JPH04249911A - Surface acoustic wave convolver - Google Patents

Abstract

PURPOSE:To offer a surface acoustic wave convolver displaying high convolution efficiency and with high yield in manufacturing and a communication system using the same. CONSTITUTION:This convolver is the surface acoustic wave convolver provided with a feature that a multi-strip coupler 7 is provided between plural waveguides 4-1 to 4-n which propagate surface acoustic waves excited from excitation electrodes 2, 3 in reverse directions with each other and an electrode 5 for output which converts the surface acoustic waves generating at the waveguides 4-1 to 4-n and propagating the surface acoustic waves in a direction traversing the surface acoustic waves to electrical signals in the surface acoustic wave convolver provided with at least two excitation electrodes 2, 3 which excite the surface acoustic wave on a piezoelectric substrate 1, the plural waveguides 4-1 to 4-n, and at least one electrode 5 for output.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave convolver, and more particularly to a split waveguide type surface acoustic wave convolver which takes out a convolution signal of two signals via a split waveguide.

0002

2. Description of the Related Art Surface acoustic wave convolvers are becoming increasingly important in recent years as key devices for spread spectrum communications. In addition, many applications as real-time signal processing devices are being considered and are being actively researched.

FIG. 8 is a schematic plan view showing an example of such a conventional surface acoustic wave convolver.

In the figure, a pair of input comb-shaped electrodes 32 and a center electrode 33 are provided on a piezoelectric substrate 1. The comb-shaped electrode 32 is an electrode that excites surface acoustic wave signals, and the center electrode 33 is an electrode that propagates the surface acoustic wave signals in opposite directions and extracts an output signal.

A signal F(t)e is applied to one side of the comb-shaped electrode 32.
xp(jωt) and the other signal G(t)exp(jωt), two surface acoustic waves F(t-x/v)exp[jω(t -x/v)]・
...(1a) and G(t-(L-x)/v)exp[jω(t-(L
-x)/v)]...(1b) is propagated. here,
v is the surface acoustic wave velocity, and L is the length of the central electrode 33.

On this propagation path, a component of the product of the above-mentioned surface acoustic waves is generated due to the nonlinear effect, and this component is transmitted to the center electrode 33
It is integrated and extracted over the range of . This output signal H(t
) is expressed by the following formula.

[0007]

[Math 1] Here, α is a proportionality constant.

[0008] Thus, two signals F from the center electrode 33
A convolution signal of (t) and G(t) can be obtained.

However, since such a configuration is generally not efficient enough, "Nakagawa et al., Transactions of the Institute of Electronics and Communication Engineers '8
6/2, Vol. j69-C, No. 2, pp190~
198, a surface acoustic wave convolver as shown in FIG. 9 is proposed.

Note that the coordinate axes shown in FIG. 9 are added for convenience and do not mean the crystal axes of the substrate.

In FIG. 9, 11 is a piezoelectric substrate;
Reference numerals 2 and 13 denote two comb-shaped electrodes for surface acoustic wave excitation, which are formed on the surface of the substrate 1 so as to be opposed to each other at an appropriate distance in the x direction. 14-1, 14-2,..., 14-n
are waveguides extending in the x direction between the electrodes 12 and 13 and formed parallel to each other on the surface of the substrate 11. Reference numeral 15 designates an output comb-shaped electrode formed on the surface of the substrate 11 at an appropriate distance from the waveguide in the y direction.

In this surface acoustic wave convolver, when an electric signal with an angular frequency ω is input to the comb-shaped electrodes 12 and 13 for excitation of surface acoustic waves, a surface acoustic wave of the frequency is excited, and the surface acoustic wave is transmitted through the waveguide 14. -1,14-2,...,14
-n propagate in opposite directions to each other in the x-axis direction, and a surface acoustic wave with an angular frequency of 2ω that propagates in the y-axis direction is generated in the waveguide due to a parametric mixing phenomenon. This surface acoustic wave reaches the output comb-shaped electrode 15, and a convolution electric signal of the above two input signals can be obtained at the output comb-shaped electrode 15.

[0013]

[Problems to be Solved by the Invention] However, in the surface acoustic wave convolver shown in FIG.
It is necessary to increase the length of 14 to n. Since the length of the output comb-shaped electrode is equal to the length of the waveguide, the length of the output comb-shaped electrode naturally increases as the interaction length increases.

Furthermore, the width of the output comb-shaped electrode finger is determined by the frequency of the convolution signal and the propagation speed of the surface acoustic wave of the substrate, so the line width becomes narrower as the input center frequency becomes higher.

For example, 128°Y.X LiN
Input center frequency 200MHz using bO3 single crystal
, in the case of a segmented waveguide type convolver with an interaction length of 6 μs, the output comb-shaped electrode fingers have a line width of 2 μm and a length of 20 mm.

The electrode finger resistance of this comb-shaped electrode is approximately 2 kΩ per comb-shaped electrode, and there is a problem in that the convolution efficiency is lowered due to this electrode finger resistance.

[0017] Furthermore, in the conventional output interdigital transducer as described above, the width of the electrode fingers is as narrow as several μm, whereas the length is long, ranging from several mm to several tens of mm, making it difficult to manufacture. However, there was a problem of poor yield.

(Object of the Invention) An object of the present invention is to solve the problems of the prior art described above, and to provide a surface acoustic wave convolver that exhibits high convolution efficiency and has a good production yield, and a communication system using the same. It's about doing.

[0019]

[Means and Effects for Solving the Problems] The above objects of the present invention include at least two excitation electrodes that excite surface acoustic waves on a piezoelectric substrate, and that the surface acoustic waves excited from the excitation electrodes are directed in opposite directions. In a surface acoustic wave convolver, the surface acoustic wave convolver has a plurality of waveguides for propagating the surface acoustic waves, and at least one output electrode for converting the surface acoustic waves generated in the waveguides and propagating in a direction transverse to the surface acoustic waves into electrical signals, This can be achieved by a surface acoustic wave convolver characterized in that a multi-strip coupler is provided between the waveguide and the output electrode.

Further, the surface acoustic wave convolver is characterized in that the multi-strip coupler converts the beam width of the surface acoustic wave generated in the waveguide and outputs it to the output electrode. It is an attempt to solve problems.

That is, in the configuration of the present invention described above, the beam width of the surface acoustic wave incident on the output electrode can be made smaller by using the multi-strip coupler. The length can be shortened. Thereby, the electrode finger resistance of the output electrode can be reduced and the convolution efficiency can be improved.

[0022] Also, since it is easy to manufacture the output electrode,
Manufacturing yield can also be improved.

[0023]

Embodiment Embodiment 1 FIG. 1 is a schematic plan view showing a first embodiment of a surface acoustic wave convolver according to the present invention.

Note that the coordinate axes in the figures are added for convenience and do not mean the crystal axes of the substrate.

In FIG. 1, 1 is a piezoelectric substrate. As the piezoelectric substrate, for example, a piezoelectric substrate such as lithium niobate can be used.

Reference numerals 2 and 3 designate surface acoustic wave excitation electrodes which are formed on the surface of the substrate 1 to face each other at an appropriate distance in the x direction. The electrodes 2 and 3 are comb-shaped electrodes made of a conductor such as aluminum, silver, or gold, and are provided so that surface acoustic waves propagate in the ±x directions.

4-1, 4-2,..., 4-n are the electrodes 2,
The waveguides are formed by extending in the x direction between the three waveguides and being arranged parallel to each other at a constant pitch on the surface of the substrate 1.

Regarding these waveguides, please refer to “
It is described in detail in ``Surface Acoustic Wave Engineering'', Institute of Electronics and Communication Engineers, pages 82-102, and includes types such as thin film waveguides and topographic waveguides. In the present invention, a Δv/v waveguide whose substrate surface is coated with a conductor such as aluminum, silver, or gold is preferred.

5 is the waveguide 4-1 on the surface of the substrate 1.
This is an output comb-shaped electrode formed at an appropriate distance from ~4-n in the y direction. It is designed to efficiently convert the signal into an electrical signal.

A multi-strip coupler 7 is formed on the surface of the substrate 1 between the electrode 5 and the waveguide 4-1. The multi-strip coupler is made of a conductor such as aluminum, silver, or gold, and by appropriately selecting the number and pitch of the strips constituting the multi-strip coupler, the surface acoustic waves propagating through the propagation path A can be efficiently transmitted. It can be transferred to propagation path B.

Regarding multi-strip couplers, C.
Maerfeld, G. W. Farnell, “N.
onsymmetrical multistrip
coupler as a surface-wave
beam compressor of large
Bandwidth”Electron. let
t. 9, pp. 432-434 (1973).

In the surface acoustic wave convolver of this embodiment, the center angular frequency ω is set to one of the excitation comb-shaped electrodes 2.
When an electric signal is input, a surface acoustic wave is excited from the excitation electrode 2 and enters the waveguides 4-1 to 4-n. Similarly, when an electric signal with a center angular frequency ω is input to the other excitation comb-shaped electrode 3, a surface acoustic wave is excited from the excitation electrode 3 and enters the waveguides 4-1 to 4-n. .

Excited by the excitation electrodes 2 and 3, respectively,
The surface acoustic waves propagating in opposite directions from both ends of the waveguides 4-1 to 4-n are caused by a parametric mixing phenomenon on the waveguides 4-1 to 4-n, resulting in a center angle that propagates in the ±y-axis direction. Surface acoustic waves with a frequency of 2ω are generated on both sides.

Here, the beam width d1 of this surface acoustic wave is
is equal to the length of each waveguide 4-1 to 4-n.

Furthermore, this surface acoustic wave corresponds to a convolution signal of the signals input to the electrodes 2 and 3, respectively.

[0036] This surface acoustic wave is then incident on the multi-strip coupler 7. In the multi-strip coupler 7, the surface acoustic wave incident on the propagation path A with a beam width d1 is emitted onto the propagation path B with a beam width d2, and is incident on the output comb-shaped electrode 5.

Therefore, the divided waveguides 4-1 to 4-n
Since the beam width of the surface acoustic wave generated by the waveguide is narrowed from d1 to d2 by the multi-strip coupler 7, the electrode length of the output comb-shaped electrode 5 is the same as that of the waveguides 4-1 to 4-n.
d2 can be made shorter than the length of . (Embodiment 2) FIG. 2 is a schematic plan view showing a second embodiment of a surface acoustic wave convolver according to the present invention.

In this figure, members similar to those in FIG. 1 are given the same reference numerals.

In this embodiment, the multi-strip coupler 7
, 8 and the output comb-shaped electrodes 5 and 6 form the waveguides 4-1 to 4-n.
are arranged and formed symmetrically on both sides.

In this embodiment, the same effects as in the first embodiment can be obtained, but in addition, in this embodiment, the surface acoustic waves generated in the waveguide are directed in both directions of the ±y axis. Therefore, by outputting these from the two output comb-shaped electrodes 5 and 6 and combining them, it is possible to obtain an output twice that of the first embodiment. In addition, by making the distances from the waveguides 4-1 to 4-n different between the two output comb-shaped electrodes 5 and 6, the output from one output comb-shaped electrode is transferred from the other output comb-shaped electrode. The output can be delayed by an appropriate time.

FIG. 3 is a block diagram showing an example of a communication system using the surface acoustic wave convolver as described above. In FIG. 3, reference numeral 125 indicates a transmitter. This transmitter spreads the spectrum of the signal to be transmitted,
It is transmitted from antenna 126. The transmitted signal is received by the antenna 120 of the receiver 124 and the received signal 101
is input to the frequency conversion circuit 102. The IF signal 103 converted into a frequency matching the input frequency of the surface acoustic wave convolver by the frequency conversion circuit 102 is input to the surface acoustic wave convolver 104 of the present invention as shown in FIG. 1 or 2. Here, the IF signal 103 is input to one input comb-shaped electrode of the convolver, for example, the comb-shaped electrode 2 in FIG.

On the other hand, the reference signal 106 output from the reference signal generation circuit 105 is input to the other input comb-shaped electrode of the surface acoustic wave convolver 104, for example, the comb-shaped electrode 3 in FIG. Then, in the convolver 104, a convolution calculation (correlation calculation) is performed between the IF signal 103 and the reference signal 106 as described above, and an output signal (conversion A rotation signal) 109 is output.

This output signal 109 is input to the synchronization circuit 108. The synchronization circuit 108 receives synchronization signals 111 and 11 from the output signal 109 of the surface acoustic wave convolver 104.
2 are generated and input to the reference signal generation circuit 105 and despreading circuit 107, respectively. Reference signal generation circuit 105
Then, the timing of the reference signal 106 is adjusted using the synchronization signal 111 and outputted. The despreading circuit 107 uses the synchronization signal 112 to return the IF signal 103 to the signal before being spread spectrum. This signal is converted into an information signal by a demodulation circuit 110 and output. FIG. 4 shows a configuration example of the despreading circuit 107.

In FIG. 4, 121 is a code generator;
3 is a multiplier. The code generator 121 includes a synchronous circuit 1
The synchronization signal 112 output from the code 12 is inputted, and the timing is adjusted by this synchronization signal 112.
2 is output. The IF signal 103 and the code 122 are input to the multiplier 123, and the result of multiplying the IF signal 103 and the code 122 is output. At this time, IF signal 103 and code 1
22, the IF signal 103 is converted into a signal before being spread spectrum and is output.

Note that if the frequency of the received signal 101 matches the input frequency of the surface acoustic wave convolver 104, the frequency conversion circuit 102 is not necessary, and the received signal 101
may be directly input to the surface acoustic wave convolver 104 through an amplifier and a filter. Further, in FIG. 3, the amplifiers and filters are omitted to make the explanation easier to understand, but amplifiers and filters may be inserted before or after each block as necessary. Furthermore, in this embodiment, the transmitted signal is received by the antenna 120, but the antenna 1
The transmitter and receiver may be directly connected by a wired system such as a cable without using the transmitter 20.

FIG. 5 is a block diagram showing a first modification of the receiver 124 in the communication system of FIG. Figure 5
In this figure, the same members as those in FIG. 3 are given the same reference numerals, and detailed explanations will be omitted.

In this example, a synchronous follow-up circuit 113 is provided,
The IF signal 103 is also input to the synchronous follow-up circuit 113. In addition, the synchronization signal 11 output from the synchronization circuit 108
2 is input to the synchronous follow-up circuit 113, and the synchronous follow-up circuit 11
A synchronizing signal 114 outputted from 3 is input to the despreading circuit 107. The example differs from the example shown in FIG. 3 in these points. Examples of the synchronous follow-up circuit include a tau dither loop circuit and a delay lock loop circuit, and any of them may be used.

In this embodiment as well, the same effects as in the example of FIG.
After roughly synchronizing in , the synchronization tracking circuit 113 synchronizes more precisely and performs synchronous tracking.
Out-of-synchronization is less likely to occur, and the error rate can be lowered.

FIG. 6 is a block diagram showing a second modification of the receiver 124 in the communication system of FIG. Figure 6
In this figure, the same members as those in FIG. 3 are given the same reference numerals, and detailed explanations will be omitted.

In this example, the output from the surface acoustic wave convolver 104 is input to the detection circuit 115, and demodulation is performed using the output of the detection circuit 115. The detection circuit 115 includes a synchronous detection circuit, a delay detection circuit, and an envelope detection circuit, which can be used depending on the signal modulation method.

Now, assuming that the received signal 101 is a signal that has been modulated with phase modulation, frequency modulation, amplitude modulation, etc.
The output 109 from the surface acoustic wave convolver 104 reflects the modulation information. In particular, the length d of the waveguide of the surface acoustic wave convolver 104 is such that the time per data bit of the received signal 101 is T, and the surface acoustic wave velocity is v.
If d=vT is satisfied, the modulation information appears at the output 109 as it is. For example, the phase modulated signal f
Assume that (t)exp(jθ) is transmitted and this signal is received as the received signal 101.

At this time, when the reference signal g(t) 106 is input to the surface acoustic wave element 104, its output 109 is
f(t)exp(j θ)g(τ−t)dt = e
xp(j θ)f(t)g(τ-t)dt...(
3), and phase modulation information appears. Therefore, the output 109 of the surface acoustic wave element 104 is detected by an appropriate detection circuit 115.
It can be demodulated by passing it through.

FIG. 7 is a block diagram showing a third modification of the receiver 124 in the communication system of FIG. Figure 7
In this figure, the same members as those in FIG. 6 are given the same reference numerals, and detailed explanations will be omitted.

In this example, a synchronous circuit 108 is provided, and the output 109 of the surface acoustic wave converter 104 is connected to the synchronous circuit 10.
8 is entered. Further, a synchronization signal 111 is outputted from the synchronization circuit 108 and inputted to the reference signal generation circuit 105. In these respects, this example differs from the example shown in FIG.

In this embodiment as well, the same effects as in the example of FIG. control, it is possible to achieve stable synchronization.

The present invention can be applied in various ways other than the embodiments described above. For example, by using the surface acoustic wave excitation electrodes 2 and 3 in the first and second embodiments as double electrodes (split electrodes), reflection of surface acoustic waves at the surface acoustic wave excitation electrodes 2 and 3 is suppressed. can.

Similarly, by making the output comb-shaped electrodes 5 and 6 double electrodes (split electrodes), reflection of surface acoustic waves at the comb-shaped electrodes 5 and 6 is suppressed, and the characteristics of the surface acoustic wave convolver are further improved. It can be made into a good one.

Furthermore, in the first and second embodiments,
The substrate 1 is not limited to a piezoelectric single crystal such as lithium niobate, but may be any material and structure that has a parametric mixing effect, such as a structure in which a piezoelectric film is added to a semiconductor or glass substrate.

In the first and second embodiments described above, the surface acoustic wave excited by the surface acoustic wave excitation electrode is directly guided to the waveguide, but a horn is provided between the excitation electrode and the waveguide. A beamwidth compressor such as a type waveguide or a multi-strip coupler may also be provided.

[0060]

As described above, according to the present invention, by providing a multi-strip coupler between the waveguide and the output comb-shaped electrode, the length of the output comb-shaped electrode can be increased compared to the conventional one. Can be shortened. Therefore, the electrode finger resistance of the output comb-shaped electrode can be reduced, and the convolution efficiency can be improved.

Furthermore, since the output comb-shaped electrode can be manufactured easily, the manufacturing yield can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing a first embodiment of a surface acoustic wave convolver according to the present invention.

FIG. 2 is a schematic plan view showing a second embodiment of a surface acoustic wave convolver according to the present invention.

FIG. 3 is a block diagram showing an example of a communication system using the surface acoustic wave convolver of the present invention.

FIG. 4 is a block diagram showing a specific configuration example of the despreading circuit of FIG. 3;

FIG. 5 is a block diagram showing a first modification of the receiver of FIG. 3;

FIG. 6 is a block diagram showing a second modification of the receiver of FIG. 3;

FIG. 7 is a block diagram showing a third modification of the receiver of FIG. 3;

FIG. 8 is a schematic diagram showing a first example of a conventional surface acoustic wave convolver.

FIG. 9 is a schematic diagram showing a second example of a conventional surface acoustic wave convolver.

[Explanation of sign]

1 Substrate, 2, 3 Electrode for surface acoustic wave excitation, 4-1
~4-n waveguide element, 5,6 output comb-shaped electrode,
7,8 Multi strap coupler

Claims (2)

[Claims] 1. At least two excitation electrodes that excite surface acoustic waves on a piezoelectric substrate; a plurality of waveguides that propagate surface acoustic waves excited from the excitation electrodes in opposite directions; In a surface acoustic wave convolver having at least one output electrode that converts a surface acoustic wave generated and propagated in a direction transverse to the surface acoustic wave into an electrical signal, between the waveguide and the output electrode, A surface acoustic wave convolver characterized by being equipped with a multi-strip coupler. 2. The multi-strip coupler converts the beam width of surface acoustic waves generated in the waveguide,
The surface acoustic wave convolver according to claim 1, wherein the surface acoustic wave convolver outputs to the output electrode.