JPS58190116A - Elastic convolver - Google Patents

Abstract

PURPOSE:To secure a necessary length of an output electrode even if a short piezoelectric substrate is used, by using a surface acoustic wave guide path including at least >=1 curve part to form an output electrode which extracts a convolution signal. CONSTITUTION:A substrate 1 is made of a material like LiNbO3, etc. having a large performance exponent M that shows the intensity of a nonlinear interaction. Then roller-screen type converters 2 and 3 which convert an electric signal into a surface acoustic wave are formed on the surface of the substrate 1, and at the same time beam compressors 4 and 5 are provided on an extending line in the propagating direction of the surface acoustic wave to decrease the beam width of the surface acoustic wave. Then two surface acoustic waves signals passed through the compressors 4 and 5 are made incident to a U-shaped convolution signal extracting electrode 6 through end surfaces opposite to each other. Thus a convolution signal having carrier angle frequency 2omega is obtained. In this case, an earth electrode 7 is provided along the electrode 6 to secure a reference potential.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an elastic convolver that extracts conpolis regions of surface acoustic wave signals propagating in opposite directions by utilizing the nonlinear effect of a sonic propagation medium.

Recently, spread spectrum communication methods have been attracting attention as communication methods have been promoted to 1% degree.

The spread spectrum communication method has a much larger frequency band (for example, 1,000
2) It transmits over a wide frequency band, and then sends it out again at the receiver, making it very effective in removing interference waves. The ideally achieved interference rejection ratio is equal to the process gain given by the product of the duration T of one chip of the signal and the bandwidth W of the transmitted signal. However, if the encoded waveform changes over time in such a way as to cause a disturbance or a disturbance to occur, intentional disturbance is possible, and some or all of the process gain can be seen to be lost. For example, in a frequency hopping system, which is one type of spread spectrum communication, the carrier wave frequency is changed for each pulse of a series of pulse trains forming each beta pit. Since the receiver knows the sequence of changes in advance, it is possible to tone the signal to II. On the other hand, in order for a jammer to cause interference, it is necessary to interfere over the entire band or to determine in advance what the carrier frequency of the next pulse will be.

In addition to the interference wave removal effect described above, a communication system that can arbitrarily change the transmission waveform has many advantages. In line with this trend, it is strongly desired that the device (correlator) that receives the spread spectrum signal be programmable, and the elastic convolver is attracting a lot of attention due to its simple structure and high performance. has been done.

Elastic convolver is lithium niobe)
Two surface acoustic wave signals are propagated in opposite directions on a piezoelectric medium such as (LiNbO5), and a composite output of these two signals is obtained. To obtain this composite signal, if some physical nonlinear frequencies of the medium for surface acoustic waves are both ω, the output signal has a carrier frequency of 2ω, and L is uniformly used as the output detection electrode. A thin metal film is used. The required length of the metal thin film electrode is 1. The length of l step of the signal to be received is τ (Mc).
.

If the surface acoustic wave velocity is t-sa (m/s-e), then υ
Must be greater than T. υ is usually 4000~4o
o.

(#l/, e, ), so a relatively long signal, for example τ
In order to obtain a convolution of No. 16 with =50 μMe, 15 to 20C11 is required as L. The shape of a conventionally known output electrode is a rectangle that extends along the propagation direction of a surface acoustic wave. Therefore, in order to handle the above signal length, the length of the piezoelectric substrate must be 15 to 204 or more.
Therefore, it is difficult to obtain a crystal substrate, and even if it can be obtained, it is extremely expensive. Furthermore, there have been many problems in manufacturing, such as difficulty in mask manufacturing and ease of damage during manufacturing.

An object of the present invention is to improve the above-mentioned drawbacks, that is, to provide a two-stick convolver which has the necessary length of convolution output electrodes despite using a shorter piezoelectric substrate than the conventional one.

According to the present invention, the first and second interdigital transducers that excite surface acoustic wave signals are disposed on the piezoelectric substrate, and the surface acoustic wave signals from the two award converters are propagated in opposite directions to each other. In the elastic convolver, the output electrode is provided with an output electrode that extracts a convolution signal of the two signals using the nonlinear effect of It has a characteristic structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to drawings showing embodiments. The figure shows an example of the elastic convolver according to the present invention.
For example, LiNb0. etc. are desirable materials. On the surface of this piezoelectric substrate, there are interdigital transducers 2 and 3 that convert electrical signals into surface acoustic waves, and a beam that narrows the beam width of the surface acoustic waves on the extension of the direction in which the surface acoustic waves propagate. Compressors 4 and 5, and an output electrode 6 for guiding the compressed $29 surface wave beam and extracting the convolution of these two signals are formed. All of these patterns (interdigital transducer beam compressor, output electrode, etc.) are made of conductive thin films;
Usually produced using photolithography technology. The manufacturing process is well known to those skilled in the art and will therefore be omitted.

Now, the beam widths of the two surface acoustic wave signals having the same angular frequency ω excited by the interdigital electrodes 2 and 3 are compressed by beam width compressors 4 and 5, respectively. Although a horn-type compressor is used as the beam width compressor in this embodiment, other types such as a compressor using a multi-strip coupler, etc. may also be used. Furthermore, the beam width compressor can be omitted by using a curved interdigital transducer that excites spherical surface acoustic waves, or by using a chirped interdigital transducer that directly excites narrow beam width surface acoustic waves efficiently. It is. The reason why it is necessary to narrow the beam of the surface acoustic wave signal is as follows. That is, as is well known, the open-ended output voltage Vo (RMS value) of a surface acoustic wave convolver is proportional to the product of two human acoustic power densities P1a/W, P, and a/W.
It is expressed by the following formula.

Vo=Pea (P, *-Pea)' (1) Here, M is the figure of merit of the nonlinear substrate material, Pea.

Pem is the human acoustic power, and W is the beam width. As is clear from the above equation, by narrowing W, the convolution output voltage Vo can be increased.

Normally, the beam width of a narrowed surface acoustic wave is about three times the wavelength of the surface acoustic wave.

The surface acoustic wave signals passing through the beam width intensifiers 4 and 5 are converted into a U-shaped convolution signal extraction electrode 6.
The light enters from opposite end faces. Since this '#jL pole 6 also has the function of a waveguide for surface waves, the surface waves propagate along this waveguide,
Both surface waves overlap each other. Then, the non-sparity of the substrate material relative to the surface waves: L'/3 ratio occurs at the electrode 6. A ground electrode 7 arranged in parallel along the output m-pole 6 is selected as the reference potential. In the embodiment, the ground electrode 7 is installed only on one side of the electrode 6, but it may be installed on both sides, or it may be installed at a position facing the electrode 6 on the surface of the 4&.

The known elastic convolver had a structure in which two input transducers and an output 11L pole were arranged in a straight line. Therefore, in order to obtain a 1g component with a longer duration, the length of the output electrode had to be increased proportionately, which required a larger piezoelectric substrate. On the other hand, if the U-shaped waveguide shown in the above embodiment is used, the effective substrate length required to form the waveguide can be reduced to 1/2 or less. Similarly, if an S-shaped waveguide having two curved waveguides is used, for example, the length can be reduced to 1/3 or less.

A more desirable condition for the output electrode 6 is that the convolution efficiency be constant regardless of location. Therefore, it is necessary that the right side of equation (1) is constant at all positions of the waveguide electrode 6. However, the performance improvement number M generally varies depending on the cut of the substrate and the propagation direction of the surface acoustic wave. Therefore, in order to correct this, it is sufficient to change the width W of the electrode 6 along the propagation direction and keep M/W constant.

For example, if the substrate 1 is Y (Y) LzNbO, and the propagation directions of the nine surface acoustic waves excited by the interdigital transducers 2 and 3 are two axes, then M for the surface waves propagating in these two directions is the X direction propagation. This is about three times as large as in the case of .

Therefore, it is desirable that the electrode width of the curved waveguide electrode section 8 be approximately 1/3 of the electrode width of the straight section.

As explained above, according to the present invention, it is possible to realize an elastic convolver having the required convolution electrode length using a piezoelectric substrate that is less than half the length of the conventional piezoelectric substrate, thereby reducing the cost and manufacturing of the crystal substrate. Its industrial value, such as its ease of use, is enormous.

[Brief explanation of the drawing]

The figure shows an embodiment of the elastic convolver according to the present invention. 1 is a piezoelectric substrate, 2 and 3 are interdigital transducers for input, 4.5 is a beam width compressor for surface acoustic waves, and 6 is a converter. The electrode for taking out the evolution signal, 8 is a ground electrode.

Claims (2)

[Claims] (1) First and second interdigital transducers that excite surface acoustic wave signals are placed on a piezoelectric substrate, and the surface acoustic wave signals from both transducers are propagated in opposite directions to suppress the nonlinear action of the substrate. In the elastic convolver equipped with an output '#tfi for weaving a composite signal of the two signals, the output electrode is composed of a surface acoustic wave waveguide including at least one curved portion. Features an elastic convolver. (2) Let W be the width of the output 11L pole and M be the nonlinear figure of merit for surface acoustic waves of the substrate material, and then set W so that M/W is one foot along the length direction of the output electrode. A two-stick convolver according to claim 1, characterized in that: