Patent Publication Number: US-11660076-B2

Title: Ultrasonic probe, ultrasonic diagnostic apparatus, and ultrasonic transmission/reception switching method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ultrasonic probe, an ultrasonic diagnostic apparatus, and an ultrasonic transmission/reception switching method. 
     2. Description of the Related Art 
     The ultrasonic diagnostic apparatus is a medical diagnostic apparatus that is non-invasive and highly safe to the human body, and the scale of the apparatus is smaller than other medical image diagnostic apparatuses such as an X-ray diagnostic apparatus and an MRI (Magnetic Resonance Imaging) apparatus. In addition, because it is an apparatus that can display in real time the movement of the test object, such as heart pulsation and movement of the fetus, by a simple operation that only applies the ultrasonic probe from the body surface, ultrasonic diagnostic apparatuses play an important role in today&#39;s medical care. 
     In the ultrasonic diagnostic apparatus, ultrasonic waves are transmitted into the subject by supplying a high voltage drive signal to each of a plurality of transducers incorporated in the ultrasonic probe. Reflected waves of ultrasonic waves generated due to the difference in acoustic impedance of the living tissue in the subject are respectively received by a plurality of transducers, and an image is generated based on the reflected waves received by the ultrasonic probe. 
     Specifically, in transmission, acoustic pulses are focused by driving the transducers by giving independent delays to a plurality of transducers, and ultrasonic beam forming and beam scanning are performed. In reception, in order to compensate for the difference in the distance from the reflection point in the living body to each transducer, phasing processing is performed which gives an independent delay to a plurality of transducers to coherently align the phases of the signals, and adds these. As described above, ultrasonic imaging requires a transmission operation and a reception operation, and inevitably involves switching from transmission to reception. At this time, a virtual image is generated due to electrical noise caused by switching from transmission to reception, and transmission/reception switching noise is input to the reception system to cause a problem of signal loss due to saturation of the reception circuit. 
     In recent years, ultrasonic diagnostic apparatuses capable of obtaining a three-dimensional stereoscopic image have been developed, and inspection efficiency can be improved by specifying an arbitrary cross section from the three-dimensional stereoscopic image to obtain a tomogram. For three-dimensional imaging, it is necessary to change the transducers in the ultrasonic probe from the conventional one-dimensional array to the two-dimensional array, that is, a 2D array, and the number of transducers increases with the square of the number of transducers in the conventional ultrasonic probe. In this case, it is impossible to increase the number of cables connecting the ultrasonic probe and the main unit by a square. For this reason, it is necessary to transfer received signals whose number is reduced by phasing addition in the ultrasonic probe to the main unit via a cable. 
     In order to realize such phasing addition in the ultrasonic probe, the functions of transmission and reception and phasing addition are realized as a beam former IC, and a transmission/reception circuit is disposed for each transducer in the IC and will be electrically connected to the transducer in a one-to-one manner. The arrangement pitch of the transducers is determined by the condition of diffraction, and is determined by the frequency of the ultrasonic wave and the scanning angle of the ultrasonic beam so that grating lobes which are generated by diffraction separately from the main lobe appear out of the scanning angle of the ultrasonic beam. That is, the area of the transmission/reception circuit for each transducer in the IC is restricted by the arrangement pitch of the transducers, and a transmission/reception circuit having a small area is required. 
     The transmission/reception switching noise is generated mainly due to transition from the OFF state to the ON state of a TRSW (Transmit/Receive-Switch, transmission/reception separation switch) disposed between the high voltage transmission circuit and the low voltage reception circuit to protect the reception circuit from the transmission high voltage signal. When taking measures against the transmission/reception switching noise with a circuit, it is necessary to take measures with a small-scale and simple circuit because of the circuit area restriction as described above. 
     JP 2012-209763 A describes that such transmission/reception switching-induced noise is reduced. 
     SUMMARY OF THE INVENTION 
     JP 2012-209763 A prevents the switching current flowing to the latch from flowing to the source side of the transmission/reception separation switch and becoming noise. 
     However, with JP 2012-209763 A, it is difficult to effectively reduce transmission/reception switching noise that is generated along with ultrasonic transmission/reception switching. 
     An object of the present invention is to effectively reduce transmission/reception switching noise generated along with ultrasonic transmission/reception switching in an ultrasonic diagnostic apparatus. 
     The ultrasonic probe according to one aspect of the present invention includes a transducer, a switch circuit connected to the transducer, a reception circuit connected to the switch circuit, a first switch element connected to a reception terminal provided between the switch circuit and the reception circuit, a first resistance element connected to a control terminal of the switch circuit, a second resistance element provided inside the reception circuit, and a second switch element provided inside the reception circuit. 
     The ultrasonic diagnostic apparatus according to one aspect of the present invention includes: an ultrasonic probe including a plurality of transducers, a transmission/reception circuit that is provided corresponding to each of the plurality of transducers and switches an ultrasonic wave from transmission to reception, an adder circuit that adds outputs of a plurality of the transmission/reception circuits, and a control circuit that controls the transmission/reception switching; and a main unit that receives the output of the adder circuit and transmits a predetermined control signal to the control circuit, the ultrasonic probe having a switch circuit connected to the transducer, a reception circuit connected to the switch circuit, a first switch element connected to a reception terminal provided between the switch circuit and the reception circuit, a first resistance element connected to a control terminal of the switch circuit, a second resistance element provided inside the reception circuit, and a second switch element provided inside the reception circuit. 
     The ultrasonic transmission/reception switching method according to one aspect of the present invention includes switching from transmission to reception without performing ultrasonic transmission before imaging a frame or volume composed of a plurality of scanning lines, acquiring first received beam data corresponding to transmission/reception switching noise generated upon switching from the transmission to the reception, thereafter performing normal ultrasonic transmission and reception to acquire second received beam data, and subtracting the first received beam data from the second received beam data. 
     According to one aspect of the present invention, it is possible to effectively reduce transmission/reception switching noise generated along with ultrasonic transmission/reception switching in the ultrasonic diagnostic apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing a circuit configuration of an ultrasonic probe of a first embodiment; 
         FIG.  2    is a timing chart illustrating the operation of the ultrasonic probe of the first embodiment; 
         FIG.  3    is a diagram showing a circuit configuration of an ultrasonic probe of a related art; 
         FIG.  4    is a timing chart illustrating the operation of the ultrasonic probe of the related art; 
         FIG.  5    is a diagram showing a circuit configuration of an ultrasonic probe of a second embodiment; 
         FIG.  6    is a diagram showing a circuit configuration of an ultrasonic probe of a third embodiment; 
         FIG.  7    is a flowchart illustrating an ultrasonic transmission/reception switching method of a fourth embodiment; 
         FIG.  8    is a diagram showing a circuit configuration of an ultrasonic probe of a fifth embodiment; 
         FIG.  9    is a diagram showing the configuration of an ultrasonic diagnostic apparatus of a sixth embodiment; 
         FIG.  10    is a diagram showing a configuration example of a sub array of an IC in an ultrasonic probe; and 
         FIG.  11    is a diagram showing a circuit configuration of the related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First, the related art will be described with reference to  FIG.  11   . 
     As shown in  FIG.  11   , a TRSW  1100  has a configuration in which a gate  1103  and a source  1104  of two MOSFETs MN 0   1101  and MN 1   1102  are connected to each other. The on/off state is obtained by applying a predetermined positive voltage to a voltage VGS between a gate G and a source S or by setting the voltage to 0V. In order to generate a predetermined VGS or 0V, the voltage between the gate  1103  and the source  1104  is controlled by level-shifting the reception/transmission, that is, an on/off control signal TRSWON  1105  by two latches LATCH 0   1106  and LATCH 1   1107 . 
     When a through current  1108  flows to the source  1104  when the latch is inverted, noise is generated and is input from a TRSWOUT  1110  to the reception circuit. Therefore, a circuit configuration is adopted in which the through current  1108  during switching of the LATCH 0   1106  flows to GND through an MP 0   1107  so that it does not flow to the source  1104 , and thus transmission/reception switching noise is reduced. Further, by providing an SW 0   1109  and turning on the SW 0   1109  during the transmission period, the noise input from the TRSWOUT  1110  to a reception system at the time of transmission is reduced to improve the isolation of transmission and reception. 
     However, in  FIG.  11   , although it can be avoided that the through current  1108  during switching of the LATCH 0   1106  contributes to noise, a through current  1111  during switching of the LATCH  1  flows to the source  1104  and becomes noise. In addition, when the VGS increases from 0V to a predetermined voltage, generation of spike noise in a transducer (TD)  1113  due to capacitive coupling via a CGD  1112  which is a gate-drain parasitic capacitance of the MN 0   1101  cannot be avoided. 
     Furthermore, although the SW 0   1109  contributes to the improvement of transmission/reception isolation, it does not contribute to the reduction of transmission/reception switching noise since the SW 0   1109  is turned OFF simultaneously with transition to reception. 
     From such a point, there is a need for a method of effectively reducing transmission/reception switching noise generated along with ultrasonic transmission/reception switching. In particular, there is a need for a method of reducing noise due to parasitic capacitance CGD coupling of a MOSFET which is essentially generated by TRSW in which two MOS transistors (MOSFETs) are connected in series. 
     Furthermore, there is a need for a method of reducing the influence of the saturation of the reception circuit, which is a problem when the noise is input to the reception circuit, and the influence of the saturation of the rear-stage circuit due to the saturation of the preamplifier, and of shortening a reception impossible period by recovering from the saturation in a short time. 
     The embodiment reduces a virtual image caused by transmission/reception switching noise generated upon switching from transmission to reception of ultrasonic waves. In addition, it is possible to shorten the reception impossible period due to the saturation of the reception circuit caused by the input of the transmission/reception switching noise to the reception circuit and to receive echo from near the body surface. 
     Also, the embodiment reduces the transmission/reception switching noise by limiting the gate charging current of the transmission/reception separation switch or fixing the reception input to GND. Furthermore, by raising the time constant of the high pass characteristic of the reception circuit and stopping the output of the reception circuit, the recovery from the circuit saturation accompanying the input of the switching noise to the reception circuit is accelerated to prevent the saturation of the rear-stage circuit. Thus, the state is sequentially switched from the state different from the steady reception state to the steady reception state. As a result, the virtual image due to the transmission/reception switching noise is reduced, and the reception impossible period in which an image cannot be obtained is shortened. 
     Hereinafter, embodiments will be described using the drawings. 
     First Embodiment 
     The circuit configuration of the ultrasonic probe of the first embodiment will be described with reference to  FIGS.  1  and  2   . 
     At the time of ultrasonic transmission, a transmission circuit (Tx)  110  drives a transducer (TD)  100  with a high voltage pulse, the transducer  100  performs electrical/mechanical conversion, and an acoustic pulse is transmitted into the living body. At the time of transmission, a switch circuit (TRSW)  101  composed of two MOSFETs is turned off to prevent a low-voltage reception low noise amplifier (LNA)  111  from being destroyed by the high voltage pulse output from the transmission circuit  110 . The switch circuit (TRSW)  101  can be turned off by setting the voltage between the gate (G)  114  and the source (S)  115  to 0V by turning off the switch (SW 0 )  112  and turning on the switch (SW 1 )  113 . 
     To switch from transmission to reception, a control signal (TRSWON) is made to transition from Lo level to Hi level. As a result, the switch  112  is turned on, the switch  113  is turned off, and the voltage VGS between the gate (G)  114  and the source (S)  115  increases. At this time, since VGVDD is Lo as shown in  FIG.  2   , the switch (SW 2 )  116  is in the OFF state, and a current flows from VDD to the gate (G)  114  through a resistor (R 0 )  117 . The charging current is limited by the resistor  117 , and VGS rises slowly, whereby transmission/reception switching noise superimposed on the transducer  100  can be reduced. 
     At this time, a GSHT  118  is Hi, and the transmission/reception switching noise superimposed on the transducer  100  passes through the switch circuit  101 . However, a switch (SW 3 ) is turned on to suppress transmission/reception switching noise with low impedance, and the transmission/reception switching noise input to the reception low noise amplifier  111  side can be reduced. 
     The transducer  100  operates around 0V during transmission and reception, at the time of transmission, for example, in case of three-value pulse transmission, transmits a pulse composed of three values, that is, a positive high voltage, a negative high voltage, and a 0V, and also at the time of reception, receives a signal with 0V as a common potential. Here, in order to receive 0V common, the reception circuit  103  needs a positive voltage and a negative voltage, and the type of power supply increases. 
     In order to prevent this, a capacitor (C 0 )  119  may be inserted in series in the reception signal path to be AC coupled. That is, by forming a high-pass filter including the capacitor  119  and a resistor (R 1 )  120 , the DC potential on the reception low noise amplifier  111  side of the capacitor  119  can be determined again. Therefore, by setting an appropriate positive voltage to a common potential (VCM)  121 , the reception circuit  103  after the reception low noise amplifier  111  can be operated between the positive VDD and GND, and the negative power supply becomes unnecessary. 
     Here, immediately after the reception transition, a switch (SW 4 )  123  is on because an LNAMUTE  122  is Hi. As a result, the low frequency side of the normal reception passband is determined by the capacitor  119  and the resistor  120 , but immediately after the reception transition it is determined by the capacitor  119  and the on resistance of the switch  123 . 
     That is, the cutoff frequency of the high pass filter immediately after the reception transition is higher than that of the normal reception state. Temporarily, when large amplitude transmission/reception switching noise passes through the capacitor  119 , the time when the input of the reception low noise amplifier  111  returns to the original common potential  121  from here is determined not by a large time constant determined from the capacitor  119  and the resistor  120  but by a small time constant determined by the capacitor  119  and the on resistance of the switch  123 . Therefore, even if transmission/reception switching noise passes through the capacitor  119 , by turning on the switch  123 , it is possible to shorten the time until the input of the reception low noise amplifier  111  returns to the VCM  121 , and return from circuit saturation can be performed in a short time. 
     Further, immediately after the reception transition, the LNAMUTE signal  122  is set to Hi to turn on a switch (SW 5 ), and the reception low noise amplifier  111  is set to a state in which the differential signal does not appear at the output (OUTP-OUTN)  109  thereof and the gain is substantially close to zero. Thus, even when transmission/reception switching noise is input to the reception low noise amplifier  111 , it is possible to prevent saturation of the rear stage without transmitting the transmission/reception switching noise to the rear stage. 
     Organize the above. As shown in the timing chart of  FIG.  2   , immediately after TRSWON transitions from Lo to Hi, the transmission/reception switching noise superimposed on the transducer  100  is reduced by slow rising of the VGS of the switch circuit  101 . Also, by suppressing the output of the switch circuit  101  to GND by the switch SW 3 , noise input to the reception low noise amplifier  111  is suppressed, and in the state where the switch  123  is turned on, the high pass filter is in a state of being able to recover in a short time also from the circuit saturation due to transmission/reception switching noise, and the reception low noise amplifier  111  is in a state of stopping the output and not saturating the rear stage. 
     From this state, although not particularly limited, the state of each circuit is made to transition from the side close to the transducer  100  toward the rear stage so as to be in the original reception state. VGVDD is raised to Hi, and the gate  114  of the switch circuit  101  is brought to the original impedance in the steady reception state. Also at this time, noise is generated, but the noise input to the reception low noise amplifier  111  can be suppressed because the GSHT is Hi. Noise is also generated when GSHT is lowered to allow a signal to be input to the reception low noise amplifier  111 . However, even if saturation occurs due to this noise, since the LNAMUTE is Hi and the cutoff frequency of the high pass filter is high, it is possible to recover from the saturation in a short time. Finally, the LNAMUTE is lowered to Lo so as to allow even the low band signal to pass through the high pass filter, so that the reception low noise amplifier  111  can output the signal to the rear stage. 
     As understood from the above, noise is also generated when the state of the circuit is made to transition to the steady reception state. Therefore, instead of taking measures by taking two states with a single circuit, the states of a plurality of circuits are set to noise suppressible states, and these are sequentially canceled and made to transition to a steady reception state, and thus making it possible to effectively suppress noise or to recover in a short time from saturation due to noise or to prevent propagation to the rear stage. 
     The sequence shown in  FIG.  2    is not particularly limited, and some measures in each circuit may be omitted depending on the absolute value of the generated noise, or the order of state transition may be interchanged. 
     According to the sequence of  FIG.  2   , there is a period in which the original reception cannot be performed between the state of transmission (Tx)  200  and the state of reception (Rx)  202 . For this reason, after transmitting an ultrasonic wave, it will not be able to receive an echo reflected and returned at the immediate vicinity of the body surface. Therefore, it is necessary to set the reception impossible period equal to or less than the ultrasonic round trip time to the shallowest point in the vicinity of the body surface where the ultrasonic image is desired to be acquired. 
     Here, in order to explain the effect of the first embodiment, a case where the present invention is not applied will be described with reference to  FIGS.  3  and  4   . Here,  FIG.  3    shows a circuit configuration for transitioning from the transmission state to the steady reception state, and  FIG.  4    shows a timing chart. 
     When a TRSWON  302  transitions from Lo to Hi, a TRSW  301  is turned on. However, when a voltage VGS between a gate  303  and a source  304  rapidly increases, large spike-like transmission/reception switching noise is superimposed on a transducer (TD)  300  by a parasitic capacitance  305 . When spike-like transmission/reception switching noise passes through a switch circuit (TRSW)  301  and passes through a high pass filter  306  composed of the capacitor C 0  and the resistor R 1 , a reception low noise amplifier (LNA)  307  is saturated and cannot output a desired signal. 
     In order to recover from saturation, the input potential of the reception low noise amplifier  307  needs to return to the vicinity of a signal common potential (VCM)  308 , but the time required for this is determined by the time constant of the high pass filter  306  and the more you design to pass the low band signal, the longer it will take to recover from saturation. 
     As described above, in the configuration of  FIG.  3    in which the first embodiment is not used, large spike-like transmission/reception switching noise is generated in a transducer  300 . This transmission/reception switching noise saturates the reception circuit, so that the transmission/reception switching noise is not superimposed on the signal, but the reception impossible period continues for a long time. In the first embodiment, it is possible to prevent the reception impossible period from continuing for a long time. 
     As described above, the ultrasonic probe according to the first embodiment includes the transducer ( 100 ), the switch circuit ( 101 ) connected to the transducer ( 100 ), the reception circuit ( 103 ) connected to the switch circuit ( 101 ), a first switch element (SW 3 ) connected to a reception terminal ( 102 ) provided between the switch circuit ( 101 ) and the reception circuit, a first resistance element ( 117 : R 0 ) connected to a control terminal ( 104 ) of the switch circuit ( 101 ), a second resistance element (R 1 ) provided inside the reception circuit ( 103 ), and a second switch element (SW 5 ) provided inside the reception circuit ( 103 ). 
     Here, the switch circuit ( 101 ) is formed of a pair of MOS transistors, and the control terminal ( 104 ) forms the gate of the MOS transistor. At least two or more elements of a first impedance ( 105 ) of the gate control terminal ( 104 ), a second impedance ( 106 ) of the reception terminal ( 102 ), a time constant ( 107 ) of the reception circuit ( 103 ), and a gain ( 108 ) of the reception circuit maintain, for a certain period of time ( 201 ) after the transmission period ( 200 ) ends, a state (state of each signal of  201 ) different from a steady reception state ( 202 ) which occurs after the certain period of time ( 201 ) elapses. In the different state (the state of each signal of  201 ) maintained for the certain period of time, a saturation signal of a constant amplitude is output. 
     The first impedance ( 105 ) of the gate control terminal ( 104 ) corresponds to the first resistance element (R 0 ) connected to the gate control terminal ( 104 ). The second impedance ( 106 ) of the reception terminal ( 102 ) corresponds to the first switch element (SW 3 ) connected to the reception terminal ( 102 ). The time constant ( 107 ) of the reception circuit ( 103 ) corresponds to the second resistance element (R 1 ) provided inside the reception circuit ( 103 ). The gain ( 108 ) of the reception circuit corresponds to the second switch element (SW 5 ) provided inside the reception circuit ( 103 ). In addition, at least two or more elements sequentially switch from the different states to the steady reception state, and after a certain period of time, all the elements transition to the steady reception state. 
     The first impedance ( 105 ) of the gate control terminal ( 104 ) is controlled by switching the resistance value of the first resistance element (R 0 ). The gain ( 108 ) of the reception circuit ( 103 ) is controlled by switching the second switch element (SW 5 ) provided between the differential outputs ( 109 ) of the reception circuit ( 103 ). 
     According to the first embodiment, it is possible to reduce a virtual image caused by transmission/reception switching noise generated upon switching from transmission to reception of ultrasonic waves. In addition, it is possible to shorten a reception impossible period due to saturation of the reception circuit by input of the transmission/reception switching noise to the reception circuit and to receive an echo from the shallow part of the body surface. 
     Second Embodiment 
     The circuit configuration of the ultrasonic probe of the second embodiment will be described with reference to  FIG.  5   . 
     As described above, the transmission/reception switching noise is caused by the coupling of a parasitic capacitance  504  of the MOSFET constituting a switch circuit (TRSW)  501 . The node of a transducer (TD)  500  fluctuates by VDD×(voltage division ratio of the transducer impedance and the impedance of a CGD capacitor  504 ) and becomes noise when the TRSWON  505  is made to transition from Lo to Hi in  FIG.  5    and a VGS of the MOS transistor (MN 0 )  502  and the MOS transistor (MN 1 )  503  rises from 0V to VDD. The noise amplitude is as follows (Math. 1). 
     
       
         
           
             
               
                 
                   
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     Where ZTD is the impedance of the transducer, j is the imaginary unit, and ω is each frequency. ZTD is a function of frequency. From this, Vnoise takes any value between 0 and VDD. There are four ways to reduce Vnoise: lower VDD, lower ZTD, lower ω, and lower CGD. When VDD is lowered, VGS of the MOS transistor becomes shallow, so that the on resistance of the switch circuit  501  is increased, thermal noise is increased, and the signal-to-noise ratio S/N of reception is degraded. If the ZTD is lowered, the load on the transmission circuit increases, and deterioration of the transmission band and the power consumption for charging/discharging of the transducer increase. Lowering ω, ie, lowering the frequency, means increasing VGS slowly. This is to turn on the switch circuit  501  slowly by limiting the gate charging current by the resistor R 0  as shown in  FIGS.  1  and  2   . 
     The method of lowering the CGD  504  in the last order can be realized by reducing a channel width Wg of the MN 0   502  in  FIG.  5   . However, if the channel width Wg is reduced, the on resistance also increases. Therefore, the channel width Wg of the MN 0   502  is made smaller than the channel width Wg of the MN 1   503 . The on resistance as the switch circuit  501  is a series resistance of the on resistance of the MN 0   502  and the on resistance of the MN 1   503 . Here, even if the channel width Wg of the MN 0   502  is changed to 0.5 times and the channel width Wg of the MN 1   503  is changed to 1.5 times from the state where the channel widths Wg of the MN 0   502  and the MN 1   503  are the same size, the area and the on resistance of the switch circuit  501  do not change. 
     However, since the parasitic capacitance CGD  504  of the MOS transistor depends on the channel width Wg, the CGD  504  of the MN 0   502  is 0.5 times the original. The CGD 2  ( 508 ) of the MN 1   503  is 1.5 times larger, but if the low-voltage NMOS switch MN 2  ( 506 ) is turned on, a TRSWOUT  507  is fixed to GND, and the fluctuation of the TRSWOUT  507  due to CGD 2  ( 508 ) coupling of the MN 1   503  is very small. From this, the value of the MN 0   502  on the transducer  500  side is decreased and the size of the MN 1   503  on the reception side is increased, and the size is unbalanced, thereby reducing transmission/reception switching noise while keeping the area and the on resistance of the switch circuit  501  constant. The difference between the size of the MN 0   502  and the size of the MN 1   503  in  FIG.  5    represents the difference of the channel width Wg. 
     Generally, the minimum channel width Wg of the MOS transistor (MOSFET) is limited by the size of the source-drain contact and the lithography accuracy by the semiconductor process, and the channel width Wg ratio of MN 0   502  and MN 1   503  is not arbitrarily determined but is restricted by the semiconductor process. 
     As described above, in the ultrasonic probe according to the second embodiment, among the pair of MOS transistors ( 502 ,  503 ) forming the switch circuit ( 501 ), the first channel width of the first MOS transistor ( 502 ) positioned on the transducer ( 500 ) side is configured to be smaller than the second channel width of the second MOS transistor ( 503 ) positioned on the reception terminal ( 102 ) side. 
     According to the second embodiment, it is possible to reduce the virtual image caused by the transmission/reception switching noise generated upon switching from transmission to reception of ultrasonic waves. 
     Third Embodiment 
     The circuit configuration of the ultrasonic probe of the third embodiment will be described with reference to  FIG.  6   .  FIG.  6    shows a case of realizing the SW 3  in  FIG.  1    by an NMOS switch, that is, a layout example of the circuit configuration of the MN 2  ( 506 ) in  FIG.  5   , as a device cross-sectional view. 
     As described above, the potential of the transducer is 0V common, and positive and negative voltages pass through the switch circuit (TRSW). If a strong echo is received, the NMOS parasitic body diode connected to the TRSW output to GND becomes the forward direction by a deep negative voltage, which may trigger latch-up and destroy the IC. 
     In order to prevent this, it is necessary to isolate the NMOS element  600  alone so that the MN 2  does not form a parasitic thyristor with another PMOS element  601 . For this purpose, an SOI (Silicon On Insulator) wafer may be used in which a buried oxide (BOX)  603  is embedded. 
     The NMOS element  600  composed of N+ source/drain and a gate of POLY silicon can prevent latch-up by being laid out in a state electrically isolated from another element not by shallow element isolation (STI (Shallow Trench Isolation)) but by DTI (Deep Trench Isolation)  602  reaching a BOX. 
     As described above, in the ultrasonic probe of the third embodiment, the first switch element (SW 3 ) is composed of an NMOS element ( 600 ) connected between the reception terminal ( 102 ) of the switch circuit ( 101 ) and the ground terminal. The second impedance ( 106 ) of the reception terminal ( 102 ) is controlled by the NMOS element ( 600 ). The NMOS element ( 600 ) is composed of an FET formed on an SOI substrate ( 604 ). The NMOS element ( 600 ) is electrically isolated by being surrounded by the DTI ( 602 ). 
     According to the third embodiment, it is possible to reduce the virtual image caused by the transmission/reception switching noise generated upon switching from transmission to reception of ultrasonic waves. 
     Fourth Embodiment 
     The ultrasonic transmission/reception switching method of the fourth embodiment will be described with reference to  FIG.  7   . 
       FIG.  7    shows an image acquisition method for reducing the influence of transmission/reception switching noise on an image as a whole system of an ultrasonic diagnostic apparatus. 
     Assuming that reception saturation due to transmission/reception switching noise is prevented, in order to prevent switching noise from being displayed as a virtual image in the image, transmission/reception switching noise data is acquired in advance for calibration, and this may be subtracted from actual image data. 
     As shown in  FIG.  7   , first, Cal data for calibration is acquired (S 700 ). 
     Next, a delay corresponding to the scanning angle and focus is set (S 701 ), transmission/reception is switched without transmission (S 702 ), and received beam data of the scanning line is acquired (S 703 ). Although not particularly limited, the scanning line data digitized by the A/D converter is stored in the memory in the main unit. 
     Next, Cal data of all the scanning lines are acquired by changing the scanning angle (S 704 ), and the Cal data acquisition ends (S 705 ). Although not particularly limited, since this Cal data acquisition wants to acquire only transmission/reception switching noise, it is preferable to leave the probe in the air so as not to return an echo due to reflection. 
     If Cal data is acquired once before product shipment and stored in the non-volatile memory, transmission/reception switching noise is always the same except for aging of the device in the IC. Therefore, it is not necessary to acquire Cal data every time of image acquisition. 
     Next, normal transmission and reception are performed to acquire a 2D image frame or 3D image volume (S 706 ). Next, a delay corresponding to the scanning angle and focus is set (S 707 ), transmission/reception is performed (S 708 ), and received beam data of the scanning line is acquired and stored in memory (S 709 ). Next, the Cal data is subtracted from the received beam data (S 710 ) and a determination is made of whether all beam scanning ends (S 711 ). If it is determined that the the beam scanning is not complete, the focus is set again (S 707 ), and if it is determined that the beam scanning ends, the image acquisition ends (S 712 ). 
     If Cal data is subtracted from the received beam data of the scanning line (S 710 ), received beam data from which transmission/reception switching noise is subtracted is acquired, and an image with a reduced virtual image is acquired. The subtraction of the Cal data from the received beam data may be performed each time received beam data is acquired as shown in  FIG.  7    or may be performed collectively after whole beam data is acquired. 
     Fifth Embodiment 
     The circuit configuration of the ultrasonic probe of the fifth embodiment will be described with reference to  FIG.  8   . In  FIG.  1   , since the reception low noise amplifier  111  is a single-ended input and a differential output, the output can be stopped by inserting the switch (SW 5 ) between the differential outputs. 
     When the reception low noise amplifier (LNA) has a single-ended output  809 , the output common voltage VCMOUT  810  of the reception low noise amplifier (LNA) is prepared in advance as shown in  FIG.  8   , and the output  809  of the reception low noise amplifier (LNA) may be shorted to the VCMOUT  810  by the switch SW 5  ( 808 ) during a period in which it is desired to stop the output. 
     Although the second harmonic distortion of the signal can be reduced by making the reception low noise amplifier (LNA) have a differential output, power consumption generally increases in a case of a differential circuit configuration. In the fifth embodiment, although the second harmonic distortion is degraded, power consumption can be reduced by using a single-ended output. The other configuration is the same as the circuit configuration of the ultrasonic probe of the first embodiment shown in  FIG.  1   , and thus the description thereof is omitted. 
     As described above, in the ultrasonic probe of the fifth embodiment, the gain of the reception circuit ( 803 ) is controlled by short-circuiting the single end output ( 809 ) of the reception circuit ( 803 ) by the second switch element ( 808 : SW 5 ) connected to the DC output common voltage ( 810 ). 
     According to the fifth embodiment, it is possible to reduce the virtual image caused by the transmission/reception switching noise generated upon switching from transmission to reception of ultrasonic waves. 
     Sixth Embodiment 
     The configuration of the ultrasonic diagnostic apparatus of the sixth embodiment will be described with reference to  FIGS.  9  and  10   . 
       FIG.  9    shows an ultrasonic probe having a two-dimensional array transducer for three-dimensional imaging and a system configuration. 
     The ultrasonic diagnostic apparatus of the sixth embodiment has an ultrasonic probe  90  and a main unit (MAIN)  94 . In the ultrasonic probe  90 , a transmission/reception circuit (Tx/Rx)  92  is disposed for each transducer (TD)  91 , and the received signals are added by an adder circuit  93  and sent to an AFE (analog front end)  95  in the main unit  94 . A grouping unit of transducer channels to be added is called a subarray  96 . 
     The processor (PU)  97  in the main unit  94  sends a control signal to an IC control logic circuit (IC CTRL)  98  in the ultrasonic probe  90 , and the IC control logic circuit  98 , in response to this, performs switching between transmission and reception and delay control for ultrasonic focusing. Although not particularly limited, when the transmission circuit is a pulser system instead of a linear amplifier system, the waveform is sent to the pulser as a digital value, so the IC control logic circuit  98  includes a waveform memory for storing waveform data transmitted by the pulser. 
     The configuration within the subarray is shown in  FIG.  10   . 
     A transmission/reception circuit  1000  per transducer includes a transmission circuit (Tx)  1020  that is composed of a high voltage MOS transistor, generates a high voltage signal, and drives a transducer (TD)  1010 , a transmission/reception separation switch (TRSW)  1030  that is turned off at the time of transmission, protects the low-voltage reception circuit from the high voltage signal, and passes a minute signal at the time of reception, a low-voltage reception low noise amplifier (LNA)  1040 , and a micro delay circuit (DLY)  1050  that performs phase alignment by delaying the transmission signal, performing beam-forming, and further delaying the received signal. The received signals phased by the minute delay circuit are added and sent to the main unit  94 . 
     A control signal group is generated by, but not particularly limited to, a logic circuit and distributed to each transmission/reception circuit  1000 . In order to reduce the number of wiring lines, only TRSWON may be wired, and logic circuits may be provided in each transmission/reception circuit  1000  to generate VGVDD, GSHT, and LNAMUTE control signals from the TRSWON signal. 
     As described above, the ultrasonic diagnostic apparatus of the sixth embodiment includes the ultrasonic probe ( 90 ) and the main unit ( 94 ). The ultrasonic probe ( 90 ) includes a plurality of transducers ( 91 ), a plurality of transmission/reception circuits ( 92 ) respectively provided corresponding to the plurality of transducers ( 91 ) and switching ultrasonic waves from transmission to reception, an adder circuit ( 93 ) for adding the outputs of the plurality of transmission/reception circuits ( 92 ), and a control circuit ( 98 ) for controlling transmission/reception switching. The main unit ( 94 ) receives the output of the adder circuit ( 93 ) and transmits a predetermined control signal to the control circuit ( 98 ). 
     As shown in  FIG.  1   , the ultrasonic probe ( 90 ) includes a switch circuit ( 101 ) connected to the transducer ( 100 ), a reception circuit ( 103 ) connected to the switch circuit ( 101 ), a first switch element (SW 3 ) connected to a reception terminal ( 102 ) provided between the switch circuit ( 101 ) and the reception circuit, a first resistance element (R 0 ) connected to the control terminal ( 104 ) of the switch circuit ( 101 ), a second resistance element (R 1 ) provided inside the reception circuit ( 103 ), and a second switch element (SW 5 ) provided inside the reception circuit ( 103 ). 
     As shown in  FIGS.  1  and  2   , the switch circuit ( 101 ) is composed of a pair of MOS transistors, and the control terminal ( 104 ) forms a gate control terminal of the MOS transistor. The control circuit ( 98 ) controls so that at least two or more elements of a first impedance ( 105 ) of the gate control terminal ( 104 ), a second impedance ( 106 ) of the reception terminal ( 102 ), a time constant ( 107 ) of the reception circuit ( 103 ), and a gain ( 108 ) of the reception circuit maintain, for a certain period of time ( 201 ) after the transmission period ( 200 ) ends, a state (state of each signal of  201 ) different from a steady reception state ( 202 ) which occurs after the certain period of time ( 201 ) elapses. Further, the control circuit ( 98 ) controls so that a saturation signal of a constant amplitude is output in different states (states of respective signals of  201 ) maintained for a certain period of time. 
     According to the above-described embodiment, it is possible to reduce a virtual image caused by transmission/reception switching noise generated upon switching from transmission to reception of ultrasonic waves. In addition, it is possible to shorten a reception impossible period due to saturation of the reception circuit by input of the transmission/reception switching noise to the reception circuit and to receive an echo from the shallow part of the body surface. 
     As described above, according to the above-described embodiment, it is possible to realize an ultrasonic diagnostic apparatus capable of performing highly reliable ultrasonic imaging with a small virtual image and targeting up to the shallow part of the body surface.