JPH0751129B2 - Ultrasonic transducer drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a drive circuit for an ultrasonic transducer, and in particular to radiate ultrasonic waves from the transducer into a subject and receive reflected echoes from the inside of the subject. The improvement of the drive circuit configuration of the ultrasonic transducer.

[Prior Art] Ultrasound that radiates ultrasonic waves into a subject such as a living body, receives reflected echoes, and displays in-subject information such as tomographic images or moving body velocity (Doppler frequency shift) Diagnostic devices are well known.

FIG. 6, FIG. 8 and FIG. 10 show a driving circuit for a conventional ultrasonic transducer, and FIG. 6 shows a commonly used circuit, while FIG. The operation signal waveform in FIG. 6 is shown.

In FIG. 6, a transistor (Tr) 10 provided as a switching element is supplied with a high voltage HV, for example, a voltage of 200 V, from a terminal C via a resistor R ₂ from a DC high voltage power source, and the transistor 10 is In the OFF state, the capacitor C ₂ is charged with a voltage of 200 V, and the diode D ₁ prevents current from flowing from the capacitor C ₂ to the ultrasonic transducer 12.

Here, when a rectangular wave trigger pulse as shown in FIG. 7 (A) is input to the terminal A, the transistor 10 is turned on, and the signal shown in FIG. Will appear. Therefore, a voltage of 200 V is applied to the ultrasonic transducer 12, which generates ultrasonic waves, which are radiated into the subject.

Then, the echo signal reflected from the inside of the subject will be received by the ultrasonic transducer 12, amplified by the amplifier 14, and then taken out from the terminal D.

[Problems to be Solved by the Invention] However, in the circuit shown in FIG.
DC high-voltage power supply determined by the high-voltage pulse voltage required for power supply, and capacitor C ₂ for accumulating high-voltage charge
Is required and these components are relatively expensive,
There is a problem that the cost cannot be reduced. It should be noted that the transistor 10 must also perform switching action with high breakdown voltage, high current, and high speed.

Further, since the transistor 10 quickly applies the voltage of the capacitor C _{2 to} the ultrasonic transducer 12, it is necessary to apply a sufficient base current to the base of the transistor 10 by the trigger pulse to operate the transistor 10 in the saturation region. is there. Therefore, the pulse voltage applied to the ultrasonic transducer 12 cannot be arbitrarily controlled by the trigger signal.

Further, the transistor 10 must be turned off promptly after driving the ultrasonic transducer 12, but in the case of the transistor 10 operating in the saturation region, the input trigger pulse is generated due to the accumulation time due to the large current switching operation. After the trailing edge of, the signal is turned off at the point p in FIG. 7 (B), and the delay time T ₁ is shifted.

The occurrence of this delay time T ₁ becomes a problem when the phase control of a plurality of ultrasonic transducers 12 is performed for electronic scanning, and in particular, there are variations in the characteristics of the individual transistors 10, so that when designing the circuit. It also becomes an obstacle.

By the way, conventionally, there is a drive circuit shown in FIG. 8 in which an ultrasonic transducer is driven by a low voltage power supply without using a DC voltage power supply.

In FIG. 8, from the low voltage power source + Vcc to the inductance L ₂ ,
The capacitor C ₂ is charged via the resistor R ₂ . And
Transistor 10 from the A terminal by a rectangular wave trigger pulse
Sufficient base current is applied to turn ON, and the charge of the capacitor C ₂ is given to the inductance L ₁ through the transistor 10. Incidentally, the inductance L ₂ is a high-voltage pulse power supply developed across the inductance L ₁ + Vcc
It is provided to prevent a short circuit to the side.

In this way, when the transistor 10 is quickly turned off when the current flowing through the inductance L ₁ reaches a predetermined value, a high voltage pulse v ₀ is generated across the inductance L ₁ , and this high voltage pulse v ₀ is It is expressed by the following equation.

v ₀ = L ₁ (di / dt) (1) In the circuit as shown in FIG. 8, as is clear from the equation (1), the larger the value of the inductance L ₁ is, the more the transistor 10 is turned off. The shorter is, the larger the high voltage pulse generated is.

However, when increasing the value of the inductance L ₁ is time-consuming to pass sufficient current to the inductance L _1,
Further, there is a problem that it is not possible to supply a sufficient voltage to the ultrasonic transducer 12 due to an increase in output impedance, and there is a limit to the method of increasing the inductance value.

If a high voltage pulse is to be obtained, the OF
It is necessary to make the F time as short as possible, but as described above, since the transistor 10 is excited to the saturation region at the ON time, the OFF time cannot be made sufficiently short.
There is a problem in that the OFF time varies depending on the characteristics of each transistor and has a large variation.

Further, in the circuit of FIG. 8, an unnecessary voltage pulse is generated at the rising edge of the trigger pulse and after the drive voltage is generated.

That is, as shown in FIG. 9, when the drive pulse shown in FIG.
The output waveform at 1 is as shown in FIG. 7B, and the signal sharply rises at the rising edge of the trigger pulse, so that an unnecessary voltage pulse is generated as shown at 100 in the figure. Further, after the high voltage pulse is output, an extra voltage pulse as shown in 101 is generated due to the reverse recovery time of the transistor. As described above, unnecessary ultrasonic waves are output from the ultrasonic transducer 12 due to the generation of the extra voltage pulse at the time of rising of the drive pulse and after the output of the high voltage pulse. Appears as a pseudo echo,
This causes a problem that the image quality is significantly deteriorated.

In particular, such an extra voltage pulse is generated by using the transistor 10 in a saturated state, which has different characteristics depending on the individual transistors, which makes it impossible to control them.

In FIG. 10, the transistor 10 in the circuit of FIG.
The circuit replaced by 0 is shown, and in this case as well, the same problem as in the circuit of FIG. 8 occurs.

OBJECT OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to configure a circuit at low cost without generating pseudo echo or the like in a short-distance image. Another object of the present invention is to provide a drive circuit for an ultrasonic vibrator, which facilitates drive control of the vibrator.

[Means for Solving the Problems] In order to achieve the above object, a drive circuit for an ultrasonic transducer according to the present invention includes a trigger generation circuit that generates a sawtooth-shaped trigger signal, and an unsaturated region due to the trigger signal. The switching circuit operates with a low voltage power supply and the unsaturated switching circuit that linearly amplifies the trigger signal, and a current that changes from this unsaturated switching circuit is input to turn off the unsaturated switching circuit to a high voltage. An inductance circuit for applying a pulse to the ultrasonic transducer,
And driving the ultrasonic transducer by a high voltage signal controlled by the sawtooth trigger signal.

The invention of claim (2) is characterized in that a diode is connected in parallel with the inductance coil provided in the inductance circuit to obtain a unidirectional drive signal.

[Operation] According to the above configuration, it is possible to operate with a low-voltage power supply, the ultrasonic oscillator and the inductance coil forming the inductance circuit are connected in parallel, and the ultrasonic oscillator and the inductance coil are unsaturated. An unsaturated switching circuit having a type transistor is provided, and a sawtooth-shaped trigger signal is supplied to the unsaturated switching circuit. Therefore, when the unsaturated transistor is turned on and off by the sawtooth trigger signal, the energy stored in the inductance coil is directly converted into a high voltage pulse and supplied to the ultrasonic transducer. As a result, good ultrasonic waves are generated.

In this case, since the unsaturated transistor operates in the unsaturated region, there is no accumulation time generated in the transistor used in the saturated region, and the OF
The F time can be made extremely fast, and the ultrasonic transducer can be excited by a good high-voltage pulse without generating an unnecessary voltage waveform in the signal supplied to the ultrasonic transducer in the low-voltage power supply. It will be possible.

[Embodiment] An embodiment of a drive circuit for an ultrasonic transducer according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a driving circuit according to the first embodiment. What is characteristic of the present invention is that a transistor is operated in an unsaturated region by a sawtooth-shaped drive trigger signal, and a transistor is operated by a trigger signal. That is, the voltage applied to the acoustic wave oscillator can be controlled.

Therefore, in FIG. 1, a trigger generation circuit 16 for generating a sawtooth-shaped trigger signal is provided, a feedback resistor R ₂ is provided, and an unsaturated switching circuit for linearly amplifying the sawtooth wave is provided. That is, the trigger generation circuit 16 is connected so that the trigger signal is input to the unsaturated transistor 18 via the capacitor C ₁ , while the feedback resistor R ₂ is connected to the emitter terminal and the base terminal together with the protection resistor R _1. There is.

The voltage V _CE between the collector and emitter of the unsaturated type transistor 18, the forward voltage drop of the diode D ₁ and V _F, the current flowing through the direct current component resistance of the inductance coil L ₁ r _L, in the inductor L ₁ When the size of the a i ₀ low voltage power supply -V _EE will be given by the following equation.

| V _EE | = i ₀ (R ₂ + r _L ) + V _CE + V _F (2) Here, assuming that the saturation voltage between the collector and emitter of the unsaturated transistor 18 is V _CE (sat), the above (2) If the low voltage power supply −V _EE is set so that V _CE > V _CE (sat) according to the formula, the unsaturated transistor 18 always operates in the active region when ON, and functions as an unsaturated switch.

An inductance coil L ₁ is inserted as an inductance circuit in parallel with the ultrasonic vibrator 12, and a diode D is connected in series with the ultrasonic vibrator 12 between the inductance coil L ₁ and the unsaturated transistor 18. ₂ is connected. This diode D ₂ is provided to reduce the withstand voltage to the ultrasonic transducer 12 by half.

According to such an unsaturated switching circuit, a sawtooth-shaped trigger signal is added to the base terminal of the unsaturated transistor 18 so that the amount of change in voltage / current can be set sufficiently small with respect to time. Therefore, it is possible to suppress the generation of an unnecessary waveform when the conventional rectangular-wave trigger signal rises. Further, since the unsaturated transistor 18 is operated in the unsaturated region, there is no accumulation time when the transistor is operated in the saturated region, and therefore an unnecessary voltage waveform is generated in the signal given to the ultrasonic transducer 12. There is no.

The magnitude i _{0 of the} current flowing through the inductance coil L ₁ is equal to the magnitude of the sawtooth wave of the input trigger signal because the unsaturated transistor 18 operates in the unsaturated region. Therefore, by changing the magnitude of the input trigger signal,
It becomes possible to control the high voltage pulse generated by the equation.

That is, according to the sawtooth-shaped trigger signal shown in FIG. 2 (A), the unsaturated transistor 18 is turned on at the rising edge of the sawtooth wave, and a linearly changing current i ₀ flows through the inductance coil L ₁ to generate energy. Will be stored. Then, when the sawtooth wave falls, the unsaturated transistor 18 turns off instantly, and the inductance coil L ₁
A high voltage pulse v ₀ obtained by the equation (1) is generated at both ends of the pulse.

This high voltage pulse is, as shown in FIG.
The waveform of the sawtooth wave (trigger signal) rises from the falling point, and it has a sinusoidal waveform that coincides with the falling position of the sawtooth waveform trigger signal. The generation position of the high voltage pulse can be changed arbitrarily.

Further, the pulse width of the high voltage pulse can be set to an appropriate value by changing the value of the inductance coil L ₁ . This can also be realized by inserting an appropriate capacitor in parallel with the ultrasonic transducer 12 as in the conventional example shown in FIG.

Although the resistor R ₂ connected to the emitter terminal of the unsaturated transistor 18 is a protection resistor for limiting current, it also functions as a feedback resistor at the same time.By changing the value of the feedback resistor R ₂ , linear amplification is performed. You can adjust the degree. Thus, appropriately changing the feedback resistor R _2, by causing a current feedback function at the emitter by the feedback resistor R _2, it can be satisfactorily operate the circuit to correct the variations in the characteristics of the unsaturated type transistor 18 .

Further, the diode D ₁ and the capacitor C ₁ perform a direct current reproducing function (clamp circuit), and thereby a sawtooth wave input as a trigger signal can be fixed at a constant level.

Further, the diode D ₂ is provided for blocking the reverse voltage with respect to the collector of the unsaturated transistor 18, so as to increase the withstand voltage of the unsaturated transistor 18, and at the same time as the unsaturated transistor 18 at the time of reception. Sound wave oscillator 12
, And separates and to secure a dynamic range for the echo signal obtained from the vibrator 12.

Then, the amplifier 14 inputs the echo signal received by the transducer 12 as in the conventional case, performs a predetermined high frequency amplification, and outputs the signal from the terminal D to a signal processing circuit for image display.

The first embodiment has the above configuration, and its operation will be described below.

First, the trigger generation circuit 16 generates a sawtooth-shaped trigger signal as shown in FIG. 2A, and this trigger signal is supplied to the unsaturated transistor 18 via the capacitor C ₁ . Then, the unsaturated transistor 18 gradually starts to conduct, and the current I ₀ starts to flow from the low voltage power supply −V _EE to the inductance coil L ₁ via the feedback resistor R ₂ and the diode D ₁ . This current I ₀ is a current in which a sawtooth wave that is a trigger signal is linearly amplified, and a changing current is applied to the inductance coil L ₁ .

In this case, as is clear by comparing FIG. 2 with FIG. 9, the unnecessary voltage waveform 100 does not occur at the rising edge of the sawtooth trigger signal. This is because the trigger signal of the present invention is a sawtooth wave, the rising of which is gentle, and it is not possible to generate an unnecessary signal generated by a sharp rising like the conventional rectangular wave pulse. Also,
Even after the high voltage pulse is generated, the unnecessary voltage waveform 101 as shown in FIG. 9 does not occur. Because the present invention turns ON / O the unsaturated transistor in the unsaturated region.
This is because the FF operation is performed, and thus the accumulation time when operating the unsaturated transistor in the saturation region does not occur.

Then, when the unsaturated transistor 18 is turned off,
The energy applied to the inductance coil L ₁ is output, and the high voltage pulse according to the equation (1) is generated, and the ultrasonic transducer 12 is driven by this.

A second embodiment of the invention is shown in FIG.
The embodiment is characterized in that the generated high voltage pulse is a unidirectional pulse.

For this reason, in the second embodiment, the diode D ₃ is inserted in parallel with the inductance coil L _1, and thus the diode D ₃ is inserted.
A unidirectional output can be obtained as shown in FIG.

FIG. 5 shows a third embodiment of the present invention, which is characterized by widening the dynamic range at the time of receiving an echo signal.

That is, the low-voltage power supply + V _CC is connected to the ground terminal F of the resistor R ₃ , and the voltage on the cathode side of the diode D _{2 is} , for example, +10.
Keep the operating voltage at a high level and set a high operating voltage. As a result, the dynamic range is expanded, and a signal that is greatly attenuated when it is reflected in the subject is received, and even a large signal that is little attenuated is received. Therefore,
It is applied to the ultrasonic transducer for short-distance and inside a subject mostly composed of substances such as stylish, for example, it is used as a circuit to drive the ultrasonic transducer for fetus observation, and a diagnostic image with good image quality is obtained. It becomes possible to obtain.

In the above-mentioned embodiment, the NPN unsaturated type transistor has been described as an example of the switching circuit element, but a similar circuit can be constructed by using a PNP unsaturated type transistor or a MOS unsaturated type transistor. Further, the sawtooth wave formed by the trigger generation circuit 16 can also have a non-linear waveform, and the non-linear waveform enables the same operation as in the above-described embodiment.

[Effects of the Invention] As described above, according to the present invention, a switching element is operated in an unsaturated region by using a sawtooth-shaped trigger signal, and a high voltage pulse generated thereby is ultrasonically transmitted through an inductance coil. Since it was given to the oscillator,
High-voltage pulses can be generated well without being affected by the input / output capacity and storage time of unsaturated transistors. In particular, this high-voltage pulse is controlled arbitrarily by a sawtooth-shaped trigger signal, Since the electronic scanning can be performed by changing the driving time and the driving voltage, the beam focusing of the array type ultrasonic probe or the like can be favorably performed and the side lobes can be reduced.

In addition, the drive circuit can be operated by a low voltage power source without using an expensive high voltage power source, which makes it possible to obtain an ultrasonic diagnostic apparatus with high safety, and also a capacitor for a high voltage. Since it is unnecessary, it is extremely useful as a driving circuit for a portable ultrasonic diagnostic apparatus that uses a battery at low cost.

Further, according to the invention of claim (2), there is an effect that a unidirectional output is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a drive circuit for an ultrasonic transducer according to the present invention, FIG. 2 is a waveform diagram showing operation signals in FIG. 1, and FIG. 3 is a second embodiment of the present invention. Circuit diagram showing an example, FIG. 4 is a waveform diagram showing operation signals in FIG. 2, FIG. 5 is a circuit diagram showing a third embodiment of the present invention, and FIG. 6 is a conventional drive circuit using a high voltage power supply. FIG. 7 is a waveform diagram showing operation signals in FIG. 6, FIG. 8 is a circuit diagram showing a conventional drive circuit driven by a low voltage power supply, and FIG. 9 shows operation signals in FIG. The waveform diagram shown in FIG. 10 is a circuit diagram showing another conventional example using a low-voltage power supply. 10 …… Transistor 12 …… Ultrasonic vibrator 14 …… Amplifier 16 …… Trigger generation circuit 18 …… Unsaturated transistor R ₂ …… Feedback resistance D ₁ , D ₂ , D ₃ …… Diode L ₁ …… Inductance coil.

Claims (2)

[Claims] 1. A trigger generation circuit that generates a sawtooth-shaped trigger signal; an unsaturated switching circuit that performs a switching operation in an unsaturated region by the trigger signal and linearly amplifies the trigger signal using a low-voltage power supply; An inductor circuit that inputs a changing current from this unsaturated switching circuit and applies a high voltage pulse to the oscillator by the OFF operation of the unsaturated switching circuit,
A drive circuit for an ultrasonic oscillator, which drives the oscillator with a high-voltage signal controlled by the sawtooth-shaped trigger signal. 2. The ultrasonic vibration according to claim 1, wherein a diode is connected in parallel with the inductance coil provided in the inductance circuit to obtain a unidirectional drive signal. Child drive circuit.