JPH036916A - Surface acoustic wave convolver - Google Patents

Abstract

PURPOSE:To obtain only a convolution signal of a corresponding input signal by extracting an output signal obtained at an output terminal of each gate electrode via a balance-unbalance converter in response to the input signal applied to each input transducer. CONSTITUTION:Input transducers are formed as the identical structure, 1st and 3rd transducers 22, 22' connect to a terminal 32 as if input signals were applied in in-phase and 2nd and 4th transducers 23, 23' connect to a terminal 33 as if input signals were applied in opposite phase. Moreover, 1st and 2nd output gate electrodes 24, 24' are connected deferentially to balance terminals 34, 34' of a balance-unbalance converter 31. Thus, reflected waves of the opposite electrodes 23, 23' are cancelled at the terminal 33 and not caused. Since the waves are propagated on the separate gate electrodes on the convolver chip, they are not interfered together to obtain a large cancellation effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave convolver, and particularly to improvements for suppressing self-convolution.

[Summary of the invention] In a surface acoustic wave convolver, two piezoelectric bodies or one piezoelectric body are provided with two gate electrodes, four or three input transducers are arranged for these electrodes, and output from each gate electrode is provided. Self-convolution is suppressed by extracting the signal through a balanced-unbalanced converter.

[Prior Art] Recently, spread spectrum communication has been attracting attention as a communication method. A correlation function is required in the reception section of this spread spectrum communication, and since the surface acoustic wave convolver has this correlation function, it is an indispensable and important component in spread spectrum communication.

For conventional surface acoustic wave convolvers, elements having the following three structures have been proposed.

(a) The separation medium structure element is an element in which, for example, silicon, which is a semiconductor, and lithium niobate, which is a piezoelectric material, are bonded with a slight gap.

(b) For example, the elastic structure element has an input comb-shaped electrode and an output gate electrode formed on a lithium niobate substrate,
This element utilizes the elastic nonlinearity of lithium niobate, which is a piezoelectric material.

(c) The layered structure is an element in which zinc oxide is formed as a piezoelectric film on a silicon substrate, which is a semiconductor, by sputtering or the like.

Conventionally, a surface acoustic wave (SAW) convolver consisting of the above-mentioned elements has SAW Sl from input electrode (input transducer) 2 and 5AW from input electrode 3 as shown in FIG.
As a result of the nonlinear interaction between S and S on the output gate electrode 4, a convolution signal is generated on the output gate electrode 4,
It can be taken out as an electrical signal from the output terminal 7.

In the figure, 1 is a piezoelectric substrate, and 8 and 9 are sound absorbing materials. However, as shown in FIG. 4, the SAW S from input electrode 2 propagates to the right, and
5AWS□ is reflected by this input electrode 3 and propagates to the left again. Similarly, 5AWSs from input electrode 3 propagates to the left and reaches the other input electrode 2, where SAWS,
There is 5AWSsm that is reflected and propagates to the right again.

As is clear from the above, in addition to the SAW S□ and 88 convolution signals, 5AWSz, Si1, and SAWS
m and s. The convolution signal of is also output from gate electrode 4
are output at the same time. In this way, the reflection from the counter electrode is due to the re-radiation phenomenon in which the SAW enters the counter electrode, where it is converted into an electrical signal, and then generates the SAW again, and the discontinuity in acoustic impedance caused by the presence or absence of metal on the counter electrode. This is due to reflection.

Here, 5AWS Yu and S1□ and SAW S2 and S.

The convolution of is self-convolution (S
It is called elf-Convolution.

This self-convolution is output as a convolution signal even when an input signal containing information is not input, or it is mixed into the original convolution signal, causing amplitude ripple and phase ripple, and the self-convolution component is suppressed. have to,
As a means for suppressing this self-convolution, there is a SAW convolver with a double track structure shown in FIG. According to this, the input transducers (IDTs) 10.11 corresponding to the first track radiate in-phase SAWs due to the geometrical arrangement of their comb-shaped electrodes, and the input transducers (IDTs) 12. 13 emits a reverse phase SAW due to its geometrical arrangement. Therefore, the SAW incident on each counter electrode has its ID
Due to the phase relationship on T, if the amplitudes of the incident waves are the same,
It can be seen that there is no cancellation and re-radiation phenomenon, and therefore self-convolution does not occur. In addition, in Fig. 3, L4, 15 is an output gate electrode, 18 is a balanced-unbalanced converter, 16.17 is an input terminal, and 19
is the output terminal.

[Problems to be solved by the invention] However, this system has two
Since the two tracks are placed very close to each other, interference between the tracks occurs, and the incident waves are not canceled on the opposing electrodes as expected in theory, resulting in a self-convolution component remaining in the output signal.

[Object of the Invention] An object of the present invention is to provide a surface acoustic wave convolver that has a simple configuration and has means that can easily suppress self-convolution.

[Means for Solving Problem A] In order to achieve the above object, a first invention includes a first output gate electrode formed in contact with a first piezoelectric body; a first and a second input transducer disposed on both ends of the first gate electrode; a second output gate electrode formed in contact with the second piezoelectric body; and third and fourth input transducers respectively disposed on both ends of the second gate electrode, and at least the first and fourth input transducers. Second. Third. The fourth input transducers have the same structure, and the first and third input transducers are connected so that signals are applied in the same phase, and the second and fourth input transducers are connected to receive signals in opposite phases. is applied thereto, and the first and second output gate electrodes are differentially connected to the balanced side terminals of the balanced-unbalanced converter.

Further, a second invention includes a first input transducer formed in contact with a piezoelectric body, a first output gate electrode and a first output gate electrode disposed on both ends of the first input transducer in contact with the piezoelectric body. the second output gate electrode, and the first output gate electrode in contact with the piezoelectric body and the first output gate electrode
a second Kugata transducer disposed on the opposite side of the input transducer; and a second Kugata transducer disposed on the opposite side of the first input transducer with respect to the second output gate electrode in contact with the piezoelectric body. 3 input transducers; The second and third input transducers are formed to have the same structure, and the second and third input transducers are connected so that signals are applied in opposite phases, and the first and second output gate electrodes are connected to each other so that signals are applied in opposite phases. The gist is that the balanced side terminals of the balanced-unbalanced converter are differentially connected.6 [Function] The output signal obtained at the output terminal of each gate electrode is transmitted in accordance with the input signal applied to each input transducer. By extracting through the balanced-unbalanced converter, the self-convolution components are canceled and only the convolution signal of each corresponding input signal can be obtained.

[Examples] The present invention will be described below with reference to examples shown in the drawings. FIG. 1 shows an embodiment of a SAW convolver according to the present invention. In the same figure, 20.21 includes first and second piezoelectric bodies, and a first . The second convolver chips 24 and 24' are first and second output gate electrodes formed in contact with the first and second piezoelectric bodies, respectively, and the first and second convolver chips 22, 23, 22', and 23' are the first The first piezoelectric body is in contact with the second piezoelectric body. The first output gate electrodes 24 and 24' each have a width of 1g arranged on both ends thereof. 2nd, 3rd. Fourth input transducer (IDT), 2
5.25' are the output terminals of the gate electrodes, 26°26'
, 28.28' are the input terminals of the input transducers, 27.27' and 29.29' are the grounded input terminals of the input transducers, 1o is the output signal extraction terminal, 11 is the balanced-unbalanced converter, and 32 .3
3 is an input signal application terminal.

Each input transducer is of equal construction, the first and third transducers 22.22' being connected to the terminal 32 such that the input signals are applied in phase, and the second and fourth input transducers 23.23'' is connected to the terminal 33 so that the input signal is applied in reverse phase. Also number 1. The second output gate electrode 24.24' is differentially connected to the balanced terminal 34.34' of the balanced-unbalanced converter 31.

When an input signal is applied to the input terminal 32, the in-phase signal is transmitted to the input terminal 26.27 of each convolver chip 20.21, and the in-phase SAW is transmitted from each IDT 22, 22'.
is emitted and propagates on the gate electrode 24°24,
The waves are received on the respective opposing electrodes 23°231. Here, the counter electrodes 23, 23' of the separate convolver chips are
The wires are connected through the terminals 28 and 29 so as to have opposite phases, and reach the terminal 33. Therefore, the reflected waves at the counter electrodes 23, 23' are canceled at the terminal 33.

Since the signals propagate on the gate electrodes of separate convolver chips, they do not interfere with each other and have a large canceling effect.On the contrary, when an input signal is applied to the input terminal 33, the signal propagates on the gate electrodes of the respective convolver chips 20 and 21. 28
, 29, and the respective IDTs 23, 23
A SAW with a phase difference of 180° is emitted from ', propagates on the gate electrode 24, and is further received on the counter electrode 22.22'.
6. Connected through 27 so that they are in phase.

The terminal 32 is reached. Therefore, the SAWs propagating with one phase difference of 180 degrees are received by the IDTs 22 and 22' having the same phase, and are canceled at the terminal 32.

Also, the electrical performance of the IDT may vary, or the terminal 3
2.33 Due to different electrical conditions, the signal received by the counter electrode is not completely canceled and returns as a reflected wave, resulting in a self-convolution component.However, Counter electrode 23.2
3' and the counter electrodes 22 and 22' are in phase between the convolver chip 21 and the convolver chip 20. This is convolver chip 2
At 0, the phase difference between the input signals of IDT22.22' and IDT23.23' is zero;

In the convolver chip 21, since the phase difference between the input signals of the IDTs 22 and 22' and the IDTs 23 and 23' is 180 degrees, the phase difference between the self-convolutions of the convolver chips 20 and 21 becomes zero. Depends on what happens.

On the other hand, for the same reason, the main convolution will be out of phase. Therefore, an in-phase self-convolution and an anti-phase main convolution appear at the output terminals 25, 25' of each convolver chip. Therefore, when the output terminal 25 of the convolver 20 and the output terminal 25 of the convolver chip 21 are connected to the balanced side of the balanced-unbalanced converter 31 that receives differential input, the in-phase "self-convolution" is canceled and the main convolution is Since the phase is opposite, it is added to the unbalanced side of the balanced-unbalanced transformer, terminal 3.
0, only the convolution signal of each input signal is output. In this way, self-convolution can be achieved by using two surface acoustic wave convolvers with the same characteristics and making simple external connections in a simple surface acoustic wave convolver configuration without particularly changing the shape of the IDT or the shape of the gate electrode. can be suppressed significantly.

FIG. 2 shows another embodiment of the present invention, in which a convolver chip 4.
A first input transducer (ID
T) 43 is formed, and first . Second output gate electrodes 45 and 46 are arranged. 42.44 is the second. With the third input transducer (IDT), the first . The second and third input transducers each have equal construction.

The second and third input transducers 42,44 are connected to the input terminal 59 such that the input signals are applied in opposite phase. Output terminals 53.54 of the first and second output gate electrodes 45.46 are differentially connected to balanced terminals 55.56 of a balanced-unbalanced converter 58. 48 and 5
1 is the second. This is the ground terminal of the third input transducer 42.44.

The self-convolution generation mechanism in the structure shown in FIG. 2 can be divided into the following three types.

First, the input signal applied to the input terminal 49 is the ID
T43 converts the light into SAW and radiates it to the left and right.

One SAW is received by the IDT 42, and the other SAW is received by the IDT 42 connected in reverse phase to the IDT 42.
The signals are received by the terminals 59 and converted into electrical signals, which have the same magnitude and a phase difference of 180°, and are canceled at the terminal 59.

There is no re-radiation and self-convolution is suppressed.

Second, the input signal applied to the input terminal 59 is divided into two through the terminal 47 of the input transducer 42 and the input terminal 52, the SAW is radiated from the IDT 2 toward the IDT 43, and at the same time, the SAW is radiated from the IDT 44 toward the IDT.
43, and the IDT 43 always receives SAWs of equal magnitude and opposite phase from both sides, so that they are canceled at T43 and re-radiation is suppressed on both sides.

Third, the input signal applied to the input terminal 59 is
, is divided into two through the terminal 52, and is connected to the SA from the IDT42.
W is emitted toward IDT43, and at the same time IDT44
The SAW is emitted toward the IDT43, and the
Two SA-Ws arrive towards T43. ID
The reflection at T43 is the second case, in which the SAW is transmitted, and the transmitted SAW becomes self-convoluted with the SAW from the counter electrode, and is generated on the two gate electrodes 45 and 46. These self-convolutions are in phase with each other.

To summarize the above about self-convolution,
In the first and second cases, if the amplitude of the input signal is equal in each input part and the phase difference is 180°, no reflected wave is generated and self-convolution does not appear on the two gate electrodes.

The third case is self-convolution that does not depend on reflection, and is self-convolution due to the SAW transmitted through the central IDT 43 and the SAW directly transmitted from the counter electrode, both of which appear on the two gate electrodes.
The phase difference between them is in phase. Further, the two gate electrodes are differentially connected to a balanced-unbalanced converter 58. Therefore, the third self-convolution described above is performed by the balanced-unbalanced converter 5.
Cancelled by 8. Thus.

Since the convolution signals on the two gate electrodes are in opposite phases and the self-convolutions are in phase, all self-convolutions are canceled and only the convolution signals are output from the output terminal 57 of the balanced-unbalanced converter. be done.

In this embodiment, since the two gate electrodes are arranged in a line in the long side direction of the convolver chip, there is almost no interference between the gate electrodes, so the canceling effect is large.

Further, by configuring the convolver structure on one wafer chip, self-convolution is significantly reduced as described above. Furthermore, a feature of the structure of the convolver described above is that the input transducers are arranged not only at both ends of the convolver chip but also at the center. Transducer input terminal 49
If a data signal is applied to both sides, SAW is emitted to both sides, so there is no so-called bidirectional loss, and output efficiency is improved.

[Effects of the Invention] As described above, according to the present invention, self-convolution in a SAW convolver can be suppressed with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are schematic diagrams showing embodiments of the present invention, respectively;
FIG. 3 is a schematic diagram showing a conventional SAW convolver, and FIG. 4 is an explanatory diagram of convolution and self-convolution. 20.21・・・・・・・・・1st. Second convolver chip, 22.22', 23.23'...
first to fourth input transducers (IDT), 24;
25・・・・・・・・・1st. second output gate electrode, 3
1...Balanced-unbalanced converter.

Claims (2)

[Claims] (1) A first output gate electrode formed in contact with the first piezoelectric body, and first and second output gate electrodes respectively disposed on both ends of the first gate electrode in contact with the first piezoelectric body. an input transducer, a second output gate electrode formed in contact with the second piezoelectric body, and third and fourth output gate electrodes respectively disposed on both ends of the second gate electrode in contact with the second piezoelectric body. an input transducer, wherein at least the first, second, third, and fourth input transducers have the same structure, and a signal is applied to the first and third input transducers in the same phase. the second and fourth input transducers are connected such that signals are applied in opposite phases, and the first and second output gate electrodes are connected to the balanced side terminals of the balanced-unbalanced converter. A surface acoustic wave convolver characterized by differential connection. (2) a first input transducer formed in contact with the piezoelectric body; a first output gate electrode and a second output gate electrode disposed on both ends of the first input transducer in contact with the piezoelectric body; a gate electrode; a second input transducer in contact with the piezoelectric body and disposed on the opposite side of the first input transducer with respect to the first output gate electrode; a third input transducer disposed on the opposite side of the first input transducer with respect to the output gate electrode, the first, second and third input transducers having the same structure; 2 and a third input transducer are connected so that signals are applied in opposite phases, and the first and second input transducers are
A surface acoustic wave convolver characterized in that an output gate electrode is differentially connected to a balanced side terminal of a balanced-unbalanced converter.