JPS6117363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present 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 the figure, 1 is a positive phase amplifier, 2 and 4 are capacitors, and 3 and 5 are resistors.

Figure 1 shows what is called a Terman type oscillator.
The resistor 3 and capacitor 2 constitute a leading phase feedback circuit connected between the input Via and the output V ₂ , and the resistor 5 and capacitor 4 constitute a slow phase feedback circuit connected to the input Via. Output of phase amplifier 1
From _V2 , a frequency at which the phase transfer characteristic of the feedback circuit to the input Via becomes zero is selected and oscillated to form a zero phase selection type oscillation circuit. FIG. 2 shows an equivalent circuit of a piezoelectric element. In the figure, 6 is a piezoelectric element, 21, 24, 25 are capacitors, 23 is a coil, and 22, 26 are resistors. The piezoelectric element shown in FIG. 2 has a resistance of 2 as shown in FIG.
2. A series circuit of a capacitor 24 and a coil 23;
It is represented by a parallel circuit with a capacitor 21. Furthermore, at the time of resonance, this equivalent circuit is a parallel circuit of a capacitor 21 and a resistor 22 as shown in FIG. 2, or a capacitor 25 and a resistor 2 as shown in FIG.
It is represented by a series circuit with 6.

FIG. 3 is a graph showing the impedance and phase frequency characteristics of the piezoelectric element.

The phase advance feedback circuit portion consisting of the resistor 3 and capacitor 2 of the Terman type oscillation circuit shown in FIG.
As long as the piezoelectric element 6 is replaced and the values of the resistor 5 and capacitor 4 are selected so as to satisfy the oscillation frequency condition and the oscillation amplitude condition, the oscillation circuit shown in FIG. 1 can be made into a piezoelectric element self-excited oscillation circuit. can.

By the way, when the piezoelectric element has a plurality of natural frequencies like an ultrasonic vibrator, there is a problem in that it is not possible to specify which frequency the self-excited oscillation circuit oscillates at. When both frequency stability and increase in acoustic output are required at the same time, such as in ultrasonic transducers, a self-excited oscillation circuit is used, and the output is often driven by a rectangular wave, so it is possible to use a higher frequency Oscillation is likely to occur.

An object of the present invention is to provide a self-excited oscillation circuit that operates stably at its lowest natural frequency even when piezoelectric elements having a plurality of natural frequencies are used.

Hereinafter, one embodiment of the present invention will be described in detail. The self-excited oscillation circuit shown in FIG. 4 is the same as that shown in FIG. 1, except that it is constructed by connecting a phase-advancing circuit consisting of a resistor 3 and a capacitor 2 as a phase-advancing feedback circuit, and a piezoelectric element 6 inserted in series in parallel. This is the same as the self-excited oscillation circuit.

In the self-excited oscillation circuit configured as described above, the values of the resistor 3 and capacitor 2 of the phase advance circuit are selected as follows.

First, when the piezoelectric element 6 is removed, the oscillation frequency oscillates at a value close to the lowest natural frequency of the piezoelectric element 6. Second, the impedance of the series circuit of the resistor 3 and capacitor 2 near the lowest natural frequency is sufficiently larger than the impedance at the resonance point of the piezoelectric element 6 and smaller than the impedance at the anti-resonance point. Thirdly, the impedance of the series circuit of the resistor 3 and capacitor 2 is not too large compared to the impedance at the high-order resonance point of the piezoelectric element 6. Incidentally, the impedance characteristics of the phase advancing circuit are shown in FIG. 3a.

If we choose the values of resistor 3 and capacitor 2 to satisfy the above conditions, oscillation at the lowest natural frequency will be less affected by the phase advance circuit consisting of resistor 3 and capacitor 2, and the piezoelectric element will Oscillates at the resonance point. Oscillation at higher-order resonance points is suppressed by the phase advancing circuit. Even if the piezoelectric element is heated to a high temperature and its impedance value changes significantly, the piezoelectric element will return to normal as soon as it returns to normal because only the phase advance circuit oscillates near its natural frequency.
Oscillatory operation at the lowest natural frequency is again possible.

As explained above, the self-excited oscillation circuit of the present invention stably oscillates at a frequency corresponding to the lowest natural frequency of the piezoelectric element 6 by appropriately selecting the values of the resistor 3 and capacitor 2 of the phase advancing circuit.

Further, in the above embodiment, an oscillation circuit using a positive phase amplifier having a sufficient gain _a0 was explained.
For the purpose of driving the piezoelectric element in a rectangular waveform, an equivalent effect can be expected by using an operational amplifier or voltage comparator that has sufficient gain and has both positive phase and inverted input terminals.

FIG. 5 shows the self-excited oscillation circuit shown in FIG. 4 configured by a voltage comparator equipped with positive phase and inverting input terminals. In the figure, 51 is an amplifier as a voltage comparator; 52 and 53 are resistors.

Here, a piezoelectric element 6 is inserted in series between the output terminal and the positive phase input terminal of the amplifier 51, and a phase advancing circuit including a capacitor 2 and a resistor 3 is connected in parallel to the piezoelectric element 6. and
A slow phase feedback circuit consisting of a capacitor 4 and a resistor 5 is connected to the inverting input terminal, and a zero position phase selection type oscillation circuit is constructed as in FIG. 4.

5a, the amplifier 1 in FIG. 4 is replaced with an amplifier 51, and a resistor 52 is used to enable single power supply operation.
A bias potential is applied using a resistor 53 and a resistor 53. This is a basic Terman type oscillator circuit, and provides the same effect as the embodiment shown in FIG.

5b and 5c are respectively modified versions of the slow-phase feedback circuit consisting of the resistor 5 and capacitor 4 shown in FIG. 5a, and are basically Terman-type oscillation circuits shown in FIG. It is clear that the same effect as a self-excited oscillation circuit can be obtained.

In particular, in the case of the embodiment shown in FIG. 5c, unlike the other embodiments described above, the phase advance circuit and the phase delay circuit are not connected in cascade, so that the oscillation conditions can be easily selected. In other words, in determining the circuit constants of the leading phase feedback circuit and the slow phase feedback circuit, it is sufficient to mainly consider the phase selection conditions. The impedance can be set independently in the phase advance circuit, bias circuit, and slow phase feedback circuit.

For this reason, as in the case of an ultrasonic vibrator, for example, sufficient frequency stability is required, and if you want to extract a larger acoustic output, even if the piezoelectric element is coupled to a transformer, as in the above embodiment, It is expected that the oscillation conditions will be satisfied.

In FIG. 6, the phase advance feedback circuit of the self-excited oscillation circuit of FIG. 5c is constructed with a piezoelectric element formed by a transformer inserted in series. In the figure, 61 is a transformer.

The impedance of the piezoelectric element 6 is converted by a transformer 61, and constitutes a phase advance feedback circuit of a Terman type oscillation circuit. Therefore, while operating as a self-excited oscillation circuit, a boosted drive waveform is applied to the piezoelectric element, making it possible to obtain high acoustic output even with a low power supply voltage.

As explained above, according to the present invention, the phase advance feedback circuit portion of the zero phase selective oscillator circuit has a simple configuration of a piezoelectric element connected in parallel with the phase advance circuit. This has the effect of providing a self-excited oscillation circuit that stably oscillates at the frequency. Furthermore, if the phase advance feedback circuit part of the zero-phase selective oscillation circuit is configured with a piezoelectric element coupled to a transformer, a self-excited oscillation circuit that can obtain high vibration output even with a low power supply voltage can be obtained. There is.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram showing a conventional electric phase selective oscillation circuit, Fig. 2 is an equivalent circuit diagram of a piezoelectric element, and Fig. 3 is an electric circuit diagram showing a conventional electric phase selective oscillation circuit.
The figure is a phase and impedance characteristic diagram of a piezoelectric element, FIG. 4 is an electric circuit diagram showing an embodiment of the present invention, and FIG.
Figure 6 is an electrical circuit diagram showing another embodiment of the present invention.
The figure is an electric circuit diagram showing still another embodiment of the present invention. In the figure, 1 is a positive phase amplifier, 2 is a capacitor, 3 is a resistor, 4 is a capacitor, 5 is a resistor, 6 is a piezoelectric element, 51 is an amplifier, and 61 is a transformer.
Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A zero phase selection type oscillator circuit in which a leading phase feedback circuit is connected between the input and output of a positive phase amplifier, and a slow phase feedback circuit is connected to the input of the positive phase amplifier, A piezoelectric element inserted in series into the phase advance feedback circuit, and an impedance connected in parallel to this piezoelectric element that is sufficiently larger than the resonance point impedance of the piezoelectric element and smaller than the anti-resonance point impedance of the piezoelectric element near the lowest natural frequency of the piezoelectric element. 1. A self-excited oscillation circuit comprising: a phase advance circuit having a phase advancing circuit; 2. The self-excited oscillation circuit according to claim 1, wherein the piezoelectric element has a plurality of natural frequencies. 3 In a zero position selection type oscillator circuit in which a leading phase feedback circuit is connected between the output terminal of the amplifier and the positive phase input terminal, and a slow phase feedback circuit is connected to the inverting input terminal, a piezoelectric element inserted in series; and a phase advancing circuit connected in parallel to the piezoelectric element and having an impedance sufficiently larger than the resonance point impedance of the piezoelectric element and smaller than the anti-resonance impedance of the piezoelectric element in the vicinity of the lowest natural frequency of the piezoelectric element. A self-excited oscillation circuit characterized by: 4. The self-excited oscillation circuit according to claim 3, wherein the piezoelectric element has a plurality of natural frequencies. 5 In a zero phase selection type oscillator circuit in which a leading phase feedback circuit is connected between the output terminal of the amplifier and the positive phase input terminal, and a slow phase feedback circuit is connected to the inverting input terminal, A piezoelectric element coupled by a transformer inserted in series, and a piezoelectric element connected in parallel to the piezoelectric element having an impedance sufficiently larger than the resonance point impedance of the piezoelectric element and smaller than the anti-resonance impedance of the piezoelectric element near the lowest natural frequency of the piezoelectric element. A self-excited oscillation circuit characterized by comprising a phase advancing circuit.