JPH0321178B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an ultrasonic receiving device that mixes a plurality of received high frequency signals with a local oscillation frequency signal, converts the frequency into an intermediate frequency signal, and adds the phased signal. .

(Prior Art) B-mode devices that obtain tomographic images are often used as ultrasonic diagnostic devices. There are various scanning methods for this device, among which electronic sector scanning is an electronic scanning method that does not involve mechanical scanning, can increase the scanning speed, and does not cause mechanical wear. It has been widely used recently because of its advantages such as no mechanical noise. An example of this electronic sector scanning method is shown in FIG. Figure A shows the state when transmitting waves, and Figure B shows the state when receiving waves. In the figure,
1 is a transducer element, which controls the phase of each transducer element 1 using a delay line 2 and emits an ultrasonic beam in the direction of the arrow. The obtained received signal is delayed through a delay line 2 and synthesized so that it is in phase with the emitted ultrasonic beam in the same direction as shown in FIG. Note that the length of the delay line 2 in the figure is proportional to the delay time.

(Problem to be Solved by the Invention) Incidentally, it is essential in the pulsed ultrasound method to perform phasing and addition of multiple received signals using a delay line, but the delay line is essentially a low-pass filter. (LPF)
Therefore, using a long delay line increases the loss of the received radio frequency signal (RF), and there is a limit to the length of the delay line that can be used. Therefore, if a received high frequency signal is frequency-converted into an intermediate frequency signal (IF) and a delay line is used, the loss can be considerably improved and a long delay line can be used. Furthermore, when the step of delay time is the same as in the case of high frequency, more accurate phasing and addition can be performed than in the case of high frequency. However, when multiplying multiple received high-frequency signals by the local oscillation frequency to obtain each intermediate frequency signal, the phase of each received high-frequency signal with respect to the local oscillation frequency signal (LF) varies depending on the arrival delay time. For this reason, correct phasing and addition cannot be performed even if the obtained intermediate frequency signal is passed through a delay line. In order to perform correct phasing and addition of intermediate frequency signals, it is necessary to adjust the phase of the local oscillation frequency signal for each received high-frequency signal, but the phase of each received high-frequency signal depends on the azimuth angle of the ultrasound beam. As it changes over time,
Adjusting the phase of the intermediate frequency signal accordingly is a hassle.

The present invention has been made in view of the above points, and an object of the present invention is to convert a plurality of received high-frequency signals into intermediate frequency signals and perform phasing and summation of the received high-frequency signals using a delay line. The object of the present invention is to realize an ultrasonic receiving device that allows easy phase adjustment.

(Means for Solving the Problem) The present invention which solves the above problem mixes a plurality of received high frequency signals with a local oscillation frequency signal, converts the signal into an intermediate frequency signal, and performs phasing and addition using a delay line. In the ultrasonic receiving device, means for inputting a local oscillation frequency signal to the starting end of a delay line, means for extracting each local oscillation frequency signal from a delay point on the delay line corresponding to the arrival delay time of each of the plurality of received high frequency signals; Means for frequency converting the corresponding received high frequency signals into intermediate frequency signals using these local oscillation frequency signals, means for inputting each converted intermediate frequency signal to each local oscillation frequency signal extraction point on the delay line, and means for outputting an intermediate frequency phasing and addition signal from the terminal end of the delay line.

(Function) The delay line for phasing and adding intermediate frequency signals is
Since it is also used as a delay line for phase adjustment of the local oscillation frequency signal, the phase of the local oscillation frequency signal always matches the phase of the received high frequency signal.

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

FIG. 1 is a block diagram of one embodiment of the present invention. In the figure, RF1, RF2, and RF3 are received high-frequency signals from each transducer element that received the ultrasound reflected from within the subject. Although the number of received high-frequency signal inputs is actually large, for convenience, the description will be made assuming that the number of received high-frequency signal inputs is the aforementioned three. Reference numeral 3 denotes a delay line having a total delay time of T for giving a predetermined delay to the received signal from each transducer element according to the distance from each direction within the subject.
The delay line 3 has taps b, c, and d between a and e at both ends, and the delay time between each tap is set as follows.

a-b; τ ₁ ′ b-e; τ ₁ a-c; τ ₂ ′ C-e; τ ₂ a-d; τ ₃ ′ d-e; τ ₃ where τ ₁ ′, τ ₂ ′, τ ₃ ' is the received high frequency signal RF1
，
The delay time is equal to the arrival delay time of RF2 and EF3, and τ ₁ , τ ₂ , τ ₃ are the delay times necessary for the intermediate frequency signal based on the received high frequency signal to be phased and added at the terminal e of the delay line 3. It is. 4 is a mixer 6A, which mixes the received high frequency signals RF1, RF2, RF3;
A local frequency oscillator (LO) that oscillates a local oscillation frequency signal for converting into an intermediate frequency signal in 6B and 6C, and the output local oscillation frequency signal is
This is a signal expressed as B cosω _L t. A resistor 5 has a resistance value equal to the characteristic impedance Z ₀ of the delay line, and is connected to one end a of the delay line 3. 7
A, 7B, and 7C are buffer amplifiers that amplify the local oscillation frequency signal output from the local frequency oscillator 4;
Pass the output signal through bandpass filters (BPF) 8A, 8B, 8
C, and input to mixers 6A, 6B, and 6C.
9A, 9B, and 9C are low-pass filters that pass only intermediate frequency signals obtained by down-converting input high-frequency signals by mixers 6A, 6B, and 6C, and cut off high-frequency signals and local oscillation frequency signals. are amplified by amplifiers 10A, 10B and 10C and input to taps b, c and d of delay line 3, respectively. Reference numeral 11 denotes a terminating resistor connected to the output end of the delay line 3 and having a resistance value equal to the characteristic impedance Z ₀ of the delay line 3. From the terminal e of the delay line 3, a signal obtained by phasing and adding all intermediate frequency signals is amplified by an amplifier 12 and output.

Next, the operation of the embodiment configured as described above will be explained. The received high frequency signal RF1 is input to the mixer 6A. On the other hand, the local oscillation frequency signal output from the local frequency oscillator 4 is input to the delay line 3 via the resistor 5, and is output from tap b after being delayed by τ ₁ '. Let this output signal be LF1. This output signal LF1 is amplified by a buffer amplifier 7A, passed through a bandpass filter 8A, and then inputted to a mixer 6A. The mixer 6A multiplies RF1 and LF1 to convert the received high frequency signal into an intermediate frequency signal. The output signal of the mixer 6A has the upper sideband signal removed by a low-pass filter 9A to become an intermediate frequency signal IF1 of only the lower sideband, which is inputted again to tap b of the delay line 3 via the amplifier 10A. . Bandpass filter 8A
prevents this intermediate frequency signal from flowing back to mixer 6A. Intermediate frequency signal input to delay line 3
IF1 reaches terminal e with a delay of τ ₁ .

The received signals RF2 and RF3 are at tap c of the delay line 3,
Local oscillation frequency signal LF output from tap d
2. Frequency converted by LF3, intermediate frequency signal
The operation in which IF2 and IF3 are outputted from the terminal e of the delay line 3 is the same as in the case of RF1, so a description thereof will be omitted.
The three delayed intermediate frequency signals are phased and summed at the end e of the delay line 3 and amplified by the amplifier 12.

Next, the state of phasing and addition in the operation of the above circuit will be explained by calculation.

The high frequency signals of frequency ω ₀ from each vibrator element are expressed as follows.

RF1; A ₁ cosω ₀ (t+τ ₁ −T) RF2; A ₂ cosω ₀ (t+τ ₂ −T) RF3; A ₁ cosω ₃ (t+τ ₃ −T) ...(1) Delay of output signal of local frequency oscillator 4 Signals LF1, LF2, LF at taps b, c, d of line 3
3 receives delays of τ ₁ ′, τ ₂ ′, and τ ₃ ′ in the delay line 3, and becomes as shown in the following equation.

LF1; Bcosω _L (t-τ ₁ ') LF2; Bcosω _L (t-τ ₂ ') LF3; Bcosω _L (t-τ ₃ ') ...(2) The relationship between delay times is shown in delay line 3 in Figure 1. As is clear from the configuration, it is as shown in the following equation.

τ ₁ +τ ₁ ′=τ ₂ +τ ₂ ′=τ ₃ +τ ₃ ′=T ...(3) The received high frequency signal and the local oscillation frequency signal are multiplied by the mixers 6A, 6B, and 6C, and the low-pass filter 9
If only the lower sidebands are extracted at A, 9B, and 9C, IF1, IF2, and IF3 of the following equations are obtained.

In the mixer 6A, from equations (1), (2), and (3), RF1×LF1=A ₁ cosω ₀ (t+τ ₁ −T)×Bcosω _L (t−τ
₁ ′)=(A ₁ B/2) [cos{ω _L (t−τ ₁ ′) −ω ₀ (t+τ ₁ −T)}+cos{ω _L (t−τ ₁ ′)+
ω ₀ (t+τ ₁ −T)}] ∴IF1=(A ₁ B/2)cos{ω _L (t+τ ₁ −T)−ω ₀ (t
+τ ₁ −T)} = (A ₁ B/2) cos {ω _IF (t+τ ₁ − T)} However, ω _L −ω ₀ = ω Similarly to _IF, IF2 = (A ₂ B/2) cos {ω _IF (t+τ ₂ −T)} IF3=(A ₃ B/2) cos{ω _IF (t+τ ₃ −T)} ...(4) IF1, IF2, and IF3 in equation (4) are further The output ΣIF is ΣIF = ( _{A 1 B} / ₂ ) cos {ω _IF (t _- T)} + (A ₂ B/ 2
) cos {ω _IF (t-T)} + (A ₃ B/2) cos {ω _IF (t-T)} = (A ₁ + A ₂ + A ₃
)(B/2) cos {ω _IF (t-T)}. In this way, by using one delay line for both the delay of the local oscillation frequency signal and the delay of the intermediate frequency signal obtained by converting the received high frequency signal, it is possible to obtain an intermediate frequency signal that is correctly phased and summed. .

A timing chart of this signal is shown in FIG. In the figure, the same parts and signals as in FIG. 1 are given the same reference numerals. In the figure, LF0 is the output signal of the local frequency oscillator 4, and the phase when the delay is 0 at the starting end a of the delay line 3 is θ. As shown in the figure, RF1 is τ ₁ ′ (=T−τ ₁ ), RF2 is τ ₂ ′ (=T−τ ₂ ), RF
3 is input as a signal with a delay of τ ₃ ′ (=T−τ ₃ ). LF1, LF2, and LF3 are the signals output from taps b, c, and d after LF0 is delayed by τ ₁ ′, τ ₂ ′, and τ ₃ ′ by delay line 3, and as shown in the figure, the phase points are θ is delayed by τ ₁ ′, τ ₂ ′, and τ ₃ ′, respectively, and maintains the same phase position with respect to RF1, RF2, and RF3. Therefore, RF1,
IF1, IF2, and IF3, which are the products of RF2, RF3 and LF1, LF2, and LF3, are also connected to the delay line 3 as signals having the same amount of delay as the original high-frequency signal.
are input to taps b, c, and d. This IF1,
The signals of IF2 and IF3 are further delayed by τ ₁ , τ ₂ , and τ ₃ toward the terminal e of delay line 3, respectively, and are phased as in-phase signals with the same delay time and summed to form ΣIF. can get. Each of these intermediate frequency signals is converted into a received high frequency signal by a local oscillation frequency signal with an equal amount of delay, and is inputted again to each position of the delay line 3, so that the received high frequency signal is converted into a special local oscillation frequency signal LF1, LF2, LF3. It is clear from FIG. 2 that phasing and addition can be performed correctly even without performing the above processing.

FIG. 4 is a block diagram of another embodiment of the invention. This embodiment is an example in which a short delay line is inserted in each mixer circuit. In the figure, parts equivalent to those in FIG. 1 are given the same reference numerals. In the figure, 13A is a delay line with a delay time τ _A , 13B is a delay line with a delay time τ _B , and 13C is a delay line with a delay time τ _C.
When compared with the delay time of the real delay line 3, the delay time is as shown in FIG. That is, as shown in the following equation.

T = τ _A + τ _B + τ _C τ ₁ = τ _A + τ _B + τ _C τ ₂ = τ _B + τ _C τ ₃ = τ _C τ ₁ ′ = 0 τ ₂ ′ = τ _A τ ₃ ′ = τ _A + τ _B 4th Assuming that there is a delay line with a delay time of 0 between the resistor 5 and the delay line 13A, the circuit in the figure is the same as the circuit in Figure 1, as is clear from the arrangement of the delay lines in Figure 5. Since they can be regarded as the same thing, it is clear that the same result as the circuit of FIG. 1 can be obtained.

As explained above, the local oscillation frequency signal is extracted from the delay point of the delay line equal to the arrival delay time of each received high frequency signal, the received high frequency signal is frequency converted, and the obtained intermediate frequency signal is converted to each local oscillation frequency signal. Since the signals are input at the signal extraction point, the phases of each signal are perfectly matched at the end of the delay line, and phasing and addition can be performed without taking any special measures.

In the above embodiment, although the frequency of the intermediate frequency signal is a single frequency, since it is a fairly high frequency (about 10 MHz), the delay line causes attenuation corresponding to the amount of delay, and the output of the mixer becomes the local oscillation frequency signal. If the level depends on the level, an amplitude error will occur due to the apparent amount of delay, so either waveform shaping the local oscillation frequency signal input to the mixer or converting the frequency to an intermediate frequency signal using a gain compensation amplifier. It is sufficient to take measures such as inserting it after doing so.

(Effects of the Invention) As described above in detail, according to the present invention, when converting a plurality of received high-frequency signals into intermediate frequency signals and performing phasing and addition on a delay line, each of the plurality of received high-frequency signals and The phase with the local oscillation frequency signal can be easily adjusted, and phasing and addition using the intermediate frequency band can be performed accurately, which has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
3 is an explanatory diagram of the electronic sector scanning method, FIG. 4 is a diagram of another embodiment of the present invention, and FIG. 5 is a delay line in the embodiment of FIGS. 1 and 4. FIG. 1... Vibrator element, 2, 3, 13A, 1
3B, 13C...Delay line, 4...LO, 6A, 6
B, 6C...Mixer, 7A, 7B, 7C...Buffer amplifier, 8A, 8B, 8C...BPF, 9A,
9B, 9C...LPF, 10A, 10B, 10C,
12...Amplifier.

Claims (1)

[Claims] 1. In an ultrasonic receiving device that mixes a plurality of received high frequency signals with a local oscillation frequency signal, converts the mixture into an intermediate frequency signal, and adds the phased signal in a delay line, means for inputting the local oscillation frequency signal to the starting end of the delay line; Means for extracting local oscillation frequency signals from respective delay points on the delay line corresponding to arrival delay times of each of a plurality of received high frequency signals, and using these local oscillation frequency signals to convert corresponding received high frequency signals into intermediate frequency signals means for frequency-converting the intermediate frequency signals, means for inputting each converted intermediate frequency signal into each local oscillation frequency signal extraction point on the delay line, and means for outputting an intermediate frequency phasing and addition signal from the terminal end of the delay line. An ultrasonic receiving device characterized by: