JPH0777579B2 - Pulser circuit for ultrasonic transducer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit (pulser circuit) for generating a pulse for driving an ultrasonic transducer of an ultrasonic diagnostic apparatus or the like.

[0002]

2. Description of the Related Art An ultrasonic diagnostic apparatus uses various ultrasonic pulses according to the mode of use. To obtain a tomographic image, a pulse with a small wave number is used to increase resolution, and when capturing a blood flow by the Doppler effect, a pulse having a relatively long duration is used for each purpose. Further, the pulse generation period is also changed according to various purposes. On the other hand, since there is a certain limit to the energy of the ultrasonic wave that is input to the human body for health reasons, when changing the wave number or the occurrence cycle of the ultrasonic pulse, the pulse amplitude also changes due to this total energy restriction. Need to change.

In order to change the amplitude of the ultrasonic pulse, the voltage of the drive pulse signal applied to the ultrasonic vibrator is changed. Since it is difficult to change the drive voltage of the circuit (pulser circuit) that generates the pulse signal for driving the ultrasonic transducer, it is difficult to operate the ultrasonic transducer in multiple modes. In order to perform (correctly, to generate drive pulses of different voltages), as shown in FIG. 3A, a dedicated pulser circuit corresponding to each mode is provided.
PUL1 to PUL3 (three in FIG. 3, but actually any number) were prepared. The pulsar circuits PUL1 to PUL3 are connected to different power supply voltages VP1 to VP3, respectively, and they are switched by the switches SW1 to SW3 according to the use mode and connected to the ultrasonic transducer OSC. Note that P1 to P3 are pulse signal inputs.

[0004]

Since the voltage of the pulse for driving the ultrasonic transducer is as high as several V to 200 V and the current is also several A, the pulser circuit PUL1 as shown in FIG. 3A is used.
If you intend to install a changeover switch on the output side of ~ PUL3, you must use a relay or a high voltage semiconductor switch as the changeover switch. However, the repetition time of the ultrasonic pulse is as short as tens to hundreds of microseconds, so that the relay cannot follow such speed. Further, there is a problem that the high voltage semiconductor switch is expensive and has a high ON resistance.

In order to avoid such a problem, FIG.
It is conceivable to provide ordinary semiconductor switches SW1 to SW3 on the inputs P1 to P3 side of the pulser circuits PUL1 to PUL3 as shown in FIG. However, in this case, since the pulser circuits PUL1 to PUL3 are connected to each other on the output side (the ultrasonic transducer OSC side), one changeover switch (for example, SW1) is turned on.
When it becomes N and the corresponding pulsar circuit PUL1 is activated, the other two pulsar circuits PUL2 and PUL3 become pulsar circuit PUL.
The load becomes 1 and the waveform of the drive pulse is distorted. The present invention has been made to solve such a problem, and an object thereof is to generate a drive pulse having a high speed and a correct waveform without using an expensive high voltage semiconductor switch. It is to provide a pulsar circuit that can do this.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to a pulser in which a plurality of unit pulser circuits for generating pulse signals for driving an ultrasonic transducer are connected in parallel. In the circuit, (a) each unit pulser circuit is connected in series between a high voltage side power source and a low voltage side power source, and is provided with two switch transistors that perform opposite opening and closing operations for the same input signal, (B) The output to the ultrasonic transducer is taken out from the connection point of both switch transistors, and (c) the forward diode is provided between each switch transistor and the output point. It is characterized by

[0007]

Since each unit pulser circuit is connected in parallel to one output line (which is connected to one ultrasonic transducer), when a certain unit pulser circuit operates (that is, that unit pulser circuit). When either the high-voltage side or the low-voltage side of the switch transistor is turned on), a voltage is applied to the low-voltage side or high-voltage side switch transistor of the other unit pulser circuit through its output line. The parasitic capacitance of the transistor is charged. However, once charged, the diode between each switch transistor and the output line is in the opposite direction to discharge, which prevents discharge of the charged electric charge of the parasitic capacitance. Therefore, once charged, the parasitic capacitance is not further charged after the second time, and when one unit pulser circuit operates, another unit pulser circuit does not become a load after the second pulse.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. The pulsar circuit of the present embodiment outputs the drive pulse Po to one ultrasonic transducer (not shown) among a large number of ultrasonic transducers that constitute the probe of the ultrasonic diagnostic apparatus. is there. This pulser circuit is composed of three unit pulser circuits connected in parallel to the ultrasonic transducer. The three unit pulser circuits are connected to power sources having different voltages, and output drive pulses Po of different modes to the ultrasonic transducer. The number of unit pulser circuits may be two or four or more.

In each unit pulser circuit, the high voltage power source VP1 ...
High-side switch transistors Q11 to Q13 and low-side switch transistors Q21 to Q23 are connected in series between VP3 and the ground (the low-voltage side power source). An output line Lout to the ultrasonic transducer is connected between both the high-side and low-side switch transistors, so that all the unit pulser circuits are connected in parallel to the ultrasonic transducer. Forward diodes DS11 to DS23 are connected between the switch transistors Q11 to Q23 and the output line Lout.

The high side switch transistors Q11 to Q13 and the low side switch transistors Q21 to Q23 of each unit pulser circuit are FETs having mutually opposite characteristics (in the example of FIG. 1, the high side switch transistors Q11 to Q13 are p-channel type, and the low side switch transistor Q21 is ~ Q23 is n
Channel type) and both switch transistors Q11 ~
Input signals P1 to P3 are input to the gate of Q23. Diode D drawn next to each switch transistor Q21-Q23
K11 to DK23 and capacitors C11 to C23 represent parasitic diodes and parasitic capacitors of the respective switch transistors Q21 to Q23. When there are no input signals P1 to P3 (at zero potential), all switch transistors Q11 to Q23 are turned off.
Has become.

Now, it is assumed that a pulsed input signal P1 as shown in FIG. 2 is applied to the first pulser circuit. The first negative pulse a turns on the high-side switch transistor Q11 and turns off the low-side switch transistor Q21, so that the potential of the output line Lout (output P
O) becomes VP1. At this time, the voltage VP1 is applied to the low-side switch transistor Q22 of the second pulser circuit and the low-side switch transistor Q23 of the third pulser circuit by the output line Lout.
The parasitic capacitances C22 and C23 of 22 and Q23 are charged with the voltage VP1 (fourth stage in FIG. 2). Therefore, the first output pulse Po
The rising edge of is slightly deformed as shown at the beginning of the second row in FIG.

When the input signal P1 of the first pulser circuit shifts to the positive side b, the high side switch transistor Q11 is turned off and the low side switch transistor Q21 is turned on, so that the potential of the output line Lout (output PO) becomes zero. .
At this time, through the output line Lout, the high side switch transistor Q12 of the second pulser circuit and the third pulser circuit,
Since Q13 is connected to the ground, the parasitic capacitances C12 and C13 of the switch transistors Q12 and Q13 are charged by the respective power supply voltages VP2 and VP3 (third stage in FIG. 2). Therefore, even at the first fall of the output pulse PO, the edge is slightly deformed (second stage in FIG. 2). At this time, the charges stored in the parasitic capacitances C22 and C23 of the switch transistors Q22 and Q23, which have been previously charged, are equal to each diode DS2.
2. It is never discharged by DS23.

Next, when the input signal P1 of the first pulser circuit shifts to the negative side c, the parasitic capacitance C2 of the low side switch transistors Q22 and Q23 of the second and third pulser circuits.
Since C2 and C23 are already charged, they are not charged any more, and the second and third pulser circuits do not become a load of the first pulser circuit. Further, at this time, the parasitic capacitances C12 and C13 of the high side switch transistors Q12 and Q13 of the second and third pulser circuits, which have been previously charged, are changed to the diode DS1.
2. Discharge is blocked by DS13 and the charge is retained as it is. Therefore, when the input signal of the first pulser circuit next shifts to the plus side d, the parasitic capacitance C of the high-side switch transistors Q12 and Q13 of the second and third pulser circuits C
Similarly, 12 and C13 are not charged and do not load the first pulser circuit. That is, after the second wave of the input pulse P1, the switch transistors of the second and third pulser circuits do not load the first pulser circuit, and the output signal P0 is output in the correct form (2 in FIG. 2). Step).

When the power supply voltage of the first pulser circuit is higher than the power supply voltages of the second and third pulser circuits (VP1> V)
P2, VP3), the high side switch transistors Q12 and Q13 of the second and third pulser circuits are a diode and a parasitic diode DK1 between the output line Lout and the high side switch transistors Q12 and Q13, respectively.
2. Protected from reverse voltage by DK13.

[0015]

In the pulser circuit of the ultrasonic oscillator according to the present invention, once the parasitic capacitance of the switch transistor of the pulser circuit other than the pulser circuit in the operating state is charged, each switch transistor and the output point Since the diode is connected between the two, its discharge is prevented. Therefore, the switch transistor of the pulser circuit in the non-operating state is not charged any more, and the waveform is not distorted after the second pulse of the pulse signal output from the pulser circuit in the operating state. Further, since the changeover switch is provided on the input side (low voltage side), it is not necessary to use an expensive high breakdown voltage semiconductor switch, and pulse output can be performed much faster than a relay.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a pulser circuit of an ultrasonic diagnostic apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing changes in the input pulse P1, the output pulse P0, and the voltages VC12, VC13, VC22, and VC23 across the parasitic capacitances C12, C13, C22, and C23 of the pulser circuit of the embodiment.

FIG. 3 is a circuit diagram showing an example of connection when a plurality of pulser circuits are connected to one ultrasonic transducer.

[Explanation of symbols]

VP1, VP2, VP3 ... Power supply voltage Q11, Q12, Q13, Q21, Q22, Q23 ... Switch transistors C11, C12, C13, C21, C22, C23 ... Parasitic capacitance DK11, DK12, DK13, DK21, DK22, DK23 ... Parasitic diode DS11, DS12, DS13, DS21, DS22, DS23 ... Discharge prevention diodes P1, P2, P3 ... Input pulse signal Lout ... Output line PO ... Output (ultrasonic transducer drive) pulse signal PUL1, PUL2, PUL3 ... Pulser circuit SW1, SW2, SW3 ... Pulser circuit selector switch OSC ... Ultrasonic transducer

Claims (1)

[Claims] 1. A pulsar circuit comprising a plurality of unit pulser circuits connected in parallel to generate a pulse signal for driving an ultrasonic transducer, wherein each unit pulser circuit comprises a high voltage side power source and a low voltage side power source. It is equipped with two switch transistors that are connected in series between them and perform opposite opening and closing operations for the same input signal, and the output to the ultrasonic transducer is taken out from the connection point of both switch transistors. A pulser circuit for an ultrasonic transducer, further comprising a forward diode between each of the switch transistors and the output point.