JPH02144048A - Drive circuit of ultrasonic vibrator - Google Patents

Abstract

PURPOSE:To constitute a circuit in low cost and to easily control the driving of a vibrator without generating a dummy echo in a short distance image by operating a switch element in an unsaturated state using a saw-tooth trigger signal and applying the high voltage pulse generated thereby to an ultrasonic vibrator through an inductance coil. CONSTITUTION:This circuit is equipped with a trigger generating circuit 16 generating a saw-tooth trigger signal, a feedback resistor R2 and an unsaturated type switching circuit for linearily amplifying the aforementioned saw-tooth trigger signal. An unsaturated type transistor 18 is always operated in an active region at an ON-time and functions as an unsaturated type switch. An inductance coil L1 is inserted as an inductance circuit in parallel to an ultrasonic vibrator 12 and a diode D2 is connected between the inductance coil L1 and the unsaturated type transistor 18 in series to the ultrasonic vibrator 12. By this method, the generation of an unnecessary waveform at the time of the rising of the trigger signal is suppressed and an unnecessary voltage waveform is not generated in the signal given to the ultrasonic vibrator 12.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a driving circuit for an ultrasonic transducer, and in particular, to a drive circuit for an ultrasonic transducer, in particular, for emitting ultrasonic waves into a subject using the transducer and receiving reflected echoes from within the subject. This invention relates to an improvement in the drive circuit configuration of an ultrasonic transducer.

[Prior Art] Ultrasonic diagnostic equipment that emits ultrasonic waves into a subject such as a living body, receives the reflected echoes, and displays internal information such as a tomographic image or velocity (Doppler shift) as an image is well-known. It is.

6, 8, and 10 show conventional driving circuits for ultrasonic transducers. FIG. 6 shows a commonly used circuit, and FIG. The operating signals in FIG. 6 are shown.

In FIG. 6, a transistor (Tr) 10 provided as a switching element is connected from a terminal C to a resistor R2.
A high voltage HV, for example, 200V, is supplied from a DC high-voltage power supply through the capacitor C2, and when the transistor 0 is in the OFF state, a current flows as shown by the arrow 1, and the capacitor C2 is charged with a voltage of 200V. This capacitor C is connected to a vibrator (T) via parallel resistors R3 and R4.
D) 12 is connected and transistor 10 is OFF
In this case, the capacitor C2 is connected to the vibrator 1 by the diode DI.
No current flows to 2.

Here, when a rectangular wave trigger pulse as shown in FIG. 7(A) is input to terminal A, the transistor 10 is turned on.
As a result, the current 12 shown in FIG. 6 will flow, and a signal shown in FIG. 7(B) will appear at point B in the diagram. Therefore, a voltage of 200 cm is applied to the vibrator 12, thereby generating ultrasonic waves, which are emitted into the subject.

The echo signal reflected from inside the subject is transmitted to the transducer 12.
After being amplified by the amplifier 14, the signal is taken out from the terminal.

[Problem to be solved by the invention'XJ] However, the circuit shown in FIG. and
Since these parts are relatively expensive, there is a problem in that costs cannot be reduced. Note that the transistor 10 must also have a high breakdown voltage, high current, and high speed switching action.

In addition, since the transistor 10 quickly applies the voltage of the capacitor C2 to the vibrator 12, it is necessary to apply a sufficient base current to the base of the transistor 10 using a trigger pulse to operate the transistor 10 in the saturation region. Therefore, the pulse voltage applied to the vibrator 12 cannot be arbitrarily controlled depending on the trigger signal.

Furthermore, the transistor 10 must be turned off immediately after driving the resonator 12, but in the case of the transistor 0 operating in the saturation region, the accumulation time due to the large current switching operation is wasted and the fall of the input trigger pulse. Later, it turns OFF at 9 points in Figure 7 (B).
t, a deviation of the delay time T1 will occur.

The occurrence of this delay time T1 becomes a problem when controlling the position of multiple oscillators 12 for electronic scanning.In particular, since the characteristics vary depending on the individual transistors, it becomes an obstacle when designing a circuit. It also becomes.

By the way, conventionally, there is also a drive circuit such as the one shown in FIG. 8, which drives a vibrator with a low voltage power source without using a DC high voltage power source.

In FIG. 8, a current 11 is passed from the low voltage power supply +Vcc,
The capacitor C2 is charged through the inductance and the resistor R2. Then, when a rectangular wave trigger pulse is input from the A terminal to the base of transistor 0, current 12 flows as shown by the arrow, and the charge of capacitor C is applied to inductance Ll. Note that the inductance L 1 is provided to prevent the high voltage pulse generated across the inductance L1 from shorting to the power supply side.

In this way, when the current 12 flows through the inductance Ll, the transistor 10 is quickly turned off within a predetermined time.
Then, a high voltage is generated across the inductance L1,
This high voltage is expressed by the following equation.

■o-L1 (di/dt)... (1) In the circuit shown in Fig. 8, as is clear from equation (1) above, the larger the value of inductance L1 is, the longer the OFF time of transistor 10 is. The shorter the length, the higher the voltage generated.

However, when increasing the value of the inductance L1, there is a problem that it takes time to flow a sufficient current through the inductance L1, and it becomes impossible to supply sufficient voltage to the vibrator 12 due to an increase in output impedance. However, there are limits to how to increase the value of inductance.

In addition, when obtaining a high voltage pulse, the transistor 10
There is a method of making the OFF time as early as possible, but as mentioned above, the transistor 10 is excited to the saturation region at the time of activation, so it is impossible to make the OFF time sufficiently quick. This off-time differs depending on the characteristics of each transistor, and there is a problem in that there is large variation.

Furthermore, in the circuit shown in FIG. 8, unnecessary voltage pulses are generated at the rise 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. 9A is input to the transistor 10, the output waveform at terminal B in FIG. 8 becomes as shown in FIG. Since the signal rises rapidly at the rising edge of , the voltage waveform drops slightly as shown at 100 in the figure. Furthermore, after the high voltage pulse is output, an extra voltage pulse as shown at 100 is generated due to the reverse recovery time of the transistor. In this way, due to the generation of extra voltage pulses at the rise of the drive pulse and after outputting the high voltage pulse,
Unnecessary ultrasonic waves will be output from the transducer 12, which will appear as false echoes in images especially at short distances, thereby causing a problem in that the image quality will be significantly degraded.

In particular, such extra voltage pulses cause transistor 10
This occurs when transistors are used in a saturated state, and each transistor has different characteristics, making it impossible to control them.

In FIG. 10, the transistor 10 of the circuit of FIG.
A circuit is shown in which the R element 20 is replaced, and the same problem as in FIG. 8 occurs in this case as well.

Purpose of the Invention The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to configure a circuit at low cost and to eliminate the occurrence of pseudo echoes in close-range images. Therefore, it is an object of the present invention to provide a drive circuit for an ultrasonic transducer, which facilitates drive control of the transducer.

[Means for Solving the Problems] In order to achieve the above object, an ultrasonic transducer drive circuit according to the present invention includes a trigger generation circuit that generates a sawtooth wave trigger signal, and a trigger signal that generates an unsaturated region by the trigger signal. There is an unsaturated switching circuit that performs switching operation and linearly amplifies the trigger signal using a low-voltage power supply. The invention according to claim (2), further comprising: an inductance circuit that applies a voltage to the vibrator, and the vibrator is driven by a high voltage signal controlled by the trigger signal waveform.
The present invention is characterized in that a diode is connected in parallel with an inductance coil provided in the inductance circuit to obtain a unidirectional drive signal.

Further, the invention according to claim (3) is characterized in that the collector voltage of the unsaturated switching circuit is set to a predetermined voltage for receiving only a reflected echo signal with low attenuation from the vibrator.

[Operation] According to the above configuration, it is possible to operate with a low voltage power supply, and the resonator and the inductance coil constituting the inductance circuit are connected in parallel, and the resonator and the inductance coil have an unsaturated transistor. An unsaturated switching circuit is provided, and a sawtooth trigger signal is supplied to the unsaturated switching circuit. Therefore, the sawtooth trigger signal causes the unsaturated transistor to turn to 0N.
- When turned OFF, the energy stored in the inductance coil is directly converted into a high voltage pulse and supplied to the vibrator, and this high voltage pulse generates a good ultrasonic wave.

In this case, the unsaturated transistor operates in the unsaturated region, so there is no accumulation time that occurs in transistors used in the saturated region, and the operating
The FF time can be made extremely fast, and the vibrator can be excited with a good high voltage pulse without causing an unnecessary voltage waveform in the signal supplied to the vibrator in a low voltage power supply.

[Example] Hereinafter, an example of an ultrasonic transducer drive circuit according to the present invention will be described based on the drawings.

FIG. 1 shows a drive circuit according to a first embodiment, and the characteristic feature of the present invention is that a sawtooth wave drive trigger signal causes the transistor to operate in an unsaturated region, and the trigger signal waveform causes the transistor to operate in an unsaturated region. This makes it possible to control the 7-generation pressure applied to the vibrator.

For this purpose, in FIG. 1, a trigger generation circuit 16 that generates a sawtooth wave is provided, and an unsaturated switching circuit that linearly amplifies the sawtooth wave is provided with a feedback resistor R2. That is, the trigger generation circuit 16 is connected so that the trigger signal is input to the unsaturated transistor ]8 via the capacitor C1, while the feedback resistor R2
is connected in parallel to the emitter terminal together with the protective resistor R1.

And unsaturated type!・VCE is the voltage between the collector and emitter of the transistor 18. If the forward voltage effect of the diode D1 is Vp and the DC resistance of the inductance coil L is r, then the low voltage power supply -VEE is given by the following equation.

VEE I 31 o (R2+r L) 10Vc
p 10Vp... (2) Here, if the saturation voltage between the collector and emitter of the unsaturated transistor 18 is VCE (s a t ), then
According to the above formula (2), v cE> V CE (S a
If the low voltage power supply -VEE is set so that
The unsaturated transistor 18 always operates in the active region when turned on, and functions as an unsaturated switch.

Further, an inductance coil L1 is inserted as an inductance circuit in parallel with the vibrator 12, and a diode D2 is connected in series with the vibrator 12 between the inductance coil L1 and the unsaturated transistor 18. This diode D2 is provided to reduce the withstand voltage to the vibrator 12 by half.

According to such an unsaturated switching circuit, a sawtooth trigger signal is applied to the base terminal of the unsaturated transistor 18 so that the change in voltage and current can be set sufficiently small with respect to time changes. Therefore, generation of unnecessary waveforms at the rise of the conventional trigger signal can be suppressed. Furthermore, since the unsaturated transistor 18 is operated in the unsaturated region, the transistor is operated in the unsaturated region Ij
Since no accumulation time occurs when operating in the region, unnecessary voltage waveforms are not generated in the signal given to the vibrator 12.

Furthermore, since the unsaturated transistor 18 operates in the unsaturated region, the magnitude i3 of the current flowing through the inductance coil Ll is proportional to the magnitude of the sawtooth wave of the incoming horn trigger signal. Therefore, by changing the magnitude of the manual trigger signal,
It becomes possible to control the high voltage pulse generated by the above equation (1).

That is, according to the sawtooth wave trigger signal shown in FIG. 2(A), the unsaturated transistor 18 is turned on at the rise of the sawtooth wave, and a linearly varying current i3 flows in the direction of the arrow in FIG. Energy will be stored in the inductance coil L1. When the sawtooth wave falls, the unsaturated transistor 18 is instantly turned off.
At both ends of L, inductance coils ■ and ■, the above (
A pulse of high voltage Vo obtained by equation 1) is generated.

This high voltage pulse, as shown in FIG. 2(B),
The waveform is a sine wave that rises from the falling point of the sawtooth wave (trigger signal) to -F, and the generation position of this high voltage pulse also coincides with the falling position of the trigger signal, so the falling time can be changed. The position where the high voltage pulse is generated 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 Ll. This is similar to the conventional example shown in FIG.
This can also be achieved by inserting a suitable capacitor in parallel with 2.

Note that the resistor R2 connected to the emitter terminal of the unsaturated transistor 18 is a protection resistor for current limiting, but it also functions as a feedback resistor, and the linear amplification degree can be adjusted by changing the value of the feedback resistor R2. Can be adjusted.

Therefore, by changing the feedback resistance R2 appropriately, this feedback resistance R2
By performing a current feedback effect at the emitter, variations in the characteristics of the unsaturated transistor 18 can be corrected and the circuit can be operated satisfactorily.

Further, the diode D and the capacitor C1 perform a DC regeneration function (clamp circuit), thereby making it possible to fix the sawtooth waveform input as a trigger signal to a constant level.

Furthermore, the diode D2 is provided to block a reverse voltage to the collector of the unsaturated transistor 18, and at the same time increases the withstand voltage of the unsaturated transistor 18, it also connects the unsaturated transistor 1B and the vibrator 1 during reception.
2 and serves to ensure 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,
Output from the terminal to the signal processing circuit for image display.

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

First, the trigger generation circuit 16 generates a sawtooth wave trigger signal as shown in FIG.
supplied to Then, the unsaturated transistor 18
gradually starts conducting, and the feedback resistor R2 and diode D1
A current I flows in the direction of the arrow from the low 7-di voltage power source -EE to the inductance coil L through the inductance coil L. This current I
3 is a current obtained by linearly amplifying the sawtooth wave that is the trigger signal, and a changing current is applied to the inductance coil Ll.

In this case, as is clear from a comparison between FIG. 2 and FIG. 9, an unnecessary voltage waveform 10
0 does not occur. This is because the trigger signal of the present invention is a sawtooth wave, and its rise is gentle, so that unnecessary signals caused by sudden rises and falls unlike conventional rectangular wave pulses are not generated. Further, even after a high voltage pulse is generated, an unnecessary voltage waveform 101 as shown in FIG. 9 is not generated. This is because the present invention uses an unsaturated transistor in the unsaturated region as 0N10FF.
This is because, since the transistor is in operation, there is no accumulation time required when an unsaturated transistor is operated in a saturated region.

Then, when the unsaturated transistor 18 is turned off, the energy applied to the inductance coil L1 is output, a voltage pulse according to the equation (1) is generated, and the vibrator 12 is thereby driven.

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 inductance coil L
A diode D3 is inserted in parallel with (1), thereby making it possible to obtain a directional output as shown in FIG. 4(B).

FIG. 5 shows a third embodiment of the present invention, which is characterized by widening the dynamic range when receiving echo signals.

In other words, a low voltage power supply is connected to the ground terminal F of the resistor R3.
is connected, and the voltage on the cathode side C of diode D2 is maintained at, for example, about +10 volts, thereby setting the operating voltage high. In this case, signals that are greatly attenuated when reflected inside the subject are not received, and only large signals that are less attenuated are received. Therefore, it is possible to obtain diagnostic images with good image quality by using it as a circuit for driving a vibrator for short-range use or a vibrator for fetal observation, which is applied inside a subject that is mostly composed of water or other substances. becomes possible.

Although the above embodiments have been described using NPN unsaturated transistors as switching circuit elements, similar circuits can be constructed using PNP unsaturated transistors or MOS unsaturated transistors. Also,
The sawtooth wave formed by the trigger generation circuit 16 can also have a non-linear waveform, and the linear waveform can perform the same operation as in the above embodiment.

[Effects of the Invention] As explained above, according to the present invention, a sawtooth trigger signal is used to operate a switch element in an unsaturated region, and the high voltage pulse generated thereby is transmitted to a vibrator via an inductance coil. As a result, high voltage pulses can be generated effectively without being affected by the input/output capacitance of unsaturated transistors, accumulation time, etc. In particular, this high voltage pulse can be arbitrarily controlled by the input trigger signal. Since electronic scanning can be performed by changing the driving time and driving voltage of each transducer, it is possible to perform beam convergence of an array type ultrasonic probe or the like well, and to reduce side lobes.

In addition, the drive circuit can be operated with a low-voltage power supply without using an expensive high-voltage power supply, making it possible to obtain a highly safe ultrasonic diagnostic device. Since it is not necessary, it is extremely useful as a low-cost drive circuit for a portable ultrasonic diagnostic device that uses batteries.

According to the invention of claim (2), there is also an effect that unidirectional output can be obtained.

Further, according to the invention of claim (3), only large signals with little attenuation are received, and an effect is produced that the circuit is useful as a circuit for driving a vibrator for short distance use or a vibrator for fetal observation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of an ultrasonic transducer drive circuit according to the present invention, FIG. 2 is a waveform diagram showing operating signals in FIG. 1, and FIG. 3 is a second embodiment of the present invention. A circuit diagram showing an example, FIG. 4 is a waveform diagram showing the operating 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. 7 is a waveform diagram showing the operating 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 is a waveform diagram showing the operating signals in FIG. 8. Waveform diagram shown, No. 10
The figure is a circuit diagram showing another conventional example using a low voltage power supply. 10... Transistor 12... Vibrator 14... Amplifier 16... Trigger generation circuit 18... Unsaturated transistor R2... Feedback resistor Dt, D2, D3... Diode L,
... Inductance coil. + 1 Daishanachiji 3rd evening J Umaba l beg 9th 11ZI Figure 1

Claims (3)

[Claims] (1) A trigger generation circuit that generates a sawtooth wave trigger signal, an unsaturated switching circuit that performs a switching operation in an unsaturated region using the trigger signal, and linearly amplifies the trigger signal using a low voltage power supply; an inductance circuit that inputs a changing current from a saturated switching circuit and applies a high voltage to the vibrator by turning off the unsaturated switching circuit; A drive circuit for the ultrasonic transducer that drives the child. (2) In the apparatus according to claim (1), the ultrasonic transducer is characterized in that a diode is connected in parallel with an inductance coil provided in the inductance circuit to obtain a unidirectional drive signal. drive circuit. (3) The device according to claim (1), wherein the collector voltage of the unsaturated switching circuit is set to a predetermined voltage for receiving only a reflected echo signal with low attenuation from the vibrator. Ultrasonic transducer drive circuit.