric film attached to the metal plate, wherein the second piezoelectric film is at least partially surrounded by and spaced apart from the first piezoelectric film; and an amplifier, wherein an output terminal of the amplifier is coupled to the first piezoelectric film, wherein a negative input terminal of the amplifier is coupled to the second piezoelectric film, and wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node.

[0063] Example 12. The audio speaker system according to Example 11, wherein during operation of the audio speaker system, the first piezoelectric membrane is configured to convert a first electrical signal at an output terminal of the amplifier into a movement of the first piezoelectric membrane, and the second piezoelectric membrane is configured to be dynamically coupled to the first piezoelectric membrane and configured to convert the movement of the second piezoelectric membrane into a second electrical signal.

[0064] Example 13. The audio speaker system according to Example 12, wherein the second piezoelectric membrane is coupled to a voltage divider comprising a first resistor and a second resistor coupled in series, wherein a first node between the first resistor and the second resistor is coupled to a negative input terminal of the amplifier.

[0065] Example 14. The audio speaker system according to Example 13, further comprising a capacitor and a third resistor coupled in series between the first node and a second node, wherein the second node is configured to receive an audio signal.

[0066] Example 15. The audio speaker system according to Example 13, further comprising: a third resistor coupled between the positive input terminal of the amplifier and the first reference voltage node; and a capacitor coupled between the positive input terminal of the amplifier and the second node, wherein the second node is configured to receive an audio signal.

[0067] Example 16. The audio speaker system of Example 11, wherein during operation of the audio speaker system, the piezoelectric diaphragm has a frequency response within a frequency band between 1 KHz and 20 KHz, wherein a maximum variation in amplitude of the frequency response is less than 3 dB within the frequency band.

[0068] Example 17. According to an embodiment, a method for playing an audio signal using a piezoelectric film includes: receiving an audio signal at a positive input terminal of an amplifier or a negative input terminal of the amplifier; supplying a reference voltage to the positive input terminal of the amplifier; sending an output signal of the amplifier to a first piezoelectric film of the piezoelectric film, wherein the first piezoelectric film is configured to convert the output signal of the amplifier into a movement of the first piezoelectric film; dynamically coupling the first piezoelectric film with a second piezoelectric film of the piezoelectric film, wherein the second piezoelectric film is configured to convert the movement of the second piezoelectric film into an electrical signal; and feeding the electrical signal back to the negative input terminal of the amplifier.

[0069] Example 18. The method of Example 17, wherein feeding the electrical signal back comprises: generating a scaled version of the electrical signal using a voltage divider; and sending the scaled version of the electrical signal to a negative input terminal of the amplifier.

[0070] Example 19. The method of Example 17, wherein receiving the audio signal comprises receiving the audio signal at a first node, wherein a capacitor and a resistor are coupled in series between the first node and a negative input terminal of the amplifier.

[0071] Example 20. The method of Example 17, wherein receiving the audio signal comprises receiving the audio signal at a first node, wherein the capacitor is coupled between the first node and a positive input terminal of the amplifier, wherein supplying the reference voltage comprises supplying the reference voltage to a second node, wherein the resistor is coupled between the second node and the positive input terminal of the amplifier.

[0072] Although the present disclosure has been described with reference to illustrative examples, this specification is not intended to be interpreted in a limiting sense. After reference to the specification, various modifications and combinations of the illustrative examples and other examples of the present disclosure will be apparent to those skilled in the art. Therefore, the appended claims are intended to cover any such modifications or examples.

Claims

1. An audio speaker system, comprising: an amplifier, wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node; and A piezoelectric diaphragm, the piezoelectric diaphragm comprising: Metal sheets; a first piezoelectric membrane attached to the metal plate, wherein the first piezoelectric membrane is configured to function as a speaker during operation of the audio speaker system; and a second piezoelectric film attached to the metal plate and spaced apart from the first piezoelectric film, wherein the second piezoelectric film is configured to function as a microphone during operation of the audio speaker system, wherein an output terminal of the amplifier is coupled to the first piezoelectric film, and wherein a negative input terminal of the amplifier is coupled to the second piezoelectric film.

2. The audio speaker system of claim 1, wherein: During operation of the audio speaker system, a microphone formed by the second piezoelectric membrane is dynamically coupled to a speaker formed by the first piezoelectric membrane.

3. The audio speaker system of claim 1 or 2, further comprising a first resistor and a second resistor, the first resistor and the second resistor being coupled in series between the second piezoelectric film and a second reference voltage node, wherein The negative input terminal of the amplifier is coupled to a first node between the first resistor and the second resistor.

4. The audio speaker system of claim 3, wherein: The second reference voltage node is configured to be coupled to an electrical ground, wherein the first reference voltage node is configured to be coupled to a voltage supply having a voltage higher than the electrical ground.

5. The audio speaker system according to any one of claims 1 to 4, further comprising: A capacitor and a third resistor are coupled in series between the negative input terminal of the amplifier and a second node, wherein the second node is configured to receive an audio signal.

6. The audio speaker system according to any one of claims 1 to 4, further comprising: a capacitor coupled between a second node and the positive input terminal of the amplifier, wherein the second node is configured to receive an audio signal; and A third resistor is coupled between the positive input terminal of the amplifier and the first reference voltage node.

7. The audio speaker system of claim 6, wherein: During operation of the audio speaker system, the voltage at the second reference voltage node is equal to electrical ground and the voltage at the first reference voltage node is greater than electrical ground.

8. An audio speaker system according to any one of claims 1 to 7, wherein: The audio speaker system has a frequency response within a frequency band between 1 KHz and 20 KHz, wherein the amplitude variation of the frequency response within the frequency band is less than 3 dB.

9. The audio speaker system of claim 1 or 2, further comprising an audio preamplifier coupled between an input terminal of the audio speaker system and the positive input terminal of the amplifier.

10. The audio speaker system of claim 9, further comprising a tone and volume control circuit coupled between the audio preamplifier and the positive input terminal of the amplifier.

11. An audio speaker system comprising: A piezoelectric diaphragm, the piezoelectric diaphragm comprising: Metal sheets; a first piezoelectric film attached to the metal plate; and a second piezoelectric film attached to the metal plate, wherein the second piezoelectric film is at least partially surrounded by and spaced apart from the first piezoelectric film; and An amplifier, wherein an output terminal of the amplifier is coupled to the first piezoelectric film, wherein a negative input terminal of the amplifier is coupled to the second piezoelectric film, and wherein a positive input terminal of the amplifier is configured to be coupled to a first reference voltage node.

12. The audio speaker system of claim 11, wherein During operation of the audio speaker system, the first piezoelectric membrane is configured to convert a first electrical signal at the output terminal of the amplifier into movement of the first piezoelectric membrane, and the second piezoelectric membrane is configured to be dynamically coupled to the first piezoelectric membrane and to convert the movement of the second piezoelectric membrane into a second electrical signal.

13. An audio speaker system according to claim 11 or 12, wherein The second piezoelectric film is coupled to a voltage divider including a first resistor and a second resistor coupled in series, wherein a first node between the first resistor and the second resistor is coupled to the negative input terminal of the amplifier.

14. The audio speaker system of claim 13, further comprising a capacitor and a third resistor, the capacitor and the third resistor being coupled in series between the first node and the second node, wherein The second node is configured to receive an audio signal.

15. The audio speaker system according to any one of claims 11 to 13, further comprising: a third resistor coupled between the positive input terminal of the amplifier and the first reference voltage node; as well as A capacitor is coupled between the positive input terminal of the amplifier and a second node, wherein the second node is configured to receive an audio signal.

16. An audio speaker system according to any one of claims 11 to 15, wherein: During operation of the audio speaker system, the piezoelectric diaphragm has a frequency response within a frequency band between 1 KHz and 20 KHz, wherein a maximum variation in amplitude of the frequency response is less than 3 dB within the frequency band.

17. The audio speaker system of claim 11 or 12, further comprising an audio preamplifier coupled between an input terminal of the audio speaker system and the positive input terminal of the amplifier.

18. A method for playing an audio signal using a piezoelectric diaphragm, the method comprising: receiving an audio signal at a positive input terminal of an amplifier or a negative input terminal of the amplifier; supplying a reference voltage to the positive input terminal of the amplifier; sending the output signal of the amplifier to a first piezoelectric film of the piezoelectric film, wherein the first piezoelectric film is configured to convert the output signal of the amplifier into a movement of the first piezoelectric film; dynamically coupling the first piezoelectric membrane to a second piezoelectric membrane of the piezoelectric membrane, wherein the second piezoelectric membrane is configured to convert movement of the second piezoelectric membrane into an electrical signal; and The electrical signal is fed back to the negative input terminal of the amplifier.

19. The method according to claim 18, wherein: Feeding the electrical signal back comprises: generating a scaled version of the electrical signal using a voltage divider; and A scaled version of the electrical signal is sent to the negative input terminal of the amplifier.

20. The method according to claim 18 or 19, wherein: Receiving the audio signal includes receiving the audio signal at a first node, wherein a capacitor and a resistor are coupled in series between the first node and the negative input terminal of the amplifier.

21. The method according to claim 18 or 19, wherein: Receiving the audio signal includes receiving the audio signal at a first node, wherein a capacitor is coupled between the first node and the positive input terminal of the amplifier, wherein supplying the reference voltage includes supplying the reference voltage to a second node, wherein a resistor is coupled between the second node and the positive input terminal of the amplifier.

22. The method according to claim 18, wherein: Receiving the audio signal comprises: receiving the audio signal by a preamplifier; and The audio signal is processed by the preamplifier to produce a first output of the preamplifier.

23. The method of claim 22, further comprising feeding the first output to the positive input terminal of the amplifier.

24. The method of claim 22, further comprising: processing said first output of said preamplifier by a tone and volume control circuit to produce a second output of said tone and volume control circuit; as well as The second output is fed to the positive input terminal of the amplifier.

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