GB1597692A

GB1597692A - Buzzer driver circuit for electronic apparatus

Info

Publication number: GB1597692A
Application number: GB198078A
Authority: GB
Original assignee: Citizen Watch Co Ltd
Current assignee: Citizen Watch Co Ltd
Priority date: 1977-01-19
Filing date: 1978-01-18
Publication date: 1981-09-09
Also published as: HK32885A

Description

(54) BUZZER DRIVER CIRCUIT FOR ELECTRONIC APPARATUS (71) We, CITIZEN WATCH COMPANY LIMITED, a corporation organized under the laws of Japan, of No. 9-18, l-chome, Nishi- shinjuku, Shinjuku-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to buzzers for portable electronic apparatus e.g. an electronic timepiece.

In a conventional electronic timepiece equipped with a buzzer, it has been a common practice to have the buzzer composed of a piezo-electric vibrating element and a metallic vibrating plate secured to the vibrating element.

In this structure, the vibrating element has one electrode connected to the low level or the grounded side of a power source and another electrode applied with a clock signal of a high voltage boosted by a booster coil. The vibrating element is reponsive to the clock pulses and vibrates, causing the vibration of the vibrating plate by which an acoustic sound is generated.

The conventional buzzer mentioned above makes use of a large number of component parts and employs the booster coil which has a large size and low efficiency.

According to the present invention, there is provided a buzzer driver circuit for electronic apparatus having a power supply which provides an output voltage between respective points having a high level and a low level potential, comprising: piezo-electric vibrating means having a piezo-electric element and a vibrating plate secured thereto; a first transfer switch connected to one terminal of said vibrating means to alternately connect said one terminal to said high level and said low level potentials of said power supply in response to a first clock pulse; and a second transfer switch connected to another terminal of said vibrating means to alternately connect said another terminal to said low level and said high level potentials in response to a second clock pulse; whereby said vibrating means is driven by a voltage ligher than said output voltage to vibrate said vibrating plate to generate an accoustic sound.

In the accompanying drawings: Figure 1 is a schematic view of a preferred embodiment of a buzzer driver circuit according to the present invention; Figure 2 is a timing chart for clock pulses applied to the driver circuit shown in Figure 1; Figure 3 is a fragmentary cross sectional view of an electronic timepiece employing one example of a buzzer driven by the driver circuit shown in Figure 1; and Figure 4 is a fragmentary cross sectional view of an electronic timepiece employing another example of a buzzer driven by the driver circuit shown in Figure 1.

Referring now to Figure 1, there is shown a preferred embodiment of a buzzer driver circuit according to the present invention, the buzzer driver circuit being specifically suited for an electronic calculator or electronic timepiece. A buzzer comprises a piezo-electric vibrating means 10 composed of, for example, a piezoelectric vibrating element, a pair of electrodes formed on the piezo-electric element, and a vibrating plate secured to the piezo-electric element. The buzzer 10 is driven by a driver circuit D compound of first and second transfer switches 12 and 14, each comprising an inverter.

The first transfer switch 12 is connected to one terminal 10a of the vibrating means 10 to alternately connect the one terminal of the vibrating means 10 to the high level VDD and the low level Vss of a power supply in response to a first clock pulse 0. The second transfer switch 14 is connected to another terminal 10b of the vibrating means 10 to connect the other terminal of the vibrating means 10 to the low level Vss andthehighlevelVDD of the power supply in response to a second clock pulse 0 which is inverted in polarity with respect to the first clock pulse 0. Each of the first and second transfer switches 12 and 14 comprises a complementary pair of a P-channel metal oxide semiconductor transistors (MOSFET) and Nchannel MOSFET.The P-channel MOSFET has its source terminal connected to the high level VDD of the power supply, and the source terminal of the N-channel MOSFET is connected to the low level Vss of the power supply. The drain terminals of the P-channel MOSFET and the N-channel MOSFET are con nected to each other and connected to the vibrating means 10. The gate terminals of the P-channel MOSFET and the N-channel MOSFET are coupled to each other and arranged to receive a clock pulse. Indicated at 16 is a variable resistor connected to the vibrating means 10 in series to adjust the flow of electric current passing through the vibrating means 10 for thereby varying the magnitude of acoustic sound.

When, in operation, the first and second clock pulses 0 and 0 having the waveforms shown in Figure 2 are applied to inputs of the first and second transfer switches 12 and 14, the N-channel MOSFET of the first transfer switch 12 is turned on and the P-channel MOSFET of the first transfer switch 12 is turned off at the time instant A shown in Figure 2. At the same time, the P-channel MOSFET of the second transfer switch 14 is turned on and the N-channel MOSFET of the second transfer switch 14 is turned off at the time instant A shown in Figure 2. Under these conditions, the high level VDD of the power supply is connected to terminal 10b and the low level Vss of the power supply is connected to terminal 1 0a so that electric current flows in a direction as shown by the arrows iA.At the time instant B shown in Figure 2, the P-channel MOSFET of the first transfer switch 12 is turned on and the N-channel MOSFET of the first transfer switch 12 is turned off, while the P-channel MOSFET of the second transfer switch 14 is turned off and the N-channel MOSFET of the second transfer switch 14 is turned on. Under these conditions, the electric current flow through the vibrating means 10 is a direction as shown by arrows ib in Figure 1.

Accordingly, the voltage E which varies in polarity between VDD and VDD as shown in Figure 2 is applied across the vibrating means 10, which is consequently driven with a voltage substantially twice that of the output voltage of the power source. This makes it possible to omit a conventional booster coil.

Figure 3 shows a fragmentary cross sectional view of an electronic timepiece incorporating one example of the buzzer. In Figure 3, the electronic timepiece is shown as comprising a case body 20 carrying thereon an annular frame 22 by which a movement 24 is supported. A back cover 26 is screwed into the case body 20 and has a plurality of perforations 26a to admit the acoustic sound therethrough. Indicated at 28 is a metal vibrating plate held in place in a watertight sealing manner between a plastics pressure ring 30 and a packing member 32 and which is electrically insulated from the back cover 26. Secured to the bottom surface of the vibrating plate 28 is a barium titanate piezoelectric vibrating element 34 provided on both of its surfaces with electrodes. One of the electrodes of the vibrating element 34 is connected to the vibrating plate 28.A metallic coil spring 36 is disposed between the vibrating plate 28 and one terminal of the movement 24 to provide an electrical connection therebetween to deliver a clock pulse 0 to the terminal 10a shown in Figure 1. Likewise, a metallic coil spring 38 is interposed between the other electrode of the vibrating element 34 and the movement 24 to deliver a clock pulse 55 to the terminal lOb shown in Figure 1. The driver circuit D is incorporated in an integrated circuit chip of the movement 24 and applies the clock pulses 55 and 0 to the vibrating element 34, by which the vibrating element 34 is caused to vibrate.The vibration of the vibrating element 34 is transmitted to the vibrating plate 28, which is consequently caused to vibrate to generate an acoustic sound. This acoustic sound is transmitted through the perforations 26a of the back cover 26 to the outside. It will now be appreciated that the piezo-electric vibrating element 34 is applied with clock pulses delivered directly from the integrated circuit chip of the movement without the provision of a booster coil and its associated parts. Thus, the driver circuit of the present invention is simple in circuit arrangement and has a high operating efficiency.

Figure 4 shows a fragmentary cross sectional view of an electronic timepiece incorporating another example of the buzzer. Reference numeral 40 denotes a case body and 42 a back cover press-fitted to the case body 40. The back cover 42 has a plurality of perforations 42a through which an acoustic sound is transmitted to the outside. A piezo-electric vibrating element 47 is mounted on a vibrating plate 46 made of a metal or other suitable material. The vibrating plate 46 is provided at its outer periphery 46a as one unit with an elastic retaining member 48 serving as a sealing member which is made by insert-molding suitable material such as rubber. The retaining member 48 is compressed between the back cover 42 and the case body 40 to provide a water-tight sealing effect therebetween. Indicated at 50 is a battery.

Since the vibrating plate 46 is integral with the elastic retaining member 48, the vibrating element 46 is elastically supported by the case body 40 so that the effective area in which the vibrating plate 46 vibrates is relatively large whereby the acoustic efficieny is high. The unitary construction of the retaining member 48 and the vibrating plate 46 makes it easy to assemble the plate 46 to the case body 40.

While the present invention has been shown and described with reference to particular embodiments by way of example, it should be noted that various other changes or modifications may be made without departing from the scope of the present invention WHAT WE CLAIM IS: 1. A buzzer driver circuit for electronic apparatus having a power supply which provides an output voltage between respective points having a high level and a low level potential, comprising piezo-electric vibrating

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. nected to each other and connected to the vibrating means 10. The gate terminals of the P-channel MOSFET and the N-channel MOSFET are coupled to each other and arranged to receive a clock pulse. Indicated at 16 is a variable resistor connected to the vibrating means 10 in series to adjust the flow of electric current passing through the vibrating means 10 for thereby varying the magnitude of acoustic sound. When, in operation, the first and second clock pulses 0 and 0 having the waveforms shown in Figure 2 are applied to inputs of the first and second transfer switches 12 and 14, the N-channel MOSFET of the first transfer switch 12 is turned on and the P-channel MOSFET of the first transfer switch 12 is turned off at the time instant A shown in Figure 2. At the same time, the P-channel MOSFET of the second transfer switch 14 is turned on and the N-channel MOSFET of the second transfer switch 14 is turned off at the time instant A shown in Figure 2. Under these conditions, the high level VDD of the power supply is connected to terminal 10b and the low level Vss of the power supply is connected to terminal 1 0a so that electric current flows in a direction as shown by the arrows iA.At the time instant B shown in Figure 2, the P-channel MOSFET of the first transfer switch 12 is turned on and the N-channel MOSFET of the first transfer switch 12 is turned off, while the P-channel MOSFET of the second transfer switch 14 is turned off and the N-channel MOSFET of the second transfer switch 14 is turned on. Under these conditions, the electric current flow through the vibrating means 10 is a direction as shown by arrows ib in Figure 1. Accordingly, the voltage E which varies in polarity between VDD and VDD as shown in Figure 2 is applied across the vibrating means 10, which is consequently driven with a voltage substantially twice that of the output voltage of the power source. This makes it possible to omit a conventional booster coil. Figure 3 shows a fragmentary cross sectional view of an electronic timepiece incorporating one example of the buzzer. In Figure 3, the electronic timepiece is shown as comprising a case body 20 carrying thereon an annular frame 22 by which a movement 24 is supported. A back cover 26 is screwed into the case body 20 and has a plurality of perforations 26a to admit the acoustic sound therethrough. Indicated at 28 is a metal vibrating plate held in place in a watertight sealing manner between a plastics pressure ring 30 and a packing member 32 and which is electrically insulated from the back cover 26. Secured to the bottom surface of the vibrating plate 28 is a barium titanate piezoelectric vibrating element 34 provided on both of its surfaces with electrodes. One of the electrodes of the vibrating element 34 is connected to the vibrating plate 28.A metallic coil spring 36 is disposed between the vibrating plate 28 and one terminal of the movement 24 to provide an electrical connection therebetween to deliver a clock pulse 0 to the terminal 10a shown in Figure 1. Likewise, a metallic coil spring 38 is interposed between the other electrode of the vibrating element 34 and the movement 24 to deliver a clock pulse 55 to the terminal lOb shown in Figure 1. The driver circuit D is incorporated in an integrated circuit chip of the movement 24 and applies the clock pulses 55 and 0 to the vibrating element 34, by which the vibrating element 34 is caused to vibrate.The vibration of the vibrating element 34 is transmitted to the vibrating plate 28, which is consequently caused to vibrate to generate an acoustic sound. This acoustic sound is transmitted through the perforations 26a of the back cover 26 to the outside. It will now be appreciated that the piezo-electric vibrating element 34 is applied with clock pulses delivered directly from the integrated circuit chip of the movement without the provision of a booster coil and its associated parts. Thus, the driver circuit of the present invention is simple in circuit arrangement and has a high operating efficiency. Figure 4 shows a fragmentary cross sectional view of an electronic timepiece incorporating another example of the buzzer. Reference numeral 40 denotes a case body and 42 a back cover press-fitted to the case body 40. The back cover 42 has a plurality of perforations 42a through which an acoustic sound is transmitted to the outside. A piezo-electric vibrating element 47 is mounted on a vibrating plate 46 made of a metal or other suitable material. The vibrating plate 46 is provided at its outer periphery 46a as one unit with an elastic retaining member 48 serving as a sealing member which is made by insert-molding suitable material such as rubber. The retaining member 48 is compressed between the back cover 42 and the case body 40 to provide a water-tight sealing effect therebetween. Indicated at 50 is a battery. Since the vibrating plate 46 is integral with the elastic retaining member 48, the vibrating element 46 is elastically supported by the case body 40 so that the effective area in which the vibrating plate 46 vibrates is relatively large whereby the acoustic efficieny is high. The unitary construction of the retaining member 48 and the vibrating plate 46 makes it easy to assemble the plate 46 to the case body 40. While the present invention has been shown and described with reference to particular embodiments by way of example, it should be noted that various other changes or modifications may be made without departing from the scope of the present invention WHAT WE CLAIM IS:

1. A buzzer driver circuit for electronic apparatus having a power supply which provides an output voltage between respective points having a high level and a low level potential, comprising piezo-electric vibrating

means having a piezo-electric element and a vibrating plate secured thereto; a first transfer switch connected to one terminal of said vibrating means to alternately connect said one terminal to said high level and said low level potentials of said power supply in response to a first clock pulse; and a second transfer switch connected to another terminal of said vibrating means to alternately connect said another terminal to said low level and said high level potentials in response to a second clock pulse, whereby said vibrating means is driven by a voltage higher than said output voltage to vibrate said vibrating plate to generate an acoustic sound.

2. A buzzer driver circuit according to Claim I, further comprising resistor means connected to one of said terminals of said vibrating means.

3. A buzzer driver circuit according to Claim 2, in which said resistor means comprises a variable resistor.

4. A buzzer driver circuit according to any of Claims 1 to 3, in which said second clock pulse is reversed in polarity with respect to said first clock pulse.

5. A buzzer driver circuit according to any of Claims 1 to 3, in which each of said first and second transfer switches comprises an inverter.

6. A buzzer driver circuit according to Claim 5, in which each said inverter comprises a complementary pair of a P-channel MOSFET and an N-channel MOSFET.

7. A buzzer driver circuit for portable electronic apparatus substantially as hereinbefore described with reference to the accompanying drawings.

8. An electronic timepiece comprising a buzzer driver circuit according to any of Claims 1 to 7, a case body, a back cover secured to the case body, a frame supported by said case body, a movement carried by said frame, an insulating pressure ring disposed in said back cover, a sealing member compressed between said frame and said back cover to hold said vibrating plate, first spring means disposed between said vibrating plate and said movement to provide a first electrical connection therebetween, and a second spring means disposed between said vibrating element and said movement to provide a second electrical connection therebetween.

9. An electronic timepiece comprising a buzzer driver circuit according to any of Claims 1 to 7, a case body, a back cover secured to the case body, and an elastic retaining member provided on the outer periphery of said vibrating plate and compressed between said case body and said back cover to elastically support said vibrating plate.

10. An electronic timepiece according to Claim 9, in which said elastic retaining member is formed by insert-molding a rubber member onto the vibrating plate.