JPS60202356A - Ultrasonic transmitting-receiving apparatus - Google Patents

Abstract

PURPOSE:To enhance an ON/OFF ratio, by forming two ultrasonic transmitting pulses by changing over two operation frequencies and forming one frequency out of the frequency band zone of a transmitting and receiving circuit. CONSTITUTION:A VCO oscillator 210 is controlled by a VCO control circuit 200 and, for example, repeats oscillation of 500MHz during a pulse width of 100nsec and that of 1,300MHz in other time regions to apply both oscillations to a power amplifier 230 through an analogue switch 220 turned ON and OFF by a pulse signal. This RF pulse electric signal is applied to a probe system 260 through a directionality coupler 240 and a matching circuit 250. The reflected signal through the circuit 250 and the coupler 240 is amplified by a receiving amplifier 270 having a band zone of 100MHz-1GHz and a component of 1,300MHz present in a base other than a reflected echo is removed. Output is amplified by an AGC amplifier 280 and converted to a video signal by a RF detector 290 and formed into an image signal by a sampling circuit 300. By this method, an ON/ OFF ratio can enhanced.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an imaging device using high-frequency ultrasonic energy;
In particular, it relates to transmitter/receiver circuits for ultrasonic microscopes.

[Background of the invention]

In recent years, it has become possible to generate and detect sound waves with high frequencies up to I GHz, and it has become possible to realize a blue wavelength of about 1 μm underwater, and as a result, it has become possible to obtain a high-resolution sound wave imaging device. That is, a concave lens is used to create a focused sound wave beam, achieving a high resolution of 1 μm. 5 A sample is placed in such a beam, and information reflecting the elastic properties of the sample is obtained by detecting the reflected and transmitted sound waves by the sample, or the sample or a sensor generating the beam is relatively mechanically scanned. It creates a two-dimensional image. (R, A, Mr. Lemon and C, F, Mr. Quates' A S
canning acoustic microsco
I EEE cat entitled pe, Na73CH148
29SU-pp423-426. Paper published in 1973).

A conventional example of an ultrasound microscope that obtains such a sound wave image is described in Section 1.
This will be explained using FIG.

FIG. 1 is a diagram showing a schematic configuration of a probe system for obtaining reflected signals from a sample. In the figure, a sound wave lens (for example, a cylindrical material such as sapphire or quartz) 20 has one end surface that is optically polished and a flat surface, and a concave spherical hole 30 formed in the other end surface. An RF pulsed electric signal applied by the pulse oscillator 5 to the piezoelectric thin film 10 formed on the plane causes an RF pulsed sound wave in the form of a plane wave to be radiated into the sound wave lens 20 . This planar sound wave is transmitted through the spherical hole 30
When reaching the point, focused ultrasound is irradiated onto the sample 50 placed at a predetermined focus by a positive focusing lens formed at the interface between the spherical hole 30 and the medium 40 (therefore, the spherical hole becomes the aperture of the lens). The sound waves reflected by the sample 50 are collected by the same lens, converted into plane waves, propagated within the sound wave lens 20, and finally converted back into RF electric signals by the piezoelectric thin film 10. When looking at the state of this received signal in the video band after detecting the RF electric signal, it becomes as shown in FIG.

Here, the horizontal axis represents the time axis, and the vertical axis represents the signal strength. In FIG. 2, waveform A is the launch signal (the above applied signal), waveform B is the echo from the interface between the lens 30 and medium 40, and waveform C is the reflected echo from the sample 50. It shows. Such a waveform is repeated with a repetition time of 1R. The reflected echo C is
Since it changes with each repetition depending on the acoustic properties at the sample location and the scanning of the sample, this reflected echo C is sampled by the receiving circuit 6 in synchronization with the repetition period, and only its intensity is extracted and used as an image signal. It is. That is, if the sample is scanned in 17 planes by the mechanical scanning system 60 and the image signal is displayed on the cathode ray tube 70 in synchronization with this mechanical scanning, a sound wave image can be obtained.

By the way, in such an ultrasound microscope, in order to sample only the reflected echo C from the sample, it is necessary to temporally distinguish it from other echoes (spurious signals such as echoes from the lens interface and multiple reflection signals). It is necessary to transmit and receive extremely short RF pulse electrical signals.

The present inventors have discovered that the conventional example has a drawback in such a short pulse RF electric signal transmitting/receiving circuit. FIG. 3 shows an example of a conventional ultrasonic transmitting/receiving circuit, in which the output of an RF continuous wave oscillator 100 is converted into an RF pulse signal with a repetition period t□ and a duration t by an RF analog switch 110. After amplifying this signal with a power amplifier 120, it is applied via a directional coupler 125 to a probe system 130 consisting of a lens and a piezoelectric film. The RF electrical signal, including the reflected ultrasound signal (as shown in FIG. 2) from the sample, is again passed through the directional coupler 12'5 to the variable RF amplifier 140.
After being amplified by the RF detector 150, it is diode-detected and converted into a video signal, and the sampling circuit 160 (sample and hold circuit, etc.) extracts the magnitude of only the echo C and sends the image to the CRT. It becomes a signal.

In such a configuration, the RF analog switch 110
It is necessary to sufficiently turn on and off the output RF multiplied signal of the F continuous wave oscillator 100. For example, the output level of the continuous wave oscillator 100 is set to OdBm, the amplification degree of the power amplifier 120 is set to 40dB, and the on/off ratio of the analog switch is set to 60dB.
dB, the output level is +40 during the duration t.
At d B ni, an RF pulse signal with an output level of -20 dBm is applied to the probe system 130 for the rest of the time. By the way, since the ratio of the magnitude of the reflected signal from the sample to the magnitude of the applied RF pulse signal, that is, the sensitivity of the probe system, is usually about -70 dB, under the above conditions, the reflection with an intensity of -30 dBm is usually Although a signal is obtained, the magnitude of this signal is smaller than the above-mentioned applied signal level when off, and the RF multiplied signals during off are added and they interfere with each other. Figure 4 shows this situation.As shown in Figure 2, when the detected signal should normally be like a wavy line, due to the above interference it becomes smaller as shown in the solid line, or sometimes becomes a negative signal. It causes it to occur. Furthermore, the off-signal is detected even in a time domain where no signal is normally obtained, and a constant base signal is provided, which has an adverse effect on the receiving system, such as oscillation. Since the on/off ratio of commercially available RF analog switches is about 60 dB, conventional attempts have been made to connect two or three stages of such analog switches in series to obtain an overall on/off ratio of 120 to 180 dB. being done. In such a case, the above off signal will be -80dBm to -140dBm,
This is because the noise level is lower than that of a commonly used receiver, and the adverse effects of the above-mentioned interference phenomenon can be removed. However, even in such a configuration, the continuous wave oscillator 100
Since it is constantly oscillating, it is necessary to reduce the amount of leakage signals and electromagnetic propagation of this oscillator to below -80 to -120 dB, which requires a great deal of effort in the electromagnetic shielding of the oscillator and the electromagnetic shielding of the connecting cable. However, the cost was also usually high.

[Purpose of the invention]

The present invention has been made in view of these points, and makes it possible to transmit and receive short RF pulse electric signals with a simple configuration, eliminates the leakage RF signal, and achieves ultrasonic transmission and reception with an excellent on/off ratio. The purpose is to provide circuits.

[Summary of the invention]

The gist of the present invention is to achieve the above object by switching the frequency of the output signal of the continuous wave oscillator, so that when it is on, it oscillates at the used ultrasonic frequency, and when it is off, it oscillates at a sufficiently distant frequency. This is what I am trying to do. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiments of the invention]

FIG. 5 shows one embodiment of the present invention, in which VCO (V
oltage Controlled 0scilla
tor) oscillator 210, RF analog switch 220
゜VCO control circuit 200, power amplifier 230, directional coupler 240, matching box 250, probe system 260, RF receiving amplifier 270, AGC (AutomaticGa
(in Control) circuit 280, RF detection wave 2
90 and a sampling circuit 300. vCO control circuit 2
00 mainly has the function of applying a pulse waveform of variable oscillation 111 to the frequency control voltage terminal of the 700 oscillator 210. For example, if the voltage-frequency characteristics of the 700 oscillator 210 are as shown in FIG.
is the frequency f.

The oscillations of and jo are repeated alternately. In this embodiment, the frequency band for transmission and reception is 100MHz to IGHz.
The pulse width t-=100naec is achieved with 700 oscillator, and the frequency control voltage is 0 to 1.
5 volt, Q volt 300MHz, 2
500MHz for volt, 13 for 15volt
00MHz characteristic is used. As a VCO control signal, Vt = 15 volts, ■, = 2 vol
Using a pulse waveform of t (t a = 100 n5ec), the 700 oscillator 210 generates 5
At 00 MHz, oscillation at 1300 MHz is repeated in other time ranges.

The output of the 700 oscillator is applied to a power amplifier 230 via an analog switch 220 that is turned on and off by a pulse signal as shown in FIG. 7(c). Therefore, the output of the power amplifier becomes as shown in FIG. As shown in FIG. 7(e), the frequency f is transmitted through the coupler 240. (=500MHz) reflected signal is obtained. When this signal is amplified by the receiving amplifier 270, if the band of this amplifier is selected from 100 MHz to IGHz (
This is achieved by amplifier selection or bandpass filters), the frequencies present at the base other than the reflected echo f□
(=1300MHz) component will be removed. As in the conventional case, the output of the receiving amplifier is amplified by the AGC amplifier 280, converted to a video signal by the RF detector 290, and only the echo C is extracted by the sampling circuit 300 to provide an image signal.

As is clear from the above description, in the present invention, unlike the conventional method of turning on and off an RF multiplied signal having a single frequency component, the present invention uses frequency components within the effective band of the transmitting/receiving system. By adopting a method of switching between 0 and 0 of the frequency component outside the band, it is possible to completely eliminate the in-band frequency component 0 at times other than the duration t of the applied signal, and the above-mentioned Provides a means to eliminate negative effects such as interference between the same frequency component and reflected echoes when off.

It is. Such a configuration can be realized simply by adding the CO control signal circuit 200 to the conventional configuration, and since it is essentially unnecessary to remove the mixing of the same frequency components by electromagnetic shielding, it can be realized easily and inexpensively. Can be done.

The VCO control circuit 200 is a commonly used TTL (Tra
ngistor transistor logi
c) It can be easily created using elements. FIG. 8 shows an embodiment of such a control circuit, in which one-shot 4
00, a pulse waveform of duration t1 as shown in FIG. 9(b) is generated. This output is, for example, an open collector TTL element 410 and a diode 430 . A circuit consisting of variable resistor 440 adjusts the low level from 0 to 15V.
By clamping to an arbitrary voltage of olt, the high level becomes low at 15 volts as shown in Figure 9 (C).
The level is converted to a VCO control voltage signal of Vvolt. Here, the capacitor 420 is inserted in order to prevent the reference voltage V of the clamp from being fluctuated by turning on and off the diode 440.

As described above, according to the present invention, it is inexpensive, simple, and CO
By adding a control circuit, we can provide an on-off ratio that cannot be obtained with conventional multi-stage analog switch systems, and by removing RF leak signals and residual RF components, we can connect these signals to the desired This provides a circuit configuration that eliminates false detections due to interference with reaction signals. Of course, as a control circuit to realize such an effect, any known technical means other than the above-mentioned embodiments may be used as long as it essentially shifts and keys the oscillation frequency.
Also, the off-frequency f is a value smaller than the on-frequency j0 (in the above embodiment, f,=500MHz and f,=500MHz).
It is clear that the same effect can be obtained even if the frequency is 30 MHz).

Further, in this embodiment, only a reflection type configuration was described as an ultrasound microscope, but the present invention can also be applied to configurations that essentially require transmission and reception of pulse waveform ultrasonic waves, such as transmission type, interference B mode, and phase difference. I would like to add that it has a great effect.

〔Effect of the invention〕

As described above, according to the present invention, an ultrasonic wave transmitting/receiving circuit with an excellent on/off ratio can be obtained, and it is possible to easily eliminate leakage signals and signal interference due to electromagnetic propagation with respect to the received signal from the probe. Can be done.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the configuration and operating waveforms of an ultrasound microscope to which the present invention is applied, Figure 3 is a block diagram showing a conventional transmitting/receiving circuit, and Figure 4 is interference caused by the circuit in Figure 3. FIGS. 5 to 9 are block diagrams and waveform diagrams showing an embodiment of the present invention and its operating waveforms. 200-VCO control circuit, 210-VCO oscillator, 22
0... Analog switch, 230... Power amplifier, 240... Directional coupler, 250... Matching box, 260... Probe system, 270... RF receiving amplifier, 280 ...AGC circuit, 290...RF detector,
300... Sampling circuit 6 1 Figure

Claims (1)

[Claims] 1. In an ultrasonic transmitter/receiver circuit using pulsed ultrasonic waves,
An ultrasonic transmitting/receiving device characterized in that an ultrasonic transmitting pulse is constituted by switching between two operating frequencies, one of the frequencies being outside the frequency band of the transmitting/receiving circuit.