JPH0345797B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Doppler signal frequency conversion device, and particularly to a Doppler signal frequency conversion device used in a device for detecting or measuring the speed of movement of a reflector.

[Background technology] A pulse wave is emitted at a constant repetition frequency, the reflected wave from a reflector is received, and the distance to the reflector is measured by comparing the transmission time and reception time, and changes in the reception frequency are measured. Pulsed Doppler devices are widely used to detect and measure the velocity of a moving reflector.

Generally, the repetition frequency for emitting pulse waves is selected depending on the distance to the reflector. However, when measuring a long-distance object, if a higher frequency is selected than the repetition frequency determined by the distance to the reflector, as is well known,
Returned echoes appear at a distance closer than the actual distance, making it difficult to determine the distance.

In addition, a phenomenon similar to the above occurs when measuring the speed of a moving reflector, and if a repetition frequency that is lower than the Doppler frequency due to the speed of the reflector is selected, it appears as a low frequency due to the folding phenomenon. It becomes difficult to determine the speed.

In order to measure both distance and velocity without causing aliasing phenomena, in the case of a device that can determine not only the absolute value of velocity but also its sign, _d must be set between the maximum Doppler frequency _d and the repetition frequency _r . =
_It is widely known that in the case of a device that detects and measures only the absolute value of velocity, it is necessary to satisfy the relationship _d = _r .

Here, in a device that can determine whether the velocity is positive or negative, _d = _p・k・V= _r /2 ( _p : emitted ultrasonic frequency, k: constant, V:
maximum speed), the maximum measurable speed V is V= _r /( _2p・k). As can be understood from this equation, if the repetition frequency _r is increased in order to increase the maximum velocity V, the maximum distance of the reflector that can be measured without aliasing becomes smaller. When measuring, there is a drawback that speed cannot be measured over a long distance.

Furthermore, if the ultrasonic frequency to be emitted is selected to be low, it is not only difficult to form a transmitted wave with a narrow pulse width, but also a sharp radiation beam cannot be formed, resulting in a decrease in distance resolution and azimuth resolution. This resulted in the problem that the distance and speed of a reflector that was far away and moved at high speed could not be determined at the same time.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and its object is to provide frequency conversion of Doppler signals that can determine the distance and velocity of a reflector that is located at a long distance and moves at high speed. The goal is to provide equipment.

[Configuration of the Invention] The present invention has a Doppler signal obtained by receiving and amplifying a reflected wave from a moving reflector based on the radiation of a periodic pulse modulated wave, and a frequency corresponding to the center frequency of this Doppler signal. A first mixer mixes the Doppler signal with a reference wave signal, and a second mixer mixes the Doppler signal with a reference wave signal obtained by shifting the reference wave signal by 90 degrees. first and second complex signal converters converting into a complex signal having a part x and an imaginary part y;
Different center frequencies from complex signal converter
Input the real part x ₁ , x ₂ and the imaginary part y ₁ , y ₂ of two complex signals having ₁ and ₂ , X=x ₁・x ₂ +y ₁・y ₂ Y=x ₂・y ₁ − Real part X, imaginary part Y of the complex conjugate product shown by x ₁ y ₂ or complex product shown by X=x ₁・x ₂ −y ₁・y ₂ Y=x ₂・y ₁ +x ₁・y ₂ and a complex multiplier that obtains a complex signal having a center frequency corresponding to the difference or sum of center frequencies ₁ and ₂ by calculating the real part X and imaginary part Y of It is characterized by converting into frequency.

[Embodiments] Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a device that detects or measures blood flow in a living body using ultrasonic waves. Various necessary synchronizing signals such as repetition frequency, clock pulse, reference wave, control pulse, etc. can be obtained from the output of the frequency dividing synchronizing circuit 2. This control pulse 100 with a constant repetition frequency (for example, 4 kHz) is input to the probe 4 via the transmitter/receiver switch 3, converted into an ultrasonic wave, and emitted into the living body as an ultrasonic pulse wave.

The reflected wave from the living body is received by the probe 4 with a delay time depending on the distance between the probe 4 and the reflector, and the ultrasonic reflected wave is converted into an electrical signal by the probe 4. The electrical signal is input to the high frequency amplifier 5 via the transmitter/receiver 3 and amplified, and the output signal 101 of the high frequency amplifier 5 is input to two band filters 6 and 7.

The spectrum of the signal 101 is a line spectrum that appears at every repetition frequency (4kHz),
The envelope of the spectrum is determined by the drive pulse width and the characteristics of the probe, and as shown in FIG. Figure 2B
Since it is filtered by two filters 6 and 7 having different characteristics of filtration bands shown by 6 and 7,
The spectra of the output signals 102 and 103 of the filters 6 and 7 have two different envelopes with center frequencies of approximately 2.9MHz (6s) and 3.1MHz (7s), as shown in FIG. 2C. .

When measuring a moving reflector, as is well known, the frequency of the received wave is subject to the Doppler effect, which is proportional to the reflector velocity and the transmitted frequency, so the spectrum when the moving reflector approaches the probe is As shown by the broken line in Figure 2, it changes along the envelope. Therefore, the envelopes of the output spectra of the filters 6 and 7 also change, and in particular, since the frequency component of the spectrum 7s is higher than the frequency component of the spectrum 6s, the envelope changes with a larger deviation.

The output signals 102 and 103 of the filters 6 and 7 thus obtained are input to complex signal converters 201 and 202, respectively, and converted into complex signals. The complex signal converter 201 includes two mixers 8 and 9, a 90 degree phase shifter 12, and two low-pass filters 1.
4 and 15, and a complex signal converter 20
Similarly to the complex signal converter 201, mixer 1
0,11 and 90 degree phase shifter 13 and low pass filter 16,
The signal conversion in the complex signal converters 201 and 202 will be explained below.

Output spectra 6s, 7 of signals 102, 103
s consists of many line spectra that are integral multiples of the repetition frequency, but to simplify the explanation, we will focus on a single central spectrum and set this frequency to 1,
2. Assuming that the amplitude is the same and that this is A, and the time is t, the signals 102 and 103 are expressed as Acos2π( ₁ +k ₁ v)t...(1) Acos2π( ₂ + _k2v )t...(2).

where k is the proportionality constant, v is the velocity, k ₁ v and k ₂ v
indicates the change in frequency due to the Doppler effect.

The signal 102 is transmitted to the terminal 3 of the switch 31.
1 to the mixers 8 and 9, and the reference wave signal 104 is input from the frequency-divided synchronization circuit 2 to the other input of the mixers 8 and 9 via the terminal 33 of the switch 33. The frequency of the reference wave signal 104 is input to the mixer 8 at a continuous wave frequency ₁ (2.9MHz) which is an integral multiple of the repetition frequency, and the reference wave signal 104 is
04 is phase-shifted by 90 degrees by a 90-degree phase shifter 12 and input to the mixer 9. Therefore, mixer 8
The reference wave signal input to mixer 9 has a phase of 90
When the amplitude is set to 1, this is expressed by the following equation.

cos2π ₁ t …(3) sin2π ₁ t …(4) If equation (3) above is the real part of a complex number and equation (4) is its imaginary part, then both equations together become a complex reference wave, so the mixer The mixer output signals calculated by 8 and 9 are signals that have a complex relationship with each other.

As a result, a signal 106 proportional to the product of equation (3) and equation (1) is generated in the output signals of these mixers 8 and 9. The signal 106 is expressed by the following formula Acos2π ₁ kvt + cos2π (2 ₁ + ₁ kv)t (5), and is input to the low-pass filter 14 that cuts off frequency components of 500 kHz or higher. )
The high frequency component of 2 ₁ (5.8MHz) in the equation is removed, and the output signal 110 becomes a signal expressed by the following equation.

Acos2π ₁ kvt …(6) Similarly, in the mixer 9, an output proportional to the product of equations (1) and (4) appears, so the output signal 111 of the low-pass filter 15 is Asin2π ₁ kvt …(7) When the signals expressed by equations (6) and (7) are put together, they become a complex signal expressed by the following equation.

Z ₁ =A{cos2π ₁ kvt+isin2π ₁ kvt} =x ₁ +iy ₁ (8) Here, i is a complex signal, and x ₁ ·y ₁ is expressed by the following equation.

x ₁ = Acos2π ₁ kvt, y ₁ = Asin2π ₁ kvt (9) On the other hand, in the complex signal converter 202, the frequency of the complex reference wave is a continuous wave frequency that is an integral multiple of the repetition frequency.
₂ (3.1MHz), and two output signals 11
2,113 can be expressed as a complex equation as in the complex signal converter 201 as follows.

Z ₂ =A {cos2π ₂ kvt+i sin2π ₂ kvt} =x ₂ +i y ₂ (10) Here, x ₂ and y ₂ are expressed by the following formula.

x ₂ = Acos2π ₂ kvt, y ₂ = Asin2π ₂ kvt …(11) Analog signal signal obtained as above
z ₁ and z ₂ are converted into digital signals by analog-to-digital converters 18, 19, 20, and 21 to improve calculation accuracy, and these four digital signals x ₁ ,
y ₁ , x ₂ , y ₂ are complex multipliers 20 composed of multipliers 22, 23, 24, 25 and adders/subtractors 26, 27
3 is input.

The multipliers 22, 23, 24, and 25 calculate x ₁ · x ₂ , y ₁ · y ₂ , x ₂ , y ₁ , and x ₁ · y _{2 ,} respectively, and the outputs of the multipliers 22 and 23 are Adder/subtractor 2
The outputs of the multipliers 24 and 25 are input to the adder/subtracter 27. Here, when the adder/subtracter 26 is operated as an adder and the adder/subtracter 27 is operated as a subtracter, the output Z ₀ (X, Y) of the complex multiplier 203
The X and Y of are given by the following formula.

X=x ₁・x ₂ +y ₁・y ₂ …(12) Y=x ₂・y ₁ −x ₁・y ₂ …(13) The above X and Y are expressed as (8), ( 10) Eq.
They are the real and imaginary parts of the conjugate product of Z ₁ and Z ₂ .

Z ₀ = Z ₁ ^*・Z ₂ = (x ₁ − iy ₁ ) (x ₂ + iy ₂ ) = x ₁・x ₂ +y ₁・y ₂ +i (x ₁・y ₂ −x ₂・y ₁ ) =X+iY ...(14) Then, when formulas (12) and (13) are calculated by substituting formulas (9) and (11), they become as follows.

X=A ² {cos2π ₁ kvt・cos2π ₂ kvt + sin2π ₁ kvt・sin2π ₂ kvt} =A ² cos2π ( ₂ − ₁ ) kvt …(15) Y=A ² {cos2π ₁ kvt・sin2π ₂ kvt −sin2π ₁ kvt・cos2π ₂ kvt} = A ² sin2π ( ₂ − ₁ ) kvt (16) The outputs X and Y of the complex multiplier 203 obtained in this way are input to the arithmetic unit 28, and the calculation formula shown by the following equation is The amplitude A is calculated by .

(X ² + Y ₂ ) ^1/4 = (A ⁴ ) ^1/4 = A (17) Then, the output of the arithmetic unit 28 is divided into the dividers 29 and 30
The signal X or Y input to the other input terminal of these dividers is divided by the output signal of the arithmetic unit 28, that is, A.

Therefore, the outputs of terminals c and d of each divider 29 and 30 are obtained from equations (15), (16), and (17) and are expressed as follows.

Acos2π( ₂ − ₁ )kvt…(18) Asin2π( ₂ − ₁ )kvt…(19) Also, if the adders and subtracters 26 and 27 are operated as a subtracter and 27 as an adder, contrary to the above case, Equations (12) and (13) are obtained.

X′＝x ₁・x ₂ −y ₁・y ₂ …(20) Y′＝x ₂・y ₁ +x ₁・y ₂ …(21) The above X′, Y′ is Z It becomes the real part and imaginary part of the complex product of ₁ and Z ₂ .

Z ₀ ′=Z ₁・Z ₂ = (x ₁ + iy ₁ ) (x ₂ + iy ₂ ) = x ₁・x ₂ −y ₁・y ₂ +i (x ₂・y ₁ +x ₁・y ₂ ) =X′ +iY'...(22) When this equation (22) is calculated in the same way as equations (15) and (16), it becomes the following equations (23) and (24).

X'=A ² cos2π( ₁ + ₂ )kvt...(23) Y'= ^A2sin2π ( ₁ + ₂ )kvt...(24) Then, it is calculated by A in the dividers 29 and 30, and the terminals c and d are The output is as follows.

Acos2π( ₂ + ₁ )kvt...(25) Asin2π( ₂ + ₁ )kvt...(26) Next, when the contacts of switches 31, 32, 33, and 34 are switched to the terminal e side, the signal 101 is sent to mixer 8. , 9, 10, 11 and input to the other input terminal, the frequency of the reference wave is changed to a continuous wave frequency ₀ which is an integral multiple of the repetition frequency. The behavior of Kotoki is the same as when ₁ = ₂ = ₀ in equations (25) and (26), so the following equation is obtained.

Acos4π ₀ kvt …(25′) Asin4π ₀ kvt …(26′) At this time, since the operation of only the converter 201 is the same as the operation at frequency ₁ described above, 110,
The signals obtained from terminals A and B of 111 are expressed by the following equation.

Acos2π ₀ kvt …(27) Asin2π ₀ kvt …(28) This signal is the same as the output signal of a conventional quadrature detector.

Therefore, if we compare equations (27) and (28) with equations (18) and (19) obtained when implementing the present invention, we find that the transmission center frequency _{is 1} − ₂ (3.1MHz) instead of _0. −2.9M
Hz), that is, it is understood that it is the same as the Doppler signal obtained when transmitting waves are radiated at 200kHz.

As described above, according to the present invention, the repetition frequency
_r , the Doppler signal obtained when this ₀ is essentially changed to ₁ − ₂ without changing the transmission frequency ₀ , and as mentioned above, ₀ is 3MHz and ₁ − ₂ is 200k.
Hz, it is possible to measure a maximum speed 15 times faster than when using 3MHz.

Also, the output signals of terminals c and d shown by equations (25), (26) or (25)', (26)' _{are 1} + ₂ (3.1MHz + 2.
This is the Doppler signal obtained when radiating 9MHz = 6MHz) or ₂₀ (2 x 3MHz = 6MHz). This means that a Doppler signal that is substantially the same as when 6MHz is radiated to the subject is obtained, and it is possible to accurately measure the velocity of a resistive reflector without changing _r and ₀ .

Furthermore, according to the present invention, it is possible to convert the Doppler signal frequency without changing the frequency or repetition frequency of the radiation wave, so it is possible to perform highly accurate speed measurements with a desired conversion amount depending on the speed to be detected or measured. possible.

Furthermore, the signals at terminals a, b include Doppler information similarly to the signals at terminals c, d, and the signals at terminals a, b,
The outputs of c and d can be used as phase detection video signals or quadrature detection video signals.

FIG. 3 shows an apparatus using Doppler signals frequency-converted according to the present invention (part 204 in FIG. 1).
is shown, which is a commonly used type of pulsed Doppler device. The Doppler video signal from the frequency converter of the terminals c, d or terminals a, b is connected to the terminals C, D in FIG. It is input to hold circuits 52 and 53. The sampling pulse sent from the frequency division synchronization circuit 2 (FIG. 1) is applied to the sample and hold circuits 52 and 53 with a predetermined time delay from the transmission time, so the Doppler signal of the reflector at a predetermined distance (depth) is extracted. . Then, unnecessary signals are removed from the Doppler signal by Doppler filters 54 and 55 composed of low-pass filters, and an arithmetic circuit 5
6, and the output of the calculation circuit 56 is input to the measurement display 57, and the calculated speed of the reflector is displayed.

In addition, the output signals of terminals a, b, c, and d are
It is also possible to feed this video signal to other types of Doppler devices that require a phase-detected video signal. A device that measures and displays flow velocity distribution by determining the correlation between
It can be applied to two-dimensional Doppler devices such as Doppler) devices.

[Effects of the Invention] As explained above, according to the present invention, the Doppler signal frequency can be changed without changing the frequency of the radiation wave or the pulse repetition frequency. , velocity can be measured accurately, and even with a low-velocity reflector, velocity can be measured with higher precision than in the past.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a preferred embodiment of the Doppler signal frequency conversion device according to the present invention, FIG. 2 is a spectrum diagram illustrating the frequency-converted Doppler signal, and FIG. FIG. 2 is a block diagram of a pulsed Doppler apparatus using a Doppler signal obtained by using a pulsed Doppler signal. DESCRIPTION OF SYMBOLS 1... Oscillator, 2... Frequency division synchronous circuit, 3... Transmission/reception switching circuit, 4... Probe, 5... Amplifier, 6, 7... Band filter, 8, 9, 10, 11... Mixer, 12, 1
3... 90 degree phase shifter, 14, 15, 16, 17... Low pass filter, 18, 19, 20, 21... Analog-to-digital converter, 22, 23, 24, 25... Multiplier, 26, 27... Addition/subtraction device , 28... Arithmetic unit, 2
9, 30...Divider, 50, 51...Digital-to-analog converter, 52, 53...Sample hold circuit,
54, 55... Doppler filter, 56... Arithmetic circuit,
57... Display circuit, 201, 202... Complex signal converter, 203... Complex multiplier, 204... Pulse Doppler device.

Claims (1)

[Claims] 1. A Doppler signal obtained by receiving and amplifying a reflected wave from a moving reflector based on the radiation of a periodic pulse modulated wave, and a reference wave having a frequency corresponding to the center frequency of this Doppler signal. a first mixer for mixing the Doppler signal and a reference wave signal obtained by shifting the reference wave signal by 90 degrees; and first and second complex signal converters for converting the two complex signals having mutually different center frequencies f ₁ and f ₂ from the first and second complex signal converters into complex signals having an imaginary part y and an imaginary part y. Input _the real part x ₁ , _{x 2} and _the imaginary part y ₁ , _{y 2 and create the} complex conjugate _product shown by Compute _the real part _X and _{imaginary part} Y _{of the} complex _{product represented} by and a complex multiplier for obtaining a complex signal with a center frequency corresponding to the difference or sum of center frequencies f ₁ and f ₂ , and converts the Doppler signal from the motion reflector to a desired frequency. Doppler signal frequency conversion device. 2. In the device according to claim 1, a division operation in which the output complex signal is divided by the fourth root of the sum of the square of the real part X and the square of the imaginary part Y of the complex signal output from the complex multiplier. 1. A Doppler signal frequency conversion device comprising: