JPH09181702A - Surface acoustic wave element and demodulator for spread spectrum communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an output of a correlation peak signal and to obtain a timing signal for generating a timing pulse with high precision. SOLUTION: An input electrode 15, a timing signal electrode 16, an intermediate output electrode 17 and a delay output electrode 18 are formed to a surface acoustic wave element 11 and number of pairs of interdigital electrodes of the timing signal electrode 16 is selected less than number of pairs of interdigital electrodes of the intermediate output electrode 17 and the delay output electrode 18. When an SS signal is given to the input electrode 15, a timing signal is outputted from the timing signal electrode 16 with a shorter output time than that of a correlation peak signal outputted from the intermediate output electrode 17 and the delay output electrode 18.

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 having a structure in which a matched filter and a delay unit are integrally provided and a demodulator for spread spectrum communication provided with the surface acoustic wave device.

[0002]

In recent years, spread spectrum (hereinafter referred to as S) which is resistant to noise and excellent in confidentiality has been developed.
Communication systems have started to attract attention, and along with this, development of transmission / reception devices has been advanced.

Generally, in the SS communication system, an SS signal which is a transmission signal is obtained by first-modulating a predetermined code sequence having a predetermined high bit rate with an information signal, and thereafter,
The modulated signal is secondarily modulated to generate an SS signal in a wide frequency band.

In this case, the above code sequence includes, for example,
There are pseudo noise (Pseudo Random Noise, hereafter abbreviated as PN) series, etc., and direct modulation method (Dire
ct Sequense, hereinafter abbreviated as DS system) or frequency hopping system (Frequency Hopping, hereinafter abbreviated as FH system).

In such an SS communication system, when SS modulation is performed by the DS system using, for example, a PN code sequence, a demodulation device for demodulating the SS signal in the receiver performs SS modulation in the transmitter. The same PN code used at this time is used, and the received SS signal is
It is configured to be extracted as an information signal when it matches the code pattern.

As a demodulation device for an SS communication device, a surface acoustic wave device (Surface Acoustic Wave Device, hereinafter referred to as S) is used because it can be realized with a relatively simple structure.
A matched filter and delay means are configured by an AW element), and transmission data is demodulated based on a correlation peak signal output from the matched filter and delay means. An example is shown in FIG.

In FIG. 3, the matched filter 1 has S
It is composed of an AW element, and the input terminal to which the SS signal is input is connected to the input electrode formed in the cross finger electrode pattern corresponding to the same PN code as in the SS modulation, and the output for outputting the correlation peak signal. The electrodes are connected to the input terminals of the arithmetic circuit 2, the amplifier 3 and the timing pulse generating circuit 4 via the output terminals.

The amplifier 3 amplifies the correlation peak signal given from the matched filter 1 and outputs it to the delay line 5.
The delay line 5 is composed of a SAW element similarly to the matched filter 1, and delays the signal given from the matched filter 1 through the amplifier 3 by one cycle of the PN code and outputs the delayed signal to the arithmetic circuit 2. . The arithmetic circuit 2 is
The product of the information signal supplied from the matched filter 1 and the delay signal supplied from the delay line 5 is calculated, and the calculation result is output to the identification reproduction circuit 6.

The discriminating / reproducing circuit 6 discriminates and reproduces the transmission data based on the timing pulse given from the timing pulse generating circuit 4 with respect to the signal of the operation result given from the arithmetic circuit 2. The timing pulse generation circuit 4 is
Timing pulses required for the reproduction processing of the transmission data in the identification reproduction circuit 6 are generated based on the correlation peak signal given from the matched filter 1 and output to the identification reproduction circuit 6.

By the way, generally, since the conversion efficiency of the SAW element is low, when the matched filter 1 and the delay line 5 are connected to each other as in the above-mentioned configuration, it is necessary to interpose the amplifier 3 and S / There is a problem that the N ratio deteriorates. Therefore, in order to avoid such a problem, FIG.
As shown in FIG. 3, a configuration in which the matched filter 1 and the delay line 5 are integrally provided is considered.

This is an input electrode 8 in which a cross finger electrode pattern is formed on the piezoelectric substrate 7 in a pattern corresponding to the same PN code as in the SS modulation, and an intermediate output electrode in which the cross finger electrode pattern is formed in a normal form. 9 and the delay output electrode 10 are arranged with a predetermined interval. And the input electrode 8
The portion sandwiched between the intermediate output electrode 9 and the intermediate output electrode 9 serves as a matched filter, and the portion sandwiched between the intermediate output electrode 9 and the delay output electrode 10 serves as a delay line. The delay line intervals are periodically output from the matched filter. It is set to the distance that the SAW transmits in the time required for one cycle of the signal to be transmitted.

With the above structure, the information signal is output from the intermediate output electrode 9 corresponding to the output terminal of the matched filter 1, and the delay signal is output from the delay output electrode 10 corresponding to the output terminal of the delay line 5. It According to this structure, since the output signal from the intermediate output electrode 9 is directly input to the delay line in the SAW state, it is not necessary to provide the amplifier 3 unlike the configuration shown in FIG. The adverse effect can be significantly reduced, and the device can be downsized.

By the way, in the SAW element, the larger the number of electrode pairs of the interdigitating electrodes of the intermediate output electrode 9 and the delay output electrode 10 is set, the longer the output time of the output signal becomes. For example, as shown in FIG. 5, the intermediate output electrode 9a and the delay output electrode 10 in which the number of electrode pairs of the interdigital electrodes is 5 are set.
In the configuration in which a is provided, as shown in FIG. 7, the output time of the output signal becomes long, and the intermediate output electrode 9 and the delayed output electrode 10 are provided.
In the configuration of FIG. 4 in which the number of electrode pairs of the interdigital electrode of 1 is 1,
As shown in FIG. 6, the output time of the output signal is shortened. Therefore, the configuration shown in FIG. 5 makes it possible to obtain a more stable signal for demodulation processing than the configuration shown in FIG. This is because if the output time of the correlation peak signal is short, the arithmetic processing in the arithmetic circuit 2 may not be performed accurately.

On the other hand, from the point of view of generating the timing pulse, since the timing signal is generated based on the correlation peak signal and the delay signal, a large number of electrode pairs of the interdigital electrodes are formed as shown in FIG. When the intermediate output electrode 9a and the delayed output electrode 10a are used, the longer the output time of the output signal is, on the contrary, a factor of lowering the accuracy in establishing the timing signal. Therefore, in order to accurately generate the timing signal, the intermediate output electrode 9 having a structure in which the number of electrode pairs of the interdigital electrode as shown in FIG. 4 is small.
The configuration using the delayed output electrode 10 is better. This is because a steep peak can be obtained by shortening the output time of the output signal.

That is, in the case where the matched filter 1 and the delay line 5 are configured as one SAW element as described above, the timing pulse generating circuit 4 to the discrimination reproducing circuit 6 are set as the condition for setting the number of electrode pairs of the interdigital electrodes. There is a trade-off relationship between the condition for outputting the timing pulse at the correct timing and the condition for the accurate calculation processing in the calculation circuit 2. Therefore, in the conventional configuration, the number of electrode pairs of the intermediate output electrode 9 and the delay output electrode 10 must be set to an intermediate value that does not pose a practical problem in consideration of both conditions. As a result, it is the current situation that the characteristics are sacrificed to some extent.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a matched filter and a delay means in one body while being able to sufficiently obtain an output of a correlation peak signal. An object of the present invention is to provide a surface acoustic wave element that can also output a timing signal for generating a timing pulse with high accuracy, and a demodulation device for spread spectrum communication configured using the surface acoustic wave element.

[0017]

A surface acoustic wave device of the present invention is a spectrum composed of a piezoelectric substrate which is a propagation path of a surface acoustic wave, and a plurality of pairs of interdigital electrodes formed at predetermined positions on the piezoelectric substrate. An input electrode to which a diffused signal is input, an intermediate output electrode composed of a plurality of pairs of interdigital electrodes formed at predetermined intervals on the propagation path so as to form a matched filter with the input electrode, A delay output electrode composed of a plurality of pairs of interdigitating electrodes formed at predetermined positions on the propagation path so as to form an intermediate output electrode and a delay means; and a delay output electrode formed on the propagation path of the piezoelectric substrate. It is characterized in that it is provided with a timing signal electrode having an interdigital electrode having a smaller number of electrode pairs than the intermediate output electrode and the delayed output electrode.

According to the above surface acoustic wave device, when the spread spectrum signal is input to the input electrode, the correlation peak signal is output from the intermediate output electrode forming the matched filter and the correlation peak signal is output from the delayed output electrode. 1 than signal
A signal delayed by the period is output, and a signal corresponding to the correlation peak signal can be obtained from the timing signal electrode at a predetermined timing.
Then, in this case, the timing signal electrode is
Since the number of electrode pairs of the interdigital electrode is set to be smaller than that of the intermediate output electrode, it is possible to obtain a signal having an output time shorter than that of the correlation peak signal, so that the accuracy of the timing signal can be improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the surface acoustic wave device of the present invention is applied to a demodulator for spread spectrum communication will be described below with reference to FIGS. 1 and 2. A surface acoustic wave element (hereinafter abbreviated as SAW element) 11 constitutes a matched filter 12 and a delay line 13 as a delay means, and is configured as follows. That is, the piezoelectric substrate 14 formed in a long shape and capable of propagating surface acoustic waves is made of, for example, a single crystal of quartz or a material of ceramic, and has an input electrode 15 and a timing signal electrode on its upper surface. 16, an intermediate output electrode 17, and a delay output electrode 18 are formed.

The input electrode 15 is arranged on one end side of the piezoelectric substrate 14 and is composed of a plurality of pairs of interdigitated electrode electrodes which face each other. Are formed so as to match the bit pattern of the PN code. The timing signal electrode 16 is
The electrodes are arranged at a predetermined distance from the input electrode 15 along the traveling direction of the surface acoustic wave, and are formed in a normal pattern in which the number of electrode pairs of the interdigital electrodes is two.

The intermediate output electrode 17 is arranged at a position spaced apart from the input electrode 15 by sandwiching the timing signal electrode 16 in the traveling direction of the surface acoustic wave.
The interdigitated electrodes are formed in a regular pattern in which the number of electrode pairs is eight. The intermediate output electrode 17 constitutes the matched filter 12 together with the input electrode 15, and is converted from the surface acoustic wave propagating through the piezoelectric substrate 14 when the SS signal matching the cross finger electrode pattern of the input electrode 15 is input. The output signal is output as a correlation peak signal.

The delay output electrode 18 is arranged at a position corresponding to the propagation distance of one cycle of the SS signal along the traveling direction of the surface acoustic wave from the intermediate output electrode 17, and is arranged at the position of the interdigital electrode. The electrodes are formed in a regular pattern in which the number of electrode pairs is eight. Then, this delayed output electrode 18
Is for configuring the delay line 13 together with the intermediate output electrode 17, so that the same correlation peak signal is output as a delay signal after being delayed by one cycle from the timing at which the correlation peak signal is output from the intermediate output electrode 17. It has become.

The timing pulse generating circuit 19 operates on the basis of the signal given from the timing signal electrode 16 to SS.
It outputs a timing pulse synchronized with the signal cycle. The arithmetic circuit 20 includes an intermediate output electrode 17 and a delay output electrode 18.
The signal input from is calculated, and the calculation result is output to the identification reproduction circuit 21.

The discriminating / reproducing circuit 21 discriminates and reproduces the transmission data for the signal of the arithmetic result given from the arithmetic circuit 20 based on the timing pulse given from the timing pulse generating circuit 19. The arithmetic circuit 20 and the identification / reproduction circuit 21 constitute the demodulation means in the present invention.

Next, the operation of the above configuration will be described with reference to FIG. First, in the SAW element 11, when the SS signal is applied to the input electrode 15, the SS signal
When the signal matches the pattern of the interdigital electrodes of the input electrode 15, it propagates toward the timing signal electrode 16 which is a propagation path as a large SAW signal. When this SAW signal reaches the timing signal electrode 16, a part of the SAW signal is converted into an electric signal, and the timing signal electrode 1
A component of the SAW signal which is output from 6 as a timing signal (see FIG. 2A) and does not contribute to the conversion propagates toward the intermediate output electrode 17.

The SAW signal is transmitted to the intermediate output electrode 1
7, when a part of the SAW is converted into an electric signal in the intermediate output electrode 17 and is output as a correlation peak signal from the intermediate output electrode 17 (see FIG. 7B), the remaining SAW
The signal component propagates towards the delayed output electrode 18.

Further, when the SAW signal reaches the delay output electrode 18, a part of the SAW signal is converted into an electric signal in the delay output electrode 18 and is output from the delay output electrode 18 as a delay signal ((c) in the figure). )reference). in this case,
The delayed signal is output at a timing delayed by one period from the correlation peak signal.

In this case, in the SAW element 11, when the SAW signal propagating through the piezoelectric substrate 14 is converted into an electric signal, the output time increases as the number of electrode pairs of the interdigital electrodes of the electrodes to be detected increases. become longer. Therefore,
The number of electrode pairs of the interdigitating electrodes of the timing signal electrode 16 is
Since the number of electrode pairs of the interdigitating electrodes of the intermediate output electrode 17 and the delayed output electrode 18 is set to be smaller, the signal output from the timing signal electrode 16, that is, the timing signal is the intermediate output electrode 17 and the delayed output electrode 18. The output time is shorter than the signal output from. As a result, a signal with a narrow output time width and high accuracy as a timing pulse can be obtained from the timing signal electrode 16.

In the timing pulse generating circuit 19, a timing adjusting circuit (not shown) provided inside the timing pulse generating circuit 19 delays the signal so as to coincide with the output timing of the correlation peak signal output from the intermediate output electrode 17, and a synchronizing circuit (not shown) performs correlation. A signal synchronized with the peak signal is generated and output as a timing pulse.

In the arithmetic circuit 20, the intermediate output electrode 1
Both the information signal output from 7 and the delay signal output from the delay output electrode 18 are subjected to arithmetic processing, and the arithmetic result is output to the identification and reproduction circuit 21.

In the identification / reproduction circuit 21, the signal of the operation result given from the operation circuit 20 is reproduced as transmission data by giving an accurate data identification point by the timing pulse given from the timing pulse generation circuit 19. To do.

As described above, according to the demodulator for SS communication of the present embodiment, since the SAW element 11 is provided with the timing signal electrode 16 for obtaining the timing signal independently, the timing signal is independently provided. Further, the number of electrode pairs of the interdigitating electrodes of the timing signal electrode 16 is set to two, and the number of electrode pairs of the interdigitating electrodes of the intermediate output electrode 17 and the delay output electrode 18 is set to eight. Therefore, the intermediate output electrode 17 and the delay output electrode 18
While the configuration is set to obtain a sufficient output for performing the arithmetic processing, the timing signal electrode 16 can be set to a small number of electrode pairs of the interdigitated electrode which is an appropriate condition of the timing signal. Therefore, it is possible to adopt a configuration in which both conditions are optimally set.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. That is,
Although the timing signal electrode 16 is formed between the input electrode 15 and the intermediate output electrode 17 in the present embodiment, the present invention is not limited to this.
It may be formed at any position between 7 and the delay output electrode 18 or outside the delay output electrode 18.

The number of electrode pairs of the interdigital electrodes of the timing signal electrodes 16 may be one or three or more, which is larger than the number of electrode pairs of the interdigital electrodes of the intermediate output electrode 17 and the delay output electrode 18. Only a few settings are required. It should be noted that it is preferable to use one pair as the timing pulse in order to improve the accuracy, but it is preferable to set a plurality of pairs if one pair is not sufficient according to the level of the detectable signal.

Furthermore, the larger the number of electrode pairs of the interdigitating electrodes of the intermediate output electrode 17 and the delayed output electrode 18, the larger the output can be set, so that the noise resistance characteristic can be improved. . In this case, the number of electrode pairs of the crossing finger electrodes that can be set is determined by the piezoelectric substrate 14
It is the number that can be formed within the defined distance between the two.

[0036]

As is apparent from the above description, according to the surface acoustic wave device of the first aspect, the timing signal electrode is provided in the propagation path of the surface acoustic wave independently of the intermediate output electrode and the delayed output electrode. The timing signal can be obtained independently, and the number of electrode pairs of the interdigitating electrodes of the timing signal electrodes is smaller than the number of electrode pairs of the interdigitating electrodes of the intermediate output electrodes and the delay output electrodes. Since it is configured to be formed, it is possible to obtain sufficient output for performing arithmetic processing on the intermediate output electrode and the delay output electrode, and it is possible to accurately output the timing signal.

According to the demodulator for spread spectrum communication of the second aspect, the timing signal generation means generates the demodulation timing signal based on the output signal obtained from the timing signal electrode, and the demodulation means demodulates the demodulation timing signal. Since the signal obtained from the intermediate output electrode and the delay output electrode is calculated based on the timing signal for demodulation and demodulated and output, an accurate data identification point can be given to the demodulation means, and accurate calculation processing can be performed. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an electrical configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of an output signal from each electrode.

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a diagram showing another conventional surface acoustic wave element.

FIG. 5 is a view corresponding to FIG. 4 showing still another conventional example.

FIG. 6 is a view corresponding to FIG. 2 in FIG.

FIG. 7 is a view corresponding to FIG. 2 in FIG.

[Explanation of symbols]

In the drawing, 11 is a surface acoustic wave element, 12 is a matched filter, 13 is a delay line (delay means), 14 is a piezoelectric substrate, and 15
Is an input electrode, 16 is a timing signal electrode, 17 is an intermediate output electrode, 18 is a delayed output electrode, 19 is a timing pulse generation circuit (timing signal generation means), 20 is an arithmetic circuit (demodulation means), and 21 is an identification reproduction circuit. (Demodulation means).

Claims (2)

[Claims] 1. A piezoelectric substrate serving as a propagation path of a surface acoustic wave, an input electrode composed of a plurality of pairs of interdigital electrodes formed at predetermined positions on the piezoelectric substrate, and an input electrode to which a spread spectrum signal is input, and the input electrode. And an intermediate output electrode composed of a plurality of pairs of interdigital electrodes formed at predetermined intervals on the propagation path so as to form a matched filter, and the propagation to form a delay means with the intermediate output electrode. A delay output electrode composed of a plurality of pairs of interdigitated electrodes formed at predetermined intervals on the path, and an electrode pair having a smaller number of electrode pairs than the intermediate output electrode and the delay output electrode formed on the propagation path of the piezoelectric substrate. A surface acoustic wave device, comprising: a timing signal electrode having an interdigital electrode. 2. The surface acoustic wave element according to claim 1, and a timing signal generating means for generating a demodulation timing signal based on an output signal obtained from the timing signal electrode provided in the surface acoustic wave element. A demodulation means for calculating a signal obtained from both the intermediate output electrode and the delayed output electrode of the surface acoustic wave element based on the demodulation timing signal output from the timing signal generation means to obtain a demodulation output. A demodulator for spread spectrum communication, characterized in that