JPH0121472B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for generating arbitrary frequency signals, and in particular, realizes a device suitable for use in generating polyphase frequency signals whose phase or frequency changes periodically. do.

For example, as a device for forming a directional reception beam, a device that performs phase synthesis is generally used in many cases. That is, a large number of transducers are arranged on the same plane, and the phase relationship of each transducer is adjusted to form a directional received beam in a specific direction. for example,
As shown in Figure 1, the received signals from a large number of oscillators _Z1 to Zn arranged on a plane
The phase is shifted from S ₁ to Sn. Then, set the phase shift amount of each phase shifter _S1 to Sn to be 2π/λ(n-1)dsinθ n=1, 2, 3,...n, and add the phase-shifted signals. When added in circuit A, a directional characteristic can be formed in the θ direction.

In the above, in order to change the pointing direction θ, it is sufficient to change the phase shift time of the phase shifters S ₁ to Sn. However, in order to vary the pointing direction θ over a wide range, the phase shift times of the phase shifters S ₁ to Sn must be greatly varied. In a normal phase shifter, it is impossible to change the phase shift time to such a large extent. Therefore, conventionally, when changing the directivity direction θ, as shown in Fig. 2, phase shifters S1 _' to Sn' are provided separately from the phase shifters _S1 to Sn, and the output of the adder circuit A' is The phase shift times of the phase shifters S ₁ ' to Sn' are set so that a directional characteristic is formed in the θ' direction. Therefore, in this configuration, it is necessary to prepare a phase shifter specific to each direction of directivity, so in order to change the direction in a wide range at every fixed angle, it is necessary to prepare a very large number of phase shifters. Requires a phaser. This has the disadvantage that the device becomes extremely large and expensive.

Figure 3 shows a principle diagram of forming a directional reception beam without using a phase shifter as described above, and in the figure, Z ₁ to Zn indicate oscillators arranged in the same way as in Figure 1. . After each received signal of the transducers Z ₁ to Zn is amplified by each preamplifier P ₁ to Pn,
Each of the mixing circuits M ₁ to Mn mixes the local signal sent from the signal generator SG corresponding to each of the mixing circuits M ₁ to Mn and the received signal of the vibrator Z ₁ to Zn. Then, the mixed outputs of the mixing circuits _M1 to Mn are led to the adding circuit Σ and added. The output of the adder circuit Σ is guided to a filter circuit FF to extract a specific frequency component.

In the above, the i-th oscillator is Si (t) = Eisin (ωt + Ai) ... (1) Also, the local oscillator signal mixed with this received signal in the mixing circuit Mi is Ui (t) = Visin (ωc + Bi) ...(2), then the mixed output is Ci(t) = Si(t)・Ui(t)=Eisin(ωt+Ai)×Vi
sin(ωct+Bi) = 1/2EiVi{cos[(ω−ωc)t+(Ai−Bi)]−
cos [(ω+ωc)t+(Ai+Bi)]}...(3) As is clear from equation (3), the mixed signal Ci(t) is the difference between the received signal Si(t) and the local signal Ui(t) It is composed of frequency and sum frequency components. Since the adder circuit Σ sends out the added output of the mixed output expressed by equation (3) for each mixer circuit _M1 to Mn, the filter circuit
Assuming that the difference frequency component of the mixed output is extracted in the FF, the output of the filter circuit FF is CT(t) = Σ1/2EiVicos {(ω-ωc)t + (Ai-Bi)} ...(4) It is expressed as

In equation (4), when Ai=Bi (5), each output of the mixing circuits _M1 to Mn becomes in phase, and the filter output Ct becomes maximum. Therefore,
At this time, the filter output Ct is the i-th oscillator Zi
The received signal has a phase difference Ai with respect to the first oscillator.
This shows that directivity is formed in the direction θ that causes . In other words, the phase difference Bi of the local oscillator signal in equation (2) is Ai
By setting , a directional reception beam can be formed in the θ direction, and by changing the phase difference Bi, the directional direction θ can be changed.

In Fig. 3, if the arrangement interval of the vibrators _Z1 to Zn is d, and the wavelength of the received signal is λ, then in equation (1), Ai = 2π/λ(i-1)dsinθ...(6) Therefore, , to form directivity in the θ direction, the local oscillator signal Ui(T) can be obtained by substituting equation (6) into equation (2) as follows: Ui(t)=Visin {ωct+2π/λ(i-1)dsinθ} ...(7) As is clear from equation (7), the local oscillator signal Ui(t)
By changing the phase term θ, the directivity characteristic θ of the received signal can be changed.

Now, assuming that the directivity direction θ of the received signal is changed to θs in time Ts, θ=θs/Tst (8) where 0≦t≦Ts. Therefore, by substituting equation (8) into equation (7), Ui(t)=Visin{ωct+2π/λ(i-1) dsin(θs/Tst)}=Visin2π{fc+(i-1) ABsinBt/Bt }t ...(9) is given. However, ωc=2πfc, A=d/λ, and B=θs/Ts. In equation (9), Fci=fc+(i-1)ABsinBt/Bt...(10) represents the frequency term of the local oscillator signal Ui(t), and when the directivity direction θ is changed from 0 to θs in time Ts , the frequency Fci of the local oscillator signal Ui(t) changes according to equation (10). Conversely, the frequency of the local signal Ui(t)
By changing Fci according to equation (10), the directivity direction of the received signal given as the output of the filter FF in FIG. 3 can be changed arbitrarily.

The object of the present invention is to generate a frequency signal whose frequency or phase changes with time as described above, and furthermore, it is an object of the present invention to generate a frequency signal in which the frequency or phase changes with time. Realize a suitable device.

In equation (10), when t=0, sinBt/Bt=1, so Fci=fc.Also, in equation (9), when t=0, Ui(t)=0, therefore, t=0, that is, the pointing direction. When θ=0, the local oscillation signals guided to the mixing circuits M ₁ to Mn each have a frequency of fc and are in phase. Then, when the pointing direction changes to θ, the frequency of each local oscillator signal changes according to equation (10).

FIG. 4 shows an embodiment of the present invention, and shows an example of generating a local oscillation signal whose frequency and phase are regulated as described above.

In FIG. 4, a clock pulse sent from a clock pulse source 1 is divided into frequency by a frequency dividing circuit 2.
After being frequency-divided by 2, it is sent to counter 3. Counter 3 counts these clock pulses and sends the counted value to read-only memory 4.

The read-only memory 4 contains at least the counter 3
It has memory addresses corresponding to the counting capacity of , and amplitude data for each phase of a desired frequency signal is written in each memory address. In the embodiment shown in FIG. 4, the amplitude data for each phase is stored as 1-bit data, and the stored data at each memory address specified by the counter 3 is output as a 1-bit output of either a low level or a high level. Sent with . This storage output of the read-only memory 4 is latched by a latch circuit 5 and then sent out as an output signal. The latch circuit 5 latches the data stored in the read-only memory 4 using the latch pulse train sent from the latch pulse generation circuit 6, and outputs a voltage (current) corresponding to the stored data. In addition, in the above,
The frequency division ratio of the frequency dividing circuit 2 need not be limited to 1/2, and may be set as appropriate.

5a shows the pulse train of the clock pulse source 1, and pulse train b shows the output of the frequency divider circuit 2. FIG.
The latch pulse generation circuit 6 is composed of a logic circuit,
A latch pulse shown in FIG. 5C is generated using pulse train a and frequency-divided pulse b. The latch circuit 5 latches the read output of the read-only memory 4 at the rising edge of the latch pulse C. On the other hand, the count value of the counter 3 changes at the rising edge of the frequency-divided pulse b, and data at a different memory address in the read-only memory 4 is read out accordingly. The stored data is sent out with a delay of Δt. FIG. 5d shows the readout output of the stored data, and Δt from the rising edge of the frequency-divided pulse b.
Only there is a time delay. The latch circuit 5 latches this readout output at the rising edge of the latch pulse C and sends it out. Therefore, as shown in FIG. 5e, the latch circuit 5 maintains its output at a high level when the stored data at the designated memory address is at a high level.
When the stored data at the designated memory address is at a low level, the latch output also sends out a rectangular wave that changes to a low level.

As is clear from the above, the repetition period and phase of the rectangular wave e can be arbitrarily set by appropriately writing stored data at each storage address in the read-only memory 4. For example, when the count value of counter 3 changes from time t=0 to t=Ts, the phase matches equation (9), and
A rectangular wave train whose repetition frequency changes according to equation (10) can be obtained. It should be noted that the local oscillation signal expressed by equation (9) exactly corresponds to the fundamental wave component of the rectangular wave train shown in FIG. 5e. Therefore, when using the rectangular wave train e as a local signal, after mixing the rectangular wave train e and the received signal Si(t) of the vibrator Zi,
The filter FF may be operated to extract the mixed component for the fundamental wave of the rectangular wave sequence e from the mixed signal.

FIG. 6 shows a specific example of changing the directivity direction of the received beam from -θ to +θ using seven transducers Z ₁ to Z ₇ arranged on a plane based on the above.

In FIG. 6, it is assumed that the arrangement interval of the transducers Z ₁ to Z ₇ is d, and a received signal in the θ direction is received. Now, if the received signal of the transducer Z ₄ is U ₄ (t) = Esin2πft, then each received signal U ₁ (t) of the transducers Z ₁ to Z ₇
to U ₇ (t) are expressed as follows.

S ₁ (t) = Esin (2πft + 6πd / λsinθ) S ₂ (t) = Esin (2πft + 4πd / λsinθ) S ₃ (t) = Esin (2πft + 2πd / λsinθ) S ₄ (t) = Esin (2πft) S ₅ (t )=Esin(2πft−2πd/λsinθ) S ₆ (t)=Esin(2πft−4πd/λsinθ) _S7 (t)=Esin(2πft−6πd/λsinθ) ……(11) And as shown in Fig. 7 So, the receiving direction θ is -
Assuming that it is changed from -θs to θs in 2Ts time from time Ts to time Ts, the receiving direction θ is as a function of time T as θ=θs/Tst (-Ts≦t≦Ts) ……(12) expressed. Therefore, by substituting equation (12) into equation (11), S ₁ (t) = Esin (2πft + 6πd / λsinθs / Tst) S ₂ (t) = Esin (2πft + 4πd / λsinθs / Tst) S ₃ (t) = Esin (2πft + 2πd / λsinθs / Tst) S ₄ (t) = Esin (2πft) S ₅ (t) = Esin (2πft - 2πd / λsinθs / Tst) S ₆ (t) = Esin (2πft - 4πd / λsinθs / Tst ) S ₇ (t)=Esin(2πft−6πd/λsinθs/Tst)…
...(11)' On the other hand, the local oscillator signal mixed with each of the above received signals in the mixing circuits M ₁ to M ₇ is expressed as U ₁ (t)=V・sin (2πfct+φ1) U ₂ (t)=V・sin (2πfct+φ2) U ₃ (t)=V・sin(2πfct+φ3) U ₄ (t)=V・sin(2πfct+φ4) U ₅ (t)=V・sin(2πfct+φ5) U ₆ (t)=V・sin(2πfct+φ6 ) U ₇ (t) = V・sin (2πfct + φ7) (13) As explained above, the phases φ1 to φ1 of each of the local oscillator signals U ₁ (t) to U ₇ (t) By matching φ7 with the phase of each received signal S ₁ to S ₇ , the directivity direction of the received signal is set to −θs.
It can be changed from to +θs. Therefore, equation (13) is U ₁ (t)=V・sin(2πfct+6πd/λsinθs/Tst
) U ₂ (t)=V・sin(2πfct+4πd/λsinθs/Tst
) U ₃ (t)=V・sin(2πfct+2πd/λsinθs/Tst
) U ₄ (t)=V・sin(2πfct) U ₅ (t)=V・sin(2πfct−2πd/λsinθs/Tst
) U ₆ (t)=V・sin(2πfct−4πd/λsinθs/Tst
) U ₇ (t)=V・sin(2πfct−6πd/λsinθs/Tst
)...(13)' In formula (13)', if we set d/λ=A θs/Ts=B, then (13)' is transformed as follows.

U ₁ (t)=V・sin2π(fc+3ABsinBt/Bt)t U ₂ (t)=V・sin2π(fc+2ABsinBt/Bt)t U ₃ (t)=V・sin2π(fc+ABsinBt/Bt)t U ₄ (t) =V・sin2πfc・t U ₅ (t)=V・sin2π(fc−ABsinBt/Bt)t U ₆ (t)=V・sin2π(fc−2ABsinBt/Bt)t U ₇ (t)=V・sin2π( fc−3ABsinBt/Bt)t...(14) Therefore, as is clear from the above explanation, the local oscillation signals guided to the mixing circuits _M1 to _M7 are at the time t.
= 0, that is, when the directivity direction of the received signal matches the front direction with respect to the transducer array surface, the phases of each local oscillation signal match, and when −Ts≦t≦Ts, the phase of each local oscillation signal matches. Frequency Fc ₁ to Fc ₇
Fc ₁ = fc + 3ABsinBt / Bt Fc ₂ = fc + 2ABsinBt / Bt Fc ₃ = fc + ABsinBt / Bt Fc ₄ = fc Fc ₅ = fc - ABsinBt / Bt Fc ₆ = fc - 2ABsinBt / Bt Fc ₇ = fc - 3ABsinBt / Bt ...... ( 15) All you have to do is make it as follows. For example, if fc=50×10 ³ Hz d=λ/2, θs=π/4, Ts=1 msec, A=d/λ=1/2 B=θs/Ts=π/4×10 ³ Therefore, when time t=-Ts, [Fc ₁ ] 50×10 ³ +1060 [Hz] t= _-TS Also, when time t=0, sinBt/Bt=1, so [Fc ₁ ] 50×10 ³ +1178 [Hz] t=0 Also, when time t=Ts [Fc ₁ ] 50×10 ³ +1060 [Hz] t=T _S Therefore, the pointing direction changes from -45 degrees to +45 degrees in 2 msec.
When changing the local oscillator signal to the mixing circuit _M1 , its frequency _Fc1 changes from a frequency higher than the reference frequency fc by 1060Hz to a frequency higher by 1178Hz, and then returns to a frequency higher by 1060Hz. It changes like that. This frequency change is represented by curve _R1 in FIG. Also, other curves R ₂ to R ₇ are frequencies Fc ₂ to Fc ₇ of other local oscillator signals.
represents a change in

The read-only memory 4' in FIG. 6 repeatedly sends out a rectangular wave train whose frequency coincides with each of the frequencies Fc ₁ to Fc ₇ of the local oscillator signal. The read-only memory 4' includes seven sets of the read-only memories 4 shown in FIG. 4, and output terminals 01 to 07 independently read data stored at storage addresses designated by the counter 3.

The counter 3 counts the output pulses of the 1/2 frequency divider 2 in the same manner as in FIG. 4, and the storage address of the read-only memory 4' is designated by the counted value. Therefore,
The pulse train sent from the frequency dividing circuit 2 to the counter 3 is set to be sufficiently smaller than the period of the rectangular wave train generated by reading out the data stored in the read-only memory 4'. For example, if the repetition frequency of the rectangular wave train used as a local oscillator signal is 50 KHz, the period is 20 μsec, so if the counting pulse of counter 3 is set to a period of about 0.5 μsec, the period of the rectangular wave train is 1 wavelength. It can be memorized with an accuracy of 1/40. Also, when counting for 2 msec with a 0.5 μsec clock, the count value of counter 3 is
4000, a read-only memory 4' having 4000 storage addresses for each data output 01 to 07 is used.

The rectangular wave trains sent out from each of the output terminals 01 to 07 by reading the data stored in the read-only memory 4' are combined with the respective received signals in the mixing circuits _M1 to _M7 , and added by the adder Σ. After being
A frequency component of a specific frequency is extracted by the filter circuit FF in the same manner as in FIG. Therefore, when the count value of the counter 3 changes once, the received signals in each direction from -θs to θs are sequentially transmitted from the filter FF. Since the counter 3 performs the counting operation in an extremely short period of 2 msec as described above, the direction change of the received signal is also performed within this short period of time. Therefore, the filter
The received signals in each direction transmitted from the FF are time-divisionally transmitted on substantially equidistant lines. Therefore, when the counter 3 repeatedly performs counting operations, the filter circuit FF sends out received signals in each direction on the equidistant line for each distance. In addition, each output terminal 01 of the read-only memory 4'
The stored data sent out from the respective latch circuits 51 to 57 are latched and then sent to the respective mixing circuits _M1 to _M7 . The received signals in each direction sent out in time series from the filter circuit FF are amplified by the video amplifier 12 and then guided to the brightness terminal of the cathode ray tube display 7. The cathode ray tube display 7 has its deflection coil 8
By guiding the sweep wave from the sweep circuit 9,
A sector raster is formed. The sweep operation of the sweep circuit 9 is performed in conjunction with the counting operation of the counter 3. That is, the transmitter 9 periodically transmits ultrasonic pulses from the transmitter 11 in a wide range of directions, and at the same time sets the counter 3 and the sweep circuit 9 to check the direction of the received signal and the cathode ray tube display 7. Match the sweep direction. Note that the transmitter 11 is a vibrator Z _1
Z7 may also be used for transmitting and receiving waves.

As described above, the present invention can obtain any frequency signal whose frequency or phase changes at a desired repetition period by reading out the data stored in the memory circuit. Therefore, as shown in FIG. 6, it is possible to obtain a suitable device with a relatively simple configuration for use in forming a receiving beam in a desired direction. Alternatively, it can also be used to form a transmission beam for transmitting ultrasonic signals in a desired direction to obtain a suitable device. In other words, when transmitting an ultrasonic signal in a desired direction, the excitation phase of each transducer is adjusted so that the ultrasonic waves transmitted from multiple ultrasonic transducers form equal phase wavefronts in the desired direction. Just set it. Therefore, in this case, the ultrasonic signal can be transmitted in the desired direction simply by exciting the vibrator with the rectangular wave train of the latch circuits ₅₁ to ₅₇ shown in FIG. However, in the case of wave transmission, the stored data may be written in the storage circuit 4' so that the frequency of the rectangular wave train matches the resonant frequency of the vibrator.
Then, the phase of each rectangular wave train, and thus the frequency, is changed over time in the same manner as above, and the equal phase wavefront of the ultrasound transmitted from each transducer is changed over time, thereby transmitting waves. The direction of the beam can be changed over time.

In addition, in the above, since the memory circuit 4' is a high-density integrated circuit that is commercially available, the circuit configuration can be made much smaller and lighter than the conventional device, and the price can be made sufficiently low. can do.

[Brief explanation of drawings]

1, 2, and 3 are diagrams for explaining an apparatus for forming an ultrasonic reception beam, FIG. 4 is a diagram showing an embodiment of the present invention, and FIG. 5 is a diagram for explaining its operation. Figure 6 shows an embodiment in which the present invention is applied to an apparatus for forming an ultrasonic receiving beam, and Figure 7 shows an embodiment of the present invention.
8 and 8 show diagrams for explaining the operation.

Claims (1)

[Claims] 1. A memory circuit in which amplitude data for each phase of a frequency signal whose frequency or phase changes by a specific amount at a specific time is written in advance in a memory address corresponding to each phase; a clock pulse train generation circuit that generates a clock pulse train with a cycle sufficiently small compared to the signal cycle; and a clock pulse train generation circuit that counts the clock pulse train and cycles through the memory addresses of the memory circuit to which the counted value corresponds at the specified time. and a latch circuit that outputs a voltage (current) corresponding to the stored data read each time the counting circuit specifies a memory address in the memory circuit until the next stored data is read. An arbitrary frequency signal generation device comprising: