Demodulation Signal Generator for Air Pulse Generator

Abstract

A demodulation signal generator coupled to an air pulse generator including a pair of flaps includes a resonant circuit. The resonant circuit generates a first demodulation signal and a second demodulation signal. As the resonant circuit and the pair of flaps jointly perform a resonant operation, the first demodulation signal and the second demodulation signal are generated through the jointly performed resonant operation and have opposite polarities. The pair of flaps performs a differential shift to form an opening to perform a demodulation operation for a modulated pressure change.

Description

Technology Field

[0001] The present application relates to a driving circuit or a demodulation signal generator, and more specifically, to a driving circuit or a demodulation signal generator capable of driving a pair of flaps to perform differential movement and consuming low power. Background Technology

[0002] Speaker drivers and back enclosures are two major design challenges in the speaker industry. Conventional speakers struggle to cover the entire audio frequency band, for example, from 20 Hz to 20 KHz. To produce high-fidelity sound with a sufficiently high sound pressure level (SPL), both the radiating / moving surface and the volume / size of the back enclosure must be sufficiently large for conventional speakers.

[0003] Ultrasonic air pulse generators have been researched to generate air pulses or sound that overcome the design problems faced by conventional speakers. In the case of ultrasonic air pulse generators containing capacitive actuators, high power consumption is expected when operating at ultrasonic rates, making them unsuitable for portable or consumer electronic devices.

[0004] Therefore, designing the driving circuit to operate a low-power ultrasonic air pulse generator is an important objective in the field.

[0005] Therefore, the main objective of the present application is to improve upon the disadvantages of the prior art by providing a demodulation signal generator.

[0006] An embodiment of the present invention discloses a demodulation signal generator connected to an air pulse generator. The demodulation signal generator comprises: a first node coupled to a first flap and a second node coupled to a second flap; and a resonant circuit coupled to the first node and the second node, configured to produce a first demodulation signal at the first node and a second demodulation signal at the second node. The air pulse generator comprises a film structure, the film structure comprises a pair of flaps, and the pair of flaps comprises a first flap and a second flap. The resonant circuit and the pair of flaps co-perform a resonant operation, and through the co-performed resonant operation, a first demodulation signal and a second demodulation signal are generated. The first demodulation signal and the second demodulation signal have opposite polarities. By receiving the first demodulation signal and the second flap receiving the second demodulation signal, the pair of flaps performs a differential movement. The differential movement is configured to form an opening to perform demodulation operations for modulated air pressure variations generated by the film structure.

[0007] These and other objectives of the present invention will become apparent to those skilled in the art after reading the following detailed description of preferred embodiments illustrated in the various drawings and figures. Brief explanation of the drawing

[0008] FIG. 1 illustrates a schematic diagram of an air pulse generator according to an embodiment of the present application. FIG. 2 illustrates a wiring method according to an embodiment of the present application. FIG. 3 illustrates a schematic diagram of a demodulation signal generator according to an embodiment of the present application. FIG. 4 illustrates a schematic diagram of a demodulation signal generator according to an embodiment of the present application. Figure 5 illustrates the timing diagram of the demodulation signal generator of Figure 4. FIG. 6 illustrates a schematic diagram of a demodulation signal generator according to an embodiment of the present application. Figure 7 illustrates the timing diagram of the demodulation signal generator of Figure 6. FIG. 8 illustrates a schematic diagram of a demodulation signal generator according to an embodiment of the present application. FIG. 9 illustrates a schematic diagram of a detection and control circuit according to an embodiment of the present application. Specific details for implementing the invention

[0009] In the present invention, the term "combined" may mean a direct or indirect connection. "Component A is combined with Component B" may indicate that Component A is directly connected to Component B, or that Component A is connected to Component B through some component C.

[0010] The contents of U.S. Application No. 18 / 321,757 are incorporated herein by reference.

[0011] FIG. 1 illustrates an air-pulse generator (APG) (1) according to an embodiment of the present application. The APG (1), which can be used for sound playback or cooling applications, comprises a film structure (10). The film structure (10) is configured to perform a modulation operation to generate an ultrasonic acoustic / air wave (UAW) according to a sound signal (SS), and to perform a demodulation operation to generate an ultrasonic pulse array (UPA) according to the ultrasonic acoustic / air wave (UAW). The modulation operation is performed through a common-mode movement of the film structure (10), and the demodulation operation is performed through a differential-mode movement of the film structure (10). Sound corresponding to the sound signal (SS) is reproduced through a low-pass filtering effect unique to the natural / physical environment and the human auditory system.

[0012] As taught in No. 18 / 321,757, the film structure (10) comprises a pair of flaps (102). The pair of flaps (102) is actuated to perform a modulation operation by performing a common mode shift, which is intended to generate an ultrasonic acoustic / air wave (UAW). Meanwhile, the pair of flaps (102) is also actuated to perform a demodulation operation by performing a differential mode shift (or differential shift for simplicity), which is intended to generate an ultrasonic pulse array (UPA) at a pulse rate (e.g., 192KHz) according to the ultrasonic acoustic / air wave (UAW).

[0013] A pair of flaps (102) includes a first flap (101) and a second flap (103). Both flaps (101 and 103) are coupled to a modulation signal generator (16) to receive a modulation signal (SM) and are operated to perform common mode shift and modulation operations. Meanwhile, the flaps (101 and 103) are coupled to a demodulation signal generator (14) to receive a first demodulation signal (+SV) and a second demodulation signal (-SV), respectively. Since the demodulation signals (+SV and -SV) generally have opposite polarities with respect to a specific level, the flaps (101 and 103) can perform not only demodulation operations but also differential mode shift. Specifically, the differential mode shift is configured to form an opening (112) (shown in FIG. 2) to perform demodulation operation for a modulated air wave or pressure change (UAW) generated by the film structure (10) or the flap pair (102).

[0014] The modulation signal (SM) has a modulation frequency, and the modulation frequency is the pulse rate (e.g., 192 kHz). The demodulation signal (+SV / -SV) has a demodulation frequency. Due to the differential mode shift of the flap pair, the demodulation frequency can be half the pulse rate or half the modulation frequency (e.g., 96 kHz).

[0015] A detailed wiring scheme between the APG and the (inverse)modulation signal generator is illustrated in FIG. 2, wherein the scheme (131-133) is shown. The APG (1) includes a first actuator (101A) placed on a flap (101) and a second actuator (103A) placed on a second flap (103). The actuator (101A / 103A) includes a top electrode and a bottom electrode. In one embodiment, the actuator (101A / 103A) also includes a piezoelectric layer which may be made of PZT (lead zirconate titanate, which is capacitive) sandwiched between the top electrode and the bottom electrode. In one embodiment, the demodulation signal generator may be coupled to one electrode of the actuator (101A / 103A), and the modulation signal generator may be coupled to another electrode of the actuator (101A / 103A). For example, the demodulation signal generator may be coupled to the upper electrode of the actuator (101A / 103A), and the modulation signal generator may be coupled to the lower electrode. In one embodiment, the modulation signal generator and the demodulation signal generator may be coupled to at least one electrode of the actuator (101A / 103A).

[0016] FIG. 3 illustrates a schematic diagram of a demodulation signal generator (14) according to an embodiment of the present application. The demodulation signal generator can be viewed as a driving circuit configured to drive a pair of flaps to perform not only demodulation operations but also differential mode shifting. In addition to having nodes (N101 and N103) coupled to flaps (101 and 103) respectively, the demodulation signal generator (14) generally includes a resonant circuit (140). The demodulation signal generator (14) generates a demodulation signal (+SV) to the flap (101) through the node (N101) and generates a demodulation signal (-SV) to the flap (103) through the node (N103). By the resonant circuit (140) and the pair of flaps (102) (flaps (101 and 103)) jointly performing resonant operations, demodulation signals of opposite polarity (+SV and -SV) are generated.

[0017] For example, FIG. 4 illustrates a schematic diagram of a demodulation signal generator (24) according to an embodiment of the present application. The demodulation signal generator (24) comprises a resonant circuit (240), nodes (N101 and N103), and a switch (SW 1H , SW 1L , SW 2H , SW 2L ...includes ). The resonant circuit (240) is or may include a swapping module (242). The swapping module (242) includes an inductor (L) and a switching unit (SW ER ...includes ). In the embodiment illustrated in FIG. 4, the switching unit includes a switch (SW ER1 Includes ). The swapping module (242) is coupled between node (N101) and node (N103).

[0018] FIG. 5 illustrates a timing diagram of a demodulation signal generator (24). The swapping module (242) is conducted during a conduction period, for example, T12 or T21 as illustrated in FIG. 5. The demodulation signal (+SV) reaches a high voltage level (V) after the conduction period (T12). H At the low voltage level (V) L) is swapped to, and the demodulated signal (-SV) is at a low voltage level (V) after the conduction period (T12). L At the high voltage level (V) H ) is swapped to. Likewise, the demodulated signal (+SV) is swapped to a low voltage level (V) after the conduction period (T21). L At the high voltage level (V) H ) is swapped to, and the demodulated signal (-SV) is at a high voltage level (V) after the conduction period (T21). H At the low voltage level (V) L It is swapped with ). Therefore, after the conduction period (T12 / T21), the voltage level of the first demodulation signal (+SV) and the voltage level of the second demodulation signal (-SV) are swapped. Meanwhile, the demodulation signal (+SV) and the demodulation signal (-SV) can be seen as having opposite polarities.

[0019] Referring to FIGS. 4 and FIGS. 5, a switch (SW 1H and SW 1L ) is connected to the node (N101), and the switch (SW 2H and SW 2L ) is connected to node (N103). Switch (SW 1H and SW 2H ) is high voltage (V H Receives ), and the switch (SW 1L and SW 2L ) is low voltage (V L Receives ).

[0020] During the T1 period (conduction period prior to T12), the switch (SW 1H , SW 2L ) is conducting / ON and the switch (SW 1L and SW 2H As ) is cut off / OFF, the demodulated signal (+SV) is high voltage (V H It is at ) and the demodulated signal (-SV) is at low voltage (V L It is in ). During the T1 period, no current flows through the swapping module (242) and the switching unit (SW ER ) is turned OFF.

[0021] During the T2 period (conduction period after T12), the switch (SW 1H and SW 2L ) is OFF, and the switch (SW 1L and SW 2H As ) is turned ON, the demodulation signal (+SV) is at a low voltage (V L It is at ), and the demodulated signal (-SV) is at high voltage (V H It is in ). During the T2 period, no current flows through the swapping module (242) and the switching unit (SW ER ) is turned OFF.

[0022] During the conduction period (T12), the switch (SW 1H , SW 1L , SW 2H , SW 2L ) is OFF, and the switch unit (SW ER ) is ON. Current is formed from node (N101) to node (N103), causing the demodulation signal (+SV) to decrease and the demodulation signal (-SV) to increase. Therefore, the electrical energy stored in the capacity corresponding to actuator (101A) will be transferred to the capacity corresponding to actuator (103A).

[0023] Likewise, during the conduction period (T21), the switch (SW) 1H , SW 1L , SW 2H , SW 2L ) is OFF, and the switch unit (SW ER ) is ON. Current is formed from node (N103) to node (N101), causing the demodulation signal (+SV) to increase and the demodulation signal (-SV) to decrease. Therefore, the electrical energy stored in the capacity corresponding to actuator (103A) will be transferred back to the capacity corresponding to actuator (101A).

[0024] Switch (SW in FIG. 4) 1H , SW 1L , SW 2H , SW 2L and SW ER1By the ON-OFF operation of (meaning) the demodulation signal generator (24) can generate demodulation signals (+SV and -SV) having waveforms exemplified at the top of FIG. 5. Note that even the demodulation signals (+SV and -SV) applied to the capacitive actuators (101A and 103A) contain many transitions within the period (T12 / T21) while the APG is operating, and the power consumed by the flap pair (102) and the demodulation signal generator (24) is low because the energy is recycled back and forth between N101 and N103 with the help of the resonant circuit (240).

[0025] When a demodulation signal (+SV, -SV) is applied to the flaps (101 and 103), the flap pair (102) can perform differential movement.

[0026] In the present application, a pair of flaps performing differential movement 1) during a transient state / period, one flap moves toward a first direction and the other flap moves toward a second direction opposite to the first direction; or 2) during a steady state / period, one flap is actuated to bend upward and the other flap is actuated to bend downward.

[0027] The differential movement applying the demodulation signal generator (24) satisfies both 1) and 2) mentioned above. Specifically, during the steady-state period (T1) shown in FIG. 5, the flap (101) applies the demodulation signal (+SV) to the high voltage (V H It is operated to bend upward upon receiving the ) and the flap (103) receives the demodulation signal (-SV) at a low voltage (V L It is operated to bend downward upon receiving the ) signal. During the steady state period (T2), the flap (101) receives the demodulated signal (+SV) at a low voltage (V L It is operated to bend downward upon receiving the ) and the flap (103) receives the demodulation signal (-SV) at a high voltage (V HIt is operated to bend upward by receiving it. During the transition period (T12) between T1 and T2, the flap (101) moves toward the -Z direction, and the flap (103) moves toward the +Z direction opposite to the -Z direction.

[0028] Additionally, during the conduction / transient / transition period (T12 / T21), the inductor (L) in the resonant circuit (240) and the capacitance of the piezoelectric layer in the actuator (101A / 103A) will (jointly) perform LC (inductance-capacitance) resonance. The LC resonance conducts current from N101 to N103 during the T12 period and conducts current from N103 to N101 during the T21 period.

[0029] FIG. 6 illustrates a schematic diagram of a demodulation signal generator (34) according to an embodiment of the present application. The demodulation signal generator (34) is similar to the demodulation signal generator (24), and thus the same components are indicated by the same symbols. Unlike the demodulation signal generator (24), the switching unit (SW) within the swapping module (342) or resonant circuit (340) of the demodulation signal generator (34) ER ) is a switch (SW) coupled between the inductor (L) and the node (N103). ER2 It further includes ), where the switch (SW ER1 and SW ER2 ) is a switching unit (SW ER ) forming, and an inductor (L) and a switching unit (SW ER ) forms a swapping module (342). In the present application, a switch unit (SW ER ) being ON means the switch (SW ER1 ) and switch (SW ER2 It means that all ) are turned ON, and the switch unit (SW ER ) being OFF means the switch (SW ER1 ) and switch (SW ER2 It means that at least one of ) is turned OFF.

[0030] In one embodiment, the switch (SW ER1 / SW ER2 ) can be implemented as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) having body diodes (BD1 / BD2) shown at the bottom of FIG. 6. Switch (SW ER1 / SW ER2 ) is a switch (SW ER1 / SW ER2 The body diodes (BD1 / BD2) are configured to cut off current when ) is OFF. In one embodiment, the anode of the body diodes (BD1 / BD2) may be coupled to nodes (N101 / N103), and the cathode of the body diodes (BD1 / BD2) may be coupled to an inductor (L). In this case, the body diodes (BD1 / BD2) are a switch (SW ER1 / SW ER2 Prevents current from flowing from inductor (L) to N101 / N103 when ) is OFF.

[0031] In the case of a two-switch swapping module (342), it is not necessary to turn off both switches simultaneously at the end of the conduction period. Instead, given the appropriate configuration of the body diode, it is sufficient to turn off only one switch at a time at the end of the conduction period (T12 / T21). For example, at the end of the conduction period (T12) where the demodulation signal (+SV) decreases and the demodulation signal (-SV) increases (or the voltage at node (N101) is less than the voltage at node (N103) at the end of the conduction period T12), the switch (SW ER1 ) is turned OFF and the switch (SW ER2 ) can be kept ON. In this case, the body diode (BD1) having the configuration shown in FIG. 6 blocks the current from the inductor to the node (N101). Likewise, at the end of the conduction period (T21), the switch (SW ER2 ) is turned OFF and the switch (SW ER1 ) can be kept ON.

[0032] Switch (SW) ER1 and SW ER2 Refer to FIG. 7 for the timing of ). One switch (SW ER1 or SW ER2 Turning ) at once reduces the toggling rate of each switch, thereby further reducing the power consumption of the switches in the swapping module (342).

[0033] Switch (SW) ER1 and SW ER2 Note that ) is not limited to being located on both sides of the inductor (L) as shown in FIG. 6. In one embodiment, a switch (SW ER1 and SW ER2 ) can be located on the same side of the inductor (L) (not shown), where the body diode (BD1 / 2) is a switch (SW ER1 / 2 When ) is OFF, the current flowing through it can still be blocked. Switch (SW ER1 and SW ER2 As long as ) is connected between node (N101) and node (N103), this is within the scope of the present application.

[0034] In addition to LC resonance utilized by the resonance circuit (240 / 340), CMOS (complementary metal oxide semiconductor)-MEMS (micro electro mechanical systems) resonance / oscillation can also be used to generate a demodulated signal (±SV).

[0035] FIG. 8 illustrates a schematic diagram of a demodulation signal generator (44) according to an embodiment of the present application. The demodulation signal generator (44) includes a start-up circuit (442) or a resonance circuit (440) that may include the same. The resonance circuit (440) or the start-up circuit (442) is coupled to the flaps (101 and 103) and generates a demodulation signal (±SV) by utilizing the resonance property of the flaps (101 / 103), which can be seen as co-performing resonant operation with the flap pair (102). The start-up circuit (442) includes a transimpedance amplifier (444), a detection-and-control circuit (446), and a variable gain amplifier (VGA) (448).

[0036] The transimpedance amplifier (444) includes a first input terminal coupled to the flap (101) to receive current i+ and a second input terminal coupled to the flap (103) to receive current i-. The transimpedance amplifier (444) generates an output signal (Vo) according to current i+ and current i-. As illustrated in FIG. 8, the transimpedance amplifier (444) includes an operational amplifier and a feedback resistor and a feedback capacitor coupled between the input terminal and the output terminal.

[0037] The detection and control circuit (446) is coupled to the output terminal of the transimpedance amplifier (444). The detection and control circuit (446) is configured to perform a detection operation according to a signal (Vo), wherein the detection operation may be an amplitude detection, a phase detection, a frequency detection operation, or a combination thereof.

[0038] The detection and control circuit (446) controls the VGA (448) so that the startup circuit (442) within the closed loop (46) satisfies the Barkhausen criterion, namely a loop gain greater than or equal to 1 and a loop phase equal to an integer multiple of 0 or 2π. Therefore, the flap pair (102) and the resonance circuit (440) will jointly perform CMOS-MEMS resonance / oscillation.

[0039] In one embodiment, the detection and control circuit (446) may include an amplitude control circuit (4461) (shown in FIG. 9), so that the amplitude control circuit (4461) can control the VGA (448) to form an automatic gain control (AGC) loop to satisfy the Barkhausen criteria.

[0040] In one embodiment, the detection and control circuit (446) can perform a frequency detection operation to track the resonant frequency of the flaps (101 / 103). The frequency detection operation can be performed by applying a frequency-sweep test signal. In one embodiment, the detection and control circuit (446) may include a phase lock loop (PLL) circuit (4462) (shown in FIG. 9). The PLL circuit (4462) is configured to perform a frequency detection operation to track the resonant frequency of the flaps (101 / 103) or the flap pair (102).

[0041] In one embodiment, a loop filter (not shown in FIG. 8) may be included to avoid unwanted oscillation.

[0042] The loop (46) formed by the flap pair (102) and the resonant circuit (440) will perform a self-sustaining oscillation operation. Under self-sustaining oscillation, the displacement amount of the flaps (101 / 103) can be amplified by a factor of Q. Q is the quality factor of the mechanical resonance mode of 101 and 103. Thus, the input signal amplitudes of +SV and -SV are reduced by a factor of Q to maintain the desired displacement, and the power is Q 2 It decreases by a factor of two.

[0043] Note that FIG. 8 merely illustrates an example of an oscillation start circuit. The demodulation signals (+SV and -SV) may be generated by any type of oscillation start circuit or frequency detection circuit, but are not limited thereto. As long as resonance / oscillation is formed between the flap pair and the resonance circuit, this falls within the scope of the present application.

[0044] Additionally, the demodulation signal generator (44) may include a phase shifter (41) coupled between the flap (101) and the flap (103). The phase shifter (41) is configured such that the phase difference between the demodulation signal (+SV) and the demodulation signal (-SV) is 180°, thereby causing the demodulation signal (+SV) and the demodulation signal (-SV) to have opposite polarities. When the demodulation signals (+SV and -SV) are applied to the flaps (101 and 103), the flap pair (102) can perform differential shifting, and the differential shifting satisfies 1) of the above paragraph by applying the demodulation signal generator (44).

[0045] Additionally, the demodulation signal generator (44) may include a frequency multiplier (43) that receives the output signal of the starting circuit (442), denoted as SV_out, and is coupled to the starting circuit (442). The frequency multiplier (43) is configured to generate an output signal (SM_ref) by doubling the frequency of SV_out, thereby generating a modulation signal (SM) according to the signal (SM_ref), wherein the frequency of the output signal (SM_ref) is twice the frequency of the output signal (SV_out), so that the demodulation frequency becomes half of the modulation frequency or half of the pulse rate when the modulation frequency is the pulse rate.

[0046] Note that the resonant operation jointly performed by the resonant circuit (240 / 340) and the flap pair utilizes the electrical resonance of the internal components; and the resonant operation jointly performed by the resonant circuit (440) and the flap pair utilizes the mechanical resonance of the internal components.

[0047] One of the greatest advantages of a demodulation signal generator that generates a demodulation signal (±SV) by utilizing resonance is reduced power consumption. Resonance operation is not limited to the LC or CMOS-MEMS resonances mentioned above. A demodulation signal generator equipped with a resonance circuit utilizing any resonance to generate an opposite polarity demodulation signal generator is within the scope of this application.

[0048] In summary, the present application utilizes a resonant circuit to jointly perform a flap pair and a resonant operation to generate a demodulated signal (±SV) having opposite polarity, wherein the resonant operation may be an LC resonance or a CMOS-MEMS resonance satisfying the Barkhausen principle.

[0049] Those skilled in the art will readily observe that various modifications and changes to the apparatus and method may be made while maintaining the teachings of the present invention. Accordingly, the above disclosure should be interpreted as being limited only by the scope and limitations of the appended claims.

Claims

Claim 1 A demodulation signal generator coupled to an air pulse generator, comprising a first node coupled to a first flap and a second node coupled to a second flap; and includes a resonant circuit coupled to the first node and the second node and configured to generate a first demodulation signal on the first node and a second demodulation signal on the second node, wherein the air pulse generator includes a film structure, wherein the film structure includes a pair of flaps, wherein the pair of flaps includes the first flap and the second flap, wherein the resonant circuit and the pair of flaps jointly perform a resonant operation so that the first demodulation signal and the second demodulation signal are generated through a jointly performed resonant operation, wherein the first demodulation signal and the second demodulation signal have opposite polarities, wherein the first flap receives the first demodulation signal and the second flap receives the second demodulation signal so that the pair of flaps perform a differential movement, wherein the differential movement is configured to form an opening to perform a demodulation operation for a modulated pressure change generated by the film structure, and wherein the air pulse generator includes a first actuator disposed on the first flap and the second A demodulation signal generator comprising a second actuator disposed in a flap, wherein the first actuator comprises a first electrode and the second actuator comprises a second electrode, wherein the first node is coupled to the first electrode and the second node is coupled to the second electrode, wherein the first actuator comprises a third electrode and the second actuator comprises a fourth electrode, and wherein the third electrode and the fourth electrode receive a modulation signal so as to cause the flap pair to perform a common mode shift to generate the modulated pressure change. Claim 2 A demodulation signal generator according to claim 1, wherein the resonant circuit includes a swapping module, the swapping module is configured to conduct during a conduction period, and the first voltage level of the first demodulation signal and the second voltage level of the second demodulation signal are swapped after the conduction period. Claim 3 In paragraph 2, the swapping module is a demodulation signal generator comprising an inductor and a switching unit coupled between the first node and the second node. Claim 4 A demodulation signal generator according to paragraph 3, comprising a first switch, a second switch, a third switch, and a fourth switch, wherein the first switch and the second switch are coupled to the first node, and the third switch and the fourth switch are coupled to the second node. Claim 5 A demodulation signal generator according to claim 4, wherein during a first period prior to the conduction period, the first switch and the fourth switch are conducted and the second switch and the third switch are cut off, and during a second period after the conduction period, the first switch and the fourth switch are cut off and the second switch and the third switch are conducted. Claim 6 In paragraph 5, the switching unit is blocked during the first period or the second period, a demodulation signal generator. Claim 7 In paragraph 4, the first switch and the third switch receive a first voltage, and the second switch and the fourth switch receive a second voltage, a demodulation signal generator. Claim 8 In paragraph 3, the switching unit is a demodulation signal generator comprising a fifth switch and a sixth switch coupled between the first node and the second node. Claim 9 In claim 8, the demodulation signal generator in which the fifth switch and the sixth switch are conducted during the conduction period. Claim 10 In claim 8, the fifth switch comprises a first body diode having a first anode coupled to the first node, and the sixth switch comprises a second body diode having a second anode coupled to the second node, wherein during the conduction period, the first voltage of the first node decreases and the second voltage of the second node increases, and at the end of the conduction period, the first voltage is smaller than the second voltage and the fifth switch is turned off, a demodulation signal generator. Claim 11 In paragraph 8, at the end of the conduction period, the sixth switch remains in a conduction state, a demodulation signal generator. Claim 12 A demodulation signal generator according to claim 8, wherein the 6th switch is blocked during the 1st period prior to the conduction period, and the 5th switch is blocked during the 2nd period after the conduction period. Claim 13 A demodulation signal generator according to claim 1, wherein the air pulse generator generates a plurality of air pulses at a pulse rate, the plurality of air pulses are generated according to the modulated air pressure change, and the demodulation frequency of the first demodulation signal is half the pulse rate. Claim 14 A demodulation signal generator coupled to an air pulse generator, comprising a first node coupled to a first flap and a second node coupled to a second flap; and includes a resonant circuit coupled to the first node and the second node and configured to generate a first demodulation signal on the first node and a second demodulation signal on the second node, wherein the air pulse generator includes a film structure, wherein the film structure includes a pair of flaps, wherein the pair of flaps includes the first flap and the second flap, wherein the resonant circuit and the pair of flaps jointly perform a resonant operation so that the first demodulation signal and the second demodulation signal are generated through a jointly performed resonant operation, wherein the first demodulation signal and the second demodulation signal have opposite polarities, wherein the first flap receives the first demodulation signal and the second flap receives the second demodulation signal so that the pair of flaps perform a differential movement, wherein the differential movement is configured to form an opening to perform a demodulation operation for a modulated pressure change generated by the film structure, wherein the resonant circuit includes a starter circuit, and oscillation is generated by the starter circuit and the pair of flaps. Demodulation signal generator. Claim 15 In claim 14, the starting circuit comprises a transimpedance amplifier, wherein the transimpedance amplifier comprises a first input terminal coupled to the first flap and a second input terminal coupled to the second flap, wherein the transimpedance amplifier is configured to receive a first current corresponding to the first flap and a second current corresponding to the second flap, wherein the transimpedance amplifier outputs a first output signal according to the first current and the second current, and a demodulation signal generator in which the first demodulation signal and the second demodulation signal are generated according to the first output signal of the transimpedance amplifier. Claim 16 In claim 15, the starting circuit further comprises: a detection and control circuit coupled to the output terminal of the transimpedance amplifier and configured to perform a detection operation according to a first output signal of the transimpedance amplifier; and a demodulation signal generator further comprising a variable gain amplifier (VGA) controlled by the detection and control circuit, wherein the first demodulation signal is generated according to a second output signal of the variable gain amplifier. Claim 17 In claim 16, the detection and control circuit includes an amplitude control circuit, and a demodulation signal generator in which an automatic gain control (AGC) loop is formed by the amplitude control circuit and the VGA. Claim 18 In claim 16, the detection and control circuit comprises a demodulation signal generator including a Phase Lock Loop (PLL) circuit configured to perform a frequency detection operation to track the resonant frequency of the first flap. Claim 19 In paragraph 15, the above-mentioned transimpedance amplifier is a demodulation signal generator comprising an operational amplifier. Claim 20 In claim 19, the above-mentioned transimpedance amplifier is a demodulation signal generator comprising a feedback resistor coupled between the input terminal and the output terminal of the above-mentioned operational amplifier. Claim 21 In claim 19, the above-mentioned transimpedance amplifier is a demodulation signal generator comprising a feedback capacitor coupled between the input terminal and the output terminal of the above-mentioned operational amplifier. Claim 22 A demodulation signal generator according to claim 14, further comprising a phase shifter coupled to the first flap and the second flap, wherein the phase shifter configures the phase difference between the first demodulation signal and the second demodulation signal to be 180°. Claim 23 A demodulation signal generator according to claim 14, further comprising a frequency multiplier coupled to the starting circuit and configured to receive a third output signal of the starting circuit and generate a fourth output signal, wherein the frequency of the fourth output signal is twice the frequency of the third output signal, a modulation signal is generated according to the fourth output signal, and the modulation signal is configured to drive the film structure so that the film structure generates the modulated pressure change. Claim 24 delete Claim 25 delete

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