JPH0454457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a Doppler sound generating section of an ultrasonic current meter, and more particularly to a method for converting the frequency of a Doppler signal and outputting the same.

(b) Background of the Technology The ultrasonic Doppler blood flow meter related to the present invention irradiates the blood flow inside the subject with ultrasound as a measurement wave, and calculates the frequency difference between the reflected wave from blood cells etc. and the measurement wave. By detecting this, the state of blood flow is measured. By converting the signal representing the frequency difference between the detected reflected wave and the measured wave into an acoustic output, the measuring person can detect the subject's blood flow by hearing without looking at the display, and can operate the ultrasonic Doppler blood flow meter. becomes easier.

However, in recent years, there has been a demand for detection of blood flow conditions not only in the heart and aorta and veins, but also in small blood vessels. It is necessary to increase the frequency of Specifically, a frequency of 5 to 40 MHz is used.

However, by increasing the frequency of the measurement wave, the frequency displacement (Doppler signal frequency) between the measurement wave and the reflected wave also increases, and the Doppler signal frequency may exceed an audible frequency.

Therefore, it is necessary for the acoustic output signal to be in an audible range that can be heard by the measurer, not to be harsh on the ears, and to be able to hear changes in the output sound.

(c) Prior Art and Problems Conventionally, as a method of converting a Doppler signal into an acoustic signal, a frequency conversion means shown in FIG. 1 has been used. In FIG. 1, 10a and 10b are delay circuits having a function like a FIFO buffer that temporarily stores input data and then sequentially outputs it, 11 is an analog data selector, 12a and 12b are digital data selectors, and 13a, 13b, and 13c are , are oscillators that generate digital signals (clocks) having frequencies f1, f2, and f3, respectively.

For details of this frequency conversion means, please refer to the patent application filed in 1983.
-135190, so a detailed explanation will be omitted, but the contents disclosed here can be summarized as follows.

That is, the frequency of the oscillator (clock) is f
1>f2 (for example, f2=1/4f1), and
f3 is a clock for switching between writing and reading for the delay circuits 10a and 10b, and also controls the analog data selector 11 to alternately switch the delay circuits 10a and 10b, so that the output of the delay circuit is transferred to the next one. It is for sending to an analog amplifier (not shown).

In this frequency conversion means, the Doppler signal is
1 clock timing, and the output is sent to the two delay circuits 10a and 10b.
Then, at the clock timings of f1 and f2, the delay circuit 10a accumulates for a half cycle of the clock timing of f3, and when the delay circuit 10a accumulated at the clock timing of f1 is full, the delay circuit 10a accumulates the delay at the clock timing of f1 and f1, respectively. The contents of the circuit 10a are output by controlling the analog data selector 11 at the clock timing f2. Specifically, 1/4 of the sampling data stored in the delay circuit 10a is output.

Then, while the output signal of the delay circuit 10a is being output, the delay circuit 10b is controlled to switch its operation so that it samples and accumulates the Doppler signal at the clock timing of f1. .

Thereafter, the same operation is repeated to control the Doppler signal taken in at the clock timing f1 to be output through the analog data selector 11 at the clock timing f2.

Therefore, by setting f1 and f2 in advance, desired frequency conversion can be performed. By setting the output signal read out at f2 to have an audible frequency, the Doppler signal can always be acoustically output as a signal within the audible frequency range.

At this time, the clock f3 for switching the outputs of the delay circuits 10a and 10b is controlled within a range where the switching noise generated by the switching operation is not unpleasant to the ears and the response time for reading and outputting the Doppler signal is not too slow. Lower frequencies (e.g. 30
Hz) is selected.

However, as is clear from Figure 1, in this conventional method, the circuit is complicated, and in addition to the switching noise mentioned above, there is also noise due to a phase shift at the time of switching (switching does not always occur in the same phase). (Since this noise is not so-called harmonic noise, it results in frequency dispersion).

(d) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention provides a method for listening to clear Doppler sound using a simple circuit and without noise (i.e., frequency dispersion) caused by phase shift during switching that occurs in the conventional method. The purpose of this invention is to provide a frequency conversion circuit that can perform the following functions.

(e) Structure of the Invention According to the present invention, the object is to irradiate a medium with a measuring wave, which is an ultrasonic wave of a constant frequency, and receive a reflected wave from the medium, so that the measuring wave and the reflected wave are separated. a frequency displacement detection means for detecting a frequency displacement of the medium and outputting a frequency displacement signal according to the detected frequency displacement; and an acoustic signal output means for converting the frequency displacement signal into an acoustic signal corresponding to the movement of the medium. In the Doppler sound generating section of the ultrasonic anemometer, which is equipped with a frequency conversion means for converting the frequency displacement signal into a signal in the audible frequency range, the frequency component of the Doppler signal and the amplitude This is achieved by providing a circuit that separates the components, reduces the separated frequencies, and then resynthesizes both, and performs Doppler analysis on the Doppler signal in an audible frequency band that can be heard by humans. There is an advantage that Doppler sound can be heard with almost no time delay or frequency dispersion.

(f) Examples of the invention First, to summarize the gist of the present invention, the present invention includes the following:
The output of the Doppler detection circuit (i.e. Doppler signal) is separated into a frequency component and an amplitude component, the frequency component is reduced by means such as frequency division, and then resynthesized, and after digital/analog conversion, The purpose is to obtain the desired Doppler sound by applying a filter.

Embodiments of the present invention will be described in detail below with reference to the drawings.
Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 shows digital signal waveforms at various parts in Fig. 2 when the frequency of the sampled Doppler signal is reduced to 1/4. FIG.

In the drawing, 21 is an absolute value circuit (ABS),
Specifically, the absolute value is obtained by performing an exclusive OR operation on the sign bit and each data. However, when the sign is negative, 1's complement is taken, and the sampled Doppler signal value becomes a value smaller by 1, but there is no practical problem. A frequency converter (f.conv) 22 divides the frequency of the code bit. 23
is a multiplier (mult) that changes the sign, specifically the output of the absolute value circuit (ABS) 21 and the output (sign bit) of the frequency converter (f.conv) 22.
The multiplication result is obtained by exclusive ORing with Again, if the sign bit is negative,
Although the sampled Doppler signal value is 1 smaller, there is no practical problem. 24 is a low pass filter (LPF).

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 2 with reference to FIG.

Now, the sampled Doppler signal IN is separated into two pieces of code bit data, one of which has its absolute value taken in an absolute value circuit (ABS) 21, and is input to a multiplier (mult) 23. Ru. (This is the ABS output in FIG. 3.) The other sign bit is converted into a 1/4 period digital signal by a frequency dividing circuit such as a binary counter, and is input to a multiplier (mult) 23. be done.
(This is the f.conv output in Figure 3) In the multiplier (mult) 23, the output of the absolute value circuit (ABS) 21 and the frequency converter (f.conv)
The output of 22 is subjected to the above-mentioned "multiplication with reassignment of signs", and the mult output shown in FIG. 3 is obtained.

The mult output is passed through a low pass filter (LPF) 24
To actually output Doppler sound, it is necessary to perform digital/analog conversion, but this must be placed before the low-pass filter (LPF) 24. Good.

(g) Effects of the Invention As explained above in detail, the ultrasonic current meter Doppler sound generator of the present invention separates the sampled Doppler signal into code bits and data, and the data is transmitted through the absolute value circuit ( ABS) is converted to absolute value data,
The code bit is frequency-divided by a frequency converter (f.conv), for example, to 1/4, and the respective output signals are combined by a multiplier (multiplying by ±1) to obtain a frequency-divided Doppler signal. It is configured to perform digital/analog conversion and pass through a low-pass filter (LPF) to obtain Doppler sound in the audible range, and the absolute value circuit (ABS) and multiplier (mult) are exclusive OR The circuit and frequency converter (f.conv) can be realized with a small amount of hardware such as one or multiple flip-flops, and the time delay and frequency dispersion that occur in conventional methods can be eliminated, so the product This has the effect of making medical diagnosis more economical and making medical diagnosis more reliable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional Doppler signal frequency conversion method, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 shows a method for converting the Doppler signal frequency by 1/2. Regarding the case of setting it to 4,
FIG. 3 is a diagram showing signal waveforms at various parts in FIG. 2; In the drawing, 10a and 10b are delay circuits;
1 is an analog data selector, 12a, 12b are digital data selectors, 13a, 13b, 1
3c is an oscillator, 21 is an absolute value circuit (ABS), 22
23 represents a frequency converter (f.conv), 23 represents a multiplier (mult), 24 represents a low pass filter (LPF), and IN represents a sampled Doppler signal.

Claims (1)

[Claims] 1. Irradiate a medium with a measurement wave that is an ultrasonic wave of a constant frequency, receive a reflected wave from the medium, detect a frequency displacement between the measurement wave and the reflected wave, and generate a signal according to the detected frequency displacement. An ultrasonic current meter comprising a frequency displacement detection means for outputting a frequency displacement signal, and an acoustic signal output means for converting the frequency displacement signal into an acoustic signal and corresponding to the movement of the medium,
In the Doppler sound generating section of the ultrasonic anemometer, which is equipped with a frequency conversion means for converting the frequency displacement signal into a signal within the audible frequency range, the frequency component and amplitude component of the Doppler signal are separated, and the separated frequency is reduced. What is claimed is: 1. An ultrasonic current meter Doppler sound generator characterized by having a circuit for resynthesizing the two.