JPH0621752A - Surface acoustic wave element and demodulator using thereof - Google Patents

Abstract

PURPOSE:To make the circuit small and provide the demodulation circuit with less deterioration in the signal quality by fabricating the demodulation circuit through the use of a surface acoustic wave element having a delay circuit function so as to omit the use of a delay circuit and a multiplier or the like. CONSTITUTION:An input electrode exciting a surface acoustic wave and an output electrode converting the surface acoustic wave into an electric signal are provided on a piezoelectric substrate of a surface acoustic wave element, either electrode of the electrodes 12, 13 has plural taps (1-N) and the other electrode has two taps (p1, p2), and let a center interval of the two taps (p1, p2) be L[m], let a transmission speed of an input signal inputted to the input electrode be A[bit/sec], let a propagation speed of the surface acoustic wave be V[m/sec], then the relation of L=nV/A is satisfied substantially, where (n) is a positive integer. The demodulation circuit of the demodulator is fabricated by employing the above-mentioned surface acoustic wave element.

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 device,
In particular, the present invention relates to a surface acoustic wave tapped delay line in which one of the input / output electrodes is composed of a plurality of taps, and a demodulator using the same.

[0002]

2. Description of the Related Art A surface acoustic wave is a wave in which energy is concentrated and propagates in the vicinity of the surface of a substrate, and signals can be easily input and output on the surface of the substrate, and it is attracting attention as a signal processing element.

FIG. 6 is a diagram showing a conventional surface acoustic wave device. The operating principle will be described below with reference to FIG.

In the figure, an input electrode 12 for exciting a surface acoustic wave and an output electrode 13 for converting the surface acoustic wave into an electric signal are arranged and formed on a piezoelectric substrate 11. The input electrode 12 is composed of a plurality of taps provided at equal intervals on the surface acoustic wave propagation path. Each tap is formed of a so-called comb-shaped electrode, and each tap is composed of one pair or a plurality of pairs of electrode fingers.

When a signal is applied to the input electrode 12, a surface acoustic wave is excited at each tap. The surface acoustic waves excited by each tap are combined and propagated toward the output electrode 13. Since the combined surface acoustic wave is converted into an electric signal at the output electrode 13, the output is a combined output obtained by time-sampling the input signal.

The polarity of the surface acoustic wave can be switched by the arrangement of the electrode fingers in each tap, and as a result, the sum of the values to which the polarities of each tap are added is sampled as an output. . Therefore, by setting the polarity of each tap appropriately, the tap operates as a correlator, and the output becomes maximum when the input signal and the tap pattern of the input electrode 12 match.

This surface acoustic wave element functions similarly even if the input electrode and the output electrode are exchanged. In that case, the output becomes maximum when the input signal and the tap pattern of the output electrode of the surface acoustic wave element match. .

FIG. 7 is a diagram showing a conventional demodulation device using the conventional surface acoustic wave element shown in FIG. In the figure, the received signal is input to the conventional surface acoustic wave element 20 through an amplifier, a filter, a frequency converter and the like (not shown). The output of the surface acoustic wave element 20 is divided into two, one of which is directly input to the multiplier 25 and the other of which is input to the multiplier 25 after passing through the delay circuit 26. When a signal modulated by a predetermined code sequence is received and coincides with the tap pattern of the surface acoustic wave element 20, as an output of the surface acoustic wave element,
Correlation peak appears.

Here, the tap pattern of the surface acoustic wave element 20 matches the code sequence of 1-bit signal. Therefore, a correlation peak appears from the surface acoustic wave element 20 for each bit of the signal, and the modulation information of the signal is stored in this correlation peak. That is, in the case of the phase modulation signal, the phase modulation information is stored in the carrier of the correlation peak.

The output of this surface acoustic wave element is divided into two, one is directly input to the multiplier 25, the other is delayed by a signal of n bits, and the signal is input to the multiplier 25 to perform n-bit differential detection. To demodulate the signal.

[0011]

As described above, since the conventional surface acoustic wave device does not include a device having a positive delay circuit function, a demodulation circuit is manufactured using this surface acoustic wave device. In order to do so, it is necessary to particularly include the delay circuit as shown in the above-mentioned conventional example.

However, since the delay circuit generally has a large loss, an amplifier must be inserted before and / or after the delay circuit, and a non-linear element called a multiplier must be used. Is large and the signal quality is deteriorated.

(Object of the Invention) An object of the present invention is to realize a surface acoustic wave device having a delay circuit function and to manufacture a demodulation circuit using the same, thereby obtaining a delay circuit and a multiplication which have been conventionally required. The object is to provide a demodulation circuit in which the circuit and the like are omitted and the signal quality is less deteriorated by omitting the devices and the like.

[0014]

In order to solve the above-mentioned problems, a surface acoustic wave device of the present invention is provided with an input electrode for exciting a surface acoustic wave on a piezoelectric substrate and converting the surface acoustic wave into an electric signal. An output electrode is provided, one of the input electrode or the output electrode is composed of a plurality of taps, the other electrode is composed of two taps, and the center line distance L [m] of the two taps is The transmission speed of the input signal input to the input electrode is A [bit / sec], and the propagation speed of the elastic surface is V
[M / sec], n is a positive integer, and L = nV / A is substantially satisfied.

Another object of the present invention is to solve the above-mentioned problems by a demodulator using the surface acoustic wave element described above.

[0016]

According to the present invention, two taps are connected to L = nV / A
By detecting the output level of the surface acoustic wave element in which the electrodes arranged apart from each other as the input electrode or the output electrode are detected, it is possible to easily determine whether the two data n-1 bits apart have the same sign or different signs. Therefore, when the demodulation circuit is configured using the surface acoustic wave device of the present invention, the delay circuit and the multiplier are not required, the circuit scale can be reduced, and the deterioration of the signal quality can be suppressed.

[0017]

[First Embodiment] FIG. 1 is a schematic view showing a first embodiment of a surface acoustic wave device according to the present invention.

In FIG. 1, reference numeral 11 is a piezoelectric substrate. As the piezoelectric substrate 11, for example, a piezoelectric material such as quartz or lithium niobate can be used.

Reference numeral 12 is an input electrode arranged and formed on the surface of the substrate 11. The input electrode 12 is a comb-shaped electrode and is made of a conductor such as aluminum, silver, or gold. The input electrode 12 is composed of N taps arranged at equal intervals on the surface acoustic wave propagation path.

Reference numeral 13 denotes an input electrode 1 on the surface of the substrate 11.
2 is an output electrode arranged and formed so as to face 2.
The output electrode 13 is a comb-shaped electrode and is made of a conductor such as aluminum, silver or gold. The output electrode 13 is composed of two taps p1 and p2 which are arranged on the surface acoustic wave propagation path at appropriate intervals. Here, the distance L [m] between the center lines of the taps is A [bit / sec] of the transmission speed of the input signal input to the input electrode, and V is the propagation speed of the surface acoustic wave.
As [m / sec], L = V / A is substantially satisfied. The tap p1 and the tap p2 have the same shape and the same polarity. Therefore, the electric signal is taken out in phase with the unmodulated surface acoustic wave.

The present embodiment will be described in detail below.

When a signal is applied to the input electrode 12, the surface acoustic wave is excited and propagates toward the output electrode 13. Here, the input electrode 12 has N taps, and the signal 1
It has a length of one bit. The surface acoustic waves generated at each tap are superposed and propagated toward the output electrode 13. Therefore, when the signal 1 bit matches tap 1 to tap N, the superposed surface acoustic waves propagate as a correlation peak signal. At the output electrode 13, the surface acoustic wave is converted into an electric signal at each tap, combined by two taps, and taken out. Here, since the distance L between the center lines of the two taps substantially satisfies L = V / A, the tap p2 is different from the output from the tap p1 near the input electrode 12.
The output from is a signal 1 / A [seconds] ago, that is, a signal 1 bit before. The output from the output electrode 13 becomes a combined output of the output of the tap p1 and the output of the tap p2. Therefore, if the output from the tap p1 and the output from the tap p2 have the same phase, the outputs are added, and if they have the opposite phase, they are canceled.

Therefore, a large correlation peak is obtained when two consecutive bits of the signals input to the surface acoustic wave element of this embodiment have the same phase, and no correlation peak is obtained when the signals have opposite phases. Data can be easily demodulated by simply detecting the output level of the surface acoustic wave element.

In particular, when the signal is a DPSK signal, the magnitude of the output level of the surface acoustic wave element directly corresponds to "1" and "0" of the data, so that the demodulation can be performed more easily.

The distance L between the two taps is L = nV
If it is configured to satisfy / A (n is a positive integer), then n
Bit delay detection can be performed.

[Second Embodiment] FIG. 2 is a schematic view showing a second embodiment of the surface acoustic wave device according to the present invention.

In this embodiment, the two taps p1 and p2 of the output electrode 14 have different shapes and opposite polarities. Therefore, it differs from the first embodiment only in that the signal is extracted in the opposite phase with respect to the unmodulated surface acoustic wave signal.

In this embodiment, the same effect as that of the first embodiment can be obtained. However, in the present embodiment, when two consecutive bits of the signal input to the surface acoustic wave element have opposite phases,
A large correlation peak appears in the output, and in the case of the same phase, the output is canceled.

[Third Embodiment] FIG. 3 is a schematic view showing a third embodiment of the surface acoustic wave device according to the present invention.

In this embodiment, the surface acoustic wave device of the first embodiment and the surface acoustic wave device of the second embodiment are arranged and formed on the same substrate, and the input electrode 12 is composed of two surface acoustic wave devices. Have in common.

In this embodiment, since the two elements are formed on the same substrate, the functions can be diversified and the overall scale when using the two elements can be reduced.

In the present embodiment, the input electrode 12 is shared by the two surface acoustic wave devices, but it goes without saying that the same effect can be obtained if they are provided separately for each.

It goes without saying that the same effect can be obtained by exchanging the input electrode 12 and the output electrodes 13 and 14 in the first and second embodiments.

In the first, second and third embodiments, the input electrode 12 and the output electrodes 13 and 14 are double electrodes (strip electrodes) so that the input electrode 12 and the output electrodes 13 and 14 are The reflection of surface acoustic waves can be suppressed.

Furthermore, in the first, second, and third embodiments, the piezoelectric substrate 11 is not limited to a piezoelectric crystal such as quartz or lithium niobate, but a piezoelectric film is added to a semiconductor or glass substrate, for example. It may be a structure.

[Fourth Embodiment] FIG. 4 is a block diagram of a demodulator using the surface acoustic wave device of the present invention as a fourth embodiment of the present invention.

In the figure, 20 is a surface acoustic wave element of the present invention, 21 is a detection circuit for envelope detection of the output of the surface acoustic wave element 20, and 22 is data "1" or "1" depending on the output from the detection circuit 21. It is a data determination circuit for determining "0". In the figure, an amplifier, a filter, etc. are omitted for simplification, but if necessary, they may be inserted before and / or after each circuit.

This embodiment will be described in detail with reference to FIG. The received signal is input to the surface acoustic wave element 20 through an amplifier, a filter, a frequency conversion circuit, etc. (not shown). The surface acoustic wave element 20 is the surface acoustic wave element of the present invention, and particularly, in the taps of the output electrode as shown in FIG. 1, the taps in the half area near the input electrode and the half area far from the input electrode are provided. A certain tap is a surface acoustic wave element configured by the same tap series (the input electrode and the output electrode of the surface acoustic wave element may be interchanged).

Here, the received signal is a signal obtained by further modulating a phase-modulated signal with a predetermined code sequence, a so-called spread spectrum signal. When two consecutive bits of this signal have the same phase, the surface acoustic wave element 20 outputs the signal. A large correlation peak is output, and no output is obtained when the phase is opposite. Therefore, the data demodulation is performed by inputting the output of the surface acoustic wave element 20 to the detection circuit 21, extracting the envelope, and determining by the data determination circuit 22 whether or not the signal level exceeds a predetermined threshold value. .

Here, the surface acoustic wave element 20 is a surface acoustic wave element as shown in FIG. 2, that is, two taps of the output electrode are converted into electric signals in opposite phases to the unmodulated surface acoustic wave. It may be a surface acoustic wave element configured as described above (the input electrode and the output electrode of the surface acoustic wave element may be replaced). In this case, no output is obtained when two consecutive bits of the signal input to the surface acoustic wave element 20 have the same phase, and a large correlation peak is obtained when they have opposite phases.

[Fifth Embodiment] FIG. 5 is a block diagram showing another embodiment of a demodulator using the surface acoustic wave element of the present invention as a fifth embodiment of the present invention.

In the figure, 201 and 202 are the first and second surface acoustic wave devices 211 and 2 of the present invention, respectively.
12 is the first surface acoustic wave device 201 and the second surface acoustic wave device 201, respectively.
2 is a detection circuit for envelope-detecting the output from the surface acoustic wave element 202, 23 is a comparison circuit for comparing the output levels of the detection circuit 211 and the detection circuit 212, and 24 is a demultiplexer. It should be noted that although an amplifier, a filter, and the like are omitted in the figure for simplification, they are inserted at the front stage and / or the rear stage of each circuit as necessary.

This embodiment will be described in detail with reference to FIG. The received signal is input to the demultiplexer 24 and divided into two through an unillustrated amplifier, filter, frequency conversion circuit, etc., one is input to the first surface acoustic wave element 201, and the other is input to the second elastic surface. It is input to the wave element 202.

The first surface acoustic wave element 201 is the surface acoustic wave element of the present invention, and in particular, the tap and the input electrode in the half region near the input electrode among the taps of the output electrode as shown in FIG. This is a surface acoustic wave element in which the taps in the far half area are formed of the same tap series (the input electrode and the output electrode of the surface acoustic wave element may be exchanged).

The second surface acoustic wave element 202 is a surface acoustic wave element as shown in FIG. 2, that is, the tap series in the half of the taps of the output electrode far from the input electrode is close to the input electrode. Is a surface acoustic wave element constituted by a series in which the phases of the tap series in the region are reversed (the input electrode and the output electrode of the surface acoustic wave element may be exchanged).

Here, if the received signal is a signal modulated with a predetermined code, that is, a so-called spread spectrum signal, the output of the first surface acoustic wave element 201 is output when two consecutive bits of the signal have the same phase. A large correlation peak appears, and in the case of the opposite phase, a large correlation peak appears in the output of the second surface acoustic wave element 202. Therefore, the first surface acoustic wave element 2
Data demodulation can be performed by inputting the outputs of 01 and the second surface acoustic wave element 202 to the detection circuits 211 and 212 respectively, extracting the envelope, and comparing the levels of both.

In this embodiment, two surface acoustic wave devices 201 are used.
Since the data levels are compared by comparing the output levels of 202 and 202, the level of the received signal is stronger than that of the demodulator of the fourth embodiment.

Further, the first and second surface acoustic wave devices 201 and 202 of this embodiment may be integrated into one as shown in FIG.

[0049]

As described above, according to the surface acoustic wave device of the present invention, it is possible to detect the output level of the device.
It is possible to obtain the effect that it is possible to determine whether consecutive two-bit or n-bit separated signals have the same phase or opposite phases. For this reason,
When a demodulation circuit is configured using this, a delay circuit and a multiplier can be omitted, so that the circuit scale can be reduced and deterioration of signal quality can be suppressed.

[Brief description of drawings]

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

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

FIG. 3 is a schematic view showing a third embodiment of the surface acoustic wave device according to the present invention.

FIG. 4 is a block diagram showing a first embodiment of a demodulation device according to the present invention.

FIG. 5 is a block diagram showing a second embodiment of the demodulation device according to the present invention.

FIG. 6 is a schematic view showing a conventional surface acoustic wave element.

FIG. 7 is a block diagram showing a conventional demodulation device.

[Explanation of symbols]

 11 substrate 12 input electrode 13, 14 output electrode 20, 201, 202 surface acoustic wave device 21, 211, 212 detection circuit 22 data judgment circuit 23 comparison circuit 24 demultiplexer p1, p2 tap

Claims (13)

[Claims] 1. A piezoelectric substrate is provided with an input electrode for exciting a surface acoustic wave and an output electrode for converting the surface acoustic wave into an electric signal, and one of the input electrode or the output electrode has a plurality of electrodes. The other electrode is composed of two taps, and the distance between the center lines of the two taps is L
[M], the transmission speed of the input signal input to the input electrode is A [bit / sec], and the propagation speed of the surface acoustic wave is V
[M / sec], where n is a positive integer, and is configured to substantially satisfy L = nV / A. 2. The input electrode is an electrode having the plurality of taps, the output electrode is an electrode composed of the two taps having the same polarity, and when the unmodulated signal is input to the input electrode, the output The surface acoustic wave device according to claim 1, wherein the electric signals output from the electrodes have the same phase. 3. The input electrode is an electrode having the plurality of taps, the output electrode is an electrode composed of the two taps having opposite polarities, and when a non-modulated signal is input to the input electrode, The surface acoustic wave device according to claim 1, wherein the electric signals output from the output electrodes have opposite phases. 4. The input electrode is an electrode composed of the two taps having the same polarity, the output electrode is an electrode having the plurality of taps, and is output when an unmodulated signal is input as an input signal. The surface acoustic wave element according to claim 1, wherein the electric signals that overlap each other have the same phase. 5. The input electrode is an electrode composed of the two taps having opposite polarities, the output electrode is an electrode having the plurality of taps, and when an unmodulated signal is input as an input signal, an output is produced. The surface acoustic wave element according to claim 1, wherein the electric signals to be overlapped overlap each other in opposite phases. 6. A piezoelectric substrate is provided with an input electrode for exciting a surface acoustic wave and an output electrode for converting the surface acoustic wave into an electric signal, and one of the input electrode or the output electrode has a plurality of electrodes. The other electrode is composed of two taps, and the distance between the center lines of the two taps is L
[M], the transmission speed of the input signal input to the input electrode is A [bit / sec], and the propagation speed of the surface acoustic wave is V
[M / sec], wherein n is a positive integer, and a surface acoustic wave element configured to substantially satisfy L = nV / A is used. 7. In the surface acoustic wave device, the input electrode is an electrode having the plurality of taps, and the output electrode is an electrode composed of the two taps having the same polarity,
The demodulator according to claim 6, wherein when an unmodulated signal is input to the input electrode, the electric signals output from the output electrode have the same phase. 8. In the surface acoustic wave device, the input electrode is an electrode having the plurality of taps, and the output electrode is an electrode composed of the two taps having opposite polarities.
The demodulator according to claim 6, wherein when a non-modulated signal is input to the input electrode, an electric signal output from the output electrode has an opposite phase. 9. In the surface acoustic wave device, the input electrode is an electrode composed of the two taps having the same polarity, the output electrode is an electrode having the plurality of taps, and an unmodulated signal is used as an input signal. 7. The demodulator according to claim 6, wherein, when is input, the output electric signals overlap each other in phase. 10. In the surface acoustic wave device, the input electrode is an electrode composed of the two taps having opposite polarities, the output electrode is an electrode having the plurality of taps, and an unmodulated input signal is provided. The demodulator according to claim 6, wherein when the signals are input, the output electric signals are overlapped in opposite phases. 11. A demultiplexer for demultiplexing a received signal into at least two, first and second surface acoustic wave elements, and outputs of the first and second surface acoustic wave elements are respectively detected. At least a first and a second detection circuit and a comparison circuit for comparing the output levels of the first and the second detection circuits are provided, wherein the first surface acoustic wave element serves as an input electrode, It has an electrode having a plurality of taps and an electrode composed of the two taps having the same polarity as an output electrode, so that when an unmodulated signal is input as an input signal, the electric signals output have the same phase. The second surface acoustic wave element has an electrode having the plurality of taps as an input electrode, and an electrode having the two taps of opposite polarities as an output electrode. , No modulation signal as input signal When you enter the demodulation device according to claim 6, characterized in that the electrical signal output is configured to be opposite phase. 12. The first surface acoustic wave device has an electrode having the plurality of taps as an output electrode, and an electrode made of the two taps of the same polarity as an input electrode, When a non-modulated signal is input as the signal, the output electric signals are configured to overlap each other in phase, and the second surface acoustic wave element includes an electrode having the plurality of taps as an output electrode. , An electrode composed of the two taps having opposite polarities as an input electrode, and when an unmodulated signal is input as an input signal, the electric signals to be output are overlapped in opposite phases. The demodulation device according to claim 11, wherein 13. The demodulator according to claim 6, wherein the input signal is a spread spectrum signal.