JP2001136049A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device used for a matched filter that can correlatively detect a plurality of spread signals. SOLUTION: Normalized interdigital electrodes 2, 7 are arranged on both sides of a coded interdigital electrode 3 in the propagation direction of a surface acoustic wave, and the surface acoustic wave device is configured by combining a plurality of sets of comb electrodes each set consisting of the normalized interdigital electrodes 2, 7 and the coded interdigital electrode 3. Since the matched filter with a simple structure can detect a plurality of spread signals, this configuration is mush effective to the miniaturization and the enhanced functions of radio equipment utilizing the spread spectrum processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device, and more particularly to a matched filter type surface acoustic wave device used for spread spectrum communication.

[0002]

2. Description of the Related Art Spread spectrum communication is widely used in communications because of its advantages such as being resistant to interference and interference and being able to use frequency resources effectively. In particular, recently, it has attracted attention as a communication method for LANs and mobile telephone systems. A surface acoustic wave device used as a matched filter is used as a signal detection element in spread spectrum communication, and can detect a correlation signal without using a synchronization signal with respect to a spread signal to which a fixed pseudo noise signal is added. Is used as a simple correlating element that does not consume.

As shown in FIG. 2, a conventional surface acoustic wave device has a logarithmic regular IDT 2 corresponding to the chip length of an encoded signal used for diffusion on the surface of a piezoelectric substrate 1 and an encoding device. IDT 3 consisting of sunk tap electrodes
Was formed. Other components of the element include a shield electrode 4 for suppressing a direct wave between the regular IDT 2 and the coded IDT 3, and a sound absorbing material 5 for preventing an unnecessary reflected wave reaching the chip end face. Etc. were provided. Reference numeral 6 in the figure denotes a bonding pad.

[0004]

Since the conventional surface acoustic wave device has an electrode pattern in which the coded IDTs are fixed, only a spread signal corresponding to the pattern can be detected. However, in actual applications, there are many demands for a system that has a plurality of channels and can switch between them to respond to a plurality of communication terminals. Therefore, the conventional surface acoustic wave device cannot cope with this.

It is an object of the present invention to provide a surface acoustic wave device capable of detecting a plurality of spread signals by correlation.

[0006]

In order to achieve the above object, a first means comprises a piezoelectric substrate, and regular IDTs and coded IDTs formed on the surface of the piezoelectric substrate. It is intended for a surface acoustic wave device.

[0007] With respect to the propagation direction of the surface acoustic wave, a normal IDT is disposed on both sides of the coded IDT, and a plurality of normal IDTs disposed on both sides thereof. A plurality of sets of interdigital electrodes are formed, with one set of encoded interdigital electrodes as one set,
Each of the interdigital transducer sets is electrically connected.

A second means is that, in the first means, two sets of interdigital electrodes are formed, and each of the coded interdigital electrodes of the set of interdigital electrodes is arranged in the propagation direction of the surface acoustic wave. A plurality of coded interdigital transducers formed offset from each other, and a distance between a first normal interdigital transducer and a second normal interdigital transducer in the first set; The distance between the first regular IDT and the second normal IDT in the set is arranged so as to have a phase difference of 波長 of the wavelength of the main response surface acoustic wave. And

A third means is that, in the first means, two sets of IDTs are formed, and each of the two sets of IDTs in each of the two sets of IDTs. Is further provided with a third regular IDT electrode.

As described above, in the surface acoustic wave device of the present invention, regular IDTs are arranged on both sides of the coded IDT with respect to the propagation direction of the SAW, and these are set as a set. A plurality of IDTs are formed on the surface of the piezoelectric substrate.

Further, each of the coded interdigital transducers of the above-mentioned interdigital transducer electrode set is composed of a plurality of coded interdigital transducer electrodes formed so as to be shifted from each other in the propagation direction of the surface acoustic wave. The propagation path length of the surface acoustic wave of the interdigital transducer set and the propagation path length of the second set of interdigital transducers are formed so as to differ from each other by a half of the wavelength of the main response surface acoustic wave. ing.

In the first set of interdigital transducers, when a spread signal is input to the first normal type interdigital transducer and a carrier wave is input to the second normal type interdigital transducer, it corresponds to the coding of the spread signal. As a result, a standing wave is generated at the position of a specific coded IDT due to interference with the carrier.

For example, at a certain position, the phase of the carrier wave is n / 2 cycles (n =
(0, ± 1, ± 2,...), The standing wave does not stand at this time because the phase of the code 0 spread signal is reversed. The position where the standing wave stands depends on the phase of the input spread signal and the carrier, and by adjusting the phase, it is possible to generate a standing wave at any coded IDT.

[0014] A second set of interdigital transducers, separate from the interdigital transducer set, has a first set of interdigital transducers as compared to the first set of interdigital transducers.
The distance between the normal interdigital transducer and the second normal interdigital transducer is shifted by a half of the wavelength of the main response surface acoustic wave corresponding to the input carrier. A standing wave does not stand for a signal with a carrier phase of n / 2 periods, but a standing wave stands for a spread signal of code 0.

Therefore, by arranging the coded IDT at a position where the standing wave stands, a signal corresponding to the code 1 of the spread signal is detected by the first set of coded IDTs. In two sets of coded IDTs, the code of the spread signal is 0.
Is detected, and the correlation signal is detected by electrically connecting the coded IDTs of the first and second sets.

Further, on the same surface acoustic wave propagation path,
By arranging different coded interdigital electrodes so as to be shifted from the coded interdigital electrodes in phase,
Different correlation signals can be detected by adjusting the phase of the input signal.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, FIG. 1 shows an electrode configuration diagram of a surface acoustic wave device according to Embodiment 1 of the present invention. Piezoelectric substrate 1
ST-cut quartz substrate is used. On the piezoelectric substrate 1, a first regular IDT 2, an encoded IDT 3, a shield electrode 4, a sound absorbing material 5, a bonding pad 6, a second regular IDT 7, and a common electrode 8 are provided. It is formed at a predetermined position.

First and second regular type interdigital transducers 2,
The IDT 7 and the IDT 3 are electrically connected by a common electrode 8 to a first set and a second set of electrodes. In the first set, the distance between the first regular IDT 2 and the coded IDT 3 is L1, and the distance between the second normal IDT 7 and the coded IDT 3 is L2. Also, the distance between the first regular IDT 2 and the coded IDT 3 in the second set of IDTs is L3, the second normal IDT 7 and the coded IDT 3 If the distance between them is L4, the distances L1 and L3 are equal and the distance L
2 and L4 are the first set of second normal type interdigital transducers 7 so that a phase difference is generated by half the wavelength of the main response surface acoustic wave.
And a second set of second regular IDTs 7.

Next, the operation of the surface acoustic wave device according to the present invention will be described. FIG. 3 shows a signal input / output state of the surface acoustic wave device of the present invention. The surface acoustic wave device 9 includes a diffusion signal Ss
And a carrier signal Sc, and a correlation signal So is output. In the present embodiment, the phase shifter 10 is provided on the input path of the carrier signal Sc. For example, the diffusion signal Ss is input to the first normal-type interdigital transducer 2, and the carrier signal Sc is input to the second normal-type interdigital transducer 7.

FIG. 4 schematically shows these signal waveforms.
Diffusion signal Ss converted to surface acoustic wave by IDT
On the other hand, the carrier signal Sc propagating from the opposite direction is superimposed, and in the phase relationship in the figure, as shown by the signal Ss + Sc, the code 1 has the same phase and the code 0 has the opposite phase.
Accordingly, a standing wave corresponding to the spreading code is generated at a specific position on the surface acoustic wave propagation path, and a signal is detected by disposing the coded IDT 3 at this position.

Assuming that the set of the first and second normal-type IDTs 2 and 7 and the coded IDT 3 in the signal detection is a first set, the second set of IDTs has a spread signal Ss
Since the phase of the carrier signal Sc differs from that of the carrier signal by a half wavelength, as shown in FIG. 5, the code 1 has the opposite phase and the code 0 has the same phase, so that the signal of the code 0 is detected. The encoding IDTs 3 are connected by a common electrode 8 so that the first set of outputs and the second set of outputs have the same phase, and the correlation signal S
o can be taken out.

Next, as an example, when the phase of the carrier signal Sc is shifted by a half wavelength by the phase shifter 10, in the first and second sets of interdigital transducers, the same stationary state is obtained at a position shifted by 1/4 wavelength. The waves will rise.

FIG. 6 shows such a change in the standing wave waveform by a solid line and a broken line. As shown in the figure, by arranging the coded ID electrodes B, which are differently coded from the coded ID electrodes A, at different positions of 1/4 wavelength phase, it is possible to detect different correlation signals. It can be done. That is, the surface acoustic wave device 9 of the present embodiment can detect a plurality of correlation signals by adjusting the phase shifter 10.

Next, a second embodiment of the present invention will be described with reference to FIG. In the surface acoustic wave device 9 of the present embodiment, a third regular IDT 11 is further provided outside the second regular IDT 7. Other configurations of the interdigital transducer are the same as those of the first embodiment of the present invention. The second and third normal-type interdigital transducers 7 and 11 are arranged so as to cause a phase difference between the surface acoustic waves excited by the respective electrodes.

The detection of the correlation signal is performed in the same manner as in the first embodiment of the present invention, except that the input of the carrier is switched between the second and third normal type interdigital transducers 7 and 11 using an external switch or the like. Therefore, the position where the standing wave is generated can be changed. As in the first embodiment, if the coded IDTs 3 are arranged in accordance with the respective standing waves, the spread signal S that is correlated by switching the switch is detected.
s can be selected.

Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, a first regular IDT 2 and a second regular IDT 7 on a piezoelectric substrate 1 are provided.
And the formation of the coded IDT 3 is the same as that of the first embodiment of the present invention.
Only the first set of first normal IDTs 2 and the second set of first normal IDTs 2 have a phase difference of の of the wavelength of the main response surface acoustic wave corresponding to the carrier. It is arranged so that it occurs.

That is, in the first set, the distance between the first regular type IDT 2 and the coded IDT 3 is L1,
The distance between the second regular IDT 7 and the coded IDT 3 is L2, and the distance between the first normal IDT 2 and the coded IDT 3 in the second set of IDTs. Is L3, and the distance between the second regular IDT 7 and the coded IDT 3 is L4, the distances L2 and L4
Are equal, and the distances L1 and L3 produce a phase difference of 波長 of the wavelength of the main response surface acoustic wave, so that the first set of first normal type interdigital transducers 2 and the second set of first normal type An interdigital electrode 2 is arranged.

By arranging as described above, as in the first embodiment of the present invention, for example, if the spread signal Ss of code 1 is detected by the first set of coded IDTs 3,
In the second set of coded IDTs 3, the spread signal S
s is detected, and the electrical signal detected by both electrodes is taken out by the common electrode 8 so as to have the same phase, thereby obtaining the correlation signal So.
Is detected.

In the above embodiment, the electrodes are configured so that two spread signals can be detected. However, the present invention is not limited to the two spread signals. It is also possible to configure the coded IDTs 3 with IDTs corresponding to two or more spread signals.

As such an example, FIG. 9 shows a part of a coded IDT corresponding to three spread signals. A,
The electrode pairs B and C are arranged to be shifted from each other in phase, and the coded IDT 3 is composed of the electrode pairs A, B and
A plurality of Cs are arranged corresponding to the spread signal length and the coding of the spread signal and the tap length in units of C.

FIG. 10 schematically shows standing wave waveforms A, B, and C detected at the respective electrode pairs A, B, and C. As described above, the input signal according to the method of the present invention is used as described above. By adjusting the phase or selecting the input electrode, the position of the generated standing wave is determined, and a desired spread signal is detected.

[0032]

As described above, according to the present invention, since a plurality of spread signals can be used with a matched filter having a simple structure, it is possible to improve the function and reduce the size of a wireless device using a spread spectrum system. It has a great effect.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a surface acoustic wave device according to Embodiment 1 of the present invention.

FIG. 2 is a plan view showing a configuration of a conventional surface acoustic wave device.

FIG. 3 is a plan view showing a signal input / output state of the surface acoustic wave device according to the present invention.

FIG. 4 is a schematic diagram showing a relationship between input and output waveforms of a first set of interdigital transducers of the surface acoustic wave device of the present invention.

FIG. 5 is a schematic diagram showing a relationship between input and output waveforms of a second set of interdigital transducers of the surface acoustic wave device of the present invention.

FIG. 6 is a diagram showing a positional relationship between a generated standing wave and a coded IDT.

FIG. 7 is a plan view illustrating a configuration of a surface acoustic wave device according to Embodiment 2 of the present invention.

FIG. 8 is a plan view showing a configuration of a surface acoustic wave device according to Embodiment 3 of the present invention.

FIG. 9 is a plan view showing a part of the configuration of the coded IDT corresponding to three spread signals according to the present invention.

FIG. 10 is a diagram showing a waveform detected by the coded IDT of FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 1st normal type interdigital electrode 3 Encoding interdigital electrode 4 Shield electrode 5 Sound absorbing material 6 Bonding pad 7 2nd normal type interdigital electrode 8 Common electrode 9 Surface acoustic wave device 10 Phaser 11 Third Regular type IDT electrodes

Claims (3)

[Claims] 1. A surface acoustic wave device comprising a piezoelectric substrate, and regular IDTs and coded IDTs formed on the surface of the piezoelectric substrate. A plurality of sets of normal IDTs are arranged on both sides of the IDT, and a combination of a plurality of normal IDTs and one coded IDT disposed on both sides is a set. A surface acoustic wave device, wherein a set of IDTs is formed and each IDT is electrically connected. 2. The surface acoustic wave device according to claim 1, wherein two sets of the interdigital transducers are formed, and each of the coded interdigital transducers of the interdigital transducers is mutually connected in the propagation direction of the surface acoustic wave. A plurality of coded interdigital transducers formed at different positions, a distance between the first normal interdigital transducer and the second normal interdigital transducer in the first set, and a first interdigital transducer in the second set. Characterized in that the distance between the normal type interdigital transducer and the second normal type interdigital transducer has a phase difference of 波長 of the wavelength of the main response surface acoustic wave. Wave device. 3. The surface acoustic wave device according to claim 1, wherein two sets of the interdigital transducers are formed, and each of the two sets of the interdigital transducers is on the side of the second regular interdigital transducer. A surface acoustic wave device further comprising a third regular type IDT.