JP3144796B2 - Changeover switch and ultrasonic diagnostic apparatus using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a high withstand voltage changeover switch for selecting a transducer in an ultrasonic diagnostic apparatus or the like.

[Prior art]

A conventional ultrasonic diagnostic apparatus selects an element group constituting a transmission / reception aperture among a plurality of transducers arranged in an array,
A drive pulse applied to each of these elements is shifted from each other by a predetermined time to form a focused beam at a predetermined position, and the beam is scanned by moving the aperture while sequentially shifting the element group to form one screen. Is what you do. Conventional switches are disclosed in JP-A-56-12846 and JP-A-57
As described in US Pat. No. -153639, the on / off of the diode is controlled by the bias. Also, MO
An example using an SFET is shown in FIG. This is an example in which a region between the drain and source of a high breakdown voltage MOSFET is used. Input end (drain)
When a transmission pulse train is applied to Vx and a voltage higher than Vth is applied to the gate of the MOSFET, the signal passes, and when the voltage is lower than Vth, it is cut off. In addition, although a weak reception signal is input from the source, it can be similarly controlled by turning on and off the MOSFET.

[Problems to be solved by the invention]

In the above-mentioned prior art, in the case of a diode switch, the bias requires switching of a potential equal to or higher than the pulse height of a pulse for driving the ultrasonic vibrator, and the switching time is long. In the case of a MOSFET switch, as shown in FIG.
When a VH transmission pulse is applied, the source potential of the MOSFET becomes VH
And the gate potential rises to the gate-source capacitance Cgs, Vb
+ VH. This value decreases with the time constant of Cgs and the resistance until the applied pulse falls. Since the source changes -VH on the way, the gate potential becomes equal to or lower than Vb. By the repetition,
In the MOSFET, Vgs turns off Vth. Improvements can be seen by increasing the resistance and increasing the specific number, but the switching time is slowed. Therefore, there is a problem that a large number of transmission pulses cannot pass as shown in FIG. An object of the present invention is to provide a switch capable of passing a large number of transmission pulses without delaying the switching time.

[Means for Solving the Problems]

In order to achieve the above object, a configuration is adopted in which a first diode is connected to a side for supplying an ON potential to the gate of a MOSFET, and when OFF, the switch is forcibly grounded by a switch.

[Action]

After the gate of the MOSFET is swung, the escape path is cut off because the first diode is off, and the gate potential is maintained. Therefore, even if the source becomes low potential, Vb is held,
The MOSFET remains conductive and unaffected by repetition. Turning off the MOSFET can be realized by grounding with a switch.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating the principle of the present invention. The MOSFET-M1 constitutes a bidirectional switch, and a gate control circuit 3 for controlling a gate voltage of the MOSFET-M1 comprises an ON / OFF signal or a gate drive signal 1 for applying an ON voltage, and an OFF circuit 2 for extracting a gate charge. When a pulse of peak voltage Vh is input to Vx, M1
Of the gate potential Vg is higher than the potential Vb applied from V1.
Gate of M1. Source capacity Instantaneously, Vb + Vh. Until the pulse goes down, it conventionally decreases through this gate drive circuit. The gate drive circuit 1 is configured to cut off the escape route. The OFF circuit 2 is a circuit that lowers M1 to an OFF potential. FIG. 2 shows a first embodiment of the present invention. The terminal V1 is connected to the anode of the first diode D1 via the first resistor R1, and the cathode of the diode is connected to the gate of the MOSFET. The gate is grounded by a second switch sw.2. When the second switch is off, the gate potential of the MOSFET becomes almost the potential applied to the terminal V1. What is applied to the terminal V1 may be a DC power supply or a signal for controlling on / off. When a pulse with a wave height of Vh is applied at multiple waves,
The gate potential of the MOSFET becomes Vh + Vb. This potential does not decrease because the first diode is turned off by the reverse bias, and when the applied pulse falls to 0 V, Vb can be secured, the MOSFET can be kept on and the multi-wave number can pass. FIG. 3 shows an example in which the off circuit 2 is constituted by a diode D2 and a MOSFET-M2. Input signals of opposite phases to V1 and V2. Alternatively, V1 may be a DC power supply sufficient to turn on M1. In the latter case, when off, M2 turns on and current flows from the power supply. In addition, since there are two terminals V1 and V2, the number of terminals can be reduced by inserting the inverter 4 between V1 and V2 as shown in FIG. 4, and current can be prevented from flowing. If a MOSFET is used for SW2 in FIG. 3 or FIG.
When a pulse is applied to the gate of M1. Source capacity And M2 output capacity And Vy is smaller than Vx. Also, when the pulse is applied for the first time after turning on from off, the cathode of D2 is at a low potential, The current to charge the battery flows. As a result, the cathode potential of D2 rises. Generally, the capacitance of MOSFET is drain. It becomes smaller as the source potential becomes higher. Therefore, when the pulse of the next block is applied, Vy is larger because is smaller than the beginning. Therefore, in this configuration, it is necessary to reduce the absolute value and the variation of the capacity of M2 as much as possible and to suppress the stray capacity. Also, M1 Needs to be set to a large value as long as the switching time permits, to reduce the load effect. FIG. 5 shows an example in which the effect of the capacitance of M2 is removed by setting the cathode of D2 to the Vh potential via a resistor. Next, considering the case where a burst of a bipolar pulse is applied, when -Vh, Vg becomes -Vh + Vb, and D1 is forward-biased and Vg
Rises. With this repetition, there is a fear that Vgs may exceed the allowable Vgs of M1 and be destroyed. Figure 6 shows the gate of M1. This is protected by inserting a Zener diode between the sources. C1 is inserted in M1 In order to increase. FIG. 7 shows an example in which a switch is combined with another switch to reduce leakage when the switch is turned off. Here, a diode switch is used. When V4 is equal to or higher than the applied voltage, the effect is further enhanced. 12 switches 1
Indicates a switch of the present invention. When M1 is off, the cathode of D3 is at a high potential, and D3 is turned off by reverse bias, so that a dual effect of a diode and a MOSFET can be obtained. Set V3 to ground and R2 to a coil that does not contribute to resonance.
Can be suppressed to a negative potential to suppress DC fluctuations caused by turning on and off the switch at the Vw end. FIG. 8 is an example of application to an ultrasonic diagnostic apparatus. The piezoelectric vibrator 7 applied to the driver 9 having the maximum aperture by the timing circuit 10 for focusing the transmission wave and passing through the transmission / reception separation circuit 8 is driven with each phase by the changeover switch 6. The weak signal reflected by the radiated ultrasonic wave from the subject and received again by the piezoelectric vibrator 7 passes through the changeover switch 6 and is transmitted and received by the transmission / reception separation circuit 8 to the signal processing circuit 11.
It is led to. The switch is used as the changeover switch. Although a MOSFET was used for the above sw.2, this is not the only case.

【The invention's effect】

ADVANTAGE OF THE INVENTION According to this invention, favorable switch characteristics can be implement | achieved for element selection etc. of an ultrasonic diagnostic apparatus.

[Brief description of the drawings]

FIG. 1 shows the principle of the present invention, FIGS. 2 to 7 show an embodiment of the present invention, and FIG. 8 shows an application example of an ultrasonic diagnostic apparatus. FIG. 9 shows a conventional example. DESCRIPTION OF SYMBOLS 1... Gate drive circuit 2... Off circuit 3... Gate control circuit 12... Switch 14 4... Inverter 5... Other switches 6. 8 transmission / reception separation circuit, 9 driver 10 timing generation circuit, 11 signal processing circuit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazuo Takasugi 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-63-175517 (JP, A) JP-A-64 −62015 (JP, A) Actually open 57-53733 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03K 17/00-17/70

Claims (3)

(57) [Claims] In a changeover switch for controlling and switching a gate voltage of a MOSFET, a cathode of a first diode and an anode of a second diode are connected to the MOSF.
Connected to a gate of the ET, an anode of the first diode is connected to a power supply via a resistor, a cathode of the second diode is grounded via a switching element, and the MOSFET is turned on and off by the switching element. A changeover switch for controlling on / off of a switch. 2. A plurality of piezoelectric vibrators for transmitting and receiving ultrasonic waves,
A transmission / reception separation circuit for separating transmission and reception of ultrasonic waves, an element selection circuit for selecting the piezoelectric vibrator for transmitting and receiving ultrasonic waves, and a signal processing circuit for processing a signal received by the piezoelectric vibrator In the diagnostic device, the element selection circuit is connected to each of the plurality of piezoelectric vibrators, and the element selection circuit has a cathode of a first diode and an anode of a second diode connected to a gate of a MOSFET, An anode of the first diode is connected via a resistor to an input source for inputting a signal for turning on / off the MOSFET, and a cathode of the second diode is grounded via a switching element; An ultrasonic diagnostic apparatus wherein on / off of the MOSFET is controlled by on / off of an element. 3. A plurality of piezoelectric vibrators for transmitting and receiving ultrasonic waves,
An ultrasonic wave comprising: a transmission / reception separating circuit for separating transmission and reception of the sound wave; an element selection circuit for selecting the piezoelectric vibrator for transmitting and receiving the ultrasonic wave; and a signal processing circuit for processing a signal received by the piezoelectric vibrator. In the diagnostic device, the element selection circuit is connected to each of the plurality of piezoelectric vibrators, and the element selection circuit has a cathode of a first diode and an anode of a second diode connected to a gate of a MOSFET, An anode of the first diode is connected via a resistor to an input source for inputting a signal for turning on / off the MOSFET, and a cathode of the second diode is grounded via a switching element; The device is turned on and off by an inverted signal of the signal for turning on and off the MOSFET, and turning on and off the MOSFET.
An ultrasonic diagnostic apparatus that controls turning off.