JPH05329154A - Delay circuit for ultrasonic diagnostic system - Google Patents

Abstract

PURPOSE:To perform properly termination to change in characteristic impedance produced with making delay time of a variable delay line variable prepared by connecting in ladder-like shape an inductor to a diode with a variable capacity and to eliminate change in output voltage of a received signal caused by making impedance of a terminal circuit variable. CONSTITUTION:A variable resistance circuit 44 is provided on one terminal of a variable delay line 42 and it is possible to change the input impedance by changing bias electric current and to attempt to match characteristic impedance of the variable delay line 42 to the above described input impedance. On another terminal of the variable delay line 42, a terminal output circuit 46 is provided. The terminal output circuit 46 has a function to attempt matching of impedances like the variable resistance circuit 44 and a function to convert a value of electric current of a receiving signal to a value of electric voltage being proportional to the value of electric current. Therefore, the value of electric current is converted to the value of electric voltage regardless of the magnitude of an input impedance of the terminal output circuit 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a delay circuit for an ultrasonic diagnostic apparatus which delays and adds each received signal in order to perform receiving dynamic focus.

[0002]

2. Description of the Related Art In the medical field, an ultrasonic diagnostic apparatus for obtaining a tomographic image in a living body by transmitting and receiving ultrasonic waves is utilized. In an ultrasonic diagnostic apparatus, in order to obtain a high-resolution image, reception dynamic focus is performed in which the focus during reception is changed with time.
It is done as follows.

FIG. 6 shows a schematic structure of a conventional ultrasonic diagnostic apparatus. This conventional example is disclosed in JP-A-56-11.
2234.

The array transducer 10 is formed by arranging a plurality of ultrasonic transducers 10a. The ultrasonic transducer 10 transmits and receives ultrasonic waves in a living body. The reflected wave from the living body is received by each ultrasonic vibrating element 10a, each received signal is amplified by the amplifier 12, and then input to the delay circuit 14. In this conventional example, two delay circuits 14-1 and 14-2 having the same configuration are provided in parallel with each other. This is because while one delay circuit is delaying each received signal, the other delay circuit changes the setting of the delay time, specifically, switches the delay line tap, and uses both circuits alternately. This is to prevent mixing of switching noise of the electronic switch 18. The details are as follows.

In receiving dynamic focus,
Since a plurality of stages of focus points are set for one reception beam, it is necessary to change the setting of the delay time a plurality of times, that is, to switch the delay line taps in one reception. In the delay circuit 14-1, each received signal is first input to the voltage / current conversion circuit (V / I conversion circuit) 16,
The voltage value of the received signal is converted into a current value. This is because in the delay line described later, addition of each received signal is performed by current. The reception signal output from the V / I conversion circuit 16 is input to one of the taps via the electronic switch 18. Here, the electronic switch 18 selects a plurality of taps output from the delay line 20, and the delay time is set according to the location of the selected tap. The delay line 20 is formed by connecting an inductor and a capacitor in a ladder shape, delays the received signals input from the taps, adds the signals, and sends the added signals to the amplifier 22.
In the delay line 20 of FIG. 6, the received signal input on the left side is delayed more. The received signal amplified by the amplifier 22 passes through the electronic switch 26 and the display unit 2
4, the tomographic image and the like are displayed. During this time, tap switching is performed in the delay circuit 14 to change the focus distance. Next, the electronic switch 26 is inverted, the delay circuit 14-2 is selected, and the same operation as above is performed. A control circuit 28 controls the electronic switches 18 and 26.

As the electronic switch 26, one having a small switching noise is used. Since such a switch is expensive, it cannot be used for a large number of electronic switches 18. By doing so, the dynamic focus can be realized while preventing the switching noise of the electronic switch 18 from appearing in the image.

As described above, the conventional delay circuit 14 shown in FIG. 6 requires two circuits in order to prevent switching noise from being mixed in the received signal. Therefore, there is a problem that the circuit scale increases and the cost increases. Therefore, a delay circuit without switching noise is proposed in Japanese Patent Laid-Open No. 3-52311.

FIG. 7 shows a main structure of a conventional ultrasonic diagnostic apparatus capable of eliminating such switching noise. In this conventional example, the variable delay line 30 is configured by connecting a plurality of inductors L and a plurality of variable capacitance diodes VC in a ladder shape, and controls a reverse voltage applied to the variable capacitance diodes VC by the control circuit 32. By doing so, the capacitance value is controlled, and as a result, the delay time is controlled.

The received signal is converted into a current by the V / I conversion circuit 34 and then input to one of the taps, and the variable delay line 30 having the delay time set by the control circuit 32.
Is output through.

By the way, the delay time T in the delay line
_D is represented by T _D = n√ (LC). However, L is 1
It is the inductance of the section, and C represents the capacitance of one section. Further, n represents the number of stages in the section.

The characteristic impedance Z ₀ of each section of the delay line is represented by Z ₀ = √ (L / C).

Therefore, it is understood that when the capacitance C of the variable capacitance diode is changed by the control circuit 32, the delay time and the characteristic impedance of the variable delay line 30 are changed. On the other hand, if both ends of the variable delay line 30 are left open, there is a problem that reflection occurs.

Therefore, in this conventional example, a variable resistance circuit 36 is provided at both ends of the variable delay line 30, and by varying the resistance value of the variable resistance circuit 36, the ends of both ends of the variable delay line 30 are terminated. Is going. Specifically, the input impedance of the variable resistance circuit 36 is matched with the characteristic impedance of the variable delay line 30 to prevent reflection. The control of the variable resistance circuit 36 is performed by the control circuit 32.
The impedance variable control of the variable resistance circuit 36 is executed in conformity with the reverse voltage control of the variable capacitance diode.

However, since the received signal is input to the variable delay line 30 as a current signal by the V / I conversion circuit 34, when the input impedance of the variable resistance circuit 36 changes, even if the input received signal is constant, Output terminal 3
There arises a problem that the output voltage appearing at 8 changes. That is, the output voltage at the output terminal 38 is
This is because it is the product of the input impedance of 6 and the received signal current.

Therefore, in the conventional example shown in FIG. 7, a multiplier 40 is provided, and the multiplier 40 outputs an output signal of a coefficient having a value corresponding to the delay time sent from the control circuit 32. The output signal is corrected by multiplying by.

[0016]

Therefore, in the conventional example shown in FIG. 7, a correction circuit such as a multiplier 40 must be additionally provided, which makes the circuit complicated and the control complicated. was there.

The present invention has been made in view of the above conventional problems, and an object thereof is to appropriately terminate a variable delay line formed of a variable capacitance diode and an inductor, and to terminate the variable delay line. An object of the present invention is to provide a delay circuit for an ultrasonic diagnostic apparatus in which the level of the output signal does not change even if the input impedance of the circuit to be performed is changed.

[0018]

In order to achieve the above object, the present invention includes an inductor and a variable capacitance diode, and the capacitance of the variable capacitance diode is changed by a capacitance control signal, whereby the delay time can be changed. A variable delay line and a terminating circuit provided at one end of the variable delay line, the variable resistance circuit whose input impedance changes according to an impedance control signal, and the other end of the variable delay line. A termination circuit, the input impedance of which changes according to the impedance control signal, and which performs current / voltage conversion on the received signal current output from the variable delay line in proportion to its current value; A circuit for outputting the capacitance control signal and the impedance control signal, for moving the focus point of ultrasonic waves. Then, the delay time of the variable delay line is controlled, and the input impedance of the variable resistance circuit and the terminal variable delay circuit is controlled to match the characteristic impedance of the variable delay line that changes according to the delay time. A delay control circuit, wherein the current value of the delay signal is converted into a voltage value without being affected by a change in the input impedance of the termination output circuit.

[0019]

According to the above construction, the delay time can be varied by the control of the delay control circuit. Along with that, the characteristic impedance of the variable delay line changes.However, by changing the input impedance of the variable resistance circuit and the termination output circuit and matching it with the characteristic impedance of the variable delay line, impedance matching can be performed. Are prevented. The termination output circuit performs current / voltage conversion on the received signal current at the same time as impedance matching as described above. That is, the received signal is input as a current from the tap of the variable delay line, is delayed by the variable delay line, flows into the termination output circuit, and is converted into a voltage value proportional to the current value. Therefore, even if the input impedance of the termination output circuit changes due to impedance matching due to the change in the delay time, the output voltage does not change without correction unless the input received signal changes.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the variable delay circuit of the ultrasonic diagnostic apparatus according to the present invention.

This variable delay circuit has a variable delay line 4 having substantially the same structure as the conventional variable delay line 30 shown in FIG.
2 and the variable resistance circuit 4 is provided at both ends of the variable delay line 42.
4 and a termination output circuit 46 are provided. The delay control circuit 48 controls the delay time of the variable delay line 42 and the input impedance of the variable resistance circuit 44 and the termination output circuit 46.

Also in the variable delay circuit shown in FIG. 1,
Similar to the conventional example shown in FIG. 7, the received signal 100 is first subjected to voltage / current conversion and then input to any tap of the variable delay line 42.

The variable delay line 42 is formed by connecting a plurality of inductors L and a variable capacitance diode VC in a ladder shape in the same manner as in the conventional example shown in FIG. 7, and has both ends thereof on the anode side of the variable capacitance diode VC. An inductor L _S is connected to keep the potential at 0V. A high resistance can be connected instead of the inductor L _S.

The capacitor C _S is a variable capacitance diode V
This is for grounding the cathode side of C in an alternating current. The capacitors C1 and C2 are connected to the variable resistance circuit 44.
And the terminal output circuit 46 to output only the AC component, and to separate those circuits from the variable delay line 42 in terms of DC. The values of L _S , C _S , C ₁ and C ₂ are selected so that they can be ignored at the frequency of the received signal. Variable delay line 4
The operation of No. 2 is similar to that of the conventional example of FIG. 6, and the delay time is controlled by the control signal VC1 output from the delay control circuit 48. At the same time, its characteristic impedance also changes. By the way, the frequency of the received signal is about several MHz, and the repetition frequency of the ultrasonic pulse is several kHz.
Here, the control signal VC output from the delay control circuit 48
1, VC2 are generated based on the synchronization signal SYNC input to the delay control circuit 48, which is a substantially sawtooth signal synchronized with the repetition frequency of the ultrasonic pulse.

The variable resistance circuit 44 will be described below.

The variable resistance circuit 44 is connected to a constant current circuit 50 whose passing current value is controlled by a delay control circuit 48, and two diodes 52 and 5 in this embodiment connected in series.
4 and the one end of the variable delay line 42 is connected between the diode 52 and the constant current circuit 50. The anode side of the diode 54 is connected to the ground.

By the way, the internal resistance (rd) of the diode changes depending on the magnitude of the current (bias current) flowing through the diodes 52 and 54. Here, rd is represented by rd = 26 × 10 ⁻³ / I (300 ° K). Therefore, if the value of the current flowing through the constant current circuit 50 is controlled, the value of the current flowing through the diodes 52 and 54 changes, and as a result, the variable delay line 42 of the variable resistance circuit 44 changes due to the change in the resistance value expressed by the above equation. The impedance viewed from the side, that is, the input impedance of the variable resistance circuit 44 can be changed.

When the impedance is increased, the bias current may be decreased, but the bias current cannot be extremely decreased because it needs to be sufficiently larger than the received signal current flowing out from the variable delay line 42. If you want to make it extremely small, increase the number of diodes and conversely 1
If the number is sufficient, either of the diodes 52 and 54 may be removed.

FIG. 3 shows an example of a specific configuration of the constant current circuit 50 shown in FIG. This is a so-called current mirror circuit. Impedance control signal V
Although I ₁ changes when C2 is changed, I ₂ also changes because I ₁ = I ₂ in the current mirror. This I ₂ may be used as the bias current of the diodes 52 and 54 of the variable resistance circuit 44.

Further, in FIG. 4, the second part of the variable resistance circuit 44 is shown.
Examples are given. The signal from the variable delay line 42 is input to the input terminal of the amplifier 56, and the feedback resistor Rf is provided between the output terminal of the amplifier 56 and the input terminal thereof. The gain of the amplifier 56 can be changed by changing the impedance control signal VC2.

Such a voltage-controlled variable gain amplifier can be realized by using, for example, a multiplier. As a result, the input impedance Zin can be changed by the following equation.

Z _in = R _f / (1 + A) where A is the gain of the amplifier 56 and the input impedance of the amplifier is sufficiently high. The variable resistance circuit shown in FIG. 4 is also disclosed in JP-A-3-52311.

Next, the termination output circuit 46 will be described.

The termination output circuit 46 has two functions:
It has a function of achieving impedance matching and a function of performing current / voltage conversion on the current of the reception signal output from the variable delay line 42.

In FIG. 1, a constant current circuit 62 is connected via a diode 60 to the emitter of a transistor 58 whose base is grounded. This constant current circuit 62 is
Impedance control signal VC2 from the delay control circuit 48
The magnitude of the passing current is controlled by.

The other end of the variable delay line 42 is connected between the constant current circuit 62 and the diode 60.

A load resistance R _L for extracting an output voltage is connected to the collector of the base-grounded transistor 58, and a voltage of + V is applied to the load resistance R _L. The potential on the collector side of the transistor 58 is taken out as a voltage value. This termination output circuit 4
6, the input impedance, that is, the impedance viewed from the variable delay line 42 side is the transistor 5
8 is determined by the operating resistance between the base and the emitter and the operating resistance of the diode 60. That is, considering the impedance viewed from the variable delay line 42 side, the load resistance R _L is in a state as if it does not exist.

Therefore, regarding the input impedance of the termination output circuit 46, it is understood that the equivalent circuit of the termination output circuit 46 is the variable resistance circuit 44.

Therefore, like the variable resistance circuit 44,
In this termination output circuit 46 as well, by controlling the passing current value of the constant current circuit 62, the currents flowing through the transistor 58 and the diode 60 change, and the operating resistances thereof change, so that the input impedance can be changed. By appropriately setting the passing current value of the constant current circuit 62, the input impedance of the termination output circuit 46 can be matched with the characteristic impedance of the variable delay line 42.

As in the case of the variable resistance circuit 44,
To increase the impedance, more diodes may be provided on the emitter side of the transistor 58, while the diode 60 may be removed if the base-emitter resistance of the transistor 58 is sufficient.

On the other hand, the received signal current output from the variable delay line 42 is the diode 6 because the current value of the constant current circuit 62 is determined by the impedance control signal VC2.
0 to flow into the emitter of the transistor 58 (note that the expression that the received signal current flows into the emitter of the transistor 58 means that the transistor 58 has the constant current circuit 6).
Since the bias current flows due to 2, it means that the current actually increases or decreases around the value of the bias current.
The same applies below).

Due to the nature of the transistor that the emitter current and the collector current of the transistor are substantially equal to each other, almost all the received signal current flowing into the emitter of the transistor 58 is output to the collector of the transistor 58. Then, by flowing through the load resistance R _L , the current XR _L
Is converted into a voltage represented by.

That is, the received signal current is converted into a voltage value proportional to the current value and output regardless of the magnitude of the input impedance. In this case, according to the impedance control signal VC2, the current value of the constant current circuit 62,
That is, since the bias current is controlled, the increase / decrease in the bias current appears as an offset voltage in the output voltage, but as described above, the frequency of ultrasonic waves and the repetition period of ultrasonic pulses are sufficiently different in frequency. for,
Both can be easily separated by a filter circuit or the like, that is, only the received signal can be extracted.

FIG. 5 shows a second embodiment of the termination output circuit 46.

In this embodiment, the delayed reception signal is supplied to the input terminal of the amplifier 64, and the signal output from the output terminal of the amplifier 64 is input to the base of the transistor 66. Transistor 66 emitter and amplifier 6
A capacitor 6 connected in series with the input terminal of 4
8 and a feedback resistor R _f are provided.

The capacitor 68 has a function of blocking direct current, and is selected to a value that can be ignored for the frequency of the received signal.

A constant current circuit 70 is connected to the emitter of the transistor 66, and a load resistance R _L is connected to the collector of the transistor 66, and the output voltage is taken out.

Since the transistor 66 functions as an emitter follower for the feedback circuit composed of the capacitor 68 and the feedback resistor Rf, the input impedance of the termination output circuit is the same as that of the variable resistance circuit of FIG. .. Further, the control of the input impedance is performed by the impedance control signal VC2 output from the delay control circuit 48, as in the case of the variable resistance circuit of FIG.

On the other hand, the received signal current output from the variable delay line 42 almost flows into the feedback resistor Rf because the impedance of the input of the amplifier 64 is set high.
Since the current value of the constant current source 70 is fixed, the feedback resistor R
The current passing through f flows into the emitter of the transistor 66. Due to the nature of the transistor, that is, the emitter current and the collector current of the transistor are substantially equal, the received signal current is output to the collector of the transistor 66 and is converted into a voltage proportional to the current value by flowing through the load resistor RL.

FIG. 2 shows the configuration when the variable delay circuit according to the present invention is applied to an ultrasonic diagnostic apparatus. Each reception signal output from the array transducer 80 is selected by the switch circuit 82, and V / I is output via the preamplifier 84.
It is sent to the conversion circuit 86, and voltage / current conversion is performed.

The received signal converted into a current is input to any tap of the variable delay line included in the variable delay circuit 88 configured as shown in FIG. 1 according to its delay time.
In the variable delay circuit 88, the received signals are delayed and added, and the added received signals are sent to the display section 90 to display a tomographic image or the like. The timing control circuit 91 controls the variable delay circuit 88. In addition,
The timing control circuit 91 also controls the transmission circuit 92, and a drive signal at the time of transmission is supplied from the transmission circuit 92 to the array transducer 80 via the switch circuit 82.

According to the ultrasonic diagnostic apparatus as described above, it is possible to avoid the occurrence of switching noise of the electronic switch at the time of setting the delay amount, and to provide a correction circuit for the received signal after delay which is conventionally required. The configuration of the variable delay circuit can be simplified without the need, and the number of circuits that need to be controlled is reduced, so that control can be facilitated.

[0054]

As described above, according to the delay circuit of the ultrasonic diagnostic apparatus of the present invention, the delay time can be changed by the control signal changing in a sawtooth shape.
Generation of switching noise of the electronic switch can be avoided. Further, since the variable delay line can be properly terminated and the received signal current can be converted into a voltage value proportional to the current value and output, an output voltage that is not affected by the input impedance of the termination circuit can be obtained. it can. Therefore, it is possible to reduce the number of correction circuits required in the related art, simplify the circuit, and reduce the number of circuits that require control, which facilitates control.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a variable delay circuit according to the present invention.

FIG. 2 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus provided with a variable delay circuit according to the present invention.

FIG. 3 is a circuit diagram showing a configuration of a constant current circuit.

FIG. 4 is a circuit diagram showing a second embodiment of a variable resistance circuit.

FIG. 5 is a circuit diagram showing a configuration of a second embodiment of a termination output circuit.

FIG. 6 is a block diagram showing a schematic configuration of a conventional ultrasonic diagnostic apparatus.

FIG. 7 is a circuit diagram showing a second example of a conventional variable delay circuit.

[Explanation of symbols]

 42 variable delay line 44 variable resistance circuit 46 termination output circuit 48 delay control circuit

Claims (3)

[Claims] 1. A variable delay line including an inductor and a variable capacitance diode, wherein a capacitance of the variable capacitance diode is changed by a capacitance control signal, thereby changing a delay time, and a variable delay line provided at one end of the variable delay line. A variable resistance circuit whose input impedance changes according to an impedance control signal, and a termination circuit provided at the other end of the variable delay line, the input impedance of which changes according to the impedance control signal. And a termination output circuit that performs current / voltage conversion on the received signal current output from the variable delay line in proportion to the current value, and a circuit that outputs the capacitance control signal and the impedance control signal. , The delay time of the variable delay line is controlled according to the movement of the focus point of the ultrasonic wave, and A delay control circuit that controls the input impedance of the variable resistance circuit and the termination output circuit to match the characteristic impedance of the variable delay line that changes according to the delay time. A delay circuit for an ultrasonic diagnostic apparatus, wherein the current value of the delay signal is converted into a voltage value without being affected by the change in 2. The delay circuit of the ultrasonic diagnostic apparatus according to claim 1, wherein the termination output circuit is connected to a grounded base transistor having the other end of the variable delay line connected to an emitter, and an emitter of the transistor. A constant current circuit capable of varying a current value according to an impedance control signal from the delay control circuit, and a delay signal of the ultrasonic diagnostic apparatus, wherein the received signal is extracted from the collector of the transistor. circuit. 3. The delay circuit of the ultrasonic diagnostic apparatus according to claim 1, wherein the termination output circuit has an input terminal connected to the other end of the variable delay line, the amplification factor of which is an impedance from the delay control circuit. An amplifier circuit controlled by a control signal; a transistor whose output terminal is connected to the base; and a feedback resistor provided between the emitter of the transistor and the input terminal of the amplifier circuit, A delay circuit for an ultrasonic diagnostic apparatus, which is configured to extract a received signal from the collector of the transistor.