JP2688440B2 - Electronic scanning ultrasonic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an ultrasonic wave generated by reflecting ultrasonic waves from an ultrasonic vibrator group in which a large number of minute ultrasonic vibrators are arranged in an array. The present invention relates to an electronic scanning ultrasonic device that receives and analyzes vibration groups, and more particularly to a matrix circuit of a switching device provided for sequentially scanning ultrasonic vibrators for transmission and reception.

[Conventional technology]

FIG. 4 is a conventional configuration diagram of an electronic scanning circuit used in an ultrasonic device.

In an ultrasonic diagnostic apparatus that visualizes the inside of a human body by ultrasonic waves, or an ultrasonic device such as an ultrasonic deep injury apparatus that visualizes scratches inside a member, etc., a probe 19 is used to Do the conversion. Usually, the probe 19 is configured by arranging n micro ultrasonic transducers in an array, and the continuous m
(<N) ultrasonic transducers are simultaneously selected for transmission / reception, and m ultrasonic transducers that are selected at the same time are shifted one by one to perform scanning, and an image based on the received ultrasonic signals is displayed. Try to change.

When selecting a vibrator, first select the vibrator selection circuit.
At 20, select m transducers from 1 to m to transmit / receive ultrasonic waves, then select m transducers from 2 to m + 1 to transmit / receive, one transducer at a time in order. It shifts and simultaneously selects and transmits m transducers. Therefore, m output signal lines 2 (j) (j: 1 to m) are taken out from the n signal lines 1 (i) (i: 1 to n).

On the other hand, the beam control circuit 40 for electronically focusing and deflecting the ultrasonic beam is configured by adding the outputs of the delay circuits 41 and the delay circuits 41 provided for the respective m transducers and having different delay amounts. And an adder circuit 42 for outputting to an amplifier (not shown). For example, among the selected m transducers, the transducer at the end and the transducer in the middle have different distances to the ultrasonic reflection source of the subject, and the ultrasonic delay amount corresponding to this difference in distance is In order to give a corresponding delay, it is necessary to input the output signal of each transducer to the delay circuit 41 corresponding to the difference in distance at the time of reception. Since m oscillators are sequentially scanned out of n oscillators, it is necessary to sequentially change the oscillators connected to each delay circuit 41. Therefore, the output signal 2
The matrix circuit 11 is provided between (j) and the beam control circuit 40.

When 1 to m transducers are first selected, the m signal lines 2 (j) may be input to the beam control circuit 40 in the same order. Therefore, the switch at the intersection of the circles in the matrix circuit 11 in FIG. 9 is closed, and the signal on the signal line 2 (j) is transmitted to the signal line 3 (j). Next, when the vibrators of 2 to m + 1 are selected, the switch marked with Δ is closed and the delay circuit connected to each selected vibrator is also changed. Thereafter, in the same manner, each time the selected transducer is sequentially scanned, the switch connecting the signal lines 2 (j) and 3 (j) in the matrix circuit 11 is also shifted.

The conventional kutrix circuit 11 is an m × m cross-point switch, and the same number of switches as the number m of selected transducers are connected to each signal line. Therefore, each signal line is connected to a parasitic capacitance such as an input capacitance or an output capacitance for m switches. This parasitic capacitance is a measure of the high frequency band of the circuit.
There is a relationship between H and the following expression (1).

fH = 1 / (2πRC) (1) In this formula (1), R is the impedance of the circuit connected to the signal line, and at high frequencies, consider using a coaxial cable for connection to other circuits. Normally set to 55Ω. C is the sum of the parasitic capacitances of the switches connected to the signal lines. As shown in this equation (1), when C becomes large, there is an effect that the high frequency band of the circuit is lowered, and particularly when the number m of simultaneously selected transducers becomes large, the capacitance C
Also becomes large, and bandwidth reduction becomes a big problem.

By the way, in order to improve the resolution of an ultrasonic diagnostic apparatus or the like, it is necessary to increase the ultrasonic frequency. Therefore, it is necessary to widen the area of the receiving circuit that handles analog signals in particular. However, the parasitic capacitance C of the matrix circuit becomes an obstacle to widening the band.

To reduce the parasitic capacitance C, the number of switches may be reduced. For this reason, in the conventional technique described in Japanese Patent Publication No. 62-18019, the matrix circuit is provided in multiple stages to reduce the number of switches. FIG. 10 shows an improved matrix circuit based on the prior art described in Japanese Patent Publication No. Sho 62-18019. The matrix circuit is a first matrix circuit 12 (1).
By setting the two stages of the second matrix circuit 12 (2),
We are reducing the number of switches.

[Problems to be solved by the invention]

FIG. 11 shows the number m of simultaneously selected transducers in this technique.
And the number of switches.

As is apparent from FIG. 11, the number of switches can be reduced as compared with the conventional method by using the method disclosed in Japanese Patent Publication No. 62-18019. However, the number of simultaneously selected transducers m
If the number of switches is increased, the number of switches will be increased accordingly, and the parasitic capacitance will also be increased.
Therefore, this conventional technique does not provide a fundamental solution for widening the band of the receiving system.

In order to avoid the band reduction, the impedance R may be reduced by the amount of increase in the capacitance C in the equation (1) so that the product of RC does not increase. However, in order to reduce the impedance R, for example, if the impedance of the circuit connected to the signal line is reduced from 50Ω to 10Ω and the coaxial cable with the same 10Ω impedance is used for connection with other circuits, the same voltage amplitude is obtained. Therefore, a new problem arises that a large amount of current must be passed. In this example, it is necessary to pass a current five times as large as that when the impedance is 50Ω, and an amplifier with a large output current is required as an amplifier for driving the signal line, resulting in an increase in current consumption and an increase in heat generation.

An object of the present invention is to provide an ultrasonic device having high resolution that is not adversely affected by parasitic capacitance.

[Means for solving the problem]

The above object can be achieved by providing a signal line of a matrix circuit used in the ultrasonic device with an inductor function and configuring an LC delay line with the inductor and the capacitance of the switch.

[Action]

In the conventional technique, the capacitance C of the matrix circuit becomes large because the capacitance of each switch is added. However, in the present invention, the capacitance of each switch is not separated by the inductor and added. Therefore, even if the number of switches increases, the parasitic capacitance C of the circuit does not increase with it, and the circuit characteristics do not deteriorate in the high frequency region. This allows the use of high frequency ultrasound to achieve high resolution.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

Before explaining specific embodiments of the present invention, the principle and effects of the present invention will be described.

FIG. 4 (a) is an equivalent circuit of one signal line in the conventional matrix circuit, in which m capacitors Ci (the parasitic capacitance of the switch between the intersecting signal lines) are equal in number to the selected oscillators. Are connected in parallel, and the total capacitance is C = Ci × m. On the other hand, FIG. 4B is an equivalent circuit of one signal line of the matrix circuit according to the example of the present invention. In this example, each switch (represented by a capacitance Cd) is connected by a minute inductor L.
That is, the inductor L and the capacitance C form an LC delay line. Now, consider the frequency bands of the conventional example and the embodiment of the present invention shown in FIG.

The frequency band in the conventional example of FIG. 4 (a) is −3 dB lower high frequency of the RC circuit configured by the output resistance R of the signal line drive circuit 60 (amplifier) and the parasitic capacitance C connected to the signal line. It is evaluated at fH. The fH is calculated by the following equation (2).

R: Output resistance, Ci: Parasitic capacitance of switch As described above, the frequency fH decreases in inverse proportion to the number m of simultaneously selected transducers.

On the other hand, in the embodiment of the present invention shown in FIG. 4 (b), the frequency band is evaluated by the cutoff frequency fc of the LC delay line. The fc is calculated by the following equation (3).

L: Inductor Cd: Switch circuit capacitance Here, the specific value of L and Cd is the impedance of this LC delay line. Is determined so as to match the output resistance R of the signal line drive circuit (amplifier). The impedance matching is
This is to prevent signal reflection at the end of the LC delay line, and is a measure that is usually taken when handling high frequency signals. Note that the capacitance Cd is not limited to the parasitic capacitance of the switch circuit, and a capacitor may be used together. From the equation (3), it can be seen that the cutoff frequency fc does not depend on the length of the delay line. The fact that the cut-off frequency fc does not depend on the length of the delay line means that the frequency band at high frequencies does not decrease even if the number m of simultaneously selected transducers is increased and the LC delay line is lengthened.

The outline of the frequency characteristic is as shown in FIG. In the conventional example, the transmissibility gradually decreases from the frequency fH as the frequency increases, and the frequency fH decreases as the simultaneous selection frequency m increases. On the other hand, in the embodiment of the present invention, the transmissivity does not change up to the vicinity of the cutoff frequency fc, and the characteristic is that it rapidly decreases when approaching the cutoff frequency fc. Moreover, it is irrelevant to the number m of simultaneously selected transducers. Therefore, it is apparent that the present invention has a wider frequency band than the conventional example when the frequency fH is equal to or lower than the frequency fc. In most cases where the number m of simultaneously selected transducers is large, fH ≦ fc, and the matrix circuit of this method has a wider band.

Next, a specific embodiment of the present invention will be described with reference to FIG. In the matrix circuit 10 used in the electronic scanning circuit shown in FIG. 1, the signal lines 2 (1) to 2 (m) and the signal lines 3 (1) to 3 (m) are connected in series with the minute inductor 101. Connected and configured. At the intersection of the signal line 2 and the signal line 3 (this intersection is the middle point of the inductor 101 in each signal line), both signal lines are connected by the switch circuit 102 having a high input / output impedance. There is. That is, the input terminal of the switch circuit 102 is connected to the signal line 2, and the output terminal of the switch circuit 102 is connected to the signal line 3. As the switch circuit 102, various switch circuits and those that operate equivalently thereto can be used. For example, various switch circuits shown in FIGS. 2B, 2C, and 2D can be used as the switch circuit 102 (FIG. 2A).

The switch circuit shown in FIG. 2B changes the gain by changing the bias VB of the single gate. The switch circuit of FIG. 7C changes the gain by changing the bias VB of the second gate of the dual gate FFT. The switch circuit shown in FIG. 3D is a circuit that utilizes the fact that the high frequency resistance of the diode 8 can be changed by the bias VB. Note that the capacitors C1 and C2 are connected to the input / output of the various switch circuits shown in FIG. 2, but the capacitor C1 input to the input is connected to the signal line 2 together with the input capacitance Ci of the FET.
Used in combination with inductors (1) to 2 (m) to form an LC delay line. Similarly, the capacitance C2 input to the output is the same as the output capacitance Co of the FET, together with the signal lines 3 (1) to 3
Used in combination with the (m) inductor to form an LC delay line.

Next, the frequency band of the matrix circuit according to the embodiment shown in FIG. 1 will be compared with the conventional example. The frequency band of the matrix circuit 10 of this embodiment is evaluated by the cutoff frequency fc of the LC delay line as described above. In the present embodiment, specific values of the inductor and the capacitance are: inductor L = 0.05 μH, capacitor capacitance C1 = C2 = 15 pF FET parasitic capacitance Ci = Co = 5 pF. On the other hand, a comparison will be made with the case where the parasitic capacitance of the switch Ci = Co = 5 pF impedance R = 50 Ω is set as the optimum value in the conventional example. FIG. 3 shows the results of calculating the cutoff frequency fc of the present embodiment and the −3 dB reduction frequency fH of the conventional example in the above numerical example. The impedance of the delay line of the matrix circuit in this embodiment is 50Ω which is a general value in a high frequency circuit. That is, As can be seen from Fig. 3, the cut-off frequency fc is 318MHz regardless of the number m of simultaneously selected transducers, but the -3dB lowering frequency fH of the improved conventional example (Japanese Patent Publication No. 62-18019) is the simultaneous selected oscillation. Even when the number m of children is "8", it is 265 MHz, and when the number m of simultaneously selected transducers is "32", it is 159 MHz. That is, the matrix circuit 10 of the present embodiment has a wider band than the conventional example, although the capacitor capacitance is added to the input and output of the switch circuit 102.

As described above, by using the matrix circuit of the present embodiment in the ultrasonic device, it is possible to eliminate the decrease in the frequency band due to the capacitance, and to increase the ultrasonic frequency to achieve high resolution. The matrix circuit 10 of this embodiment is
Then, there is a difference in the propagation delay time of the signal in each signal line depending on the signal path, but this can be corrected by the delay circuit 41 of the beam control circuit 40, so there is no problem. Specifically, the delay circuit 41 is a variable delay circuit, and the matrix circuit 10
The difference in the propagation delay time that occurs depending on the switching situation of is corrected.

In the above-described embodiment, the switch circuits connected to one signal line are all separated by the inductor. However, the present invention is not limited to this, and as shown in FIG. 6, the same effect as that of the above embodiment can be obtained by forming a group with some switch circuits and separating the groups with inductors 101 '. Can be obtained. The embodiment shown in FIG. 6 has the effect that the matrix circuit 10 'can be miniaturized by integrating one switch circuit group 122 into an IC. Further, at this time, a bias circuit described later can be integrated into an IC to achieve miniaturization and high performance.

Next, an embodiment of a switch drive circuit that finely adjusts the bias of the high input / output impedance switch circuit 102 of the matrix circuit to compensate for variations in transmissibility will be described with reference to FIGS. 7 and 8. If the matrix circuit has a variation in transmissibility, image unevenness occurs when a diagnostic result is visualized by an ultrasonic diagnostic apparatus or the like, which causes erroneous diagnosis. Therefore,
Reducing variability is an important issue. FIG. 7 is a diagram showing the relationship between the bias voltage VB applied to the gate of the FET shown in FIGS. 2B and 2C and the transmissibility (forward conductance). At Voff where the bias voltage is Vth or less, the transmissibility is “0”, which corresponds to the switch off state.
When the bias voltage exceeds Vth, the transmissibility gradually increases, which corresponds to the switch on state. In this way, the transmissibility can be changed by changing the bias voltage, and the FET can perform an operation equivalent to that of the switch. As a circuit for changing the bias voltage, a bias circuit 31 having a structure as shown in FIG. 8 can be used. The bias circuit 31 is provided corresponding to the switch circuit 102, and turns on the switch 32 according to a command from the switch control circuit 30.
It is turned off and the bias voltage VBx is changed and applied to the corresponding switch circuit 102 in the matrix circuit 10 of FIG. The bias voltage VB is obtained by dividing the voltage Vcc-Voff by the resistors R1 and R2 of the bias circuit 31. If switch 32 is on, Therefore, the switch circuit 102 can be turned on by determining the value of the resistor R1 or the resistor R2 so that VB> Vth. Also,
When the switch 32 is off, VB = Voff <Vth (5), and the switch circuit 102 can be turned off. Here, the eighth
As is clear from the figure, when VB> Vth, the transmissibility can be changed by changing the bias voltage. Further, from the equation (4), it can be seen that the bias voltage VB is changed by changing the value of the resistor R1 or the resistor R2. Therefore, the values of the resistors R1 and R2 of the bias circuit corresponding to the switch circuit 102 of the matrix circuit 10 are finely adjusted (when the bias circuit 31 is integrated into an IC as described above, the adjustment of the resistors R1 and R2 is performed by trimming, for example. By adopting the configuration described above, it is possible to compensate for variations in the transmissibility of each switch circuit 102. As a result, there is no unevenness in the image on the ultrasonic diagnostic apparatus or the like, and the cause of erroneous diagnosis is eliminated.

〔The invention's effect〕

According to the present invention, since the adverse effect of the capacitance can be eliminated, it is possible to increase the frequency of the ultrasonic device, that is, increase the differentiation capability, and it is possible to compensate for the variation in the transmissibility of the matrix circuit, so that there is no image unevenness. There is an effect that a good received image can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an electronic scanning circuit used in the ultrasonic apparatus according to the first embodiment of the present invention, and FIGS. 2 (a), (b),
(C) and (d) are various configuration diagrams of the switch circuit used in the matrix circuit shown in FIG. 1, FIG. 3 is an explanatory diagram of comparison of frequency bands between the embodiment shown in FIG. 1 and a conventional example, and FIG. (A) and (b) are equivalent circuit diagrams of one signal line of the conventional example and the example shown in FIG. 1, respectively, and FIG. 5 is a frequency characteristic comparison diagram of the example shown in FIG. 1 and the conventional example. FIG. 6 is a configuration diagram of a matrix circuit used in the ultrasonic device according to the second embodiment of the present invention, FIG. 7 is a graph showing the relationship between the transmissibility of the FET used in the switch circuit and the bias voltage, and FIG. FIG. 9 is a block diagram of a bias circuit, and FIG. 9 is a block diagram of a conventional electronic scanning circuit.
Figure 10 is a block diagram of the matrix circuit according to the improved conventional example.
FIG. 11 is an explanatory diagram of the relationship between the number of simultaneously selected transducers and the number of switches in the conventional example. 1 (i) ... Oscillator signal line, 2 (j) ... Matrix input signal line (oscillator output signal line), 3 (j) ... Matrix output signal line, 10, 10 '... Matrix circuit, 19 ... Probe , 20 ...
Transducer selection circuit, 30 ... Switch control circuit, 31 ... Bias circuit, 40 ... Beam control circuit, 41 ... Delay circuit, 42 ... Addition circuit, 101, 101 '... Inductor, 102 ... Switch circuit, 103
... terminator.

Claims (11)

(57) [Claims] 1. An n (≧ 2) oscillators arranged in an array, and a beam control circuit for delaying transmission / reception signals of m (<n) oscillators selected from the oscillators, In an electronic scanning ultrasonic apparatus including a plurality of crosspoint switches connecting between the m oscillators and the beam control circuit, the crosspoint switch is configured with a switch having high input / output impedance,
An electronic scanning ultrasonic device, wherein each switch is connected by an inductor. 2. An n (≧ 2) transducers arranged in an array, and a beam control circuit for delaying transmission / reception signals of m (<n) transducers selected from the transducers. In an electronic scanning ultrasonic apparatus including a plurality of crosspoint switches connecting the m transducers and the beam control circuit, the plurality of crosspoint switches are divided into a plurality of groups, and An electronic scanning ultrasonic device, characterized in that a connecting wire of the above is used as an inductor. 3. An n (≧ 2) transducers arranged in an array, and a beam control circuit for delaying transmission / reception signals of m (<n) transducers selected from the transducers. In the electronic scanning ultrasonic apparatus including the matrix circuit provided between the m oscillators and the beam control circuit and connecting them, the matrix circuit is configured by an LC delay line. Electronic scanning ultrasonic device. 4. The switch according to claim 3, wherein the switch connecting the signal line connected to the vibrator and the signal line connected to the beam control circuit of the matrix circuit is a high input / output impedance switch. Electronic scanning ultrasonic device. 5. The electronic scanning ultrasonic apparatus according to claim 4, wherein the high input / output impedance switch is provided between a signal line connected to a transducer and a signal line connected to a beam control circuit. An electronic scanning ultrasonic device, characterized in that it is a switch whose signal transmission rate is adjustable. 6. The electronic scanning ultrasonic apparatus according to claim 4, wherein the high input / output impedance switch is composed of a semiconductor switch circuit, and a bias circuit for adjusting a bias voltage of the semiconductor switch circuit is provided. A characteristic electronic scanning ultrasonic device. 7. An n (≧ 2) oscillators arranged in an array and a beam control circuit for delaying transmission / reception signals of m (<n) oscillators selected from the oscillators. In a matrix circuit having a cross point switch which is provided between and which selectively connects a signal line connected to the m oscillators and a signal line connected to the beam control circuit, A matrix circuit characterized by being connected by an inductor. 8. An n (≧ 2) oscillators arranged in an array and a beam control circuit for delaying transmission / reception signals of m (<n) oscillators selected from the oscillators. In a matrix circuit having a crosspoint switch provided between the signal lines connected to the m transducers and the signal line connected to the beam control circuit, a plurality of crosspoint switches are provided. The matrix circuit is characterized in that the inductors are used as the connecting lines for connecting the groups into groups. 9. The matrix circuit according to claim 7, wherein each crosspoint switch is formed of a semiconductor switch circuit, and a bias circuit for adjusting a bias voltage of each semiconductor switch circuit is provided. 10. A semiconductor chip for an electronic scanning ultrasonic device, wherein the grouped crosspoint switches in the matrix circuit according to claim 8 are integrated into a semiconductor integrated circuit. 11. The semiconductor chip according to claim 10, wherein the bias circuit according to claim 9 is also mounted on the same chip.