JPH03125512A - Matching filter - Google Patents

Abstract

PURPOSE:To bring a shape of an envelope of a compression pulse and an impulse reply pulse close to a desired shape by increasing a gap between a tap of an output side interdigital electrode and a dummy electrode wider than a gap between electrode fingers forming the tap. CONSTITUTION:A gap D between a tap 4 and a dummy electrode 7 is selected wider than a gap (g) between electrode fingers 5 forming the tap 4 as twice the gap (g). The strength of the electrode field caused at both sides of the 1st dummy electrode 7 shown in dotted lines is smaller than the strength of the electric field caused between the electrode fingers 5 shown in solid lines. Thus, when an electric signal is applied to an output side interdigital electrode 3, the difference of the electric field strength caused between the taps is small. Then when a surface acoustic wave excited by an input interdigital electrode is made incident in the output side interdigital electrode 3, the dispersion in signal reception for each tap 4 having caused in a conventional filter among electric signals received by each tap 4 is decreased and the shape of an envelope of a compression pulse and an impulse reply pulse is made close to a desired shape.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a matched filter that outputs an electrical signal sampled for a predetermined time from a surface acoustic wave obtained by inputting an electrical signal.

[Conventional technology]

Figure 4 shows, for example, IEEE Transactions on Microwave Theory and Technics (IEEE TRANSACTI○NS ON).
MICROWAVE THEORY A, ND
TECNIQUES) Vol, MTT-21, Nα4.
This is a configuration diagram showing a conventional matched filter shown in April 1973, pages 263 to 271. In the figure, 1 is a piezoelectric substrate, 2 is an input-side interdigital electrode, 3 is an output-side interdigital electrode, and 4 is an output-side interdigital electrode. The taps forming the output-side interdigital electrode 3 are electrode fingers 5 forming the taps 4 of the input-side interdigital electrode 2 and the output-side interdigital electrode 3, and 6 is a lead wire.

Next, the operation will be explained. By applying an electric signal to the input-side interdigital electrode 2 provided on the piezoelectric substrate 1, surface acoustic waves are excited from the input-side interdigital electrode 2. The excited surface acoustic waves propagate on the piezoelectric substrate 1 and reach the output side interdigital electrode 3. The surface acoustic waves reaching the output interdigital electrode 3 are sequentially received by a plurality of taps 4 constituting the output interdigital electrode 3, and are converted into electrical signals. Tap 4 has multiple electrode fingers 5
, and as shown with the symbol - in the figure,
Each positive color has a negative polarity. The electrical signal output from each tap 4 has a phase difference of 180 degrees depending on whether the polarity of the tap 4 is positive or negative. Therefore, when an impulse as shown in FIG. 5(a) is input to the input side interdigital electrode 2, the output side interdigital electrode 3
The electrical signal received at
0 depending on the polarity of tap 4. It becomes a π modulated waveform.

Furthermore, when a waveform modulated by O2π is input to the input-side interdigital electrode 2 with the polarity arranged by temporally reversing the polarity provided to the tap 4, as shown in FIG. 5(c), the output side A compressed pulse having a sharp peak as shown in FIG. 5(d) is obtained from the interdigital electrode 3. Figure 6 is 1'Acoustic Signal Processing Devices' Technical Report Number EC0M-0023.
-F, Ninis Army Electronics Command Fort Monmars, New Jersey (“A
cousic Signal, Processj
ngDevj, ces, ” Technical,
Report NCLE COM-=0023
-F, U, S, Army Electronic
csCon+n+and, Fort Monmo
uth, N, J, ) 1973.2~
27, and in the document "Surface Wave Devices and Their Applications," Nikkan Kogyo Shimbun, 1978, p. 171.

FIG. 2 is another configuration diagram of a conventional matched filter of this type. In the figure, only a part of the output side interdigital electrode 3 is shown in an enlarged manner for the sake of simplicity. In the figure, 7 is a dummy electrode. In FIG. 6, unlike the so-called solid electrode structure shown in FIG. 4, the tap 4 has a so-called double electrode structure in which the electrode fingers 5 constituting the tap 4 are arranged so as to alternately intersect two each from the top and bottom. This suppresses multiple reflections of surface acoustic waves that occur within 4.

Furthermore, a dummy electrode 7 is inserted between the taps 4. This dummy electrode 7 has a surface acoustic wave propagation speed at the tap 4 portion in the output side interdigital electrode 3;
This is provided to suppress multiple reflections of surface acoustic waves between the metal tabs 4 due to differences in surface acoustic wave propagation speed between the taps 4. In the figure, an electrode finger 5 and an electrode finger 5 forming a tap 4 are shown.
The distance between the two is expressed in g. Also, the electrode finger 5 of tap 4
The distance between the dummy electrode 7 and the dummy electrode 7 is represented by d. As shown in the figure, in the conventional matched filter of this type, the interval g and the interval d are made equal. By the way, in this type of matched filter, the level of the peak of the envelope of the compressed pulse and the level of the side lobe as shown in FIG. 5(d) depend on the number of taps 4 forming the output interdigital electrode 3 and It is determined by the polarity arrangement of tap 4. The number and polarity of the taps 4 are generally selected such that the peak level of the envelope of the compressed pulse is large and the level of the side lobe is small. The shape of the envelope of the compressed pulse will differ from the desired shape if there are variations between the electrical signals output from each tap 4. Further, the shape of the impulse response envelope shown in FIG. 5(b) deviates from a desired shape, for example, a constant value, if there are variations between the electrical signals output from each tap 4. FIG. 7 is a diagram schematically showing a part of the output side interdigital electrode 3 of the conventional matched filter of this type shown in FIG. As an example, FIG. 7 shows a case where the polarities of the taps 4 are arranged as positive, positive, negative, and positive from the left. For the sake of explanation, the taps 4 will be referred to as a first tap, a second tap, etc. in order from the left.

Also, the dummy electrodes 7 between the taps 4 are arranged in order from the left as a first dummy electrode, a second dummy electrode, etc.
It is called... In the figure, when an electric signal is applied to the output-side interdigital electrode 3, an electric field is generated between the electrode fingers 5, as shown by solid arrows in the figure.

Furthermore, as shown by dotted arrows in the figure, an electric field is also generated between the first tap 4 and the first dummy electrode 7 and between the first dummy electrode 7 and the second tap 4. arise. This is because there is a potential difference between the electrode fingers 5 that sandwich the first dummy electrode 7, so that an electric field is generated between the two electrode fingers 5 via the dummy electrode 7.

Since tap 4 and dummy electrode 7 are adjacent to each other, the magnitude of the electric field shown by the dotted line cannot be ignored compared to the magnitude of the electric field shown by the solid line that occurs between electrode 6 and finger 5 in tap 4. It becomes the size. On the other hand, there is no potential difference between the electrode fingers 5 that sandwich the second dummy electrode 7. Therefore, no electric field is generated between the second tap 4 and the second dummy electrode 7 and between the second dummy electrode 7 and the third tap 4. Similarly, no electric field is generated on either side of the third dummy electrode 7. Therefore, for example, in the second tap 4, an electric field is generated between the electrode fingers 5 in the tap 4 and between the tap 4 and the dummy electrode 7 in the second tap 4. On the other hand, in the third tap 4, the electric field is generated only between the electrode fingers 5 within the tap 4. Thus, in the matched filter having the conventional configuration shown in FIG. 6, when an electric signal is applied to the output-side interdigital electrode 3, the electric field generated at the tap 4 differs for each tap 4. The above has explained the case where an electric signal is applied to the output-side interdigital electrode 3 to excite a surface acoustic wave.
Conversely, the same applies when surface acoustic waves are incident on the output-side interdigital electrode 3. That is, when a surface acoustic wave is incident on the output-side interdigital electrode 3, the electric field generated at each tap 4 varies from tap to tap. Therefore, variations occur in the electrical signals received by each tap 4 from tap to tap. For this reason, the shapes of the compressed pulse envelope and the impulse response envelope obtained by the matched filter end up being different from the desired shapes.

[Problem to be solved by the invention]

Since the conventional matching tileter is configured as described above, there were variations in the electric field of each tap 4, so the shape of the envelope of the compression pulse and the shape of the envelope of the impulse response could not be the same as the desired shape. There were issues such as deviation from the original position.

This invention was developed in order to solve the above-mentioned problems, and its purpose is to obtain a matched filter that can bring the shape of the envelope of a compressed pulse and the shape of the envelope of an impulse response close to a desired shape. do.

[Means to solve the problem]

In the matched filter according to the present invention, the interval between the tap of the output-side interdigital electrode and the dummy electrode is larger than the interval between the electrode fingers constituting the tabs.

[Effect]

The matched filter of this invention reduces the influence of variations in the electric field generated between taps via the dummy electrode in the output-side interdigital electrode, and allows the shape of the compressed pulse envelope or impulse response envelope to be shaped into a desired shape. Make it possible to get closer.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a piezoelectric substrate, 2 is an input side interdigital electrode, 3 is an output side interdigital electrode, 4 is a tap, 5 is an electrode finger,
6 is a lead wire, and 7 is a dummy electrode. FIG. 2 is an enlarged view of FIG. 1, in which a part of the output side interdigital electrode 3 is enlarged. In FIG. 2, the distance between the tap 4 and the dummy electrode 7 is different from that in FIG.
and the electrode finger 5, for example, 2 of the distance g.
That's more than double that. FIG. 3 is a diagram schematically showing a part of the output side interdigital electrode 3 in order to explain the present invention in detail. Similar to FIG. 7, FIG. 3 shows a case where the polarities of the taps 4 are arranged as positive, positive, negative, and positive from the left. In the figure, when an electric signal is applied to the output-side interdigital electrode 3, an electric field is generated between the electrode fingers 5 in the tap 4, as shown by solid arrows in the figure. This is similar to the case shown in FIG. However, since the interval between the tap 4 and the dummy electrode 7 is made wider than the interval between the electrode fingers 5 in the tap 4, the first dummy electrode 7 indicated by the dotted line in the figure The magnitude of the electric field generated on both sides of is smaller than the magnitude of the electric field generated between the electrode fingers 5 in the tap 4 shown by the solid line.

Therefore, in the matched filter according to the present invention, when an electric signal is applied to the output-side interdigital electrode 3, the difference in the electric field generated between the taps 4 is small.

In other words, when the surface acoustic waves excited by the input-side interdigital electrode 2 are incident on the output-side interdigital electrode 3, the conventional variations in the electrical signals received at each tap 4 are reduced. 9 10- can be reduced. Therefore, the matched filter according to the present invention has the effect that the shape of the envelope of the compressed pulse and the shape of the envelope of the impulse response can be brought closer to a desired shape. Note that when using a material with a large electromechanical coupling coefficient, which represents the conversion efficiency between electricity and surface acoustic waves, as the piezoelectric base (Fil), one tap is required to set the insertion loss of the matched filter to the desired value. The number of electrode fingers 5 per 4 is
This is smaller than when using a material with a small electromechanical coupling coefficient. Therefore, when an electric field is generated between the taps 4 and the dummy electrodes 7, variations in the electric field generated at each tap 4 for each tap 4 become large, and the influence on the compression pulse and impulse response becomes large.

Therefore, as the piezoelectric substrate 1, materials having a large electromechanical coupling coefficient, such as LiNbO3, LiTaO3°Bi, 2
The effects obtained by the present invention are particularly large when crystals such as GeO2o or piezoelectric thin films such as Zn○ are used. Note that materials with a large electromechanical coupling coefficient are described in detail in, for example, the document "Surface Wave Devices and Their Applications", Nikkan Kogyo Shimbun, 1978, pages 71-130.

〔Effect of the invention〕

As described above, according to the present invention, the interval between the tap of the output interdigital electrode and the dummy electrode is configured to be wider than the interval between the electrode fingers constituting the tap, so that compression pulses and There is an effect that the shape of the envelope of the impulse response can be brought closer to a desired shape.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a matched filter according to an embodiment of the present invention, FIG. 2 is a block diagram showing an enlarged part of FIG. 1,
FIG. 3 is a block diagram schematically showing a part of the output-side interdigital electrode of a matched filter according to an embodiment of the present invention, FIG. 4 is a block diagram showing a conventional matched filter, and FIG. 5 is a block diagram of a conventional matched filter. A signal waveform diagram of each part of the matched filter to explain the operating principle of the matched filter. Figure 6 is a configuration diagram showing another conventional example of the matched filter. Figure 7 is a diagram of one of the output-side interdigital electrodes of the matched filter in Figure 6. It is a block diagram which shows the part typically. 1 is a piezoelectric substrate, 2 is an input-side interdigital electrode, 31-12- is an output-side interdigital electrode, 4 is a tap, 5 is an electrode finger, and 7 is a dummy electrode. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Daikimi Masuo 13-

Claims (1)

[Claims] A plurality of sets of taps each consisting of an input-side interdigital electrode for inputting an electrical signal, an output-side interdigital electrode placed opposite to the input-side interdigital electrode, and a plurality of electrode fingers forming the output-side interdigital electrode. and dummy electrodes placed between these taps on a piezoelectric substrate, the distance between the taps and the dummy electrodes is equal to the distance between adjacent electrode fingers constituting the taps. A matched filter characterized in that it is larger than .