JPS6347076Y2 - - Google Patents

Description

[Detailed Description of the Invention] An object of the present invention is to use an ultrasonic delay line to construct a comb-shaped filter that has a simple configuration, has little variation in performance, and is inexpensive.

Ultrasonic delay lines take advantage of the fact that the speed of sound waves is approximately 1/100,000 times smaller than the speed of electrical signals, and convert electrical signals into ultrasonic waves from several tens of microseconds to several tens of microseconds.
This is a functional element that converts the signal back into an electrical signal after obtaining a delay time of 100μsec.

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 6
It has a rectangular shape, and 2 and 2' are ceramic piezoelectric elements or transducers. The transducers 2, 2' include 3, 3', 3'', 3
An electrode shown in is formed and fixed to the glass retardation medium 1 by adhesive, soldering, or the like. Further, 4, 4', 4'', 4 are lead wires for supplying and taking out electrical signals to the transducers 2, 2', and electrodes 3, 3', 3'', 3
It is attached by soldering or other methods.

By the way, when an electric signal is applied to one of the transducers 2 and 2' (transducer 2 in this case), the transducer 2 mechanically vibrates, and ultrasonic waves are generated in the glass delay medium 1. radiated. This ultrasonic wave propagates along the path shown by the arrow in FIG. Occurs for 3 hours.
At this time, if the sound speed 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 2' is: It is expressed as t=l/υ. That is, the electrical signal is delayed by t.

In addition, in order to remove unnecessary signal components due to diffuse reflection that occurs when ultrasonic waves propagate within the glass delay medium 1, it is generally done to fix an absorbing material such as resin on the surface of the glass delay medium 1, as shown in 5. It is being said. .

By the way, when a signal E _A = αsinωt is applied to the ultrasonic delay line, and the signal delayed by time τ ₀ is E _B ,
Considering the sum of E _A and E _B , |E _C |=|E _A +E _B |=|αsinωt+βsin(ωt−τ ₀
)｜ =｜√ ² + ² +2 ₀・sin(ωt+
)|=|Asin(ωt+)| However, = tan ^-1 |βsinωτ ₀ /(α+βcosωτ ₀ )| A=√| ² + ² + 2 ₀ . That is, the amplitude A is Amax=α+β;ω(n)max=2nπ/τ ₀・ω (n=
0,1,2,…) Amin=α−β;ω(n)min=(2n+1)π/τ ₀・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 ₀ =1/τ _{0 H} ″=(n+1)min−(n)=2n+3/2τ ₀ −
2n+1/2τ ₀ = 1/τ ₀ τ ₀ = 1/ _H ′=1/ _H ″ In this way, using an ultrasonic delay line with a delay time τ ₀ and adding the delayed signal and the through signal,
Since the output signals exhibit the same phase with a period of 1/τ ₀ , a unique filter is obtained in which the pass band and attenuation band appear alternately. The amount of attenuation 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
``'''' is a matching resistor, 8 and 8' are munching coils, and 9 is a mixing variable resistor. a and b are the input and output terminals of the comb filter circuit. By the way, the equivalent circuit of the ultrasonic delay line is as shown in FIG. 10,10',
11 and 11' are capacitances between the terminals of the transducer and internal mechanical impedance, and as described above, 7, 7', 8, and 8' are matching resistors and coils.

The capacitors 10, 10' and the coils 8, 8' constitute a resonant circuit, which prevents the impedance from decreasing due to the capacitors 10, 10' and reduces insertion loss. Further, the resistors 7 and 7' both serve as a resistor and a load resistor for driving the ultrasonic delay line 6, and at the same time serve to lower the Q of the aforementioned resonant circuit and widen the passband width. Moreover, resistor 7 and coils 8, 8',
The capacitors 10 and 10' constitute a phase shift circuit, and by varying any one of them, 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 7' and the coils 8 and 8'.

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 you try to adjust the variable resistor 9 to a resistance value that matches the insertion loss,
The impedance seen from the ultrasonic delay line changes significantly, making it impossible to obtain the desired performance. Therefore, as shown in Fig. 3, a comb-type filter circuit was devised in which the load resistors 7' to 7'''' 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. It was.

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 13'', and when an electrical signal is applied to one of the surface electrodes, Transducer 12 vibrates, producing an electrical signal (undelayed signal) at the other electrode that is mixed with the propagating delayed signal. This is a comb filter with a built-in mixing impedance.The comb filter has a built-in mixing impedance.The comb filter shown in Fig. 6 has the same concept as Fig. 5. The difference is the external impedance 14 in Figure 5.
is simply replaced with a capacitor 14' formed on the transducer 12, and the capacitance is made variable by trimming the electrodes.

However, although the comb-shaped filter shown in FIGS. 5 and 6 has the advantage of having a simple structure and the ability to quickly obtain comb-shaped characteristics, it is difficult to miniaturize it because the shape of the glass retardation medium 1 is limited, and moreover, it is difficult to manufacture. Since it is not possible to correct the error in the delay time that occurs above, it has been impossible to obtain sufficient performance.

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

Embodiments of the present invention will be described below with reference to FIGS. 7 and 8.

FIG. 7 is a circuit diagram showing the configuration of the present invention, in which matching impedances 8, 8', 7'' to 7'' are obtained from the comb filter circuit shown in FIG.
``'''' is removed. That is, the comb filter of the present invention is constructed as follows.

15 is a glass delay medium, 16, 16' are transducers fixed to this glass delay medium 15, 17, 17', 17'', 17 are electrodes of the transducers 16, 16', and 18 is an ultrasonic delay line. ,
19 and 20 are matching impedances formed in the ultrasonic delay line 18; 21 to 23 are lead wires;
24 is a signal source, 19' is a matching resistor, and 25 is a case.

In this way, the comb filter of the present invention is made possible by widening the band of the ultrasonic delay line 18. The ultrasonic delay line 18 and matching impedances 19, 20 are housed in a case 25, and lead wires 21, 22, 23 are drawn out from the case 25.

FIG. 8 shows a specific structural example of the present invention. The case and terminals are omitted. The present invention has a structure in which two transducers 16 and 16' are attached to the slope of the pentagonal glass delay medium 15, which has a rectangular cross section with one corner cut out at 45 degrees.
An electrode 17' formed on the surface of the electrode glass delay medium 15 side of each transducer 16, 16';
An electrode 26 is formed in the middle of the electrode 17'', and a resistor material 27, 28 such as carbon is formed by a method such as printing or baking between the electrode 26 and the electrodes 17', 17''. Further, the electrode 26 has a lead wire 21
is attached using a method such as soldering. Further, electrodes 17, 17 are formed on the other surfaces of the transducers 16, 16', and are connected by a lead wire 22 to have the same potential. A lead wire 23 is also drawn out from the electrode 17''.

The comb filter of the present invention having the above configuration has the feature that comb characteristics can be easily obtained by simply connecting a signal source and a matching resistor, and moreover, it does not include a resistor as a matching impedance. Since the comb-shaped filter characteristics are adjusted in advance, it has a great feature such as that the comb-shaped filter characteristics will not deteriorate due to variations in matching resistance when installed in actual equipment.

Furthermore, since a resistor corresponding to the matching impedance is formed directly on the glass delay medium, a comb filter can be constructed without taking up any space. Moreover, by trimming the resistor, the level of the through signal and the amount of delay of the delayed signal can be adjusted optimally, so a comb filter with very good performance can be obtained.

[Brief explanation of drawings]

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 circuit configuration diagram of a conventional comb filter circuit using a four-terminal ultrasonic delay line, Figure 4 is an equivalent circuit diagram of the comb filter circuit, and Figures 5 and 6 are each of other conventional examples. FIG. 7 is a circuit diagram of a comb filter showing the basic configuration of the present invention, and FIG. 8 is a diagram of a comb filter according to the present invention. 15... Delay medium, 16, 16'... Transducer, 17, 17', 17'', 17'''''... Electrode, 18... Ultrasonic delay line, 19, 20... Matching impedance, 19'...Matching resistor, 21-23...Lead wire, 24...Signal source,
25... Case, 26... Electrode, 27, 28...
resistance.

Claims (1)

[Scope of utility model registration request] A three-divided electrode is formed on the oblique side corresponding to the cut-out side of a pentagonal glass retardation medium in which one corner of a rectangular cross section is cut out at 45 degrees, and one of the three divided electrodes is , a resistor material such as carbon is formed from the first electrode located between the two electrodes toward the second and third electrodes, and a piezoelectric ceramic or the like is formed on each of the second and third electrodes. consisting of 2
A plurality of transducers are attached, and the fourth and fifth electrodes facing the second and third electrodes on the surfaces of the first and second transducers are electrically connected to each other using lead wires. A comb-shaped filter configured to set the voltage to zero potential, apply an electrical signal input from a lead wire attached to the first electrode, and extract an output electrical signal from the lead wire attached to the second or third electrode. .