JPH0374560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic circuit using a piezoelectric ultrasonic transducer made of piezoelectric ceramic for both transmission and reception.

A conventional transmitting circuit or receiving circuit for an ultrasonic transducer using piezoelectric ceramics has been provided as shown in FIG. Figure 1a shows the transmitting circuit, where ₁₁ is an ultrasonic transducer for transmitting waves, and 3 is a transmitting amplification circuit that amplifies the transmitted signal and drives the ultrasonic transducer ₁₁ . be. Figure 1b shows the receiving circuit, 1
₂ is an ultrasonic transducer for receiving waves, 2 is an ultrasonic transducer 1 ₂
This is a receiving wave amplification circuit that amplifies the output from the receiver and outputs a received signal. RL is a load resistance connected in parallel to the ultrasonic transducer ₁₂ . Here, in the wave transmitting circuit shown in FIG. 1a, the ultrasonic transducer 1 is
₁ , a waveform as shown in FIG. 3 is output. In the figure, t ₁ is the regular ultrasound transmission section, and t ₂
is the section in which the reverberant signal is transmitted. That is, a relatively long reverberation time occurs as damped vibration due to the residual energy of the ultrasonic transducer 1 ₁ . FIG. 4 shows a transmitting/receiving circuit that operates an ultrasonic transducer with such reverberation by switching between transmitting and receiving waves with one ultrasonic transducer. 4 is a transmission/reception switching circuit,
It switches between transmitting and receiving ultrasonic waves. In the circuit shown in FIG. 4, when the ultrasonic transducer 1 is driven, ultrasonic waves as shown in FIG. 5 are transmitted. t ₁ indicates a wave transmission section, t ₂ indicates a reverberation signal section, and t ₃ indicates an unreceivable section. In other words, the received signal cannot be detected while there is reverberation due to the transmitted ultrasound signal.
In particular, since the reverberant signal section is relatively long, there is a problem in that it is difficult to detect objects at short distances.

The present invention has been provided in view of the above-mentioned points, and provides an ultrasonic circuit whose purpose is to improve pulse responsiveness during pulse driving of an ultrasonic transducer.

Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 6 shows the basic circuit, in which a circuit in which two coils L ₁ and L ₂ are connected in series to the ultrasonic transducer 1 is connected in parallel, and a load resistance RL is connected in parallel with the other data L ₂ . Connected. Further, a wave transmitting circuit or a wave receiving circuit is connected to both ends of the load resistor RL. coil
The inductance of L ₁ and L ₂ is determined by the following formula.
Let the resonance frequency of the ultrasonic transducer 1 be f ₀ .

L ₁₀ +L ₂₀ = 1/(2πf ₀ ) ² Co (H) However, L ₁₀ and L ₂₀ are the inductances of the coils L ₁ and L ₂ , and Co is the capacitance value of the ultrasonic transducer 1.

In other words, the ultrasonic transducer 1 has a certain capacitance value Co
This capacitance value Co and the coil L ₁ ,
A parallel resonant circuit is formed by the inductance _L2 , and its resonant frequency is approximated to the resonant frequency fo of the ultrasonic transducer 1. At this time, the impedance Z relative to the frequency f seen at both ends of the ultrasonic transducer 1 is as shown in FIG. Note that this is an example in which the resonance frequency fo of the ultrasonic transducer 1 is 40 KHz. In this way, by configuring a parallel resonant circuit in which the circuit impedance is minimized at the resonant frequency of the ultrasonic transducer 1, the Q of the ultrasonic transducer 1 is lowered and reverberation is attenuated. be able to. Therefore, as shown in Figure 8 a and b, the reverberation time changes from t 2 shown in Figure 8 a, which does not constitute a resonant circuit, to t ₂ , shown in Figure 8 b, which constitutes a resonant circuit.
t ₂ ', making it possible to transmit or receive waves with good pulse response.

As mentioned above, the ultrasonic transducer 1 has a coil L ₁ ,
By connecting L ₂ in parallel to form a parallel resonant circuit, the reverberation time can be significantly shortened, but problems arise due to the following characteristics of the ultrasonic transducer 1. In other words, the capacitance value Co of the ultrasonic transducer 1 using piezoelectric ceramic changes greatly depending on changes in the surrounding temperature. The value is +
It is 0.8 (%/℃). In this way, when the capacitance value Co of the ultrasonic transducer 1 changes greatly depending on the temperature, the resonant frequency of the parallel resonant circuit with the external coils L ₁ and L ₂ changes greatly, and the ultrasonic transducer This results in a large deviation from the resonant frequency fo of 1, and the reverberation reduction effect is lost. In order to prevent this, a capacitor _C1 , which has a temperature change characteristic opposite to the capacitance change of the ultrasonic transducer 1, is connected in parallel to the ultrasonic transducer 1 for temperature compensation, as shown in Figure 9. coil to reduce changes in total capacitance.
This eliminates temperature-related changes in the resonant frequency of the parallel resonant circuit with L ₁ and L ₂ . FIG. 10 shows the characteristics of temperature and each capacity. Straight line A shows the temperature characteristics of the ultrasonic transducer 1, and straight line B shows the temperature compensation capacitor whose characteristics are opposite to those of the ultrasonic transducer 1.
This is the temperature characteristic of C ₁ . As an example, the temperature characteristic of this capacitor _C1 is -1.0 (%/°C). Therefore, due to both characteristics, the capacitance due to temperature change is canceled out, so that there is not much change in capacitance as a whole. Figure 11 shows the relationship between temperature and resonant frequency, where the solid line C shows the resonant frequency characteristics of the ultrasonic transducer 1, and the broken line D shows the resonant frequency characteristics of the parallel resonant circuit when a capacitor _C1 is provided. It can be seen that there is almost no difference in the characteristics from the ultrasonic transducer 1, and that temperature compensation has been performed. On the other hand, a dashed-dotted line E shows the resonant frequency characteristic of the parallel resonant circuit without temperature compensation, that is, when the capacitor _C1 is not connected. Therefore, if the capacitor _C1 is not provided, the resonant frequency of the resonant circuit will change greatly due to temperature changes, and as mentioned above, if temperature compensation is not provided, the ultrasonic transducer 1
The reverberation reduction effect disappears. As shown in Fig. 12, coil L ₁ and coil L ₂ shown in Fig. 9 are integrated to form coil L ₃ , and temperature compensation capacitor C ₁ , coil L ₃ and load resistor RL are all connected in parallel. It is also a good connection. In this way, by reducing the change in the resonant frequency of the parallel resonant circuit due to temperature changes, it is possible to configure a drive circuit for the ultrasonic transducer 1 with a stable pulse response within the operating temperature, and to stabilize the reverberation time. It can be made small.

FIG. 13 shows an embodiment in which one ultrasonic transducer 1 is used for both transmission and reception. Similar to the configuration in FIG. 9, a temperature compensation capacitor C ₁ is connected in parallel to the ultrasonic transducer 1, and both coils L ₁ ,
Connect the series circuit of L ₂ to the capacitor C ₁ in parallel,
A load resistor RL is connected to both ends of the coil _L2 . The output generated at both ends of this load resistor RL is input to the receiving wave amplification circuit 2. Furthermore, the transmission amplification circuit 3 is connected from the connection point of both coils L ₁ and L ₂ via diodes D ₁ and D ₂ connected in antiparallel.
Note that, as shown in FIG. 14, this configuration may of course be a configuration in which diodes D ₁ and D ₂ are added to the configuration shown in FIG. 12. However, when a single ultrasonic transducer 1 is used for transmitting and receiving waves, the transmitted signal is amplified in the transmitting amplification circuit 3, and its peak value is a large signal of several tens of volts. Therefore, the diodes D ₁ and D ₂ have low impedance, and the output of the transmission amplification circuit 3 is directly applied to the ultrasonic transducer 1, and the ultrasonic transducer 1 transmits an ultrasonic signal. When this wave transmission is completed, the ultrasonic conversion signal received and output to the ultrasonic transducer 1 is a small signal of several mV or less, so the diodes D ₁ and D ₂ become high impedance and pass through the transmission amplification circuit. 3, and a signal is output to the received wave amplification circuit 2. At this time, the capacitance value Co of ultrasonic transducer 1 and the coil
The parallel resonant circuit with L ₁ and L ₂ greatly shortens the reverberation time of the transmitted signal, and the capacitor
Since C ₁ prevents the reverberation time from increasing due to temperature changes, it is possible to transmit and receive waves using a single ultrasonic transducer 1. Therefore, when one ultrasonic transducer 1 is used for both transmission and reception, the reverberation time after transmission is short and the ultrasonic pulse reflection type switch is stable against temperature changes. This greatly improves the short-range detection ability of the system.

As described above, the present invention includes a coil that forms a parallel resonant circuit that reduces the impedance at both ends of the ultrasonic vibrator with respect to the resonance frequency of the ultrasonic vibrator with the capacitance of the ultrasonic vibrator. Therefore, the Q of the ultrasonic transducer can be suppressed to a small value using a parallel resonant circuit consisting of the capacitance of the ultrasonic transducer and the coil, thereby attenuating the reverberation, which has the effect of shortening the reverberation time. be. Therefore,
When detecting an object by transmitting and receiving ultrasonic waves using one ultrasonic transducer, objects at a short distance can also be detected.

[Brief explanation of drawings]

Figures 1a and b are the transmitter circuit diagram and receiver circuit diagram of the conventional example, Figure 2 is the ultrasonic transducer driving waveform diagram of the same as above, Figure 3 is the operating waveform diagram of the same as above, and Figure 4 is the same as the above. A circuit diagram for both transmission and reception, Fig. 5 is an operating waveform diagram of the same as above, Fig. 6 is a basic circuit diagram of an embodiment of the present invention, Fig. 7 is a resonance impedance characteristic diagram of frequency and impedance of the same as above, Fig. 8 a, b are the same operating waveform diagrams as above,
Figure 9 is a circuit diagram of the same temperature compensated type as above, Figure 10
The figure is a characteristic diagram of capacitance against temperature change, same as above.
Figure 11 is a characteristic diagram of temperature and resonant frequency same as above,
FIG. 12 is a circuit diagram of another embodiment of FIG. 9, FIG. 13 is a circuit diagram of a transmitting/receiving type, and FIG. 14 is a circuit diagram corresponding to FIG. 12. 1 is an ultrasonic transducer, 2 is a reception amplification circuit, 3 is a transmission amplification circuit, L ₁ and L ₂ are coils, D ₁ and D ₂ are diodes, and C ₁ is a capacitor.

Claims (1)

[Claims of Claims] 1. An ultrasonic wave device comprising a coil constituting a parallel resonant circuit that reduces the impedance at both ends of the ultrasonic vibrator with respect to the resonance frequency of the ultrasonic vibrator with the capacitance of the ultrasonic vibrator. circuit. 2. The ultrasonic circuit according to claim 1, comprising a capacitor that compensates for temperature changes in capacitance of the ultrasonic transducer. 3 A receiving amplification circuit for amplifying the receiving output of the ultrasonic transducer is connected to the ultrasonic transducer equipped with the above-mentioned coil, and a transmitting signal for driving the ultrasonic transducer is applied to the ultrasonic transducer. 3. The ultrasonic circuit according to claim 1, wherein the wave amplification circuit is connected to the ultrasonic transducer including the coil through anti-parallel connected diodes.