JPH0112424Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention aims to provide a comb filter that can extract both C-shaped and Y-shaped comb characteristics at the same time. This ultrasonic delay line takes advantage of the fact that the speed of sound waves is approximately 1/100,000 times smaller than the speed of electrical signals, and converts electrical signals into ultrasound waves.
This is a functional element that converts the signal back into an electrical signal after obtaining a delay time of 10 μsec to several 100 μsec. FIG. 1 shows an example of the basic structure of an ultrasonic delay line. 1 is a delay medium made of a material such as glass and has a hexagonal shape, and 2 and 2a are ceramic piezoelectric elements, that is, transducers. Electrodes indicated by 3, 3a, 3b, and 3c are formed on the transducers 2, 2a, and are fixed to the glass delay medium 1 by adhesive, soldering, or the like. Further, 4, 4a, 4b, 4c are lead wires for supplying and extracting electrical signals to the transducers 2, 2a, and are attached to the electrodes 3, 3a, 3b, 3c by a method such as soldering. By the way, when an electric signal is applied to one of the transducers 2 and 2a (transducer 2 in this case), the transducer 2 mechanically vibrates and an ultrasonic wave is emitted into the glass delay medium 1. This ultrasonic wave propagates along the path shown by the arrow in FIG. 1 and reaches the other transducer 2a, which mechanically vibrates and transmits the electrical signal to the electrode 3b
Occurs between 3c. At this time, if the sound velocity in the glass delay medium 1 is υ and the path length is l, the time t required for the ultrasonic wave to reach from one transducer 2 to the other transducer 2a is t =
It is expressed as l/υ. In other words, the electrical signal is delayed by t. Furthermore, in order to remove unnecessary signal components due to diffused reflection that occurs when ultrasonic waves propagate within the glass delay medium 1, it is common practice to fix an absorbing material 5 such as resin on the surface of the glass delay medium 1 as shown in the figure. It is being done.

By the way, we apply a signal E _A = αsinωt to the ultrasonic delay line, and the signal delayed by time τ _O is set as E _B.
Considering the sum of E _A and E _B , |E _C |=|E _A +E _B |=|αsinωt+βsin(ωt−τ _O
)｜ =｜√ ² + ² +2 _O・sin(ωt
+) | = | Asin (ωt+) | However, = tan ^-1 | β sin ω τ _O / (α + β cos ω τ _O ) | A = √ ² + ² + 2 _O. That is, the amplitude A is Amax=α+β;ω(n)max=2nπ/τ _O・ω (n=0,1,2,...) Amin=α−β;ω(n)min=(2n+1)π/τ _O・ω (n=0, 1, 2,...).

Here, if the frequency interval between adjacent maximum values or minimum values is _H ′, _H ″, then _H ′=(n+1)max−(n)max=n+1/τ ₀
−n/τ _O =1/τ _{O H} ″=(n+1)min−(n)min=2n+3/2τ
₀ −2n + 1/2τ _O = 1/τ _O τ ₀ = 1/ _H ′ = 1/ _H ″. In this way, using an ultrasonic delay line with delay time τ _O and adding the delayed signal and the original signal, , 1/τ _O
Since the output signals show the same phase with a period of
A unique filter in which attenuation regions appear repeatedly is obtained. The attenuation amount of this filter characteristic becomes maximum when α=β, that is, when the amplitudes of the undelayed signal and the delayed signal become the same level. This is called a comb filter, and its characteristics are shown in Figure 2.

A practical comb filter circuit for obtaining such comb filter characteristics is shown in FIG. Here, 6 is an ultrasonic delay line, 7-7
d is a matching resistor, 9 is a variable resistor for mixing, and 8 and 8a are matching coils. a and b are the input and output ends of the comb filter circuit. By the way, the equivalent circuit of the ultrasonic delay line is as shown in FIG. 10,10
a, 11, 11a are the inter-terminal capacitance and internal mechanical impedance of the transducers 2, 2a, and as described above, 7, 7a, 8, 8a are matching resistors and coils.

Here, the capacitors 10, 10a and the coils 8, 8a constitute a resonant circuit, which prevents a decrease in impedance due to the capacitors 10, 10a and reduces insertion loss. Further, the resistors 7 and 7a both serve as a resistor and a load resistor for driving the ultrasonic delay line 6, and at the same time, the resonance sharpness Q of the resonant circuit is
It has the role of lowering the passband and widening the passband width. Moreover, the resistor 7, the coils 8, 8a, and the capacitors 10, 10a constitute a phase shift circuit, and by varying any one of these, the phase of the circuit, that is, the delay time can be changed.

As described above, the performance of the ultrasonic delay line depends entirely on the matching impedance of the resistors 7 and 7a and the coils 8 and 8a.

In the circuit of Fig. 4, a variable resistor 9 for mixing is connected as shown by the broken line to obtain the comb filter characteristics shown in Fig. 2, and in order to maximize the attenuation amount, the ultrasonic delay line If an attempt is made to adjust the variable resistor 9 to a resistance value commensurate with the insertion loss, the impedance seen from the ultrasonic delay line will change significantly, making it impossible to obtain the desired performance. Therefore, as shown in FIG. 3, a comb filter circuit was devised in which the load resistors 7a to 7d on the output side are assembled into a bridge so that the performance does not change even if the variable mixing resistor 9 is varied.

However, since the circuit is complicated and requires many man-hours for adjustment, a comb-shaped filter as shown in FIG. 5 was devised. This has one transducer 12 attached to one side of a polygonal glass delay medium 1 to form divided surface electrodes 13 to 13b. When an electric signal is applied to one of the surface electrodes, a transducer The user 12 vibrates and sends an electrical signal (undelayed signal) to the other electrode.
is generated and mixed with the propagated delayed signal. Then, due to the external impedance 14,
After adjusting the voltage levels of the undelayed signal and the delayed signal that are mixed through this filter, the casing is applied, and it is a comb filter with a built-in mixing impedance. The fifth one is shown in Figure 6.
The comb filter has the same concept as the one shown in the figure, but the difference is that the external impedance 14 in FIG.
This is simply a replacement for a, and in this case, the capacitance is made variable by trimming the electrodes. Further, 13c is an electrode.

FIG. 7 shows an example in which a comb filter is constructed using an ordinary four-terminal ultrasonic delay line. In this embodiment, one terminal each of the input and output transducers 12, 12a, that is, the electrodes 13a,
13c or 13 and 13b are common, and a variable impedance 15 (Z) is connected between it and the ground.

FIG. 8 shows a comb filter using a three-terminal ultrasonic delay line. In the ultrasonic delay line used in this embodiment, the input and output transducers 12 and 12a have a common ground.
An impedance 15 is connected between this earth terminal and the earth.

FIG. 9 is an equivalent circuit of the comb filter circuit shown in FIG. 8. Here, 16, 16a are equivalent capacitances of the transducers 12, 12a.

Here, as shown in the figure, if we consider the case where voltage E _A is applied to the input terminal, the voltage E _A is divided into equivalent capacitance 16 of transducer 12 and impedance 15 . In other words, the equivalent capacity is
If C _O , E _A = αsinωt, then E _C = Z/Z+1/ωCoE _A = Z/Z+1/ωCo・αsinωt Also, if the delayed signal that has passed through the ultrasonic delay line is E _B , then E _B = βsin( When Z/Z+1/ωCo・α=β Z/Z+1/ωCo=β/α (=insertion loss of ultrasonic delay line) at ωt−τ _O ), the attenuation of the comb filter characteristic becomes maximum. .

By the way, the drawback of these various comb filters is that they can only extract the comb characteristics of either the C-shape or the Y-shape, which limits their applications.

The present invention eliminates the above-mentioned drawbacks of the prior art.

An embodiment of the present invention will be described below with reference to FIG. 10.

The embodiment shown in FIG. 10 will be described below. FIG. 10 is a block diagram schematically showing the comb filter of the present invention, in which two piezoelectric transducers 18, 18a are attached to one or more sides of a polygonal glass delay medium 17. It is being The transducers 18, 18a have electrodes 19, 19a, 19b on opposing surfaces, respectively.
19c is provided, and the input terminal 20 is connected to the electrode 19 of this transducer 18, and the electrode 19 of the other transducer 18a is connected to the input terminal 20.
A mixing impedance 21 is connected between the oscilloscope and the oscillator b. Furthermore, an output terminal 22 is connected to the electrode 19b of the transducer 18a.

Furthermore, an earth terminal 23 is connected to the electrode 19a of the transducer 18, and an output terminal 24 is connected to the electrode 19c of the transducer 18a. In addition, the input terminal 20, the output terminals 22, 2
4 has matching impedance 25, 25
a and 25b are connected.

In this way, the mixing impedance 21 is connected between the input side and the output side to mix the through signal and the delayed signal to obtain comb filter characteristics.
These are housed in a case 26.

Note that the mixing impedance 21 may be connected before the matching impedance 25 as shown by the broken line.

In the above configuration, the opposing electrodes 19, 19a of the input side transducer 18 and the opposing electrodes 19b, 19c of the output side transducer 18a are not set to the same potential, but the opposing electrodes of the output side transducer 18a are The feature is that outputs are taken out from both electrodes 19b and 19c through output terminals 22 and 24, and matching impedances 25a and 25b as load resistances are connected between the two outputs and ground.

As described above, the object of the comb filter of the present invention is to obtain a comb filter that can simultaneously obtain C-shaped comb characteristics and Y-shaped comb characteristics, which was impossible with conventional comb filter configurations. .

In the embodiment shown in FIG. 10, when a sinusoidal input signal is applied to the input terminal, this input signal is applied to the input side transducer 18 via the matching impedance 25, and is converted into ultrasonic vibration. The delay medium 17 is advanced to reach the output side transducer 18a, and the output side transducer 18a is vibrated.
Sinusoidal signals having phases different by 180° from each other are generated at opposing electrodes 19b and 19c of 8a. Also,
The input signal is branched into one that is applied to the input side transducer 18 and one that passes through the mixing impedance 21 . The branched input signal is passed through the mixing impedance 2 as a so-called through signal without being delayed.
1, the delayed signal is attenuated to the same level as the delayed signal and mixed with the delayed signal appearing at the electrode 19b of the output side transducer 18a, creating a comb filter characteristic, and the matching impedance 25a
is taken out to the output terminal 22.

Further, the through signal is mixed with the delayed signal appearing at the electrode 19c through the capacitance formed by the opposing electrodes 19b and 19c of the output side transducer 18a to form a comb filter, and the matching impedance 25b is taken out to the other output terminal 24. That is,
As stated above, the comb filter characteristics taken out from the output terminals 22 and 24 have a phase difference of 180° from each other, that is, C
This means that the Y-shaped and Y-shaped comb filter characteristics are formed at the same time.

Since the comb filter of the present invention is constructed as described above, it has almost the same structure as a conventional comb filter, but it has C-type filter characteristics and Y-type filter characteristics, making it suitable for various uses. It can be expanded and has great practical value.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing a general ultrasonic delay line.
Figure 2 is a diagram explaining the comb filter characteristics, Figure 3
The figure is a block diagram of a comb filter using a conventional 4-terminal ultrasonic delay line, Figure 4 is an equivalent circuit diagram of the same comb filter, and Figures 5 and 6 are respective examples of other conventional comb filters. FIGS. 7 and 8 are block diagrams of other conventional comb filters, FIG. 9 is an equivalent circuit diagram of the comb filter circuit, and FIG. 10 is a diagram of the comb filter of the present invention. FIG. 1 is a configuration diagram showing an example. 17... Delay medium, 18, 18a... Transducer, 19, 19a, 19b, 19C... Electrode, 20... Input terminal, 21... Mixing impedance, 22, 24... Output terminal, 23...
...Earth terminal, 25, 25a, 25b...Matching impedance.

Claims (1)

[Scope of utility model registration request] Two input-side and output-side transducers are pasted on one or more sides of a polygonal glass delay medium, and one electrode of each of the input-side and output-side transducers is connected via a mixing impedance. one electrode of the input transducer is connected to the input terminal, the other electrode of the input transducer is connected to the ground terminal, and both of the output transducer A comb filter characterized in that each electrode is connected to an output terminal from which an output is taken out, and further, a matching impedance is coupled to each of the input terminal and two output terminals.