JPH0370238B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit that drives a piezoelectric buzzer without a coil and is suitable for use in small electronic devices such as electronic watches, clocks, and pocket calculators.

Conventionally, the drive circuit for a so-called piezoelectric buzzer, in which a thin plate of piezoelectric ceramic is bonded to a diaphragm, has the electrodes on each side of the piezoelectric element parallel to both ends of the iron-core coil.
This was connected in series with the emitter and collector of a bipolar transistor and connected to both ends of the power supply, giving the base an acoustic signal for driving. Intermittent current flow by the transistor induces a high voltage in the coil to drive the buzzer. On the other hand, in recent years, electronic watches, calculators, and other small electronic devices are required to have greater variety and beauty in sound, as well as further integration of circuits and extreme cost reductions. In the conventional circuit, the induced voltage of the coil has a spike waveform, the drive circuit has only one signal input, and the presence of a coil element and a bipolar element are all disadvantageous to the above requirements.

The present invention connects a pair of complementary MOS transistors to the high potential side and low potential side of a power supply, respectively, and connects each terminal of a two-terminal piezoelectric element to the connection point of each pair of P channel transistor and N channel transistor. The piezoelectric buzzer driving circuit is further characterized in that an acoustic signal of a different frequency or waveform is supplied to each pair of transistors, and with this configuration, the drawbacks of the prior art can be eliminated and the sound signal can be improved. The aim is to simultaneously achieve the diversity and beauty of circuits, increase circuit integration, and reduce costs. Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block circuit diagram of a crystal alarm watch using a drive circuit 1 of the present invention. 2 is a crystal oscillator, 3 is a frequency divider, 4 is a clock circuit that counts, for example, hours and minutes and holds the data; 5 is a memory for alarm set time, and the value in this memory matches the data in clock circuit 4. When alarm operation signal 6
A reference circuit that outputs 7, when receiving signal 6,
Gate circuit 9 for passing intermediate output 8 of the frequency divider
and 10 are 2 of different frequencies of the buzzer drive circuit 1.
This is a sub-frequency divider that creates input signals φ ₁ and φ ₂ of two acoustic frequencies, respectively. A waveform shaper for further adjusting the output of each frequency divider to an appropriate pulse width is not shown, but it may be provided. Buzzer drive circuit 1 is P
Consisting of channel transistors 11 and 13 and N-channel transistors 12 and 14, a pair of complementary MOS inverters are connected between DC power supplies _VDD and _VSS , and a piezoelectric buzzer 15 is connected to the connection point of the CMOS transistors. φ ₁ and φ ₂ become input signals for each inverter. As a power source, a silver battery, a lithium battery, or a battery boosted by a booster circuit is used.

FIG. 2 shows an example of the input signals φ ₁ and φ ₂ of the drive circuit and the terminal voltage φ ₁ -φ ₂ of the piezoelectric buzzer 15. Since the frequencies of φ ₁ and φ ₂ are slightly different, the pulse width of φ ₁ − _{φ 2} changes with time,
The sound intensity changes in the same way, and the sound is heard as a beat sound to the ear. This adds variation to a monotonous tone, and provides a softer and more pleasant modulated sound than the conventionally used modulated sound using pulses. In the waveform example shown in FIG. 3, the frequency ratio of the signals φ ₁ and φ ₂ is 3:2 (generally a simple integer ratio), and their chord is φ ₁
This is the case where it is output as −φ ₂ . Figure 4 shows a waveform A that is a mixture of two sine waves A and B with the same frequency ratio.
-B, but this ideal harmonic waveform is roughly similar to the φ ₁ - φ ₂ waveform created with the rectangular wave in Figure 3, and the buzzer driven by this waveform plays a chord (of course, the harmonics are not It is understandable that it outputs (including the following). This mixing effect is also suitable for outputting a much smoother chord than when a premixed input signal is applied to a conventional drive circuit that generates a spike waveform.

Figure 5 shows an AND gate 1 as a waveform shaping circuit for signals φ ₁ and φ ₂ in order to control the sound intensity.
6 is a partial block diagram of another embodiment in which numerals 6 and 17 are attached to the input section of the drive circuit 1. FIG. Examples of these original input signals φ ₃ , φ ₄ , φ ₅ , and φ ₆ are shown in FIG. φ ₃ and φ ₄ are acoustic signals with a frequency ratio of 2:1, and when φ ₅ and φ ₆ are steady inputs at a logic “1” level, they are applied as they are to the drive circuit 1, and the signal φ ₃ −φ ₄ is generated. The driving waveform is an octave chord like this. However, _φ5
And when correction signals φ ₅ and φ ₆ (same frequency as φ ₄ ) are added to φ ₆ for changing the pulse width also created by the sub frequency divider and waveform shaping circuit, each AND gate 16, 17 The outputs φ ₁ and φ ₂ are changed as shown in the figure, and the drive output φ ₁ −φ ₂ is still an octave sum sound waveform, but the pulse width becomes narrower. In other words, the tone is similar, but the volume is lower. The application of the signals φ ₅ and φ ₆ can be applied or not applied at will by the user, or can be automatically changed depending on the alarm set time period or the function used, thereby making it possible to diversify the usage and make it more convenient.

As another example of changing the volume, although not shown, the acoustic drive signal is intermittent at a high frequency higher than the audible frequency, and the volume is controlled by the presence or absence or degree of the intermittent. Furthermore, the gate inputs of the CMOS transistors may be separated without being combined, and different signals may be applied to these terminals.

As is clear from the above description of each embodiment, the present invention allows diversification of the tone and volume of the piezoelectric buzzer, and at the same time, does not require a special mixing circuit for mixing signals and does not require a coil element. In addition, since the structure is suitable for circuit integration, it is possible to reduce the size and cost of the device.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing one embodiment of the present invention, FIGS. 2, 3, and 4 are waveform diagrams of the input signals shown in FIG. 1, and FIG. 5 is a partial circuit of another embodiment. The block diagram, FIG. 6, is an input signal waveform diagram of FIG. 1... Buzzer drive circuit, 11, 12, 13, 1
4...Pair of CMOS transistors, 15...Piezoelectric buzzer, _φ1 , _φ2 ...Drive input signals.

Claims (1)

[Claims] 1. Connect a pair of complementary MOS transistors to the high potential side and low potential side of a power supply, respectively, and connect each terminal of a two-terminal piezoelectric element to the connection point of each pair of P channel transistor and N channel transistor, and By providing a plurality of acoustic signal generating means that output mutually different frequencies, and selectively coupling each output terminal of the acoustic signal generating means to the input terminal of each pair of transistors, the transistors of each pair 1. A piezoelectric buzzer drive circuit, characterized in that the piezoelectric buzzer drive circuit is configured to supply acoustic signals of different frequencies or waveforms to the piezoelectric buzzer.