JPH0473804B2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention propagates surface waves in directions opposite to each other from input transducers provided on a substrate near both ends of the substrate, facing each other. , Differential Phiase Shift Keying with two divided output gates between their input transducers
The present invention relates to a surface acoustic wave device used as a convolver (hereinafter abbreviated as DPSK).

B. Summary of the Invention Disclosed is a surface acoustic wave convolver in which an electrode made of a metal film is disposed between two divided output gates in the DPSK convolver. When the distance between the electrode end and the output gate end is l ₁ , the wavelength of the surface acoustic wave is λ ₀ , and a positive integer is n ₁ , l ₁ =n ₁ /2λ ₀ . The convolver can be an elastic convolver or a monolithic convolver made of a piezoelectric film formed on a semiconductor substrate.

C. Prior Art Conventional surface acoustic wave convolvers include (a) a separation medium convolver that couples a semiconductor and a piezoelectric material through a small gap, and (b) an elastic convolver that utilizes the nonlinearity of the piezoelectric substrate itself. (c) A monolithic convolver with a layered structure in which a piezoelectric thin film is formed on a semiconductor substrate is known.

The separation medium convolver shown in (a) has the disadvantage of poor productivity because it is very difficult to control the air gap. (b)
The elastic convolver requires a large amount of surface acoustic wave energy to utilize the elastic nonlinearity of the piezoelectric substrate. On the other hand, elastic convolvers and layered structure monolithic convolvers differ from separation medium convolvers in that they are easy to assemble and thus increase productivity. Furthermore, the layered monolithic convolver shown in (c) utilizes the nonlinearity of the depletion layer capacitance of the semiconductor, so it has high convolution efficiency and
Because of its monolithic structure, it has the advantage of being easy to configure.

A cross-sectional view of the layered monolithic structure is shown in FIG. 5, and a top view is shown in FIG. Here, 1 is a semiconductor layer such as silicon, 2 is a piezoelectric film such as zinc oxide or aluminum nitride, 3 is an input transducer for surface acoustic waves, and 4 is an output gate.
The gate 4 is formed of a metal film such as aluminum.

For example, use a surface acoustic wave convolver for broadband communication.
It is widely known that it can be applied as a signal processing functional element such as Spread Spectrum Communication (hereinafter abbreviated as SSC).
DPSK is often used for data modulation to be transferred in SSC.

In order to convert such a DPSK-modulated signal into a matching wave using a surface acoustic wave convolver, a convolver having the structure shown in FIG. 7 has been proposed. The structure shown in Figure 7 is called a DPSK convolver, and its detailed operation is described by D. Brodtkorb.
and written by JELaynor
Ultrasonics Symposium Bulletin published in 1978
Symposium Proceedings), pages 561 to 566. In FIG. 7, 5 and 6 are output gates, which are separated at the center. 7 is a hybrid for calculating the sum and difference of the signals from both gates 5 and 6. 8,
9 is the hybrid output, 8 is the sum (Σ _put ), 9
outputs the difference ( _Δput ).

D. Problems to be solved by the invention In the DPSK convolver shown in FIG. 7, the outputs from the left and right gates 5 and 6 are two consecutive data
Shows the phase relationship between bits. Normally, the outputs from gates 5 and 6 should be coupled by hybrid 7, but since gates 5 and 6 are very close together, direct electromagnetic coupling (field) occurs between the metals of gates 5 and 6. through) occurs. For this field-through, the hybrid output 8,9
Unwanted wave output occurs in the sum and/or difference output of
This has the drawback of increasing spurious components and deteriorating characteristics.

Furthermore, the edges 10, 1 of the central part of the gate in FIG.
Since 1 is a metal end, it serves as a surface acoustic wave reflection end. Therefore, unnecessary waves are generated due to reflection of the surface acoustic waves at the ends of the central portion, causing characteristic deterioration of the hybrid outputs 8 and 9. Furthermore, this reflected wave causes self-convolution, which becomes a source of characteristic deterioration.

Therefore, an object of the present invention is to provide a surface acoustic wave convolver in which unnecessary waves are suppressed.

E. Means for Solving the Problems In order to achieve the above object, the surface acoustic wave device according to the present invention includes input transducers that are provided facing each other near both ends of the substrate, and In a surface acoustic wave device used as a DPSK convolver in which a surface wave is propagated in the direction of The gist is to include an electrode made of a metal film. The distance between the electrode end and the output gate end is l ₁ , the wavelength of the surface acoustic wave is λ ₀ , and a positive integer is
When n ₁ , l ₁ =n ₁ /2λ ₀ . The electrode made of the metal film is grounded.

F Effect Convolution signals generated at both gates are shielded by metal electrodes, and electromagnetic coupling between both gates is suppressed.

G Embodiment FIG. 1 is a top view of a surface acoustic wave DPSK convolver according to the present invention, in which output gates 5 and 6 divided into two are provided between input transducers 3 provided near both ends. , a metal electrode 12 is provided between the divided gates. A convolution signal of the input signal is obtained by nonlinear effects on the gates 5, 6 of the surface acoustic waves generated by the input transducer 3.

The metal electrode between the two gates is preferably grounded. In that way, the convolution signals generated at both gates are shielded by the metal electrode 12. Therefore, the output gates 5, 6
Among the signals appearing at the output terminals 13 and 14, the signals due to the electromagnetic coupling between the electrodes 5 and 6 are suppressed, and the signals appearing at the output terminals 13 and 14 are suppressed.
Since DPSK demodulation is easier and unnecessary waves are reduced, a high-performance DPSK convolver can be obtained.

FIG. 2 shows an enlarged sectional view of the central portion of FIG. 1. Here, l ₂ is the width of the metal electrode 12,
l ₁ is the distance between both output gates 5 and 6 and the metal electrode 12. When the surface acoustic wave is incident on this central part, the gate ends 10, 11 and the ends 15, 12 of the metal electrode 12,
A reflection occurs at 16. However, each reflective end 1
By combining the reflected waves from 0, 15, 16, and 11, it is possible to cancel the overall reflection by changing the way l ₁ is given. That is, when the distance between the electrode end and the output gate end is l ₁ , the wavelength of the surface acoustic wave is λ ₀ , and a positive integer is n ₁ , then l ₁ = n ₁ /2λ ₀ . Therefore, each reflected wave cancels out each other, and the influence of unnecessary waves is reduced.

It is clear that the above description can be applied to both elastic and layered monolithic convolvers. That is, as shown in FIG. 3, the elastic convolver has an input transducer and an output gate 5 between the input transducer 3 and a metal film such as aluminum on a piezoelectric substrate 17 made of lithium niobate or the like. 6, and a metal electrode 12 is formed between the output gates 5 and 6.

As shown in FIG. 4, the layered structure monolithic convolver has a semiconductor substrate 18 made of silicon or the like.
A piezoelectric film 19 made of zinc oxide, aluminum nitride, etc.
It has a structure in which an input transducer 3, output gates 5 and 6, and a metal electrode 12 are formed thereon. The metal electrode 12 is formed to satisfy l ₁ =n ₁ /2λ ₀ .

H Effects of the Invention As explained above, according to the present invention, in a DPSK surface acoustic wave convolver, the influence of unnecessary waves due to electromagnetic coupling between the two divided output gates and reflection of surface acoustic waves from the gate end is reduced. Furthermore, since self-convolution is suppressed, a high-performance convolver can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a top view of the surface acoustic wave DPSK convolver according to the present invention, FIG. 2 is an enlarged cross-sectional view of the vicinity of the center of FIG. 1, FIG. 3 is a cross-sectional view of the elastic convolver according to the present invention, and FIG. 4 is a cross-sectional view of a layered monolithic convolver according to the present invention, No. 5
6 and 6 are a sectional view and a top view, respectively, of a conventional layered structure monolithic surface acoustic wave convolver, and FIG. 7 is a top view of a conventional DPSK convolver. 3... Input transducer, 5, 6... Output gate, 10, 11... Central end of output gate, 12... Metal electrode, 13, 14... Output terminal, 15, 16... Metal electrode end, 17... piezoelectric substrate, 18... semiconductor substrate, 19... piezoelectric film.

Claims (1)

[Claims] 1 Surface waves are propagated in mutually opposing directions from input transducers provided near both ends of the substrate, and a surface wave is transmitted between the input transducers. In a surface acoustic wave device used as a DPSK convolver provided with two divided output gates, an electrode made of a metal film is provided between the two divided output gates, and the end part of the metal film electrode and the output The distance between the gate ends is l ₁ , the wavelength of the surface acoustic wave is λ ₀ ,
A surface acoustic wave device characterized in that it is configured to satisfy l ₁ =n ₁ /2λ ₀ when n ₁ is a positive integer. 2. The surface acoustic wave device according to claim 1, wherein the electrode made of the metal film is grounded.