JPS6127209Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention relates to a self-excited oscillation circuit that stably oscillates at the lowest natural frequency of a piezoelectric element. FIG. 1 shows an example of a conventional self-oscillation circuit, in which 1, 2, 3, and 4 are resistors, 5 is a capacitor, 6 is a voltage comparator having an inverting input terminal and a non-inverting input terminal, and 7 is a voltage comparator having an inverting input terminal and a non-inverting input terminal. The piezoelectric elements 8 and 9 are transistors, and the resistors 1 and 2 constitute a bias circuit, which is connected to a non-inverting input terminal of a voltage comparator 6 to provide a bias voltage. The resistor 3 and the capacitor 5 are a slow phase feedback circuit, to which the output signal of the voltage comparator 6 connected to the inverting input terminal of the voltage comparator 6 is fed back. Resistor 4 is a pull-up resistor for voltage comparator 6. In general, the equivalent circuit of the piezoelectric element 7 when it resonates exhibits capacitance as shown in Figure 2a, so an emitter follower circuit using complementary transistors 8 and 9 is added to increase the driving speed. . In FIG. 2, 21 is a capacitor, 22 is a resistor, 23 is a coil, and 24 is a capacitor. The value of capacitor 21 is c _d , and the value of resistor 22 is
The value of rn is the value of the coil 23, L is the value of the coil 23, and the value of the capacitor 24 is
Let the value of be c/n ² and n be an integer. capacitor 21
Ignoring this, the piezoelectric element 7 is equivalent to a series resonant circuit including a resistor 22, a coil 23, and a capacitor 24. n is the order of the resonant frequency, and when n:1, it becomes the fundamental resonant frequency. FIG. 2b shows a current waveform during resonance passing through the piezoelectric element 7, and the current i at the fundamental resonance frequency is approximately expressed by the following equation. In other words, in Fig. 2a, when the capacitor 21 is ignored, the resistor 22, the coil 23, and the capacitor 2
4 is approximated by a step response to a step voltage E of a series resonant circuit according to E.4. Next, the terminal voltage of capacitor 5 of the slow phase circuit V _-
The response to the step voltage increases with the time constant of the resistor 3 and capacitor 5. If this time constant is set to a sufficiently large value compared to the resonant frequency of the piezoelectric element 7, the self-excited oscillation circuit of FIG. 1 feeds back the output signal of the voltage comparator 6 via the emitter follower circuit to the non-inverting input terminal. It oscillates at the resonance frequency of the piezoelectric element 7, and the output Vout becomes a rectangular wave. FIG. 3 shows a voltage waveform diagram at each point in FIG. 1. First, a half cycle in which the output Vout is at a high level will be explained. If the values of resistors 1 and 2 are equal,
The potential of one terminal of the piezoelectric element 7 is Vcc/2, and a high level equal to Vcc is applied from the output Vout to the other terminal. The current flowing through the piezoelectric element 7 at this time is similar to that shown in FIG. 2b.
This current change is fed back to the connection point between resistors 1 and 2,
It is converted into a change in voltage V ₊ . This voltage waveform is
It is similar to the current waveform shown in Figure 2b, and Vcc/
It vibrates around 2. This voltage V ₊ is applied to the non-inverting input terminal of the voltage comparator 6 and fed back. Similarly, a step voltage is applied to a slow phase circuit consisting of a resistor 3 and a capacitor 5, and the terminal voltage V _- of the capacitor 5 is applied to the inverting input terminal of the voltage comparator 6. Since the time constant of this phase delay circuit is sufficiently large as mentioned above, V ^- is almost Vcc/2
It can be approximated to The high level condition of Vout remains until V ⁺ again matches ^V- , as shown in Figure 2b.

It lasts for a time exactly equal to half a period of , and then flips to a low level. Vout
1 of piezoelectric element 7 is reversed to a low level.
In contrast to the potential Vcc/2 of one terminal, a ground potential is applied to the other terminal, and V ⁺ repeats the negative half cycle of the above-mentioned vibration waveform around Vcc/2. In this way, a rectangular wave having the resonance frequency of the piezoelectric element 7 is outputted to Vout. However, the above-described self-excited oscillation circuit has the drawback that it is difficult to stably oscillate only at the fundamental frequency because it can oscillate stably even at the high-order resonance frequency of the piezoelectric element. This invention was made to solve the above-mentioned drawbacks, and its purpose is to provide a self-excited oscillation circuit that stably oscillates at the fundamental resonance frequency of the piezoelectric element. To achieve this objective, the present invention provides a self-excited oscillation circuit as described above, which is in phase with the current due to the fundamental resonance frequency of the piezoelectric element, which is conducted to the piezoelectric element according to the output signal of the voltage comparator, and which has a high-order Equipped with a feedback circuit that adds the feedback current of a certain time width required to suppress resonance to the current flowing through the piezoelectric element generated in accordance with the output signal of the voltage comparator and returns it to the non-inverting input terminal. It is. FIG. 4 is an electrical circuit diagram showing one embodiment of this invention, in which 41 is a resistor and 42 is a capacitor. In the self-excited oscillation circuit configured as shown in the figure, the voltage V ⁺ appearing at the non-inverting input terminal of the voltage comparator 6 is influenced by a feedback current from a feedback circuit consisting of a resistor 41 and a capacitor 42 . This situation is shown in FIG. FIG. 5a is the same as the current waveform shown in FIG. 2b, but the drive waveform Vout is a rectangular wave and includes high frequency components in addition to the fundamental frequency. Therefore, the addition of the high-order resonance waveform, the fundamental resonance waveform, the feedback current waveform from the parallel capacitor 21, etc. described above becomes the true current waveform, as shown in FIG. 5a. This current waveform is determined by the characteristics of the piezoelectric element 7, but if the high-order resonance characteristics are sudden, a sharper high-order vibration waveform is superimposed, and the zero point of the flow shown in FIG. Try to cross faster. The zero point of the current is the point where it intersects with the V ^- waveform mentioned above, so if it crosses before it crosses at the fundamental wave, oscillation will start at higher harmonics and stabilize at higher order oscillations. It ends up. In this case, as shown in Fig. 5b, by adding an in-phase feedback current to the current flowing through the piezoelectric element 7 and suppressing the current that crosses the zero point for a certain period of time, oscillation at the fundamental wave can be made easier. . The V ⁺ voltage waveform of the self-excited oscillation circuit shown in FIG. 4 is shown in FIG. 5c, and the Vout is shown in FIG. 5d. By the way, in the above embodiment, the resistance 21 and capacitor 22 generated by the output signal of the voltage comparator 6
However, various waveforms are possible as the feedback current waveform, and can be realized by a combination of elements such as resistors, capacitors, and coils. Further, in the above embodiment, the in-phase feedback current is added over both the positive and negative cycles of the current flowing through the piezoelectric element 7, but the same effect can be obtained by adding it only to the positive or negative half cycle. . 5e is triggered by the output voltage e,
Constant time width T required to suppress high-order resonance
In this case, the same effect as above can be expected even in this case. FIG. 6 is an electric circuit diagram showing an embodiment in which the current of the above-mentioned constant time width T is added in the negative direction. In the same figure, 61 is a constant time width T A monostable multivibrator circuit that outputs a high level of , 62 is a diode, 6
3 is a resistor, and a feedback circuit is provided using these resistors. The self-excited oscillation circuit shown in FIG. 6 is an embodiment in which the added current indicated by e in FIG. 5 is fed back. It goes without saying that if the characteristics of the monostable multicircuit and the direction of the diode 62 in FIG. 6 are reversed, a feedback circuit with a feedback current corresponding to f in FIG. 5 can be obtained. As explained above, according to the present invention, the basic oscillation of the piezoelectric element is achieved using a simple configuration in which a current in the same phase as the current fed back by the piezoelectric element is added and fed back at a phase that suppresses higher-order vibrations of the piezoelectric element. This has the effect of obtaining a self-excited oscillation circuit that oscillates stably at the frequency.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram showing an example of a conventional self-oscillation circuit, Fig. 2a is an equivalent circuit diagram when the piezoelectric element resonates, and Fig. 2b shows the current flow when the piezoelectric element resonates. Step response waveform diagram, Figure 3 is a current waveform diagram at each point in Figure 1, Figure 4 is an electric circuit diagram showing an embodiment of the present invention, Figure 5 is a diagram of each point in Figure 4 above, and feedback. FIG. 6 is an electric circuit diagram showing another embodiment of the present invention. In the figure, 1, 2, 3, 4, 41, and 63 are resistors, 5 is a capacitor, 6 is a voltage comparator, 7 is a piezoelectric element, 8 and 9 are complementary transistors, 42 is a capacitor, and 61 is a monostable multi-layer ibrator circuit,
62 is a diode. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] a voltage comparator having an inverting input terminal and a non-inverting input terminal; a slow phase feedback circuit comprising a resistor and a capacitor for feeding back an output signal of the voltage comparator to the inverting input terminal; and a non-inverting input terminal of the voltage comparator. in a self-excited oscillation circuit comprising a bias circuit that applies a bias voltage to the piezoelectric element, and a piezoelectric element that feeds back an output signal of the voltage comparator to the non-inverting input terminal, A feedback current is generated in accordance with the output signal of the voltage comparator, which is in phase with the current due to the fundamental resonance frequency of the piezoelectric element and which is necessary for suppressing higher-order resonance of the piezoelectric element, in accordance with the output signal of the voltage comparator. A self-excited oscillation circuit characterized in that a feedback circuit is provided which adds the current to the energizing current and returns it to the non-inverting input terminal.