JPH0531946B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a transducer drive circuit for an ultrasonic diagnostic device, and particularly to a method for controlling the transmission level when step-driving an ultrasonic probe to transmit pulses. Concerning variable methods.

(Prior art) In medical ultrasound diagnostic equipment, in order to minimize the harmful effects of ultrasound on living organisms, the minimum necessary transmission level is set according to the observation depth, that is, the transmission level is set when observing shallow areas. It is preferable to drop the
Most conventional methods for making the transmission level variable are a method of varying the power supply voltage supplied to a circuit that generates drive pulses, a so-called pulser circuit, and such methods have been widely used.

FIG. 6 is a configuration diagram showing an example thereof. In the figure, Q is a switching transistor, the emitter of which is connected to a common line, and the collector of which a power supply voltage E is applied via a high resistance _R1 . The power supply voltage E is variable, and the voltage can be changed as necessary. Note that a bypass capacitor _C1 is coupled to the high voltage side to bypass high frequency components. TD is a vibrator (piezoelectric element) of the ultrasonic probe, one side is connected to the common line, and the other side is connected to the collector of the transistor Q via the coupling capacitor _C2 . _R2 is simply a DC return resistor connected in parallel to the vibrator TD. DB is a diode bridge, CC ₁ ,
CC ₂ is a constant current circuit and this diode bridge
The part consisting of DB and constant current circuits CC ₁ and CC ₂ is a so-called analog switch, which turns the constant current ON and OFF.
The input and output are turned on and off depending on the and,
It is controlled so that it is OFF when transmitting ultrasonic waves and ON when receiving ultrasonic waves. REC is the first stage of the receiving circuit,
A is the first stage amplifier. At the input terminal of the first stage amplifier A, there is a diode connected in anti-parallel to prevent overvoltage input.
D ₁ , D ₂ and a low frequency removal coil L are each connected between the common lines.

In such a configuration, when a transmission trigger pulse is applied to the gate of transistor Q, the transistor is turned on and the charge charged in coupling capacitor _C2 is rapidly discharged so as to be redistributed to vibrator TD. As a result, the vibrator TD is driven (pulse driven (more accurately, equivalent step driven in this case) by the power supply voltage E). This pulse drive causes the vibrator to generate ultrasonic waves. Transducer TD
Alternatively, when ultrasonic waves are transmitted, a voltage is generated, and this voltage is transmitted to the receiving circuit via an analog switch (in this case, the switch is in the ON state).

In such a circuit, the transmission level is controlled by adjusting the power supply voltage E, but the response speed is slow due to the presence of large bypass capacitors and coupling capacitors, and the transmission level is delayed each time. There was a problem in that it was impossible to independently control the level to a desired value.

The present invention has been made in view of the above problems, and
The purpose is to provide an ultrasonic transducer drive circuit that can easily control the transmission level at high speed while keeping the power supply voltage constant.

(Means for Solving the Problems) The present invention, which solves the above problems, connects a coupling capacitor to the other end of an ultrasonic transducer whose one end is connected to a common line, and connects a coupling capacitor to the coupling capacitor through a high resistance. The ultrasonic vibration is applied to the ultrasonic vibrator by charging the coupling capacitor by connecting it to a high-voltage power source and discharging it by a switching element so as to redistribute the electric charge of the coupling capacitor to the ultrasonic vibrator. In order to obtain a large ultrasonic wave transmission level in the child drive circuit, by increasing the slew rate of the switching element,
In order to sharpen the rising edge of the driving pulse waveform applied to the ultrasonic transducer and, conversely, to suppress the ultrasonic transmission level, the slew rate of the switching element is reduced to sharpen the rise of the driving pulse waveform applied to the ultrasonic transducer. The present invention is characterized by comprising variable means for changing the slew rate of the switching element so as to make the rise of the drive pulse waveform slow.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings. FIG. 1 is a block diagram of essential parts of an embodiment of an ultrasonic transducer drive circuit according to the present invention. In the figure, parts equivalent to those of the conventional example shown in FIG. 6 are given the same reference numerals, and their explanation will be omitted. Q ₁ is in this case an N-channel enhancement type dual gate power FET (FET stands for field effect transistor). The source of FETQ ₁ is connected to the common line, and the drain is applied with a power supply voltage E (usually a constant DC voltage of 100 V) via a resistor R ₁ . In addition, a transmission trigger pulse is given to the first gate _G1 of FETQ ₁ , and an amplifier is given to the second gate _G2 .
A control voltage is applied via _A2 . The characteristics of FETQ ₁ are shown in Figure 2. That is, the first
When the transmission trigger pulse given to the gate _G1 rises from 0 to +5V, the gate _G1 becomes saturated and turns ON, but the voltage of the second gate _G2
A Vd-Id curve (Vd is drain voltage, Id is drain current) with Vq ₂ as a parameter has characteristics as shown in FIG. That is, the Id current value in the constant current region is determined according to the value of Vq ₂ .

The operation in such a configuration will be explained next.
Just before the wave transmission is executed (immediately before the wave transmission trigger pulse is applied), the coupling capacitor _C2 is charged with a voltage equal to the power supply voltage (100V). Transmit trigger pulse
When applied to the first gate G ₁ of FETQ ₁ , FETQ ₁
However, since resistor R ₁ is sufficiently large, resonator TD and FETQ ₁ act as a load for capacitor C ₂ , and the voltage Vd applied to FETQ ₁ is applied to capacitor C 2.
It gradually or rapidly decreases due to the discharge of _C2 .
The discharge during this period depends on the current limit value (determined by the applied voltage Vq ₂ of the second gate G ₂ ) in the constant current region of the FET Q ₁ . That is, the slew rate is capacitor C ₂
Determined by the value of and the current limit value of FETQ ₁ . and,
A voltage that changes in this way will be applied to the vibrator TD. Figure 3 is a diagram showing the relationship between the applied voltage Vq ₂ of the second gate G ₂ and the slew rate, and shows the relationship between the voltage Vq _{2 applied} to the second gate G 2 and the slew rate.
This indicates that the larger the slew rate is, the larger the slew rate is.

By the way, it has been confirmed that the relationship between the rise time T of the drive pulse given to the vibrator TD and the transmission level (peak-to-peak value Pp-p of the sound pressure amplitude) is as shown in Figure 4. . Figure 4 shows that the center frequency f ₀ of the resonator is 2MHz, 3.5MHz, 5MHz and
This shows the relationship between the drive pulse and the transmitted wave level for a 7 MHz one, and shows that for any center frequency, the shorter the rise time of the drive pulse, the higher the transmitted wave level.

Therefore, in order to increase the transmission level according to the exploration depth in ultrasonic exploration, that is, when the depth of interest is deep, the rise time of the drive pulse is shortened. That is, it can be seen that the slew rate should be controlled to be large. This is FETQ ₁
This can be achieved by increasing the second gate voltage Vq ₂ as the depth of interest becomes deeper.

In actual operation, the voltage Vq ₂ is set via the amplifier A ₂ to a value that produces a desired slew rate according to the desired exploration depth, and then a wave transmission trigger is applied to the first gate G ₁ . Through this procedure, the transducer TD can arbitrarily generate ultrasonic waves with various transmission levels suitable for different depths, while keeping the power supply voltage constant.

FIG. 5 shows another embodiment of the invention. 5 basically replaces FETQ ₁ in FIG. 3 with a power FET with one gate, and the slew rate is controlled by the voltage applied to the gate G. The output of differential amplifier _A3 is given to the gate voltage. Differential amplifier _A3 has its non-inverting input terminal supplied with a voltage obtained by dividing the reference voltage Vstd with a variable resistor RV, and its inverting input terminal supplied with an inverter INV.
A transmission trigger pulse (0 to 5 VTTL level) passed through a series circuit of diode D ₃ and a voltage obtained by dividing the voltage Vq at the output terminal to ⅓ by resistors of 2KΩ and 1KΩ are applied. When the transmit trigger pulse is not applied (OV), the output voltage Vq of amplifier _A3 becomes a negative saturation voltage, and when the transmit trigger pulse is applied (5V), the output voltage Vq of amplifier A3 becomes the negative saturation voltage. The voltage is proportional to the piezovoltage.
Therefore, by adjusting the variable resistor RV according to the exploration depth, the pulse voltage value applied to the gate G is controlled, and the slew rate is controlled in the same manner as in the previous embodiment, resulting in the ultrasonic transmission level being adjusted. can be controlled.

It is clear that the present invention can be practiced not only by using the power FET as described above but also by using a bipolar transistor or the like having similar current limiting characteristics.

(Effects of the Invention) As described above, according to the present invention, it is possible to control the transmission level while keeping the power supply voltage constant, and the response speed is fast, so that the transmission level can be changed at high speed. There is an advantage that it can be done.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the main part of an embodiment of the ultrasonic transducer drive circuit according to the present invention, Fig. 2 is a diagram showing the characteristics of a dual gate power FET, and Fig. 3 is a diagram showing the characteristics of the FET.
FIG. 4 is a diagram showing the relationship between the rise time of the vibrator driving pulse and the transmission level, FIG. 5 is another embodiment of the present invention, and FIG. The figure is a configuration diagram showing an example of a conventional drive circuit. E...Power supply voltage, _R1 ...Resistance, _C2 ...Coupling capacitor, TD...Resonator, _Q1 ...FET, _A2 ,
A ₃ ...Amplifier, RV...Variable resistor, INV...Inverter.

Claims (1)

[Claims] 1. A coupling capacitor is connected to the other end of the ultrasonic transducer whose one end is connected to a common line, and a high-voltage power supply is connected to this coupling capacitor via a high resistance to charge the ultrasonic transducer. A large ultrasonic wave transmission level is obtained in an ultrasonic transducer drive circuit that applies a driving pulse to the ultrasonic transducer by discharging the charge of a coupling capacitor by an element so as to redistribute it to the ultrasonic transducer. in case of,
By increasing the slew rate of the switching element, the rise of the drive pulse waveform applied to the ultrasonic transducer is sharpened, and conversely, when suppressing the ultrasonic transmission level, the slew rate of the switching element is decreased. An ultrasonic transducer drive circuit comprising variable means for changing the slew rate of the switching element so as to slow the rise of a drive pulse waveform applied to the ultrasonic transducer. 2. Claim 1, wherein the switching element is a dual-gate FET that receives a trigger pulse on one gate, and the variable means changes the control voltage applied to the remaining gate of the FET. The ultrasonic transducer drive circuit described. 3. The ultrasonic transducer drive circuit according to claim 1, wherein the switching element is an FET that receives a trigger pulse at its gate, and the variable means changes the voltage of the trigger pulse.