JPH01270860A - Ultrasonic continuous wave doppler device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory noise figure by selectively demodulating and outputting a component to have a Doppler shift out of reflected waves, which appear in the blocking area of a narrow band filter, to be returned from a target area in a receiver. CONSTITUTION:For a CW high frequency signal to be generated in a transmitting carrier generator 1, a side band is controlled by a self crystal resonator. Then, for an output signal, only the signal of a central frequency, excepting for the side band, is passed through an extremely narrow band filter 2 and an oscillator TD is excited. The receiving signal of the oscillator TD is resonated by a serial resonating circuit, which is composed of a coil L3 and a capacitor C6, and amplitude-detected by a half-waveform-fold voltage rectifying circuit to be composed of diodes D1 and D2. Thus, a Doppler beat component, which is obtained by the reflected wave from a moving object in a checked body, is demodulated. The Doppler component and a CW component are included in this output signal. However, the rectified component by a CW signal is blocked by a capacitor C10 and only the Doppler component is amplified by a low frequency amplifying circuit and signal-processed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic continuous wave Doppler apparatus that uses the same transducer for transmission and reception.

(Prior Art) An ultrasonic continuous wave used in an ultrasonic Doppler blood flow meter in which a single transducer is used for transmission and reception is already known. Conventionally, single-oscillator continuous-wave (CW) Doppler systems use a bridge circuit to separate the transmitting and receiving signals, or directly observe the terminal voltage of the transducer to which the transmitting carrier is supplied without separating the transmitting and receiving signals. I was doing things like that.

(Problem to be Solved by the Invention) However, in the method using a bridge circuit, the arm of the bridge circuit is configured such that the transmitted signal is not output to the receiving circuit, and only the received signal that has undergone Doppler shift is output. It is necessary to precisely adjust the balance state of the bridge circuit using components, but in practice it is quite difficult to make adjustments to completely eliminate the transmitted signal, and the receiving signal path must be Insertion loss is unavoidable and hinders obtaining a suitable noise figure. Furthermore, when directly observing the terminal voltage of a vibrator, conventional measures have not been taken to avoid sideband noise present in the carrier wave generation source other than using an oscillator with as little sideband noise as possible. Therefore, ultimately a good noise figure has not been obtained.

The present invention has been made in view of the above-mentioned problems, and its purpose is to avoid being affected by sideband noise of the carrier wave generation source, and to reduce the number of circuit constants on the transfer signal path that would deteriorate the noise figure. The objective is to realize a CW Doppler system with as little energy as possible.

(Means for Solving the WR Problem) The present invention for solving the above-mentioned problems includes a transmit carrier generator, a narrow band filter that removes sideband noise from a carrier signal generated by the transmit carrier generator, It is coupled to the output of the narrow band filter in a relatively loosely coupled state and is commonly used to irradiate the target continuous wave ultrasound to the test region and to receive reflected waves from the test region. Consisting of a probe having a vibrator, a receiver that receives the delivered output of the vibrator in a relatively tightly coupled state,
The receiver is characterized in that it is configured to selectively demodulate and output a component having a Doppler shift among the reflected waves returning from the target area that appear in the stopband of the narrowband filter.

(Function) The CW high frequency No. 8 whose sidebands have been suppressed by the crystal resonator generated in the transmission signal generation means has its sideband noise removed by the narrowband filtering means and becomes a superfrequency wave oscillator (hereinafter referred to as vibration). It is supplied to the vibrator through a coupling means that loosely couples it to the oscillator and the oscillator.

converted into ultrasound signals. A reflected signal containing a Doppler shift from a moving object in the target area is received by the transducer,
1111 is mainly sent to the tightly coupled receiving side by the I key means.
and only the Doppler signal is extracted.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 1 is an NPN transistor QL, a crystal resonator X1, capacitors Ct, Cz, Cs, a coil Lt, and a resistor Rt*
A transmission carrier generator using a Savaroor circuit consisting of R2* and R3* generates a high frequency continuous wave. Capacitor C4 is a filter capacitor. Reference numeral 2 denotes an ultra-narrow band filter that blocks sidebands present in the transmission high-frequency signal generated by the transmission carrier generator 1 and eliminates noise caused by the sidebands, and as shown in FIG. It is composed of ×2. TD is a transducer that converts the output of the ultra-narrow band filter 2 into a CW multiplied signal ultrasound signal and transmits it into the subject, and the reflected wave that has undergone the Doppler effect is transmitted to the same transducer TD.
The wave is received by The capacitor Cs, the coil L2, and the vibrator TD form a tuned circuit for the transmitted high-frequency signal.
The coil Lz is driven by the vibrator TD@current. Also, coil! The capacitor Ca and the capacitor Ca also form a tuned circuit, and are tightly coupled or nearly optimally coupled to the vibrator TD. The diodes Di and D2 constitute a voltage doubler rectifier circuit, and due to the resonant circuit of the coil L3 and the capacitor C6, the "carrier" appearing at the connection point of the coil L3 and the capacitor C6, which is further boosted than the received signal of the transducer TD, is Amplitude detection is performed on the composite signal of the signal and the Doppler component of the reflected wave. The capacitor Cs, the resistor R5, and the capacitor C1l are a field effect transistor (hereinafter referred to as FET) that constitutes a low frequency filter.

The operation of the embodiment configured as described above will be explained. The sideband of the CW high frequency signal generated by the transmitting carrier generator 1 is suppressed by its own crystal resonator. This output signal is passed through a polar bandpass filter 2, in which only the signal at the center frequency excluding sidebands is passed, thereby exciting the vibrator TD.

For example, the polar bandpass filter 2 has at most 1 filter as shown in FIG.
It can also be configured with two crystal resonators. The two crystal resonators are equivalent to an extremely high Q series resonant circuit, have the same resonant frequency as the crystal resonator x1, and constitute a polar bandpass filter 2 that passes the transmission frequency. This output signal is capacitor Os, coil l-2 + vibrator TD
input into a resonant circuit consisting of This resonant circuit consists of a capacitor Cs, a coil, and 2. A series resonant circuit is formed between @transducer TD, current drives the transducer TD, and the ultrasonic CW multiplied signal is transmitted into the subject. The oscillator TD is thus ′Nl
By driving the Nl dynamically, it is loosely coupled to the transmission carrier generation B1. The ultrasonic CW multiplied signal emitted from the transducer TO receives a Doppler shift from a moving object such as the blood flow of the subject, is reflected, and is received by the transducer TD.

Since the received signal of the transducer TD is loosely coupled to the transmitting side, it is mainly output to the receiving side. This signal is coil L3
The series resonant circuit consisting of the capacitor CB resonates, and due to the circuit quality Q of this resonant circuit, it is multiplied by 0 at both ends of the capacitor CB, and the amplitude is detected by the half waveform voltage doubler rectifier circuit consisting of the diodes Ds and D2. be done. By performing amplitude detection in the voltage doubler rectifier circuit in this manner, the Doppler repeat component of the reflected wave from the moving object within the subject is demodulated. This output signal contains a Doppler component and a CW acid component, but since the component rectified by the CW multiplied signal is a direct current, it is blocked by the capacitor C+o, and only the Doppler component is amplified by a low frequency amplifier circuit including FETQ2.
Signal processed.

In this embodiment described above, sideband noise is suppressed by the high-Q circuit of 1 x crystal resonator of the transmission carrier generator 1, and the sideband is further suppressed by the polar bandpass filter 2, so that the sideband is reduced. A so-called clean high frequency signal is sent to the transducer TD. Also, since the transducer TD is loosely coupled to the transmitting side and tightly coupled to the receiving side, the energy of the received signal mainly goes to the receiving circuit on the right side of the figure, and the energy of the received signal mainly goes to the transmitting circuit on the left side. No interference from the side.

Therefore, the factor of deterioration of the noise figure caused by the loss caused by the flow of the transfer signal to the transmission circuit is significantly reduced.

FIG. 3 shows a circuit of another embodiment of the present invention. In the figure, parts equivalent to those in FIG. 1 are given the same reference numerals. In this embodiment, the polar bandpass filter 2 is constituted by a crystal mechanical filter (hereinafter referred to as a crystal filter) using two crystal resonators: a crystal resonator X3 and a crystal resonator x4. In this embodiment, the three crystal resonators of the input port of the polar bandpass filter 2 also serve as the resonators of the transmission carrier generator 1. Of course, the crystal resonator used in the transmission carrier generator 1 may be used independently without using a crystal filter. Although an example is shown in which a Sabarois circuit is used for the transmitting xeria generator, a crystal excavation circuit such as a Hartley circuit or the like may also be used.

(Effects of the Invention) As explained in detail above, according to the present invention, even if the transducer is used for both transmission and reception, it will not be affected by sideband noise of the transmission carrier generation source, and the factors that attenuate the reception signal will not be affected. Since this is removed, the deterioration of the noise figure and the decrease in the SN ratio are reduced, and the practical effect is great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is a side view of the configuration of a polar bandpass filter of the embodiment, and FIG. 3 is a circuit diagram of another embodiment of the present invention. 1... Transmission carrier generator 2... Polar bandpass filter XI * X2 * Xs * X4 *... Crystal resonator TD... Oscillator

Claims (3)

[Claims] (1) A transmission carrier generator, a narrowband filter that removes sideband noise from the carrier signal generated by the transmission carrier generator, and a narrowband filter that is coupled to the output of the narrowband filter in a relatively loosely coupled state. A probe having a transducer commonly used to irradiate a target continuous wave ultrasonic wave to a test region and receive reflected waves from the test region, and a probe having a received wave output of the transducer. and a receiver that receives the reflected waves in a relatively tightly coupled state, and the receiver selectively demodulates and outputs components having a Doppler shift among the reflected waves returning from the target area that appear in the stop band of the narrow band filter. An ultrasonic continuous wave Doppler device characterized by comprising: (2) The ultrasonic continuous wave Doppler apparatus according to claim 1, wherein the narrow band filter is composed of one crystal resonator. (3) The narrow band filter is composed of a crystal mechanical filter, and the crystal resonator of the transmission carrier generator shares the crystal resonator on the input side of the crystal mechanical filter, and the output side drives the resonator. The ultrasonic continuous wave Doppler apparatus according to claim 1.