JP2000312677A - Single-oscillator ultrasonic doppler system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a configuration for separating transmission and reception without making a received noise figure adverse in a single-oscillator Doppler system. SOLUTION: In the single-oscillator Doppler system, the comparative side of a bridge circuit 3 for transmission/reception separation is composed of reactance components 8 and 9 only for separating transmission and reception without making the received noise figure adverse, another driving system is used for driving the comparative side, and operation for balancing is performed by adjusting the amplitude and phase of this separately provided driving system. There is no element of loss in the separately provided driving system and the comparative side, and a received signal is led into a receiver 12 without making the noise figure adverse with this bridge circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an ultrasonic Doppler device that uses a single transducer for both transmission and reception, and more particularly to an ultrasonic Doppler device that minimizes the loss of a path for receiving signal energy.

In a conventional ultrasonic Doppler apparatus according to the prior art, particularly an ultrasonic CW Doppler apparatus, separate transducers are used for transmission and reception, and a probe arranged so as to be adjacent to the same contact surface is used. ing. The reason why the transmitter and the receiver are separated even though the transducer is a bidirectional reversible converter is that otherwise it becomes difficult to separate the transmitting and receiving electronic circuits from each other, and the transmitting that includes the large amplitude and noise generated by the transmitter is performed. This is because a received signal buried in the signal must be detected.

However, it is still preferable in all senses to use only one oscillator instead of two oscillators.

[0004] Even if a single oscillator is commonly used for transmission and reception, transmission and reception can be separated by using a bridge or a hybrid transformer. In such a system, there are many problems such as fluctuation of the acoustic load impedance to the vibrator and automatic follow-up thereof, but the most serious problem is a comparative problem such as a bridge or a hybrid transformer. In a design that expects a balance between the dummy impedance of the side and the load impedance, half of each energy flow of the transmission / reception signal is absorbed by this dummy impedance, and therefore, the noise figure of the reception system is never 6 dB. It cannot be better.

The present invention is intended to solve such a problem, and has a configuration in which the loss of a received signal caused by a bridge or a hybrid transformer is neglected by using an essentially lossless comparison side. I do.

That is, the most characteristic point of the configuration of the present invention is that an essential point is that a signal synchronized with the transmission signal and separately supplied with a signal whose amplitude and phase are adjusted is separately supplied to the comparison side of the transmission / reception separation bridge. The configuration is such that a signal generator having a drive point internal impedance with no loss is provided.

More specifically, in the present invention, two transmission circuits having substantially equivalent capabilities are used, one of which is used for driving a vibrator for transmission with full amplitude capability, and the other is used to adjust the amplitude and phase. To provide a signal for maintaining balance to the comparison side of the bridge for separating transmission and reception or the comparison side of the hybrid transformer, and to receive the signal on the comparison side such that the latter has an essentially lossless driving point internal impedance. It is a thing to ignore the loss of.

[0008] The active bridge balance by the feedback of the evaluation result of the received signal can also be realized by a general-purpose LCR meter or a circuit technique called a so-called synthetic notch as shown in US Pat. No. 4,012,576. . However, feedback cancellation by these analog circuits is not preferred, since the cancellation signal is obtained by remodulating the carrier through a complicated path, so that the modulation noise caused by the system inevitably enters the receiver input as a contamination component. .

Therefore, in the present invention, the erase side of the comparison side is obtained from a switching drive source that always operates in saturation, and the amplitude and phase thereof are controlled by a microcontroller, thereby realizing a comparison side having essentially no noise. In addition, by making the driving point internal impedance lossless, unnecessary loss to the received signal can be neglected, and the received noise figure can be maintained as desirable as possible.

Hereinafter, one preferred embodiment of the present invention will be described with reference to the drawings. However, this is merely an example, and this example does not limit the gist of the present invention. It is obvious that experienced persons, intellectuals, and those skilled in the art can conceive and carry out countless other examples in accordance with the gist of the present invention.

[0011] In the sole figure of the accompanying drawing schematically depicted, the only transducer (2) opposes the target object (1) to obtain an ultrasonic coupling, in which the moving object (4) (eg the fetus) Doppler observation of heart, blood flow, etc.). The vibrator (2) is a plain PZT flat disk.

A bridge circuit or a hybrid transformer (3) for separating transmission and reception is connected to an electric terminal of the vibrator (2). The operation principle and the main purpose of the bridge circuit and the hybrid transformer are the same, and the case of the bridge circuit will be described here. That is, the bridge circuit has only one vibrator (2) on one side, and the first flywheel circuit (or the first flywheel circuit (or) added to the vibrator and the first binary amplifier (5) serving as a transmission driving source. A reactance (in this case, a capacitor) (7) is inserted between the low-pass filter and the low-pass filter (6). On the other hand, the other two sides of the bridge similarly form a voltage dividing circuit composed of only two reactance components (capacitors) (8) and (9), and similarly, a second binary amplifier ( 10) and a second flywheel circuit (or low pass filter) (11). The received signal is extracted from the joint between the terminals of the vibrator and the capacitors (8) and (9), which are the voltage dividing points on the comparison side, and is connected to the receiver (12) via the coupling transformer (13).

[0013] In a pure, passive bridge circuit that adheres to the principle, the terminals at the upper end in the figure are bundled, not separately, connected to one drive source, and are balanced only by the impedance relationship of each side. In the example, each drive source is separate, in particular adjusting and balancing the phase and amplitude of the signals provided by the first and second drive sources. The advantages of doing so are twofold, as described below.

First, when the equilibrium is achieved, the comparison side is not saturated because the binary amplifier of the drive source is performing a saturation operation and its input signal is synchronized with the clock. There is essentially less noise in amplitude modulation and phase modulation than when a stepped drive source is used, and in principle there is no noise. For this reason, noise is less likely to enter the receiver input due to contamination of the comparison side.

Further, since the comparison side is made up of only the reactance component, there is no lossy impedance in the circuit between the coupling transformer (13) and the vibrator for the received signal.
Therefore, in principle, all the energies of the received signals are equal to the receiver (1
2) can be introduced.

In a general, ie, pure, passive bridge circuit that adheres to the principle, the terminals at the upper end in the figure are bundled, not separately, connected to one driving source, and are balanced only by the impedance relationship of each side. Therefore, a resistance equivalent to the radiation resistance of the vibrator (2) to be compared must exist in the capacitor (9) in parallel. For this reason, for a received signal, a lossy impedance intervenes in the circuit around the coupling transformer (13) and the vibrator, and the coupling between the receiver (12) and the vibrator (2) via the coupling transformer (13) always causes loss. Therefore, the noise figure of the receiving system cannot be optimized after all.

The above situation is better understood by further emphasizing that even the flywheel circuits (6, 11) and even the binary amplifiers (5, 10) can be lossless. That is, the flywheel circuits (6, 11) can be constituted only by reactances (that is, only L and C), and the binary amplifiers (5, 10) exhibit a sufficiently low output impedance even when switched to either positive or negative. This is because it can be configured in such a manner.

Here, the control system including the microprocessor (14) detects the state of the bridge deviation from the demodulated output of the receiver by an appropriate configuration and software, and in order to balance the binary signal for driving the comparison side. Tailoring. (15) is an A / D converter for evaluating the equilibrium state of the bridge by observing the direct current or low frequency component from the result of reception demodulation. That is, the first 2 which is the main transmission drive source
As a drive signal to the value amplifier (5), for example, a square wave having a duty factor of 1: 1 at the carrier frequency is output, and the second binary amplifier (10) used for driving the comparison side has its own signal. A binary signal having a different phase and a different duty ratio is given by a pulse width modulator (not shown) to be stored, and adjusted by a predetermined algorithm or by trial and error to find the equilibrium point of this bridge. , And set the specifications approximately there. It should be noted here that amplitude modulation can be equivalently performed by duty factor modulation and is also performed. What kind of software performs such detection and control is entirely within the freedom of implementation of the present invention.

The gist of the present invention has been described with reference to the preferred embodiment. Here, in the above description, the system is C
Although it was not described whether W Doppler or pulsed Doppler, experienced persons, experts, and those skilled in the art can clearly understand that the present invention can be applied to both of them, and the gist of the present invention is to understand both. Must be interpreted as including.

[Brief description of the drawings]

The only figure is a schematic diagram showing the configuration in one preferred embodiment of the present invention. In this, (1) target object, belly of pregnant woman, etc. (2) transducer (3) bridge or hybrid transformer for transmission / reception separation (4) moving object to be detected, fetal heart, blood flow, etc. (5) first (6) First flywheel circuit (7) (8) (9) Reactance (capacitor) (10) Second binary amplifier (11) Second flywheel circuit (12) Receiver (13) ) Coupling transformer (14) Microprocessor (15) A / D converter

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[Procedure amendment]

[Submission date] August 11, 1999 (1999.8.1)
1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a schematic diagram only FIG. 1 is a schematic diagram showing a configuration in one preferred embodiment of the present invention.

[Description of Signs] (1) Target object, belly of pregnant woman, etc. (2) Transducer (3) Bridge or hybrid transformer for transmission / reception separation (4) Moving object to be detected, fetal heart, blood flow, etc. (5) No. One binary amplifier (6) First flywheel circuit (7) (8) (9) Reactance (capacitor) (10) Second binary amplifier (11) Second flywheel circuit (12) Receiver (13) Coupling transformer (14) Microprocessor (15) A / D converter

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

[0008] The active bridge balance by the feedback of the evaluation result of the received signal can also be realized by a general-purpose LCR meter or a circuit technique called a so-called synthetic notch as shown in US Pat. No. 4,016,528. . However, feedback cancellation by these analog circuits is not preferred, since the cancellation signal is obtained by remodulating the carrier through a complicated path, so that the modulation noise caused by the system inevitably enters the receiver input as a contamination component. .

Claims (1)

[Claims] 1. An ultrasonic Doppler apparatus which uses a single transducer for transmission and reception, separately supplies a signal synchronized in phase with a transmission signal and having an adjusted amplitude and phase to a comparison side of a transmission / reception separation bridge. A signal generator having an essentially lossless drive point internal impedance for performing the operation.