JPS6321198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a sounding device for an electronic timepiece having additional functions such as an alarm, a timer, a pacemaker, and a gas alarm device. The present invention reduces the number of parts built into an electronic timepiece, and also enables the sounding device to generate sound effects sufficient for its intended use.

Conventionally, sounding devices based on three different basic principles have been proposed as sounding devices built into electronic watches. The first is one that applies the piezoelectric effect, and is called a piezoelectric sounding body, which uses mechanical distortion that occurs when a voltage is applied to a flat or rod-shaped piezoelectric element as a sound source. The second type uses a moving coil placed in a magnetic field created by a permanent magnet as a sound source, and is called a moving coil type sounding body. The third type uses as a sound source a movable permanent magnet or a movable ferromagnetic body placed in a magnetic field created by an electromagnet or an electromagnet biased with a permanent magnet, and is called a movable magnet type sounding body. These three types of sounding devices each have their own characteristics and are built into electronic watches and put into practical use.However, considering the case where the sounding device is housed in a very small space like a wristwatch, the piezoelectric type is the first type. The sounding body has extremely excellent characteristics. In other words, it has advantages such as low power consumption, the thinness of the sounding body so that it can be easily placed inside a watch, and the watch case can be constructed to be waterproof at low cost. Low power consumption is a particularly important advantage for wristwatches that rely on limited battery energy.

However, since the piezoelectric sounding body is a voltage-driven type, it is necessary to apply a sufficiently high driving voltage to obtain a sufficiently large acoustic effect. Therefore, the watch has the disadvantage that it must include a built-in voltage boosting means for boosting the voltage of the battery. Conventionally, when driving a piezoelectric sounding body used in electronic watches, a method of using a coil and a switching transistor that controls the current flowing through the coil as a voltage boosting means has often been adopted. This voltage boosting means uses a switching transistor to abruptly cut off the current flowing through the coil, thereby obtaining a high differential voltage generated across the coil. It is possible to generate a voltage of This requires a large amount of man-hours to manufacture a watch, as it requires processing the coil body, fixing the coil body, and even installing transistors, which is a major factor pushing up the selling price of the watch. In order to eliminate such drawbacks, the present invention realizes a highly efficient boosting means without using coils or bipolar transistors. A detailed explanation of the present invention will be given below.

FIG. 1 is a sectional view of a piezoelectric sounding body used in the sounding device of the present invention, and has a known structure. 1
is a metal diaphragm having a thickness of about 100 μm, and a piezoelectric element 2 is uniformly bonded to one side of the diaphragm 1 over the entire surface with a conductive adhesive. Metal electrode plates 2a and 2b are provided on both sides of the piezoelectric element 2, and the electrode 2a is attached to the diaphragm 1 by the adhesive.
electrically connected to. When a voltage is applied between the diaphragm 1 and the metal electrode 2b of the piezoelectric sounding body having such a structure, distortion occurs in the piezoelectric element 2, but this distortion is transmitted to the diaphragm 1, and the diaphragm 1 also becomes distorted. will occur. When the voltage is removed, the piezoelectric element 2 and the diaphragm 1
The distortion disappears and the state returns to its natural state. By turning on and off the voltage applied between the diaphragm 1 and the electrode 2b at a constant frequency, the sounding body made up of the diaphragm 1 and the piezoelectric element 2 vibrates at a constant rate and functions as a sounding body. The material of the diaphragm is not limited to a metal plate. For example, a piezoelectric sounding body can be realized using a glass plate or a plastic plate with conductive processing applied to the adhesive surface of the piezoelectric element.

FIG. 2 shows an embodiment of a drive circuit for a sounding device for an electronic watch according to the present invention. It is something to tighten. The configuration and operation will be described below with reference to the drawings. In the figure, V _DD is the + of the battery built into the watch.
This is the potential of the side electrode, and for the sake of explanation, it is assumed that it is a reference potential of 0 volts. V _SSL is the potential of the negative electrode of the battery, which is approximately -1.5 volts when the battery is a silver oxide battery. V _SSH is twice the potential of V _SSL , which is about -3 volts when the battery is a silver oxide battery. Here, the potential V _SSH is for an electronic watch with a liquid crystal display.
The potential required for driving the liquid crystal display device is generated from a battery by another booster circuit (not shown), but the voltage conversion capability of this booster circuit is generally small, and it directly drives the piezoelectric sounding body. It is not possible to extract enough power. Referring to the drawing again, 3, 4 and 5 are the P channel.
MOS type transistor, 6, 7, 8 and 9
is an N-channel MOS type transistor.
All these transistors are provided on a C-MOS integrated circuit that constitutes the timekeeping circuit of the watch. That is, the three P-channel transistors 3, 4, and 5 are fabricated on an N-type silicon substrate (hereinafter referred to as the N-substrate) of the integrated circuit, and their drains (+ side electrodes) are all connected to the N-type substrate. It is also connected to the reference potential _VDD . The substrate of the N-channel transistor 6 is a first transistor provided on the N-channel transistor 6.
The first P-type region is connected to one side potential V _SSL of the power supply battery, and is also connected to the drain (-side electrode) of the N-channel transistor 6 to the same potential. The source (-side electrode) of the P-channel transistor 3 and the source (+-side electrode) of the N-channel transistor 6 are coupled, and these two transistors constitute a first C-MOS inverter circuit. The substrate of the N-channel transistor 7 is a second P transistor provided on the N-channel transistor 7.
type region, and the second P type region is a -
A potential V _SSH that is twice the side potential is applied. The drain (-side electrode) of the N-channel transistor 7 is also connected to the same potential V _SSH . The source (-side electrode) of the P-channel transistor 4 and the source (+-side electrode) of the N-channel transistor 7 are coupled, and the two transistors are connected to the second C-
It constitutes a MOS inverter circuit. The substrates of N-channel transistors 8 and 9 are third P-type regions provided on the N-substrate. The two N
The drains of channel transistors 8 and 9 are coupled to a third P-type region, but the third P-type region is not directly connected to a power source and has a floating potential. The source (+ side electrode) of the N-channel transistor 8 is connected to the negative side potential V _SSL of the battery. On the other hand, the source (+ side electrode) of the N-channel transistor 9 is coupled to the source (- side electrode) of the P-channel transistor 5, forming a third C-MOS inverter. transistors 3 and 6
The output terminals of the first inverter CS ₁ and the third
A capacitor 10 provided outside the integrated circuit is connected between terminals CS ₂ of the P-type region of , and a capacitor 10 provided outside the integrated circuit is connected between the output terminal BZ of the third inverter and the reference potential V _DD as shown in FIG. A structured piezoelectric sounding body 11 is also connected outside the integrated circuit. The input signals F of the three inverters are rectangular wave signals having a frequency that defines the frequency of the sound generated by the sounding body 11, and whose peak value is determined by the reference potential V _DD and the potential V _SSH . The gate input of the N-channel transistor 8 is a signal given by the output of the second inverter made up of transistors 4 and 7, and is a signal obtained by inverting the potential level of the signal F. In such a circuit configuration, the sounding body 11 has an extremely high impedance in terms of direct current and can be regarded as a capacitor, but the capacitance for a wristwatch is several tens of nanometers. In comparison, the capacitance of the capacitor 10 needs to be sufficiently large, but for wristwatches, it is sufficient to have a capacitance of several hundred nanofarads.

Next, the operation of the embodiment shown in FIG. 2 will be explained.
When the potential of signal F is low level, that is, the potential V _SSH
When equal to, P channel transistors 3, 4
and 5 are all in a conductive state. As a result, the output signal of the second inverter goes high and N-channel transistor 8 also becomes conductive, but the other N-channel transistors 6, 7 and 9 are non-conductive. At this time, the potential of the output BZ becomes equal to the reference potential _VDD due to the conduction of the transistor 5, and no voltage is applied to the sounding element 11. On the other hand, since transistors 3 and 8 are in a conductive state, these 2
The capacitor 10 is connected in parallel with the battery through two transistors. That is, one terminal CS ₁ is connected to the reference potential V _DD and the other terminal CS ₂ is connected to the negative potential V _SSL , and the battery is charged to a voltage equal to that of the power supply battery.

Next, the potential of signal F is at a high level, that is, the reference potential
At a level equal to V _DD , P channel transistors 3, 4 and 5 are all non-conductive, while N channel transistors 6, 7 and 9 are all conductive. As a result, the output signal F of the second inverter becomes low level, and the N-channel transistor 8 becomes non-conductive. The conduction of transistor 6 connects terminal CS ₁ to potential V _SSL (capacitor 1
0 and the battery are connected in series), the potential of the other terminal _CS2 of the capacitor 10 is lower than the potential V _SSL by the battery voltage. In other words, the approximate potential is the potential
V equals _SSH . At this time, since the N-channel transistor 9 is in a conductive state, the potential of the terminal CS ₂ is outputted to the output terminal BZ, and a voltage approximately twice the battery voltage is applied to the sounding element 11. At this time, the sounding body 11 is charged with electric charge, but the signal F
When the voltage returns to a low level again, discharge occurs through a short circuit caused by conduction of the P-channel transistor 5, and the voltage applied to the sounding element 11 returns to zero. By having the signal F take binary logic levels of low level and high level at a constant frequency, a DC rectangular wave voltage with a peak value equal to twice the power supply battery voltage is applied to the piezoelectric sounding body 11, and the piezoelectric sounding body 11 at the frequency is This produces distortion, and this distortion produces acoustic effects.

FIG. 3 shows that in the embodiment of the sounding body drive circuit shown in FIG. 2, transistors 4 and 7 are not used, and N
The channel transistor 8 is replaced with a diode 12, and this is another embodiment of the sounding body drive circuit that realizes the sounding device of the present invention.
In the case of this embodiment, when the signal F is at a low level,
The capacitor 10 has a P channel transistor 3
The battery voltage is charged via the diode 12. Also, when signal F is at high level, terminal CS ₂
The potential of is approximately twice the battery voltage, that is, the potential V _SSH
However, at this time, a reverse voltage is applied to the diode 12, and the current is cut off. In this way, the diode 12 can perform a switching operation similar to that of an N-channel transistor whose gate voltage is controlled. Also, the diode 12
The second P region explained in the figure is an anode, and the P
The N-type semiconductor provided on the region is made as a cathode. The sounding body driving circuit shown in FIG. 3 has fewer elements and has a simpler structure than the embodiment shown in FIG.
Although it is accompanied by power loss due to the forward voltage drop of the diode 12, it can be used satisfactorily for practical purposes.

In the two embodiments described above, the acoustic frequency control signal F has a peak value equal to twice the battery voltage. Generally, in the case of a liquid crystal display type electronic wristwatch using a silver oxide battery as a power source, it is necessary to make the liquid crystal display clear, so it is often equipped with a booster circuit that doubles the battery voltage. In such a case, it is extremely easy to set the signal F to a peak value twice the battery voltage. FIG. 4 is a block diagram showing the structure of a liquid crystal display type electronic wristwatch in which the sound generating device of the present invention is incorporated. In the drawings, arrows indicated by broken lines indicate the flow of signals, and arrows indicated by solid lines indicate the supply of power.
The battery 13 is generally a silver oxide battery, and the power from the battery 13 is transmitted to a low voltage circuit 14 including an oscillation circuit and a frequency dividing circuit, and from the low voltage circuit 14 to a high voltage circuit 16 that constitutes a timekeeping circuit. Level shift circuit 15 for adjusting the signal amplitude of the signal
and the piezoelectric sounding body 11 shown in FIG. 2 or 3.
and a sounding device 17 of the present invention including a drive circuit thereof;
The voltage is supplied to the booster circuit 18. The boost circuit 18 operates upon receiving a control signal from the low voltage circuit 14, and
The voltage supplied from 3 is converted to approximately twice the voltage, and power is supplied to the level shift circuit 15, the high voltage circuit 16, and the sound generating device 17. Pronunciation device 1
The main power supplied to 7 is directly from the battery 13, which provides the potential shown as potential V _SSL in the embodiments of FIG. 2 or 3. The power from the booster circuit 18 supplied to the sound generating device 17 provides the potential shown as the potential V _SSH in the embodiment of FIG. 2, and is an auxiliary power supply. A control signal having an amplitude approximately equal to twice the voltage of the battery 13 is transmitted from the high voltage circuit 16 to the sound generating device 17 . This control signal means the signal F in the embodiment of FIG. 2 or 3, and defines the sounding frequency of the sounding device 17 as described above. The liquid crystal display device 19 is not directly supplied with power from the battery 13 or the booster circuit 18, but is indirectly supplied with power via the liquid crystal display device drive circuit included in the high voltage circuit 16. .

The detailed explanation of the sounding device for an electronic timepiece according to the present invention has been given above.According to the present invention, when driving a piezoelectric type sounding body which has a simple structure and is relatively inexpensive, it can be It becomes possible to obtain an alternating current voltage having a peak value twice that of the power supply voltage without using a step-up coil which is difficult to store in a watch and is expensive. In addition, a pair of sounding element drive circuits as shown in Fig. 2 or 3 are provided, and each output terminal BZ
By connecting one piezoelectric sounding body between them and causing a push-pull operation, it is also possible to apply an alternating current with a peak value approximately equal to four times the battery voltage to the piezoelectric sounding body. For this reason, an electronic timepiece with a sounding device, which has conventionally been difficult to reduce in size and thickness, can be realized at a low cost. Furthermore, since there is no power loss due to coil resistance or transistor collector loss, power efficiency is extremely high. Further, in the driving method in which the back electromotive force of the coil is directly applied to the piezoelectric sounding element, the applied voltage is spike-like, so there are many harmonic components. For this reason, harmonics appear prominently in the generated sound, resulting in an unpleasant tone that is difficult to hear. However, in the drive method of the present invention, the drive voltage waveform is a charge/discharge waveform that is close to a rectangular wave, so harmonic components are You can get beautiful tones that are just to the point.

[Brief explanation of drawings]

Figure 1 is a sectional view of a piezoelectric sounding body used in the present invention, Figures 2 and 3 are circuit diagrams showing each embodiment of the drive circuit of the present invention, and Figure 4 is a block diagram of an electronic timepiece. It is. 1... Vibration plate, 2... Piezoelectric element, 3-5...P
Channel MOS transistor, 6 to 9...N channel MOS transistor, 10...Capacitor, 11...Piezoelectric sounding body, 12...Diode, 13...Battery.

Claims (1)

[Scope of Claims] 1. A first control signal which is conductive only in one logic level state of a rectangular wave control signal obtained from a timekeeping circuit of an electronic watch, which has a frequency equal to the sound generation frequency and whose peak value takes a binary logic level. Seed switching means 3,
5, 8 or 12, a second type switching means 6, 9 which conducts only at the other logic level, a battery serving as a power source, a capacitor, and a piezoelectric type sounding device having one terminal connected to one pole of the battery. and the first type switching means is between one pole of the battery and one pole of the capacitor.
(3), between one pole of the battery and the other terminal of the piezoelectric sounding body (5), and between the other pole of the battery and the other pole of the capacitor ( 8 or 12), which are connected between their respective terminals, and the second type switching means is between the other pole of the battery and one pole of the capacitor (6) and the capacitor. between the other pole of the piezoelectric sounding body and the other terminal of the piezoelectric sounding body
(9), each terminal of the capacitor and each pole of the battery are connected to each other during the period when the control signal is at one logic level, depending on the circuit configuration connected between the respective corresponding poles or terminals; The capacitor is electrically connected and the capacitor is charged, and each terminal of the piezoelectric sounding body is short-circuited to discharge the electric charge stored in the piezoelectric sounding body, and the control signal takes the logic level of the other one. During this period, the capacitor and the battery are connected in series between the terminals of the piezoelectric sounding body, and the sounding body is charged with a voltage substantially close to the sum of the charging voltage of the capacitor and the voltage of the battery. Then, the electric charge of the capacitor is partially discharged, and by repeating the above process, the terminal voltage of the piezoelectric vibrating body has an amplitude around the control signal and approximately twice the voltage of the battery. A sounding device for an electronic clock, which is characterized in that it changes with . 2 The first type and second type switching means are P-channel or N-channel switching devices provided simultaneously with the timekeeping circuit on the integrated circuit constituting the timepiece circuit.
The sounding device for an electronic timepiece according to claim 1, characterized in that the sounding device is any one of MOS transistors. 3. Pronunciation of the electronic timepiece according to claim 1, characterized in that one of the first type switching means for connecting the other pole of the battery and the other pole of the capacitor is a diode 12. Device.