JPH0478051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a high-voltage switch circuit used in an electronic scanning type ultrasound imaging device or the like.

[Technical Background of the Invention] An electronic scanning type ultrasound imaging device uses, for example, an array type ultrasound probe (hereinafter referred to as a probe) in which a plurality of ultrasound transducer elements are arranged in parallel, and uses a linear scan type ultrasound imaging device. If so, a predetermined number of adjacent ultrasonic vibrating elements are set as a set, and an ultrasonic excitation pulse is applied to each element in the set with a delay time corresponding to the position of the ultrasonic convergence point. an ultrasonic vibrating element in which the ultrasonic waves are excited and transmitted respectively, and transmitted in the form of a beam by interference due to the phase difference of the transmitted ultrasonic waves due to this delay, and the echoes of the beam-shaped ultrasonic waves are subjected to the above excitation. After capturing and converting them into electrical signals and giving them a delay corresponding to the delay time, these are added together, the time axes are aligned, and the ultrasound image signal is sent to a display device as an ultrasound video signal to display the ultrasound image on the probe. The sound wave beam is displayed at the display device screen position corresponding to the sound wave beam transmission position. Next, a new set of ultrasonic transducer elements shifted by the pitch is excited with the delay described above, and its echo is captured and delayed as described above to generate a video signal. Convert and display.

By repeating such control, ultrasound beam scanning is performed and an ultrasound image is obtained.

In addition, in the sector scan type, an ultrasonic excitation pulse with a delay time corresponding to the ultrasonic beam transmission direction is given to each ultrasonic vibrating element to cause it to transmit ultrasonic waves, and the echoes are transmitted individually. The ultrasonic beam is detected by the ultrasonic transducer and converted into an electric signal, then delayed by giving a delay time corresponding to the delay time at the time of transmission, and then added and sent to a display device to transmit the ultrasonic beam in the probe. The ultrasonic beam is displayed at a position on the display screen corresponding to the position, and the ultrasonic beam is electronically sector-scanned by controlling the transmission direction angle to change sequentially.

By the way, as mentioned above, in electronic scanning type ultrasound imaging devices, an array type probe in which multiple ultrasonic transducer elements are arranged in parallel is used as the probe, but in recent years, in order to improve resolution, a single ultrasonic transducer element has been used as the probe. The number of ultrasonic transducer elements is increased by narrowing one width, which causes the following problems.

The first point is that as the number of ultrasonic transducer elements increases, the number of cable cores increases and the cable itself becomes thicker.

As the cable becomes thicker, reliability decreases and, since the cable is directly connected to the probe, operability becomes very poor.

The second point is that a high-voltage electric signal is applied to the ultrasonic vibrating element as an excitation pulse to cause ultrasonic excitation, but a pulser circuit, which is a circuit that generates the excitation pulse, is required for the number of ultrasonic vibrating elements in the probe. Therefore, the cost of the system increases and the system also becomes larger.

However, in the case of the linear scan method, for example, pulsar circuits are prepared for the number of ultrasonic vibrating elements for one set to be excited, and a high voltage switch circuit is provided between these pulsar circuits and each ultrasonic vibrating element. If this high-voltage switch circuit is selectively switched and controlled to connect the set of ultrasonic vibration elements to be excited and the high-voltage switch circuit, the number of pulser circuits can be reduced, and the high-voltage switch circuit can be provided inside the probe. If so, the number of core wires in the cable can be reduced accordingly.

By the way, there are conventionally used high pressure switches as shown in FIGS. 1 and 2.

The device shown in FIG. 1 is of the diode switch type, and its operating principle will be explained as follows.

That is, in the figure, a is an input terminal to which an excitation pulse for ultrasonic excitation is input, and a diode D
The anode side of 1 is connected. An ultrasonic vibration element Xtal is connected between the cathode side b of this diode D1 and the ground point, and the cathode b is connected to an NPN type transistor
Connected to point e on the collector side of TR1. The emitter side of transistor TR1 is grounded, and
The base side is a control signal input terminal c via a resistor R3.
It is connected to the. Further, the point e is connected to a supply point d of the positive potential Vh via a resistor R1.

In such a configuration, a control signal for on/off control of this switch circuit is applied to the control signal input terminal c. Now, when an H level signal is applied to c, transistor TR1 is turned on, and its emitter and collector are short-circuited. This allows e
The point has zero potential, and therefore point b also has zero potential. Therefore, when an excitation pulse is applied to the input terminal a, the diode D1 becomes conductive, and a positive excitation pulse is supplied to the ultrasonic transducer element Xtal. Further, when an L level signal is applied to point c, the transistor TR1 is turned off, so that point e becomes a positive potential Vh, and point b also becomes a positive potential Vh. As a result, the diode D1 is turned off, and no excitation pulse is applied to the ultrasonic transducer element Xtal.
The above is an explanation of the configuration shown in FIG.

Next, FIG. 2 will be explained. This configuration is
This is a MOS-FET switch type high voltage switch circuit, and in the figure, a is the input terminal for excitation pulses, and b is the output terminal. There is a MOS- between terminals a and b.
The drain D and source S of FET (MOS type field effect transistor) T1 are connected to each other. Further, an ultrasonic vibration element Xtal is connected between the output terminal b and the ground point. c is a control signal terminal, and this terminal is connected to the base of the NPN transistor TR1 through a parallel connection circuit of resistor R2 and capacitor C1. Therefore, when the control signal input terminal c becomes H level, the transistor TR1 A short circuit occurs.

Incidentally, the capacitor C1 is intended to speed up the on/off operation of the transistor TR1.

The collector side of transistor TR1 is connected to the MOS-
It is connected to the gate G of FET T1, and
A Zener diode ZD1 for bias setting is connected between the gate G and source S of this MOS-FET T1 with the anode side as the source side.

Further, the gate G is connected to a terminal d to which a positive potential Vb is supplied via a resistor R1. R3
is a resistor connected in parallel to the ultrasonic vibration element Xtal.

In such a configuration, H is connected to the control signal terminal c.
When a level signal is applied, the transistor TR
1 is turned on, so the emitter potential of transistor TR1 becomes the ground potential, and the MOS-FET T
The gate potential of 1 also becomes the ground potential. Therefore,
The MOS-FET T1 is turned off, and the excitation pulse applied to the input terminal a is blocked by this FET and is not applied to the ultrasonic transducer element.

The voltage applied to the control signal input terminal c is L
When the level is reached, the transistor TR1 turns off, and therefore the gate potential of the MOS-FET T1 becomes Vb.
Therefore, MOS-FET T1 is conductive and the excitation pulse applied to input terminal a is applied to this MOS-FET T1.
It will be supplied to the ultrasonic vibration element Xtal via FET T1.

In this way, excitation pulse switching can be performed.

Here, we will compare the advantages and disadvantages of these high voltage switch circuits.

First of all, let's think about isolation. Isolation refers to leakage from the input to the output terminal or from the output to the input when the switch is off, and this is the capacitance between the terminals of diode D1 and the drain D-
It is determined by the source S capacitance.

Generally, the capacitance between the terminals of a diode is MOS-FET
It is smaller than T, and the diode switch type is better in terms of isolation.

In other words, normally, high voltage switch circuits are grouped into several channels and connected to a common terminal (COMMON) on the input side.
and use it. For example, the inputs of three channels are set to common, and only one channel is turned on and the others are turned off.

At that time, if the capacitance is large when off, there is a risk that high frequency components will be absorbed and the received signal will become smaller.
In this respect, the diode switch type is advantageous over the MOS-FET type. Another problem from the perspective of the ultrasonic transducer is the magnitude of the DC voltage that is directly applied to the ultrasonic transducer in addition to the high-voltage pulse.

Regarding this point, the diode switch type uses a DC positive potential due to diode switching.
Vh is used, and this is applied to the anode side of the diode, and since the ultrasonic vibrating element is connected to this anode, this direct current positive potential is directly applied, which is a problem.

On the other hand, in the MOS-FET type, such a direct current positive potential is not used for the MOS-FET, so the above-mentioned problem does not occur. Directly applying direct current high voltage to the ultrasonic transducer is a safety issue, and since high voltage is applied by control signals, it is not possible to generate high voltage pulses without applying high voltage excitation pulses. This results in the appearance of an audio signal whose phase is not controlled, which may result in noise on the video. Also,
Considering the lifespan of the ultrasonic transducer, it is better to keep the DC voltage applied to the ultrasonic transducer as low as possible.

Also, MOS-
FET switch type is better.

In this way, each method has its advantages and disadvantages,
A high voltage switch circuit that combines the features of both is desired.

[Object of the Invention] The present invention has been made in view of the above circumstances, and provides a high voltage switch circuit with good isolation, small input capacitance, and in which no high voltage is applied to the ultrasonic vibrating element. The purpose is to

[Summary of the invention] That is, in order to achieve the above object, the present invention
a forward-connected diode for passing a high voltage signal; a pull-up resistor connected to the cathode side of the diode for applying a DC high voltage; a control means for controlling the current flowing through the pull-up resistor; A field effect transistor is connected to the cathode side of the ultrasonic transducer to switch the high voltage signal and apply it to the ultrasonic transducer to which the high voltage signal is supplied, and a switch circuit using a diode and a field effect transistor is used in combination. Try to compensate for the shortcomings of both.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a diagram showing the basic configuration of a high voltage switch circuit according to the present invention. As can be seen from the figure, this circuit connects the input terminal a of the MOS-FET type conventional circuit explained in Fig. 2 and the drain D of MOS-FET T1.
A diode D1 is connected in series in the forward direction between the two.

In such a configuration, H is connected to the control signal terminal c.
When a level signal is applied, the transistor TR
1 is turned on, and therefore, the emitter potential of transistor TR1 becomes ground potential, and the MOS-FET
The gate potential of T1 also becomes the ground potential. Therefore,
MOS-FET T1 is turned off, so a positive potential Vh is applied to the cathode side of diode D1,
Diode D1 is turned off, and the excitation pulse applied to input terminal a is connected to this diode D1.
It is blocked by MOS-FET T1 and is not applied to the ultrasonic vibration element.

When the voltage applied to the control signal terminal c becomes L level, the transistor TR1 turns off, and therefore the gate potential of the MOS-FET T1 becomes Vb, and the MOS-FET T1 becomes conductive and the voltage applied to the input terminal a is turned off. The excitation pulse generated by this diode D1
Since the potential on the cathode D1 side of the MOS-
It will be supplied to the ultrasonic vibration element Xtal via FET T1.

In this way, excitation pulse switching can be performed.

In this circuit, the diode and MOS−
Since it uses FET, it has the advantages of both as mentioned above, and can compensate for their disadvantages.

By the way, in this circuit, MOS-FET T
A pull-up resistor R1 for supplying a high voltage positive potential to the cathode of the Vh diode D1 is connected to the drain D of the transistor 1, and a current always flows through this resistor R1 while the high voltage switch is on. This resistor R1 has a power loss of about Vh ² /R1 when the high voltage switch is on.

In this circuit, since Vh is large, R1
If the value is not increased, power loss will increase. However, if R1 is increased, the capacitance seen from the drain D of MOS-FET T1 becomes large, and the potential at point f becomes
Diode D does not recover easily to the level of Vh.
1 cannot be turned off. Therefore, resistance R1
Even if the power loss is reduced by reducing the resistance value of
so that the potential at point f quickly recovers to the level of Vh.
That is, in order to reduce power consumption and not reduce the switching speed, a transistor is connected in series with the pull-up resistor R11 as shown in FIG. 4. That is, this circuit further adds a transistor TR12 to the circuit shown in FIG. 3 to create a constant current circuit configuration, and when the high voltage switch is on, the bias voltage is applied to the resistors R16 and R15 so that the current does not exceed a certain level in the transistor TR12. The settings are as follows. However, if the value of the constant current is small, the recovery time for the Vh level at point f will still be long. Therefore, by connecting a capacitor C2 in series between the base of the transistor TR12 and the gate G of the MOS-FET T1, the falling pulse when the transistor TR11 is turned on from off is applied to the base of the transistor TR12. The collector current of this transistor TR12 is controlled to speed up the rise time of the charging voltage at point f. That is, only when the high voltage switch is turned from on to off, a large current is caused to flow, so that the recovery to the Vh level at point f is accelerated, and the operation of the high voltage switch is accelerated.

Furthermore, when the high pressure switch is turned off or on,
When a positive pulse is supplied to the transistor TR12 of the constant current circuit through the capacitor C2, the capacitor C2 controls the transistor TR12 of the constant current circuit.
Although there is a delay in the input to TR12, the high-voltage switch circuit has a small resistance value of resistor R14, so the discharge time is shortened, and therefore the transistor TR
Delaying the on time of 12 does not have much effect.
However, the high-voltage switch circuit shown in FIG. 5 attempts to turn on the transistor TR12 only when the high-voltage switch changes from on to off, without actively using the capacitor C2.

This high voltage switch circuit uses a MOS-FET T1 instead of the pull-up resistor R1 in the circuit shown in Figure 3.
A PNP type transistor TR14 is placed on the drain D side of the
and R11 are connected in series, and the transistor TR
A resistor R15 is connected between the base of 14 and the positive potential Vh. Then, an AND-type gate circuit G1 is provided which is operated by the input of the control signal input terminal c and the input of the gate control input terminal g, and the transistor TR14 is controlled to control the transistor TR14.
NPN is connected to the base side of TR14 via resistor R16.
Connect the collector of the type transistor TR15,
By grounding the emitter and turning on and off this transistor TR15, the transistor TR14 is turned on.
Make it possible to turn it off. Further, the output side of the gate circuit G1 and the transistor TR15
The transistor TR15 is connected to the base of the transistor TR15 through a resistor R17, so that the transistor TR15 can be controlled on and off by the output of the gate circuit G1.

According to this circuit configuration, when the gate control input terminal g is at H level, when an H level control signal is input to the control signal input terminal c, the transistor TR11
is turned on, the gate potential of MOS-FET T1 becomes ground level, and therefore MOS-FET T1 is turned off. Further, the output of the gate circuit G1 becomes H level, which turns on the transistor TR15, lowers the base potential of the transistor TR14, turns on the transistor TR14, and causes a large current to flow through R11 and TR14, causing the diode D1 to turn on. The cathode potential becomes Vh in a short time. Therefore, the diode D1 is turned off, and the excitation pulse input to the input terminal a is blocked by the diode D1 and the MOS-FET T1, which are turned off.

Further, when an L level control signal is applied to the control signal input terminal c, the transistor TR11 is turned off, thereby turning on the MOS-FET T1.

On the other hand, the output level of the gate circuit G1 becomes L, thereby turning off the transistor TR15. And as a result, transistor TR14
is also turned off, and the potential Vh applied to the cathode of the diode D1 is cut off by the transistor TR14.

Therefore, the excitation pulse is applied to diode D1, MOS
- It is applied to the ultrasonic vibration element Xtal through FET T1, and excitation is performed.

Now, considering isolation, as mentioned above, the isolation of a diode is determined by the capacitance between its terminals, and the isolation of a MOS-FET is determined by the capacitance between its drain and source. The level is recovered to Vh at point f by allowing absorption in a short time, the diode is turned off quickly, and after recovery to the Vh level, the positive potential Vh is quickly cut off and the MOS-FET T1 is used. By turning off the voltage, it is possible to prevent the positive potential Vh from being applied for a long time. To do this, when the control signal changes from L level to H level, a short pulse synchronized with the rise of the control signal is input as a gate control signal to the gate control signal input terminal g to turn on the transistor TR15 for a short time, and the bias resistor R15 is turned on for a short time. , R16, a constant current determined under the bias voltage determined by transistor TR14 is caused to flow from the transistor TR14 to the cathode side of the diode D1. This allows rapid recovery to the Vh level at point f.

FIG. 6 shows an example of a high voltage switch system according to the present invention, and s1 to s128 are the high voltage switch circuits (for example, those shown in FIG. 5), and these 128
Ultrasonic vibration elements X1 to X128 are connected to the output terminals b1 to b128 of the high voltage switch circuits s1 to s128, respectively. a1~a1
Reference numerals 28 denote input terminals, and these input terminals a1 to a128 are independent, and a high voltage excitation pulse is supplied to each input terminal. Whether these high voltage switches are turned on or off is determined by control signal input terminals c1 to c128, and each data is processed by a 128-bit shift register RG. A DC voltage Vh is applied to the terminals e1 to e128 of the high voltage switch circuits s1 to s128,
A voltage Vb for control is applied to the terminal d1. A speed up pulse is added to g1 to g128 to increase the speed when the high pressure switch changes from on to off. In addition, the above terminals a1 to a1
28, b1~b128, c1~c128, d1~
d128, e1 to e128, and g1 to g128 correspond to a, b, c, d, e, and g in FIG. 5, respectively.

FIG. 7 is a timing chart illustrating the operation of the high pressure switch system according to the present invention. The 128-bit shift register RG has an internal latch and stores the data signal (Fig. 7b) synchronized with the clock signal (Fig. 7a) in the order of 128 clocks, and when this data receives the 128th clock, the data signal (Fig. 7b) is stored in the 128th clock. A strobe (STROBE) signal (FIG. 7c) synchronized with the clock is outputted to output terminals c1 to c128. (This waveform is shown as c1 and c2 as representative of the 128 channels in Fig. 7 d and e.) The waveform at point f shown in Fig. 7 f shows a long time constant when the high voltage switch changes from on to off. However, when switching from off to on, the time constant is short.Therefore, as shown in Figure 7g, the gate control signal input terminal g is connected in synchronization with the strobe signal to sufficiently cover the long time constant. Provides a pulse, (SPEED UP PULSE).
When the data is at H level, this pulse passes through the gate circuit G1 in FIG.
is turned on and current flows through the transistor TR14.
When the data is at L level, the pulse is blocked by the gate circuit G1, the transistor TR15 is turned off, and therefore the transistor TR14 is also turned off.

Therefore, the power consumption of the circuit is very low.

When the previous data was H level and this time it is also H level data, the pulse passes through gate circuit G1, so transistor TR15 is turned on, but since the potential at point f has almost reached Vh level, transistor TR14 is turned on. Almost no current flows.

As described above, according to the present invention, a switch circuit with high isolation can be obtained, and the quality of images can be further improved. Furthermore, since no DC high voltage is applied to the ultrasonic transducer, image deterioration due to parasitic vibrations can be suppressed. Further, it is safe because no high DC voltage is applied to the ultrasonic transducer element, and furthermore, since the input capacitance seen from the input side can be reduced, many channels can be used as common inputs. In addition to reducing power consumption during static operation,
Switching time can be made faster.

[Effects of the Invention] As detailed above, the present invention includes a diode connected in the forward direction through which a high voltage signal passes, a pull-up resistor connected to the cathode side of this diode and applying a DC high voltage to the cathode, A control means for controlling the current flowing through the pull-up resistor;
A field effect transistor connected to the cathode side of the diode switches the high voltage signal and supplies it to the ultrasonic vibration element to which the high voltage signal is supplied, and the switching of the diode is performed in parallel by switching the field effect transistor. This makes it possible to take advantage of the strengths of diode switches and field effect transistors and compensate for their weaknesses, resulting in good isolation.Furthermore, since the field effect transistor is connected after the diode, it is possible to The applied DC high voltage for cutoff is cut off by this field effect transistor, and therefore is not applied directly to the ultrasonic transducer element, which prevents image deterioration due to parasitic vibrations, improves safety, and increases switching speed. without dropping it,
It is possible to provide a high voltage switch circuit having features such as reducing power consumption and preventing heat generation.
In particular, the present invention provides a high voltage pull-up resistor (see Figures 4 and 5) that is required when a diode switch and a field effect transistor switch are combined.
In order to solve the heat generation problem of R11) in the figure and to improve the switching speed when the high voltage switch is turned off, a control means is provided to control the current flowing through the pull-up resistor, and the value of the pull-up resistor can be reduced. By using this control means to control the current when the high voltage switch is turned off, it is possible to avoid the problem that when the diode switch is turned off earlier, a large amount of steady-state current flows, which causes heat generation in the pull-up resistor and field effect transistor. , heat generation can be suppressed without reducing the switching speed of the diode switch.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing an example of a conventional circuit, Figure 3 is a circuit diagram showing the basic configuration of the present invention, and Figure 4 is a diagram showing an example of a conventional circuit.
5 is a circuit diagram showing another embodiment of the present invention,
FIG. 6 is a block diagram showing an example of application of the circuit according to the present invention, and FIG. 7 is a time chart for explaining its operation. D1...Diode, T1...MOS-FET,
R11~R17...Resistance, TR11~TR15...
...Transistor, G1...Gate circuit, C1, C
2... Capacitor.

Claims (1)

[Claims] 1. A diode connected in the forward direction through which a high-voltage signal passes; a pull-up resistor connected to the cathode side of this diode and applying a DC high voltage to the cathode; and a current flowing through the pull-up resistor. A high voltage switch circuit comprising: a control means for controlling current; and a field effect transistor connected to the cathode side of the diode to switch the high voltage signal and provide the high voltage signal to an object to be supplied with the high voltage signal.