Sound output device and electronic apparatus

Abstract

The invention provides a sound output device and an electronic apparatus, which can output sound with good quality and the same degree as sound output from a loudspeaker through a simple structure. A sound output device (3) is provided with: a control unit (31) that outputs a PWM signal (SG); an amplifier (32) that amplifies the PWM signal; and a piezoelectric element (33) that outputs sound on the basis of a PWM signal (SL) output by the amplifier (32), the control unit outputs at least one of a first PWM signal (SG1), a second PWM signal (SG2), and a second PWM signal (SG3), the first PWM signal being a PWM signal corresponding to the sound, the second PWM signal being output prior to the first PWM signal and having a smaller duty ratio than an average duty ratio (RDA), which is an average value of duty ratios of the first PWM signal, and the second PWM signal being output prior to the first PWM signal and having a smaller duty ratio than the average duty ratio (RDA) of the first PWM signal. The second PWM signal is output after the first PWM signal and has a duty cycle less than the average duty cycle.

Description

Technical Field

[0001] The present disclosure relates to a sound output device and an electronic device. Background Art

[0002] Patent Document 1 discloses an induction heating rice cooker including a speaker and a voice output unit that outputs a voice signal to the speaker.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-325812 Summary of the Invention

[0004] The present disclosure provides a sound output device and an electronic device that can output sound with good quality comparable to that of sound output from a speaker with a simple structure.

[0005] The sound output device of the present disclosure includes: a control unit that outputs a PWM signal; an amplifier that amplifies the PWM signal; and a piezoelectric element that outputs sound according to the PWM signal output from the amplifier, wherein the control unit outputs at least one of a first PWM signal, a second PWM signal, and a third PWM signal, wherein the first PWM signal is a PWM signal corresponding to the sound, the second PWM signal is output before the first PWM signal and has a duty ratio less than a substantially average value of the duty ratio of the first PWM signal, i.e., an average duty ratio, and the third PWM signal is output after the first PWM signal and has a duty ratio less than the average duty ratio.

[0006] Moreover, the electronic device of the present disclosure includes: a control unit that outputs a PWM signal; an amplifier that amplifies the PWM signal; and a piezoelectric element that outputs sound according to the PWM signal output from the amplifier, wherein the control unit outputs at least one of a first PWM signal, a second PWM signal, and a third PWM signal, wherein the first PWM signal is a PWM signal corresponding to the sound, the second PWM signal is output before the first PWM signal and has a duty ratio less than a substantially average value of the duty ratio of the first PWM signal, i.e., an average duty ratio, and the third PWM signal is output after the first PWM signal and has a duty ratio less than the average duty ratio.

[0007] The sound output device and the electronic device of the present disclosure output at least one of a first PWM signal, a second PWM signal, and a third PWM signal to a piezoelectric element via an amplifier, wherein the first PWM signal is a PWM signal corresponding to sound, the second PWM signal is output before the first PWM signal and has a duty ratio less than a substantially average value of the duty ratio of the first PWM signal, i.e., an average duty ratio, and the third PWM signal is output after the first PWM signal and has a duty ratio less than the average duty ratio.

[0008] By outputting a second PWM signal that is output before the first PWM signal and has a duty ratio smaller than the average duty ratio, it is possible to suppress noise generated when the piezoelectric element starts to output sound corresponding to the first PWM signal. Also, by outputting a third PWM signal that is output after the first PWM signal and has a duty ratio smaller than the average value of the average duty ratio, it is possible to suppress noise generated when the piezoelectric element ends the output of sound corresponding to the first PWM signal. Therefore, it is possible to output sound with good quality comparable to the sound output from the speaker with a simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a perspective view showing a cooker according to Embodiment 1.

[0010] Figure 2 is a perspective view showing the cooker with the lid in the open state according to Embodiment 1.

[0011] Figure 3 is a diagram showing an example of the display operation unit according to Embodiment 1.

[0012] Figure 4 is a diagram showing the position of the sound output device in the cooker according to Embodiment 1.

[0013] Figure 5 is a diagram showing the structure of the sound output device according to Embodiment 1.

[0014] Figure 6 is a circuit diagram showing the structure of the amplifier of the sound output device according to Embodiment 1.

[0015] Figure 7 is a graph showing the second PWM signal according to Embodiment 1.

[0016] Figure 8 is a graph showing the third PWM signal according to Embodiment 1.

[0017] Figure 9 is a graph showing the sound output from the piezoelectric element according to Embodiment 1.

[0018] Figure 10 is a flowchart showing the processing of the control unit according to Embodiment 1.

[0019] REFERENCE SIGNS LIST

[0020] 1 Cooker (electronic device)

[0021] 3 Sound output device

[0022] 31 Control unit

[0023] 31A Processor

[0024] 311 Carrier generation unit

[0025] 312 First signal generation unit

[0026] 313 Second signal generation unit

[0027] 314 Third signal generation unit

[0028] 315 Signal output unit

[0029] 31B Memory

[0030] 316 Voice storage unit

[0031] 32 Amplifier

[0032] 321 Transistor

[0033] 33 Piezoelectric element

[0034] 331 First piezoelectric element

[0035] 332 Second piezoelectric element

[0036] NS, NE Noise

[0037] PG Control program

[0038] RD Duty ratio

[0039] RDA Average duty ratio

[0040] SG, SLPWM Signal

[0041] SG1 First PWM signal

[0042] SG2 Second PWM signal

[0043] SG3 Third PWM signal

[0044] SGC Carrier signal Detailed implementation mode

[0045] (Insights, etc. that form the basis of the present disclosure)

[0046] When the inventors conceived of the present disclosure, there were electronic devices (especially household electronic devices) such as a heating cooker equipped with a sound output device that outputs voice. Conventionally, the sound output device in such an electronic device has a speaker and an amplifier IC (Integrated Circuit) that amplifies a voice signal.

[0047] On the other hand, as an inexpensive component for outputting sound, there is a piezoelectric element. Also, the following technique is known: a PWM (Pulse Width Modulation) signal obtained by modulating the duty ratio is generated from a voice signal, and the PWM signal is amplified and input to the piezoelectric element, whereby voice can be output from the piezoelectric element.

[0048] However, the inventors have found the following problem: when outputting voice or the like from the piezoelectric element, noise is generated at the start and end of the output of voice or the like. To solve this problem, the subject matter of the present disclosure is constituted.

[0049] Accordingly, the present disclosure provides a sound output device and an electronic device that can output sound of good quality comparable to that output from a speaker with a simple structure.

[0050] Hereinafter, embodiments will be described in detail with reference to the drawings. However, sometimes detailed descriptions that are more than necessary are omitted. For example, sometimes detailed descriptions of already known matters or repeated descriptions of substantially the same structures are omitted.

[0051] In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims by these.

[0052] (Embodiment 1)

[0053] [1-1. Structure]

[0054] [1-1-1. Structure of the cooker]

[0055] Figure 1 is a perspective view showing the cooker 1. Figure 2 is a perspective view showing the cooker 1 with the lid 11 in an open state.

[0056] In addition, Figure 1 , Figure 2 and Figure 4 each describe the X-axis, Y-axis, and Z-axis. The X-axis, Y-axis, and Z-axis are orthogonal to each other. The X-axis and Y-axis are parallel to the horizontal direction. The Z-axis is parallel to the vertical direction. The X-axis represents the left-right direction. The Y-axis represents the front-back direction. The positive direction of the X-axis represents the right direction. The positive direction of the Y-axis represents the front direction. The positive direction of the Z-axis represents the upward direction.

[0057] The cooker 1 corresponds to an example of an "electronic device".

[0058] The cooker 1 includes a main body 10 and a lid 11. The main body 10 and the lid 11 are connected by a support portion 12. Thus, the lid 11 can be opened and closed relative to the main body 10 by rotating about the support portion 12. The support portion 12 is disposed on the back side of the main body 10. The back side is the negative direction side of the Y axis.

[0059] The main body 10 has a container shape with an upper opening in the installed state of the cooker 1, and a recess 14 is formed to accommodate the inner pot 13. The inner pot 13 is a container with an upper opening in a state of being accommodated in the recess 14. A convex portion 15 is formed substantially at the center of the inner bottom surface of the inner pot 13. A stirring member for stirring the foodstuffs accommodated in the inner pot 13, a plate for placing the foodstuffs when steaming the foodstuffs accommodated in the inner pot 13, etc. are mounted on the convex portion 15.

[0060] The lid 11 includes an inner lid 16 and an outer lid 17. The inner lid 16 is made of a specified metallic material and closes the opening of the inner pot 13 when the lid 11 is in the closed state. The inner lid 16 has a gasket at its outer peripheral portion. The inner lid 16 is detachably disposed on the inner surface of the outer lid 17 by fitting a specified portion such as the outer peripheral portion with the outer lid 17.

[0061] The lid 11 is formed with a steam discharge port 18. The steam discharge port 18 discharges steam to keep the pressure inside the inner pot 13 constant.

[0062] A handle 19 for fixing the lid 11 in the closed state is provided on the outer surface of the outer lid 17. The handle 19 is on the outer surface of the outer lid 17 and can rotate within a specified range in the direction indicated by the symbol R about the central portion of the outer surface.

[0063] A display operation unit 20 is provided on the outer surface of the outer lid 17.

[0064] Figure 3 It is a diagram showing an example of the display operation unit 20.

[0065] The display operation unit 20 includes a display 201. In addition, the display operation unit 20 includes a return button 202, a cancel button 203, a first switching button 204, an OK button 205, a second switching button 206, and a start button 207. In addition, the display operation unit 20 includes an LED (Light Emitting Diode). The return button 202, the cancel button 203, the first switching button 204, the OK button 205, the second switching button 206, and the start button 207 are each constituted by a touch sensor, for example.

[0066] The display 201 displays various images.

[0067] The return button 202 is a button for shifting the screen displayed on the display 201 to the previous screen.

[0068] The cancel button 203 is a button for canceling the operations on the display operation unit 20. Moreover, the cancel button 203 is a button for aborting or ending the cooking and warming that the cooker 1 is performing.

[0069] The first switching button 204 and the second switching button 206 are buttons for switching the information displayed on the display 201. Moreover, the first switching button 204 and the second switching button 206 are buttons for switching the object selected on the display 201.

[0070] The OK button 205 is a button for confirming the selection made on the display 201.

[0071] The start button 207 is a button for starting the cooking of the cooker 1.

[0072] The LED 208 is a lamp for notifying the connection status of the communication between the cooker 1 and a communication device (not shown). The communication device is connected to a network composed of a public line network, a dedicated line, other communication circuits, etc., and communicates with the server device via the network.

[0073] As described above, the cooker 1 can display the cooking history, the reservation list, and the menu list on the display operation unit 20. When the display operation unit 20 displays the cooking history, the reservation list, and the menu list, the menus are displayed in a manner that allows for switching one by one. Figure 3 Display the menu with the menu name "creamed stew" among the menus included in the cooking history. In addition, the menu name indicates the name of the menu.

[0074] When the first switching button 204 or the second switching button 206 is operated, the display operation unit 20 switches the displayed menu from the menu with the menu name "creamed stew" to another menu.

[0075] [1-1-2. Structure of the sound output device]

[0076] Figure 4 This is a diagram showing the position of the sound output device 3 in the cooker 1 in Embodiment 1.

[0077] Figure 4 This is a diagram of the back side of the cooker 1. The back side of the cooker 1 is the side where the support portion 12 described with reference to Figure 2 is arranged. As Figure 4 shown, a back cover 101 is arranged on the back side of the cooker 1. The back side refers to the negative direction side of the Y axis.

[0078] The sound output device 3 is housed inside the back cover 101. It is also possible to form an opening such as a slit in the back cover 101 to facilitate the transmission of the sound output from the sound output device 3 to the outside.

[0079] Figure 5 This is a diagram showing the structure of the sound output device 3.

[0080] As Figure 5 shown, the sound output device 3 includes a control unit 31, an amplifier 32, and a piezoelectric element 33.

[0081] The control unit 31 controls each part of the sound output device 3. Also, the control unit 31 can control each part of the cooker 1.

[0082] The control unit 31 includes a processor 31A and a memory 31B.

[0083] The processor 31A is composed of a CPU (Central Processing Unit), an MPC (MicroProcessing Unit), etc. The memory 31B is composed of a ROM (Read Only Memory), etc.

[0084] The processor 31A can be composed of multiple processors or a single processor.

[0085] The processor 31A can also be hardware programmed to implement the functions of each part described later. That is, the processor 31A can also be a structure formed by loading a control program PG as a hardware circuit. In this case, for example, the processor 31A is composed of an ASIC (ApplicationSpecific Integrated Circuit), an FPGA (Field-Programmable Gate Array), etc.

[0086] In the following description, the case where various functions of the control unit 31 are implemented by the processor 31A executing the control program PG will be described.

[0087] The memory 31B has a storage area for storing programs executed by the processor 31A and data processed by the processor 31A. The memory 31B stores the control program PG executed by the processor 31A and various voice data related to the operation of the sound output device 3, etc.

[0088] The memory 31B has a non-volatile storage area for storing programs and data non-volatilely. The memory 31B can also include, for example, a ROM, an HDD (Hard Disk Drive), an SSD (Solid State Drive), etc. as the non-volatile storage area. Also, the memory 31B can include a volatile storage area, constituting a work area for temporarily storing the programs executed by the processor 31A and the data to be processed. The memory 31B can also include, for example, a RAM (Random Access Memory) etc. as the volatile storage area.

[0089] The control unit 31 generates a PWM signal SG and outputs the generated PWM signal SG to the amplifier 32. The PWM signal SG is composed of a first PWM signal SG1, a second PWM signal SG2, and a third PWM signal SG3.

[0090] The first PWM signal SG1 is a PWM signal corresponding to the sound.

[0091] The second PWM signal SG2 is a PWM signal output before the first PWM signal. For example, the second PWM signal SG2 is output immediately before the first PWM signal.

[0092] The third PWM signal SG3 is a PWM signal output after the first PWM signal. For example, the third PWM signal SG3 is output immediately after the first PWM signal.

[0093] Regarding the second PWM signal SG2, refer to Figure 7 For further explanation.

[0094] Regarding the third PWM signal SG3, refer to Figure 8 For further explanation.

[0095] The amplifier 32 amplifies the PWM signal SG output from the control unit 31. The amplifier 32 outputs the amplified PWM signal SL to the piezoelectric element 33.

[0096] Regarding the amplifier 32, refer to Figure 6 For further explanation.

[0097] The piezoelectric element 33 outputs a sound corresponding to the PWM signal SL from the amplifier 32. The piezoelectric element 33 is composed of, for example, a first piezoelectric element 331 and a second piezoelectric element 332.

[0098] In the first piezoelectric element 331 and the second piezoelectric element 332, a diaphragm is disposed on at least one of the electrodes. The sound is output by the vibration of the diaphragm.

[0099] Regarding the piezoelectric element 33, reference is made to Figure 6 for further description.

[0100] In addition, in the following description, the case where the sound output device 3 outputs speech is described.

[0101] "Speech" corresponds to an example of "sound".

[0102] In the present embodiment, the case where the piezoelectric element 33 is composed of the first piezoelectric element 331 and the second piezoelectric element 332 is described, but the present disclosure is not limited thereto. For example, the piezoelectric element 33 may be composed of a single piezoelectric element. And, for example, the piezoelectric element 33 may be composed of three or more piezoelectric elements.

[0103] The more piezoelectric elements the piezoelectric element 33 is composed of, the more the volume output from the piezoelectric element 33 can be increased.

[0104] [1-1-3. Structure of the control unit]

[0105] Next, reference is made to Figure 5 to describe the structure of the control unit 31.

[0106] As Figure 5 shown, the control unit 31 includes a carrier generation unit 311, a first signal generation unit 312, a second signal generation unit 313, a third signal generation unit 314, a signal output unit 315, and a voice storage unit 316.

[0107] Specifically, the processor 31A of the control unit 31 functions as the carrier generation unit 311, the first signal generation unit 312, the second signal generation unit 313, the third signal generation unit 314, and the signal output unit 315 by executing the control program PG. And, the processor 31A of the control unit 31 causes the memory 31B to function as the voice storage unit 316 by executing the control program PG.

[0108] The voice storage unit 316 stores a plurality of voice signals in advance. The plurality of voice signals respectively represent, for example, guidance output to the user of the cooker 1 according to the state of the cooker 1.

[0109] For example, when the user touches Figure 3 the start button 207 shown and the cooker 1 starts cooking, the sound output device 3 outputs guidance such as "Cooking has started." The voice signal representing such guidance as "Cooking has started." corresponds to an example of the plurality of voice signals.

[0110] The carrier generation unit 311 generates a carrier signal SGC with a constant duty cycle RD. The carrier signal SGC is generated at a frequency higher than the frequency range of human audible sound. The frequency of the carrier signal SGC is, for example, 64 KHz. In addition, the frequency range of human audible sound is 20 Hz to 20 KHz.

[0111] Moreover, the carrier signal SGC is a rectangular wave. The duty cycle RD of the carrier signal SGC is, for example, 50%.

[0112] In the present embodiment, the case where the frequency of the carrier signal SGC is 64 KHz will be described, but the present disclosure is not limited thereto. The frequency of the carrier signal SGC may be any frequency higher than the frequency range of human audible sound. For example, the frequency of the carrier signal SGC may be 32 KHz. And, for example, the frequency of the carrier signal SGC may be 128 KHz.

[0113] The higher the sampling rate of the voice signal stored in the voice storage unit 316 and the frequency of the carrier signal SGC, the higher the quality of the output voice. The lower the sampling rate of the voice signal stored in the voice storage unit 316 and the frequency of the carrier signal SGC, the lower the storage capacity required for the voice storage unit 316 and the load on the processor 31A required for the processing of the first signal generation unit 312.

[0114] The first signal generation unit 312 generates a first PWM signal SG1. The first signal generation unit 312 generates the first PWM signal SG1, for example, by modulating the duty cycle RD of the carrier signal SGC using the voice signal.

[0115] The first signal generation unit 312 reads out, for example, one voice signal from among a plurality of voice signals stored in the voice storage unit 316, and modulates the duty cycle RD of the carrier signal SGC using the read-out one voice signal, thereby generating the first PWM signal SG1.

[0116] The first period P1, which is the period during which the voice corresponding to the first PWM signal SG1 is output, is, for example, several seconds to 10 seconds.

[0117] The second signal generation unit 313 generates a second PWM signal SG2.

[0118] The second PWM signal SG2 is, for example, a signal output immediately before the first PWM signal SG1. The second PWM signal SG2 is a signal with a duty cycle RD less than the average duty cycle RDA. The average duty cycle RDA is the average value of the duty cycle RD of the first PWM signal.

[0119] In addition, the average duty ratio RDA may also be the duty ratio RD of the carrier signal SGC. In this case, the average duty ratio RDA is, for example, 50%. And in this case, the process of calculating the average value of the duty ratio RD of the first PWM signal can be omitted.

[0120] The second PWM signal SG2 is a signal whose duty ratio RD gradually increases. The second PWM signal SG2 is, for example, a signal whose duty ratio RD increases stepwise. And the second PWM signal SG2 may also be, for example, a signal whose duty ratio RD increases smoothly.

[0121] The period during which the second PWM signal SG2 is output, i.e., the second period P2, is a period that is equal to or greater than a preset first threshold TH1. The first threshold TH1 is, for example, 2 milliseconds. The second period P2 is, for example, 3 milliseconds to 10 milliseconds.

[0122] Regarding the second PWM signal SG2, refer to Figure 7 for further explanation.

[0123] The third signal generation unit 314 generates a third PWM signal SG3.

[0124] The third PWM signal SG3 is, for example, a signal output immediately after the first PWM signal. The third PWM signal SG3 is a signal whose duty ratio RD is less than the average duty ratio RDA.

[0125] The third PWM signal SG3 is a signal whose duty ratio RD gradually decreases. The third PWM signal SG3 is, for example, a signal whose duty ratio RD decreases stepwise. And the third PWM signal SG3 may also be, for example, a signal whose duty ratio RD decreases smoothly.

[0126] The period during which the third PWM signal SG3 is output, i.e., the third period P3, is a period that is equal to or greater than a preset second threshold TH2. The second threshold TH2 is, for example, 2 milliseconds. The third period P3 is, for example, 3 milliseconds to 10 milliseconds.

[0127] Regarding the third PWM signal SG3, refer to Figure 8 for further explanation.

[0128] The signal output unit 315 outputs the PWM signal SG to the amplifier 32.

[0129] The PWM signal SG is composed of the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3. In other words, the signal output unit 315, for example, synthesizes the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3 to generate the PWM signal SG. Then, the signal output unit 315 outputs the generated PWM signal SG to the amplifier 32.

[0130] In the present embodiment, a case where the signal output unit 315 synthesizes the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3 to generate the PWM signal SG will be described, but the present disclosure is not limited thereto.

[0131] For example, the PWM signal SG may be generated as follows. First, the carrier generation unit 311 generates a carrier signal SGC corresponding to the signal output period PA. The signal output period PA is the sum of the first period P1, the second period P2, and the third period P3. Then, the first signal generation unit 312 modulates the carrier signal SGC of the first period P1 to generate the first PWM signal SG1. And, the second signal generation unit 313 uses the carrier signal SGC of the second period P2 immediately before the first period P1 to generate the second PWM signal SG2. Further, the third signal generation unit 314 uses the carrier signal SGC of the third period P3 immediately after the first period P1 to generate the third PWM signal SG3. In this way, the PWM signal SG can also be generated. In this case, the signal output unit 315 can omit the process of synthesizing the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3.

[0132] [1-1-4. Structure of the amplifier]

[0133] Next, Figure 6 the structure of the amplifier 32 will be described.

[0134] As Figure 6 shown, the amplifier 32 includes a transistor 321, an input resistor RA, a first resistor R1, and a second resistor R2. The transistor 321 is a so-called bipolar transistor.

[0135] The PWM signal SG is input from the control unit 31 to one end of the input resistor RA. The other end of the input resistor RA is connected to the base of the transistor 321. That is, the PWM signal SG is input from the control unit 31 to the base of the transistor 321 via the input resistor RA.

[0136] The first resistor R1 and the second resistor R2 are so-called voltage dividing resistors.

[0137] One end of the first resistor R1 is connected to the collector of the transistor 321. The other end of the first resistor R1 is connected to the second resistor R2.

[0138] The piezoelectric element 33 is connected in parallel with the first resistor R1. Specifically, the first piezoelectric element 331 and the second piezoelectric element 332 are respectively connected in parallel with the first resistor R1.

[0139] One end of the second resistor R2 is pulled up to the voltage VC. The other end of the second resistor R2 is connected to the first resistor R1.

[0140] The emitter of the transistor 321 is grounded.

[0141] When the PWM signal SG is OFF, no voltage is applied to the base of the transistor 321, so the transistor 321 is in the OFF state. In this case, current does not flow through the first resistor R1 and the second resistor R2. As a result, the voltage across the two ends of the first resistor R1 becomes "0", and the voltage input to the piezoelectric element 33 becomes "0".

[0142] When the PWM signal SG is ON, a voltage is applied to the base of the transistor 321, so the transistor 321 is in the ON state. In this case, current flows through the first resistor R1 and the second resistor R2. As a result, a divided voltage VD defined by the following formula (1) is applied across the two ends of the first resistor R1, and the divided voltage VD is applied to the piezoelectric element 33.

[0143] VD = VC × R1 / (R1 + R2) (1)

[0144] In addition, R1 represents the resistance value of the first resistor R1, and R2 represents the resistance value of the second resistor R2.

[0145] The divided voltage VD is, for example, 25V.

[0146] In this way, the PWM signal SG is amplified by the control unit 31, and the amplified PWM signal SL is applied to the piezoelectric element 33. The amplitude of the PWM signal SG is, for example, 5V. The amplitude of the PWM signal SL is, for example, 25V. That is, the amplifier 32 amplifies from 5V to 25V.

[0147] In this embodiment, the case where the transistor 321 is a bipolar transistor is described, but the present disclosure is not limited thereto. The transistor 321 is, for example, a semiconductor amplifying element such as a MOSFET (Metal - Oxide - Semiconductor Field - Effect Transistor). Also, the circuit structure of the amplifier 32 can be a half - bridge type using a plurality of semiconductor amplifying elements (bipolar transistors, MOSFETs, etc.), or a full - bridge type using a plurality of semiconductor amplifying elements (bipolar transistors, MOSFETs, etc.).

[0148] [1 - 2. Second PWM Signal]

[0149] Next, with reference to Figure 7 An example of the second PWM signal SG2 will be described. Figure 7 Three curve graphs are shown. In each of the three curve graphs, the horizontal axis is time T, and the vertical axis is the duty ratio RD of the PWM signal SG.

[0150] In each of the three curves, before time T is "0", the duty ratio RD is "0%". Also, in each of the three curves, when time T is time TA, the duty ratio RD is the average duty ratio RDA. The average duty ratio RDA is the average value of the duty ratio RD of the first PWM signal. The average duty ratio RDA is, for example, 50%. In each of the three curves, during the second period P2 from "0" to time TA of time T, the duty ratio RD of the second PWM signal SG2 gradually increases.

[0151] Also, the period from "0" to time TA of time T corresponds to the second period P2. The second period P2 is the period during which the second PWM signal SG2 is output. The second period P2 is, for example, 4 milliseconds. The period after time T is time TA corresponds to the first period P1. The first period P1 is the period during which the first PWM signal SG1 is output. The first period P1 is, for example, 4 seconds.

[0152] In Figure 7 the left graph of, the duty ratio RD of the second PWM signal SG2 gradually increases. Also, the duty ratio RD of the second PWM signal SG2 increases stepwise. Figure 7 The curve graph G11 shown in the left graph of represents the change in the duty ratio RD of the second PWM signal SG2.

[0153] As shown in the curve graph G11, when time T is "0", the duty ratio RD of the second PWM signal SG2 increases stepwise from "0%" to the duty ratio RDC. The duty ratio RDC is, for example, "17%". Also, as shown in the curve graph G11, during the period from "0" to time TB of time T, the duty ratio RD is maintained at the duty ratio RDC. Time TB is, for example, "2 milliseconds".

[0154] Then, as shown in the curve graph G11, when time T is time TB, the duty ratio RD of the second PWM signal SG2 increases stepwise from the duty ratio RDC to the duty ratio RDB. The duty ratio RDB is larger than the duty ratio RDC and smaller than the average duty ratio RDA. The duty ratio RDB is, for example, "34%". Also, as shown in the curve graph G11, during the period from time TB to time TA of time T, the duty ratio RD is maintained at the duty ratio RDB. Time TA is, for example, "4 milliseconds". That is, the second period P2 is, for example, "4 milliseconds".

[0155] Furthermore, as shown in the curve graph G11, when time T is time TA, the duty ratio RD of the second PWM signal SG2 increases stepwise from the duty ratio RDB to the average duty ratio RDA. Time TA corresponds to the time at the boundary between the first period P1 and the second period P2. In other words, time TA corresponds to the time at the start of the first PWM signal SG1.

[0156] In Figure 7 the left figure of Figure 7 , the case where the duty ratio RD of the second PWM signal SG2 increases from "0%" to the average duty ratio RDA in three stages is described, but the present disclosure is not limited thereto. For example, the duty ratio RD of the second PWM signal SG2 may also increase from "0%" to the average duty ratio RDA in two stages. Further, the duty ratio RD of the second PWM signal SG2 may also increase from "0%" to the average duty ratio RDA in four or more stages, for example.

[0157] In Figure 7 the left figure of Figure 7 , the case where the increase amount of the duty ratio RD in each stage is substantially constant (about 17%) is described, but the present disclosure is not limited thereto. The increase amount of the duty ratio RD in each stage may also gradually increase, for example.

[0158] As Figure 7 shown in the left figure of Figure 7 , when the duty ratio RD of the second PWM signal SG2 increases from "0%" to the average duty ratio RDA in three stages, the duty ratio RD may also increase as follows. For example, the duty ratio RD during the period when time T is from "0" to time TB is, for example, "10%". For example, during the period when time T is from time TB to time TA, the duty ratio RD is, for example, "25%". In this case, when time T is "0", the duty ratio RD increases from "0%" to "10%". Then, when time T is time TB, the duty ratio RD increases from "10%" to "25%". Further, when time T is time TA, the duty ratio RD increases from "25%" to "50%".

[0159] In Figure 7 the central figure of Figure 7 , the duty ratio RD of the second PWM signal SG2 gradually increases. Also, the duty ratio RD of the second PWM signal SG2 increases smoothly. Specifically, the duty ratio RD of the second PWM signal SG2 increases linearly. Figure 7 The curve graph G12 shown in the central figure of Figure 7 represents the change of the duty ratio RD of the second PWM signal SG2.

[0160] As shown in the curve graph G12, when time T is "0", the duty ratio RD is "0%", and when time T is time TA, the duty ratio RD increases linearly so as to become the average duty ratio RDA.

[0161] In Figure 7 the right figure of Figure 7 , the duty ratio RD of the second PWM signal SG2 gradually increases. Also, the duty ratio RD of the second PWM signal SG2 increases smoothly. Specifically, the duty ratio RD of the second PWM signal SG2 increases in a smooth curve shape. Figure 7 The curve graph G13 shown in the right figure of Figure 7 represents the change of the duty ratio RD of the second PWM signal SG2.

[0162] As shown in the curve graph G13, the curve corresponding to the curve graph G13 is a downwardly convex curve. The curve corresponding to the curve graph G13 is, for example, a quadratic curve. Also, the curve corresponding to the curve graph G13 is, for example, a logarithmic curve.

[0163] As shown in the curve graph G13, at time T = "0", the duty ratio RD is "0%", and at time T = time TA, the duty ratio RD increases curvilinearly so as to become the average duty ratio RDA.

[0164] [1 - 3. Third PWM Signal]

[0165] Next, with reference to Figure 8 an example of the third PWM signal SG3 will be described. Figure 8 Three curve graphs are shown. In each of the three curve graphs, the horizontal axis is time T and the vertical axis is the duty ratio RD of the PWM signal SG.

[0166] In each of the three curve graphs, when time T is earlier than time TC, the duty ratio RD is the average duty ratio RDA. Also, in each of the three curve graphs, when time T is after time TE, the duty ratio RD is "0%". The average duty ratio RDA is the average value of the duty ratio RD of the first PWM signal. The average duty ratio RDA is, for example, 50%. In each of the three curve graphs, during the third period P3 when time T ranges from time TC to time TE, the duty ratio RD of the third PWM signal SG3 gradually decreases.

[0167] Also, the period when time T ranges from time TC to time TE corresponds to the third period P3. The third period P3 is the period during which the third PWM signal SG3 is output. The third period P3 is, for example, 4 milliseconds. The period before time T = time TC corresponds to the first period P1. The first period P1 is the period during which the first PWM signal SG1 is output. The first period P1 is, for example, 4 seconds.

[0168] In Figure 8 the left graph, the duty ratio RD of the third PWM signal SG3 gradually decreases. Specifically, the duty ratio RD of the third PWM signal SG3 decreases stepwise. Figure 8 The curve graph G21 shown in the left graph of

[0169] As shown in the curve graph G21, at time T = TC, the duty ratio RD of the third PWM signal SG3 decreases stepwise from the average duty ratio RDA to the duty ratio RDB. The duty ratio RDB is, for example, 34%. Also, as shown in the curve graph G21, during the period when time T ranges from time TC to time TD, the duty ratio RD is maintained at the duty ratio RDB. Time TD is, for example, 2 milliseconds after time TC. Time TC corresponds to the time at the boundary between the first period P1 and the third period P3. In other words, time TC corresponds to the time at the end of the first PWM signal SG1.

[0170] Then, as shown in the curve graph G21, at time T = TD, the duty ratio RD of the third PWM signal SG3 decreases stepwise from the duty ratio RDB to the duty ratio RDC. The duty ratio RDC is smaller than the duty ratio RDB and larger than "0%". The duty ratio RDC is, for example, 17%. Also, as shown in the curve graph G21, during the period when time T ranges from time TD to time TE, the duty ratio RD is maintained at the duty ratio RDC.

[0171] Furthermore, as shown in the curve graph G21, at time T = TE, the duty ratio RD of the third PWM signal SG3 decreases stepwise from the duty ratio RDC to "0%". After time T = TE, the duty ratio RD of the PWM signal SG is maintained at "0%".

[0172] In Figure 8 the left figure, the case where the duty ratio RD of the third PWM signal SG3 decreases from the average duty ratio RDA to "0%" in three stages is described, but the present disclosure is not limited thereto. For example, the duty ratio RD of the third PWM signal SG3 may decrease from the average duty ratio RDA to "0%" in two stages. Also, the duty ratio RD of the third PWM signal SG3 may decrease from the average duty ratio RDA to "0%" in four or more stages.

[0173] In Figure 8 the left figure, the case where the decrease amount of the duty ratio RD in each stage is substantially constant (about 17%) is described, but the present disclosure is not limited thereto. The increase amount of the duty ratio RD in each stage may, for example, gradually decrease.

[0174] As Figure 8As shown in the left figure, when the duty ratio RD of the third PWM signal SG3 decreases from the average duty ratio RDA to "0%" in three stages, the duty ratio RD can also decrease as follows. For example, the duty ratio RD during the period when time T is from time TC to time TD is, for example, "25%". For example, during the period when time T is from time TD to time TE, the duty ratio RD is, for example, "10%". In this case, when time T is time TC, the duty ratio RD decreases from "50%" to "25%". Then, when time T is time TD, the duty ratio RD decreases from "25%" to "10%". Further, when time T is time TE, the duty ratio RD decreases from "10%" to "0%".

[0175] In Figure 8 In the central figure, the duty ratio RD of the third PWM signal SG3 gradually decreases, and the duty ratio RD of the third PWM signal SG3 decreases smoothly. Specifically, the duty ratio RD of the third PWM signal SG3 decreases linearly. Figure 8 The curve graph G22 shown in the central figure represents the change in the duty ratio RD of the third PWM signal SG3.

[0176] As shown in the curve graph G22, it decreases linearly in such a way that the duty ratio RD is the average duty ratio RDA when time T is time TC and the duty ratio RD is "0%" when time T is time TE.

[0177] In Figure 8 In the right figure, the duty ratio RD of the third PWM signal SG3 gradually decreases, and the duty ratio RD of the third PWM signal SG3 decreases smoothly. The duty ratio RD of the third PWM signal SG3 decreases in a smooth curve shape. Figure 8 The curve graph G23 shown in the right figure represents the change in the duty ratio RD of the third PWM signal SG3.

[0178] As shown in the curve graph G23, the curve corresponding to the curve graph G23 is a curve that bulges downward. The curve corresponding to the curve graph G23 is, for example, a quadratic curve. And the curve corresponding to the curve graph G23 is, for example, a logarithmic curve.

[0179] As shown in the curve graph G23, it decreases in a curve shape in such a way that the duty ratio RD is the average duty ratio RDA when time T is time TC and the duty ratio RD is "0%" when time T is time TE.

[0180] [1-4. Curved graphs showing effects]

[0181] Figure 9 The sound output from the piezoelectric element 33 will be described. Figure 9Two curves are shown. In each of the two curves, the horizontal axis is time T and the vertical axis is the amplitude A of the sound output by the piezoelectric element 33.

[0182] The first period P1 is the period during which the first PWM signal is output. The first period P1 is, for example, 4 seconds. The second period P2 immediately preceding the first period P1 is the period during which the second PWM signal SG2 is output. The second period P2 is, for example, 4 milliseconds. The third period P3 immediately following the first period P1 is the period during which the third PWM signal SG3 is output. The third period P3 is, for example, 4 milliseconds.

[0183] The upper curve G31 in the two curves represents the change in the amplitude A of the sound output by the piezoelectric element 33 when the PWM signal SG output by the control unit 31 consists only of the first PWM signal SG1.

[0184] The lower curve G32 in the two curves represents the change in the amplitude A of the sound output by the piezoelectric element 33 when the PWM signal SG output by the control unit 31 consists of the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3.

[0185] As shown in the curve G31, when the PWM signal SG output by the control unit 31 consists only of the first PWM signal SG1, the sound output by the piezoelectric element 33 includes noise NS in the second period P2. The noise NS is a pulsed signal. The amplitude A of the noise NS is of the same magnitude as the amplitude A of the speech signal.

[0186] In addition, as shown in the curve G31, when the PWM signal SG output by the control unit 31 consists only of the first PWM signal SG1, the sound output by the piezoelectric element 33 includes noise NE in the third period. The noise NE is a pulsed signal. The amplitude A of the noise NE is of the same magnitude as the amplitude A of the speech signal.

[0187] The noise NS and the noise NE are so-called popping noises.

[0188] As shown in the curve G32, when the PWM signal SG output by the control unit 31 consists of the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3, the sound output by the piezoelectric element 33 does not include the noise NS.

[0189] In this way, by outputting the second PWM signal SG2 in the second period P2, the generation of the noise NS can be effectively suppressed.

[0190] Further, as shown in the curve graph G32, when the PWM signal SG output by the control unit 31 is composed of the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3, the sound output by the piezoelectric element 33 does not include the noise NE.

[0191] In this way, by outputting the third PWM signal SG3 during the third period P3, the generation of the noise NE can be effectively suppressed.

[0192] [1-5. Processing of the control unit]

[0193] Next, with reference to Figure 10 the processing of the control unit 31 will be described. Figure 10 is a flowchart showing the processing of the control unit 31.

[0194] First, in step S101, the carrier generation unit 311 generates a carrier signal SGC with a constant duty ratio RD. The duty ratio RD of the carrier signal SGC is, for example, 50%.

[0195] Next, in step S103, the first signal generation unit 312 reads out one voice signal from the plurality of voice signals stored in the voice storage unit 316.

[0196] Next, in step S105, the first signal generation unit 312 generates the first PWM signal SG1 by modulating the duty ratio RD of the carrier signal SGC using the one voice signal read out in step S103.

[0197] Next, in step S107, the second signal generation unit 313 generates the second PWM signal SG2. The second PWM signal SG2 is, for example, a signal output immediately before the first PWM signal SG1. And, the second PWM signal SG2 is a signal with a duty ratio RD smaller than the average duty ratio RDA. The average duty ratio RDA is the average value of the duty ratio RD of the first PWM signal.

[0198] Next, in step S109, the third signal generation unit 314 generates the third PWM signal SG3. The third PWM signal SG3 is, for example, a signal output immediately after the first PWM signal. The third PWM signal SG3 is a signal with a duty ratio RD smaller than the average duty ratio RDA.

[0199] Next, in step S111, the signal output unit 315, for example, synthesizes the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3 to generate the PWM signal SG.

[0200] Next, in step S113, the signal output unit 315 outputs the PWM signal SG generated in step S111 to the amplifier 32. After that, the processing ends.

[0201] In addition, the amplifier 32 amplifies the PWM signal SG to generate a PWM signal SL. Further, the amplifier 32 outputs the generated PWM signal SL to the piezoelectric element 33. The piezoelectric element 33 outputs voice.

[0202] [1-6. Structure and Effect]

[0203] As described above, the sound output device 3 includes: a control unit 31 that outputs a PWM signal SG; an amplifier 32 that amplifies the PWM signal SG; and a piezoelectric element 33 that outputs sound based on the PWM signal SL output by the amplifier 32. The control unit 31 outputs at least one of a first PWM signal SG1, a second PWM signal SG2, and a third PWM signal SG3, where the first PWM signal SG1 is a PWM signal corresponding to the sound, the second PWM signal SG2 is output before the first PWM signal SG1 and has a duty ratio RD smaller than the average duty ratio RDA, which is the average value of the duty ratio RD of the first PWM signal SG1, and the third PWM signal SG3 is output after the first PWM signal SG1 and has a duty ratio RD smaller than the average duty ratio RDA.

[0204] Thus, by outputting the second PWM signal SG2, the noise NS generated before the first PWM signal SG1 can be suppressed. Also, by outputting the third PWM signal SG3, the noise NE generated after the first PWM signal SG1 can be suppressed. Therefore, sound with a quality comparable to that output from a speaker can be output with a simple structure.

[0205] In the sound output device 3, the duty ratio RD of the second PWM signal SG2 gradually increases.

[0206] Thus, by outputting the second PWM signal SG2, the noise NS generated before the first PWM signal SG1 can be effectively suppressed.

[0207] In the sound output device 3, the duty ratio RD of the second PWM signal SG2 increases stepwise.

[0208] Thus, by outputting the second PWM signal SG2, the noise NS generated before the first PWM signal SG1 can be effectively suppressed. Also, the second PWM signal SG2 can be generated by simple processing.

[0209] In the sound output device 3, the duty ratio RD of the second PWM signal SG2 increases smoothly.

[0210] Thus, by outputting the second PWM signal SG2, the noise NS generated before the first PWM signal SG1 can be effectively suppressed.

[0211] In the sound output device 3, the second PWM signal SG2 is output during a period above a preset first threshold TH1.

[0212] Thus, by setting the first threshold TH1 to an appropriate value to output the second PWM signal SG2, it is possible to effectively suppress the noise NS generated before the first PWM signal SG1.

[0213] In the sound output device 3, the duty ratio RD of the third PWM signal SG3 gradually decreases.

[0214] Thus, by outputting the third PWM signal SG3, it is possible to effectively suppress the noise NE generated after the first PWM signal SG1.

[0215] In the sound output device 3, the duty ratio RD of the third PWM signal SG3 decreases stepwise.

[0216] Thus, by outputting the third PWM signal SG3, it is possible to effectively suppress the noise NE generated after the first PWM signal SG1. Also, the third PWM signal SG3 can be generated by simple processing.

[0217] In the sound output device 3, the duty ratio RD of the third PWM signal SG3 decreases smoothly.

[0218] Thus, by outputting the third PWM signal SG3, it is possible to effectively suppress the noise NE generated after the first PWM signal SG1.

[0219] In the sound output device 3, the third PWM signal SG3 is output during a period above a preset second threshold TH2.

[0220] Thus, by setting the second threshold TH2 to an appropriate value to output the third PWM signal SG3, it is possible to effectively suppress the noise NE generated after the first PWM signal SG1.

[0221] In the sound output device 3, the PWM signal SG is output at a frequency higher than the frequency of the human audible range.

[0222] Thus, it is possible to effectively suppress the noise of the frequency in the human audible range generated due to the output of the PWM signal SG.

[0223] In the sound output device 3, the first PWM signal SG1 is generated by modulating the duty ratio RD of a carrier signal SGC with a constant duty ratio RD using a signal corresponding to the sound.

[0224] Thus, the first PWM signal SG1 can be generated with a simple structure.

[0225] In the sound output device 3, the sound includes at least one of voice and melody.

[0226] Thus, at least one of voice and melody can be output with good quality to the same extent as when output from a speaker.

[0227] In the sound output device 3, the amplifier 32 includes a transistor 321.

[0228] Thus, the amplifier 32 can be implemented with a simple structure.

[0229] In the sound output device 3, the piezoelectric element 33 includes a plurality of piezoelectric elements, and the plurality of piezoelectric elements are connected in parallel.

[0230] Thus, the volume of the sound output from the piezoelectric element 33 can be increased with a simple structure.

[0231] The cooker 1 includes: a control unit 31 that outputs a PWM signal SG; an amplifier 32 that amplifies the PWM signal SG; and a piezoelectric element 33 that outputs sound according to the PWM signal SL output from the amplifier 32. The control unit 31 outputs at least one of a first PWM signal SG1, a second PWM signal SG2, and a third PWM signal SG3. The first PWM signal SG1 is a PWM signal corresponding to the sound. The second PWM signal SG2 is output before the first PWM signal SG1 and has a duty ratio RD smaller than the average duty ratio RDA, which is the average value of the duty ratio RD of the first PWM signal SG1. The third PWM signal SG3 is output after the first PWM signal SG1 and has a duty ratio RD smaller than the average duty ratio RDA.

[0232] Thus, the cooker 1 exhibits the same effects as the above-described sound output device 3.

[0233] (Other Embodiments)

[0234] As described above, as an example disclosed in the present application, the above-described Embodiment 1 has been described. However, the technology in the present disclosure is not limited thereto, and can also be applied to embodiments with changes, replacements, additions, omissions, etc. In addition, the constituent elements described in the above Embodiment 1 can be combined to form a new embodiment. Therefore, other embodiments are exemplified below.

[0235] In the above-described Embodiment 1, as the "electronic device" of the present disclosure, the cooker 1 that performs cooking is exemplified. The "electronic device" of the present disclosure is not limited to the cooker 1. The "electronic device" of the present disclosure may also be a so-called home appliance device (household electronic device) such as a home bread maker, a rice cooker, a coffee maker, a microwave oven, a refrigerator, a washing machine, etc. In addition, the "electronic device" of the present disclosure may also be an industrial electronic device.

[0236] In the above-described Embodiment 1, the case where the sound output device 3 outputs voice has been mainly described, but the present disclosure is not limited thereto. It is sufficient that the sound output device 3 outputs sound. For example, the sound output device 3 may also output a melody.

[0237] In the above-described Embodiment 1, the case where the control unit 31 outputs the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3 has been described, but the present disclosure is not limited thereto. The control unit 31 only needs to output at least one of the first PWM signal SG1, the second PWM signal SG2, and the third PWM signal SG3. For example, the control unit 31 may also output the first PWM signal SG1 and the second PWM signal SG2. Also, for example, the control unit 31 may also output the first PWM signal SG1 and the third PWM signal SG3.

[0238] In the above-described Embodiment 1, the case where the duty ratio RD of the second PWM signal SG2 is gradually increased has been described, but the present disclosure is not limited thereto. For example, the amplitude of the second PWM signal SG2 may also be gradually increased.

[0239] In addition, in the above-described Embodiment 1, the case where the duty ratio RD of the third PWM signal SG3 is gradually decreased has been described, but the present disclosure is not limited thereto. For example, the amplitude of the second PWM signal SG2 may also be gradually decreased.

[0240] In the above-described Embodiment 1, as Figure 7 and Figure 8 shown, the case where the duty ratio RD of the second PWM signal SG2 changes has been described, but the present disclosure is not limited to Figure 7 and Figure 8 the curve graph shapes shown. The duty ratio RD of the second PWM signal SG2 may also be, for example, a curve graph shape obtained by combining a stepped change and a smooth change.

[0241] For example, during an initial specified period, the duty ratio RD of the second PWM signal SG2 may change in a stepped manner, and during the period after the specified period, the duty ratio RD of the second PWM signal SG2 may change smoothly. Also, for example, during an initial specified period, the duty ratio RD of the second PWM signal SG2 may change smoothly, and during the period after the specified period, the duty ratio RD of the second PWM signal SG2 may change in a stepped manner.

[0242] Moreover, when the duty ratio RD of the second PWM signal SG2 changes in a stepped manner, the period during which the duty ratio RD is constant may also be changed. For example, in Figure 7 the left figure, the period from time "0" to time TB may be longer or shorter than the period from time TB to time TA. Also, for example, in Figure 8 the left figure, the period from time TC to time TD may be longer or shorter than the period from time TD to time TE.

[0243] In the above-described Embodiment 1, with reference to Figure 7 , the case where the duty ratio RD of the second PWM signal SG2 increases linearly and the case where the duty ratio RD of the second PWM signal SG2 increases in a downwardly convex curve are described, but the present disclosure is not limited thereto. As long as the duty ratio RD of the second PWM signal SG2 increases smoothly. In other words, in the curve representing the change in the duty ratio RD of the second PWM signal SG2, for example, the curvature may change continuously.

[0244] In the above-described Embodiment 1, with reference to Figure 8 , the case where the duty ratio RD of the third PWM signal SG3 decreases linearly and the case where the duty ratio RD of the third PWM signal SG3 decreases in a downwardly convex curve are described, but the present disclosure is not limited thereto. As long as the duty ratio RD of the third PWM signal SG3 decreases smoothly. In other words, in the curve representing the change in the duty ratio RD of the third PWM signal SG3, for example, the curvature may change continuously.

[0245] In the above-described Embodiment 1, the case where the piezoelectric element 33 is composed of the first piezoelectric element 331 and the second piezoelectric element 332 is described, but the present disclosure is not limited thereto. The piezoelectric element 33 may also be composed of a single piezoelectric element. Also, the piezoelectric element 33 may be composed of three or more piezoelectric elements.

[0246] Generally, the sound pressure of a piezoelectric buzzer becomes higher at 2 kHz to 4 kHz, and lower in other frequency bands. Therefore, by performing "pre-emphasis processing" on the voice data stored in the voice storage unit 316 corresponding to the frequency characteristics of the piezoelectric buzzer, the sound can be reproduced with higher sound quality. "Pre-emphasis processing" refers to the process of pre-increasing the sound pressure of the voice data in the frequency band where the estimated sound pressure is expected to decrease due to the piezoelectric buzzer.

[0247] By attaching voice data equivalent to gradually increasing the duty ratio RD before the voice data stored in the voice storage unit 316, the processing of the second signal generation unit 313 can be reduced. And by attaching voice data equivalent to gradually decreasing the duty ratio RD after the voice data stored in the voice storage unit 316, the processing of the third signal generation unit 314 can be reduced.

[0248] Figure 5 The structure of the sound output device 3 shown is an example, and the specific installation method is not particularly limited. That is, it is not necessarily required to install hardware corresponding to each part separately, and it can also be configured to implement the functions of each part by a single processor executing a program. In addition, in the above-described embodiment, a part of the functions implemented by software can be set as hardware, or a part of the functions implemented by hardware can be implemented by software.

[0249] Figure 10 The step units of the processes shown are units divided according to the main processing contents for easy understanding of the processes, and the processes are not limited by the division method and name of the processing units. It can also be divided into more step units according to the processing contents. In addition, it can also be divided in such a way that one step unit includes more processes. And the order of these steps can also be appropriately changed within the scope that does not hinder the gist of the present disclosure.

[0250] In addition, the above-described embodiment is used to illustrate the technology in the present disclosure. Therefore, various changes, substitutions, additions, omissions, etc. can be made within the scope of the claims or their equivalents.

[0251] (Supplementary Note)

[0252] Based on the description of the above embodiment, the following technology is disclosed.

[0253] (Technology 1) A sound output device includes: a control unit that outputs a PWM signal; an amplifier that amplifies the PWM signal; and a piezoelectric element that outputs sound based on the PWM signal output by the amplifier. The control unit outputs at least one of a first PWM signal, a second PWM signal, and a third PWM signal. The first PWM signal is a PWM signal corresponding to the sound. The second PWM signal is output before the first PWM signal and has a duty ratio less than the average duty ratio, which is the approximate average of the duty ratios of the first PWM signal. The third PWM signal is output after the first PWM signal and has a duty ratio less than the average duty ratio.

[0254] According to this structure, by outputting the second PWM signal, noise generated before the first PWM signal can be suppressed. By outputting the third PWM signal, noise generated after the first PWM signal can be suppressed. Therefore, sound of good quality comparable to the sound output from the speaker can be output with a simple structure.

[0255] (Technology 2) The sound output device according to Technology 1, wherein the duty ratio of the second PWM signal gradually increases.

[0256] According to this structure, by outputting the second PWM signal, noise generated before the first PWM signal can be effectively suppressed.

[0257] (Technology 3) The sound output device according to Technology 1 or Technology 2, wherein the duty ratio of the second PWM signal increases stepwise.

[0258] According to this structure, by outputting the second PWM signal, noise generated before the first PWM signal can be effectively suppressed. Also, the second PWM signal can be generated by simple processing.

[0259] (Technology 4) The sound output device according to Technology 1 or Technology 2, wherein the duty ratio of the second PWM signal increases smoothly.

[0260] According to this structure, by outputting the second PWM signal, noise generated before the first PWM signal can be effectively suppressed.

[0261] (Technology 5) The sound output device according to any one of Technologies 1 to 4, wherein the second PWM signal is output during a period above a preset first threshold.

[0262] According to this structure, by setting the first threshold to an appropriate value and outputting the second PWM signal, noise generated before the first PWM signal can be effectively suppressed.

[0263] (Technique 6) The sound output device according to any one of Techniques 1 to 5, wherein the duty ratio of the third PWM signal gradually decreases.

[0264] According to this structure, by outputting the third PWM signal, it is possible to effectively suppress the noise generated after the first PWM signal.

[0265] (Technique 7) The sound output device according to any one of Techniques 1 to 6, wherein the duty ratio of the third PWM signal decreases stepwise.

[0266] According to this structure, by outputting the third PWM signal, it is possible to effectively suppress the noise generated after the first PWM signal. Moreover, the third PWM signal can be generated by simple processing.

[0267] (Technique 8) The sound output device according to any one of Techniques 1 to 6, wherein the duty ratio of the third PWM signal decreases smoothly.

[0268] According to this structure, by outputting the third PWM signal, it is possible to effectively suppress the noise generated after the first PWM signal.

[0269] (Technique 9) The sound output device according to any one of Techniques 1 to 8, wherein the third PWM signal is output during a period above a preset second threshold.

[0270] According to this structure, by setting the second threshold to an appropriate value and outputting the third PWM signal, it is possible to effectively suppress the noise generated after the first PWM signal.

[0271] (Technique 10) The sound output device according to any one of Techniques 1 to 9, wherein the PWM signal is output at a frequency higher than the frequency of the human audible range.

[0272] According to this structure, it is possible to effectively suppress the noise of the frequency in the human audible range generated due to the output of the PWM signal.

[0273] (Technique 11) The sound output device according to any one of Techniques 1 to 10, wherein the first PWM signal is generated by modulating the duty ratio of a carrier signal with a constant duty ratio using a signal corresponding to the sound.

[0274] According to this structure, the first PWM signal can be generated with a simple structure.

[0275] (Technique 12) The sound output device according to any one of Techniques 1 to 11, wherein the sound includes at least one of speech and melody.

[0276] According to this structure, at least one of voice and melody can be output with good quality to the same extent as when output from a speaker.

[0277] (Technology 13) The sound output device according to any one of Technologies 1 to 12, wherein the amplifier has a semiconductor amplification element including a transistor.

[0278] According to this structure, an amplifier can be realized with a simple structure.

[0279] (Technology 14) The sound output device according to any one of Technologies 1 to 13, wherein the piezoelectric element includes a plurality of piezoelectric elements, and the plurality of piezoelectric elements are connected in parallel.

[0280] According to this structure, the volume of the sound output from the piezoelectric element can be increased with a simple structure.

[0281] (Technology 15) An electronic device including: a control unit that outputs a PWM signal; an amplifier that amplifies the PWM signal; and a piezoelectric element that outputs sound according to the PWM signal output from the amplifier, wherein the control unit outputs at least one of a first PWM signal, a second PWM signal, and a third PWM signal, the first PWM signal being a PWM signal corresponding to the sound, the second PWM signal being output before the first PWM signal and having a duty ratio smaller than the average duty ratio, which is the approximate average of the duty ratios of the first PWM signal, and the third PWM signal being output after the first PWM signal and having a duty ratio smaller than the average duty ratio.

[0282] According to this structure, the same effect as the sound output device described in Technology 1 is achieved.

[0283] Industrial applicability

[0284] As described above, the sound output device and the electronic device of the present invention can be used for the purpose of outputting sound with good quality to the same extent as the sound output from a speaker with a simple structure.

Claims

1. A sound output device, comprising: A control unit that outputs a PWM signal; an amplifier, which amplifies the PWM signal; and a piezoelectric element that outputs sound according to the PWM signal output by the amplifier, The control unit outputs at least one of a first PWM signal, a second PWM signal, and a third PWM signal, wherein: The first PWM signal is a PWM signal corresponding to the sound, the second PWM signal is output before the first PWM signal and has a duty cycle that is smaller than the approximate average value of the duty cycle of the first PWM signal, i.e., the average duty cycle, and the third PWM signal is output after the first PWM signal and has a duty cycle that is smaller than the average duty cycle.

2. The sound output device according to claim 1, wherein: The duty cycle of the second PWM signal gradually increases.

3. The sound output device according to claim 1, wherein: The duty cycle of the second PWM signal increases in stages.

4. The sound output device according to claim 1, wherein: The duty cycle of the second PWM signal increases smoothly.

5. The sound output device according to claim 1, wherein: The second PWM signal is output during a period equal to or greater than a preset first threshold.

6. The sound output device according to claim 1, wherein: The duty cycle of the third PWM signal gradually decreases.

7. The sound output device according to claim 1, wherein: The duty cycle of the third PWM signal decreases in stages.

8. The sound output device according to claim 1, wherein: The duty ratio of the third PWM signal decreases smoothly.

9. The sound output device according to claim 1, wherein: The third PWM signal is output during a period equal to or greater than a preset second threshold.

10. The sound output device according to any one of claims 1 to 9, wherein: The PWM signal is output at a frequency higher than a frequency in the human audible range.

11. The sound output device according to any one of claims 1 to 9, wherein: The first PWM signal is generated by modulating the duty ratio of a carrier signal having a constant duty ratio with a signal corresponding to the sound.

12. The sound output device according to any one of claims 1 to 9, wherein: The sound includes at least one of voice and melody.

13. The sound output device according to any one of claims 1 to 9, wherein: The amplifier has a semiconductor amplifying element including a transistor.

14. The sound output device according to any one of claims 1 to 9, wherein: The piezoelectric element includes a plurality of piezoelectric elements. The plurality of piezoelectric elements are connected in parallel.

15. An electronic device comprising: A control unit that outputs a PWM signal; an amplifier, which amplifies the PWM signal; and a piezoelectric element that outputs sound according to the PWM signal output by the amplifier, The control unit outputs at least one of a first PWM signal, a second PWM signal, and a third PWM signal, wherein: The first PWM signal is a PWM signal corresponding to the sound, the second PWM signal is output before the first PWM signal and has a duty cycle that is smaller than the approximate average value of the duty cycle of the first PWM signal, i.e., the average duty cycle, and the third PWM signal is output after the first PWM signal and has a duty cycle that is smaller than the average duty cycle.

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