JPH06104688A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To simplify a means to obtain a sum and a difference output signal and to attain the operation over a wide band in the SAW element as a DPSK convolver. CONSTITUTION:Electrodes 18a, 18b-21a, 21b are formed on a substrate front surface and back surface between SAW transducers 2a, 2b on a substrate 1 opposite to each other. When an input signal is given to the transducers 2a, 2b, a convolution output signal is generated between the electrodes on the front surface and back surface of the substrate. Then a sum and a difference output signal are obtained by properly connecting terminals 22a-25b of each electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a surface acoustic wave device suitable as a DPSK convolver or the like.

[0002]

2. Description of the Related Art Spread spectrum communication SSC (Spread S
DPSK (Different
Various surface acoustic waves and SAW (Surface Acoustic Wave) elements have been proposed as DPSK convolvers for demodulators of systems using the ial phase shift keying (modulation / demodulation) system.

The DPSK convolver shown in FIG. 6 is, for example,
D. Brodtcorb, JE. Laynor, “FAST SYNCHRONIZATION IN
A SPREAD-SPECTRAM SYSTEM BASED ON ACOUSTOELECTRIC
-CONVOLVERS ”, 1978 IEEE Ultrasonics Symposium Pro
ceedings, pp.561-566.

Here, 1 is a piezoelectric substrate, 2a and 2b are S
AW transducers, 3a and 3b are output electrodes, and 4 is 2
A hybrid for taking the sum and difference of the output signals from the two output electrodes 3a and 3b, and output the sum and difference output signals from the output terminals 5 and 6, respectively. However, the hybrid 4 used to obtain the sum and difference output signals is expensive and has a large number of parts, which leads to an increase in system cost.

FIG. 7 shows another conventional DPSK convolver, in which the output electrodes 3a and 3b in FIG.
Is divided in parallel to the propagation direction of 4 to form four electrodes 7a, 7b, 8a and 8b. In this structure, the sum output is obtained from the output terminal 10 by connecting the outputs of the electrodes 7a and 7b, and the difference output is obtained from the output terminal 11 by connecting the balance-unbalance conversion transformer 9 to the electrodes 8a and 8b.

However, even with this structure, the balance-unbalance conversion transformer 9 is expensive and leads to an increase in cost.

[0007]

FIG. 8 shows a DPSK convolver having a third conventional structure, which does not require a balance-unbalance conversion transformer for obtaining a differential output, which is a drawback of the second conventional structure DPSK convolver. In this case, SAWs having phases different from each other by 180 ° are excited and propagated by the stepped transducer 13 to two tracks provided with two sets of parallel output electrodes 7a, 7b and 8a, 8b. Therefore, the output terminals 14 and 16
The phase difference between the outputs appearing at and the phase difference between the outputs appearing at the output terminals 15 and 17 are both 180 °, and the output terminal 1
A sum signal is obtained by adding the outputs of 4, 15 or the outputs of the output terminals 16, 17, and a difference signal is obtained by adding the outputs of the output terminals 14, 17 or the output terminals 15, 16. However, in this method, it is difficult to make the phase difference between the SAWs corresponding to the two tracks excited by the SAW transducer 13 constant at 180 ° in a wide band, which is suitable for an SSC in which a signal is spread over a wide band. Absent.

An object of the present invention is to provide a surface acoustic wave device capable of simplifying the means for obtaining a complicated and expensive output signal of sum and difference, which is a drawback of the conventional structure DPSK convolver, and enabling wide band operation. .

[0009]

In order to achieve the above object, a surface acoustic wave device of the present invention is formed on the surface of a piezoelectric substrate, and is divided and arranged in parallel in the propagation direction of the surface acoustic wave to be transmitted. The first four electrodes configured, the second four electrodes formed on the back surface of the piezoelectric substrate and configured to face the four electrodes, and the first electrodes facing each other. A terminal configured to extract a signal generated between the second electrodes, and at least a pair of input transducers disposed outside the electrodes formed on the surface of the substrate along the propagation direction, The summary is that

[0010]

When an input signal is applied to the pair of transducers, a convolution output signal of the input signal is generated between the first and second electrodes, and the sum and difference output signals are generated by appropriately connecting these electrodes. Can be obtained.

[0011]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows a first embodiment of the surface acoustic wave device of the present invention.
In the figure, 18b, 19b, 20b and 21b are electrodes 18a, 19a and 20 provided on the surface of the piezoelectric substrate 1, respectively.
It is an electrode provided on the back surface of the substrate 1 so as to face a and 21a. The output signal in the SAW convolver is basically taken out as a potential change of the output electrode with respect to the electrode connected to the reference potential such as ground.

In FIGS. 6 to 8 showing the conventional structure, the electrode for applying the reference potential is omitted, but it can be considered that there is an electrode connected to the ground as the reference potential on the back surface. On the other hand, in the embodiment of the present invention shown in FIG.
Two sets of four electrodes 18 divided into two in the SAW propagation direction between two sets of transducers 2a and 2b on the surface of the substrate 1.
a, 19a, 20a, 21a, and four electrodes (18b, 19b,
20b and 21b) are almost the same rectangular electrodes, and are not distinguished in advance as a ground electrode or an output electrode in the range of the element itself.

In the present embodiment, when a signal is applied to the transducer 2, the SAWs having opposite directions propagate under the electrodes 18a, 19a, 20a, 21a as shown by the arrows in FIG. Between 4 pairs of electrodes facing each other (18a-18b, 19a-19b, 20a-
A convolution signal is generated between 20b and 21a-21b). At this time, the terminals 22b from the electrodes on the back surface,
When 23b, 24b and 25b are all grounded, the signals appearing at 22a and 24a with respect to the ground potential are in-phase and exactly the same. Similarly, the signals appearing at 23a and 25a are exactly the same signals. However, for example, 18a-18
Considering the signal between b, 22a is grounded and the signal is 2
When it is taken out from 2b, it is totally 180 ° regardless of the signal and frequency when 22b is grounded and output from 22a.
It is clear that signals with opposite phases are obtained. Therefore, for example, 22b, 2 in the lead terminals of each electrode
When 3b is connected to the ground and the terminals 22a and 23a are connected to take an output, an output signal which is the sum of the signals generated in both regions is obtained. Also, the terminals 22b and 23a are connected to the ground and the terminals 22a and 23b are connected. When the signals are concatenated to obtain an output, a difference output signal is obtained. In other words, the function of the external element shown in FIGS. 6 and 7 and the function of the transducer having a different shape shown in FIG. 8 can be realized by disposing electrodes on the back surface. FIG. 2 shows an example of a combination of terminals and a method of grounding when the sum / difference signals are simultaneously taken out using a schematic diagram. Here, the sum output signal can be taken out from the terminal 26 and the difference output signal can be taken out from the terminal 27. Table 1 shows the relationship between the combination of terminals and the obtained sum and difference output signals.

[0014]

[Table 1]

SAW convolvers are roughly classified into three types, elastic type, separation medium type, and monolithic type, depending on the source and structure of the non-linearity to be used.
Of these, the elastic type and monolithic type are currently the mainstream due to the ease of manufacturing. Basically, the present invention can be applied to both of these, and for the elastic type, the first embodiment which has already been described can be applied as it is. However, in the monolithic type, the piezoelectric substrate usually has a laminated structure of piezoelectric thin film 28 / insulating film 29 / low-concentration impurity diffusion semiconductor 30 / high-concentration impurity diffusion semiconductor 31 /, as shown in the sectional view of FIG. Generally, the back surface is a low resistance layer having an ohmic electrode. Therefore, in the structure of the first embodiment, even if the electrodes themselves formed on the back surface are separated, the potentials on the back surface side of the substrate in the four regions between the transducers become uniform through the low resistance layer. Therefore, FIG. 4 shows a perspective view of the surface of a second embodiment of the present invention which solves this problem for the monolithic type, and FIG. 5 shows its sectional view. In the second embodiment of the present invention, a groove 32 is formed for separating at least the four electrodes 18b, 19b, 20b, 21b on the back surface of the substrate 1 from each other including the high-concentration impurity diffusion low-resistance semiconductor regions above them. Has been done. As a result, even in the monolithic type, the four electrodes independently appear in the potential on the back surface side of the substrate 1, and the operation of the present invention obtained in the first embodiment can be realized.

In the present invention, the region between the input transducers is divided into four regions by four electrodes arranged on the front surface of the substrate and four electrodes arranged on the rear surface of the substrate so as to face each other. It can be considered that the two regions adjacent to each other along the SAW propagation direction form one track in total. That is, the area between the transducers can be considered to be formed by two tracks.

In the description of the operation of the present invention, in both the first and second embodiments, two pairs of input transducers are provided at the ends of the element in the SAW propagation direction, straddling two tracks. Even if an independent transducer is provided for each track, and a total of four pairs of transducers are used per track, the effect of the present invention is not particularly impaired.

Further, in the second embodiment suitable for the monolithic DPSK convolver, the structure in which the groove is provided as the means for separating the four regions is shown, but this means electrically separates the low resistance portion of the four regions. Since it is intended to do so, it is possible to substitute it by forming an impurity diffusion region of opposite type (p-type impurity in n-type region, n-type impurity in p-type region) diffusion region.

Further, although the present invention can be applied to either an elastic type convolver or a monolithic type convolver, particularly when it is applied to an elastic type convolver, LiNbO ₃ (niobium) having a high elastic nonlinear efficiency is used as a substrate material. Lithium acid) single crystals are preferred. Further, as the monolithic convolver, it is advantageous to use a ZnO (zinc oxide) thin film / Si (silicon) structure or an AlN (aluminum nitride) Si structure suitable for high frequencies.

[0020]

As described above, according to the present invention, a means for obtaining a complicated and expensive output signal of sum and difference and a transducer which is difficult to keep the phase difference constant over a wide band are used outside the element. Instead, by properly combining and connecting the output terminals, the sum and difference output signals can be easily obtained.

[Brief description of drawings]

FIG. 1 is a top view showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of an output extraction method according to the first embodiment.

FIG. 3 is a sectional view of a monolithic SAW convolver.

FIG. 4 is a top view of the second embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along the line AB of the second embodiment of the present invention.

FIG. 6 is a top view of a DPSK convolver having a first conventional structure.

FIG. 7 is a top view of a DPSK convolver having a second conventional structure.

FIG. 8 is a top view of a DPSK convolver having a third conventional structure.

[Explanation of symbols]

 1 substrate 2a, 2b SAW transducer 18a-21b electrode 22a-25b output terminal

Claims (3)

[Claims] 1. A first four electrodes formed on the front surface of a piezoelectric substrate and divided and arranged in parallel in a propagation direction of a surface acoustic wave to be transmitted, and formed on a back surface of the piezoelectric substrate. A second four electrodes configured to face the above four electrodes, and a terminal configured to take out a signal generated between the opposing first and second electrodes, And a surface acoustic wave device comprising: at least a pair of input transducers arranged outside the electrodes formed on the surface of the substrate along the propagation direction. 2. The surface acoustic wave device according to claim 1, wherein the first and second electrodes are connected so as to obtain sum and difference output signals. 3. The surface acoustic wave device has a monolithic structure, and a region where the second electrode is formed is 4
The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is divided into two parts.