JPH11168351A - Surface acoustic wave device and spread spectrum communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desired frequency characteristic even if a distance between electrodes is short by varying the number of side probes formed on weighting electrodes at right/left sides with the main robe as a center. SOLUTION: The number of the side robes of the weighting electrode for matched filter output 2 is set to be four on an encoding electrode 2-side and to be two on a weighting electrode for a delay line output 4-side and are made asymmetric. The number of the side robes in the weighting electrode for a delay line output 4 is set to be two on a weighting electrode 3-side for matched filter output and to be four on a sound absorbing-side and are made asymmetric. Then, the number of electrode pairs is correspondingly and appropriately designed. In the distance 'T1' deciding delay time shorted to almost 1/3 of a former case, the surface acoustic wave element output equal to the output electrode where the number of side robes is symmetrically set to be four with the weighting electrode for a matched filter output 3 and the weighting electrode with a delay line output 4 can be obtained.

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 used in a spread spectrum demodulator and a spread spectrum communication apparatus using the surface acoustic wave device in a spread spectrum demodulator.

[0002]

2. Description of the Related Art In recent years, a spread spectrum communication system (SS communication system) which is resistant to noise and excellent in confidentiality and confidentiality has attracted attention as a communication system for consumer use. In the SS communication system, a carrier wave obtained by modulating information to be transmitted with a carrier signal is subjected to spread spectrum modulation (SS modulation) with a predetermined code sequence having a predetermined high chip rate, thereby generating a spectrum as a transmission signal. A spread signal (SS signal) is obtained. In this case, there are a pseudo-noise code sequence (PN code sequence) and a Barker code sequence (Barker code sequence) as the above-mentioned code sequences, and a direct spreading method (DS method) and a frequency hopping method (FH method) as SS modulation methods. There is.

In such an SS communication system, a demodulation device for demodulating the transmitted SS signal is required on the receiver side. For example, when SS modulation is performed by the DS method using a PN code sequence, the receiver performs demodulation using the same PN code sequence as the transmitter. The demodulation device used at this time is roughly classified into a demodulation device using an IC and a demodulation device using a surface acoustic wave element. A surface acoustic wave element used in a demodulation device has attracted attention because a photolithography technique can be used to make the demodulation device inexpensive and with a simple configuration.

[0004] The surface acoustic wave element is classified into a surface acoustic wave matched filter and a surface acoustic wave convolver according to its configuration. Since the surface acoustic wave convolver can select a PN code sequence for demodulation, it is particularly suitable for applications requiring secrecy or confidentiality. The surface acoustic wave matched filter uses a fixed PN code sequence for demodulation, but its peripheral circuits can be easily configured and the system as a whole can be inexpensive. Has been attracting attention as a demodulation device used for.

FIG. 7 is a block diagram showing a conventional spread spectrum demodulation circuit for a general DS system. In FIG. 7, reference numeral 13 denotes a surface acoustic wave matched filter that inputs an SS signal s and outputs a correlation signal, and 14 denotes a surface acoustic wave delay line that delays a correlation signal m from the surface acoustic wave matched filter 13 by a predetermined delay amount. A delay circuit 15 for integrating the correlation signal m from the surface acoustic wave matched filter 13 and a correlation signal n delayed by a predetermined delay amount from the surface acoustic wave delay circuit 14; L1, L
2 is a signal line (line).

The operation of the spread spectrum demodulation circuit shown in FIG. 7 will be briefly described. Surface acoustic wave matched filter 1
3 is converted to a correlation signal m by the surface acoustic wave matched filter 13 and then the line L
1 and L2. The correlation signal m of the line L1 is directly input to the integrating circuit 15. The correlation signal m on the other line L2 is input to the delay circuit 14 and becomes a correlation signal n delayed by a predetermined delay amount, and becomes an integration circuit 15
Is input to The integrating circuit 15 integrates the correlation signal m and the correlation signal n delayed by a predetermined delay amount to obtain a demodulated signal.

FIG. 8 is a pattern diagram showing a conventional surface acoustic wave device. 8 can be used as the surface acoustic wave matched filter 13 and the delay circuit 14 in FIG. 7 and corresponds to a data transfer rate of 1 Mbps applied to the spread spectrum demodulation circuit in FIG. It is. In FIG. 8, reference numeral 16 denotes quartz, LiN
a piezoelectric substrate made of bO ₃ or the like; 17, a coding electrode for signal input; 18, a weighted electrode for matched filter output;
9 is a delay line output weighted electrode, 20 is a ground pattern for reducing noise, and 21 is a sound absorbing material for absorbing unnecessary surface acoustic waves. FIG. 9 is an enlarged view of an input / output electrode of the surface acoustic wave device of FIG.

Next, the pattern of FIG. 8 will be described with reference to FIGS. 4 and 5 are graphs showing frequency characteristics of the conventional surface acoustic wave device. FIG. 4 shows a case where the number of side lobes is four, and FIG.
Shows the case of

A signal input encoding electrode 17 for converting an electric signal into a surface acoustic wave, and a comb-shaped electrode for converting a surface acoustic wave into an electric signal at a predetermined distance from the signal input encoding electrode 17 on a piezoelectric substrate 16. And a weighted electrode 18 for matched filter output is provided to form a surface acoustic wave matched filter. The surface acoustic wave is further separated from the weighted electrode 18 for matched filter output by a predetermined interval “T2” to generate an electric signal. And a comb-shaped delay line output weighted electrode 19 for converting into a surface acoustic wave delay line. Here, “T2” is a distance for giving a delay line signal output delayed in time by a delay time corresponding to one cycle of data to the matched filter output. The intersection width of the electrode fingers of the matched filter output weighted electrode 18 and the delay line output weighted electrode 19 changes regularly, and draws the main lobe envelope 22 and the side lobe envelope 23 as shown in the figure. The number of side lobes and the number of electrode pairs are appropriately designed in order to obtain a desired frequency characteristic. All electrodes are not shown for simplicity.

At this time, an n-bit PN is used as a code sequence.
When a code sequence is used, the input encoding electrode 17 has n comb electrode pairs corresponding to the PN code sequence, and each comb electrode pair is formed at a distance corresponding to the chip rate. A ground pattern 20 for reducing noise is formed around the input / output electrodes 17, 18, and 19 as necessary. Further, a sound absorbing material 21 is formed outside the input / output electrodes 17 and 19 as necessary for the purpose of absorbing unnecessary surface acoustic waves. In this case, a weighted electrode may be used as the signal input electrode 17, and a coding electrode may be used as the matched filter output weighted electrode 18 and the delay line output weighted electrode 19.

[0011] Such a surface acoustic wave element is used in accordance with the difference in the modulation method such as the two-phase modulation method or the four-phase modulation method in the SS communication, and the respective purposes such as code multiplexing for multi-channel or the like. A structure in which a plurality of matched filters and delay lines are arranged on the same substrate is used.

Further, such a surface acoustic wave device is liable to cause problems such as a change in the propagation speed of the surface acoustic wave, unnecessary reflection, and short-circuiting of the comb-shaped electrode due to the attachment of foreign matter to the substrate surface due to its nature. It is necessary to seal with a metal package, a ceramic package or the like, and each electrode pattern of the surface acoustic wave element and an external extraction electrode on the package side are used by being connected by wire bonding or the like.

[0013]

However, in the surface acoustic wave device having such a configuration, in order to obtain a desired frequency characteristic, it is necessary to use a side of a weighted electrode used for a matched filter output electrode and a delay line output electrode. It is necessary to appropriately design the number of lobes and the number of electrode finger pairs. The distance between the two electrodes is the sum of one data period and a predetermined delay, and is a distance for determining the amount of delay required for delay detection. Therefore, when the data transfer rate increases from 1 Mbps to 2 Mbps and 3 Mbps, it is necessary to shorten the distance between the two electrodes to approximately 1/2 and 1/3. For example, when the data transfer rate is 1 Mbps, the number of side lobes on the left and right of the main lobe is 4 Fig. 4
However, when the data transfer rate becomes 3 Mbps, the distance between the electrodes is reduced to approximately 1/3, so that the number of side lobes of the weighted electrodes is limited to two, and the frequency characteristic shown in FIG. There is a problem that only characteristics can be obtained, and the ripples in the band are large and the squareness ratio is poor.

In this surface acoustic wave device, it is required that desired characteristics can be obtained even when the data transfer rate is increased and the distance between the electrodes is reduced.

The present invention has a surface acoustic wave device capable of obtaining desired characteristics even when the data transfer rate is increased and the distance between the electrodes is reduced, and a spread spectrum demodulator using the surface acoustic wave device. An object of the present invention is to provide a spread spectrum communication device.

[0016]

According to the present invention, there is provided a surface acoustic wave device comprising at least one coded electrode and at least two weighted electrodes on a piezoelectric substrate. The weighted electrode has a configuration in which the number of side lobes formed on the weighted electrode is different on the left and right around the main lobe.

As a result, it is possible to obtain a surface acoustic wave device capable of obtaining desired characteristics even when the data transfer rate is increased and the distance between the electrodes is reduced.

A spread spectrum communication apparatus according to the present invention for solving this problem is a spread spectrum communication apparatus having at least a spread spectrum demodulation section for demodulating a signal subjected to spread spectrum modulation. A configuration having an elastic wave element is provided.

As a result, a spread spectrum communication apparatus having a spread spectrum demodulator using the above surface acoustic wave device can be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a surface acoustic wave device having at least one coded electrode and at least two weighted electrodes on a piezoelectric substrate, wherein The electrode is such that the number of side lobes formed on the weighted electrode is different on the left and right around the main lobe, and the amplitude of the ripple is reduced by increasing the number of side lobes by making the left and right asymmetric, for example, Even if the distance between the matched filter output weighted electrode and the delay line output weighted electrode is short, a desired frequency characteristic can be obtained using the weighted electrode.

According to a second aspect of the present invention, there is provided a spread spectrum communication apparatus having at least a spread spectrum demodulation unit for demodulating a spread spectrum modulated signal,
The spread spectrum demodulation unit has the surface acoustic wave device according to claim 1. An output of the surface acoustic wave device having an appropriate frequency characteristic can be obtained in the spread spectrum demodulation unit, and a good S / N error can be obtained. This has the effect that a spread spectrum communication apparatus with a low rate can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a pattern diagram showing a surface acoustic wave device according to Embodiment 1 of the present invention. A composite surface in which a surface acoustic wave matched filter and a surface acoustic wave delay line are formed on the same substrate. 3 shows an elastic wave matched filter. The configuration of the surface acoustic wave device shown in FIG. 1 corresponds to a data rate of 3 Mbps in the spread spectrum demodulation unit. FIG.
Wherein 1 is a piezoelectric substrate made of quartz, LiNbO ₃ or the like, 2 is a coding electrode for signal input, 3 is a weighted electrode for matched filter output, 4 is a weighted electrode for delay line output,
5 is an earth pattern for reducing noise, and 6 is a sound absorbing material for absorbing unnecessary surface acoustic waves. FIG. 2 shows FIG.
It is an enlarged view of the encoding electrode of the surface acoustic wave element of FIG.

Next, the pattern of FIG. 1 will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 3 is a graph showing frequency characteristics of the surface acoustic wave device of FIG.

A signal input encoding electrode 2 for converting an electric signal into a surface acoustic wave, and a comb-shaped electrode for converting a surface acoustic wave into an electric signal at a predetermined distance from the signal input encoding electrode 2 on a piezoelectric substrate 1. And a weighted electrode 3 for matched filter output are provided to constitute a surface acoustic wave matched filter. The surface acoustic wave is further separated from the weighted electrode 3 for matched filter output by an interval "T1" corresponding to a predetermined delay amount. A comb-shaped delay line output weighted electrode 4 for converting an elastic wave into an electric signal is provided to constitute a surface acoustic wave delay line. All electrode fingers are not shown for simplicity. At this time, when an n-bit PN code sequence is used as the code sequence, the coding electrode 2 is set to n corresponding to the PN code sequence.
Each pair of comb electrodes is formed at an interval corresponding to the chip rate, and the number of electrode fingers of the comb electrode pair corresponding to each bit of the encoding electrode is more than one pair and the carrier frequency The number is set to be equal to or less than the ratio (carrier frequency / chip rate) of the chip rate. In the case of the present embodiment, a carrier frequency of 200 MHz and a chip rate of 1
Since the frequency is 1 MHz, the number is 2 to 18 pairs. With such a configuration, the efficiency of converting an electric signal into a surface acoustic wave can be increased.

In the conventional example, the output electrode has a symmetrical weighted electrode structure in which the number of side lobes and the number of electrode pairs are appropriately designed in order to obtain a desired frequency characteristic. Since the data transmission rate is three times as large as in the conventional example, the distance “T1” for determining the delay time of the delay line output weighted electrode 4 with respect to the matched filter output weighted electrode 3 is changed to “T1” in the conventional example.
2), it is necessary to reduce the length to approximately 1/3 as compared with the conventional example. To obtain a desired frequency characteristic by forming a symmetric weighted electrode similar to the conventional example, the matched filter output weighted electrode 3 and the delay line There is not enough distance between the output weighted electrode 4 and the appropriate number of side lobes, and the side lobe becomes a weighted electrode having two side lobes, and only a frequency characteristic as shown in FIG. 5 is obtained. I couldn't. For this reason, the ripple in the band is large and the squareness ratio is deteriorated as compared with FIG. 4, which is the frequency characteristic when the conventional example is configured with four side lobes on one side, and a desired output of the surface acoustic wave element is obtained. There was a problem saying that there was no.

Therefore, in the present embodiment, the number of side lobes of the matched filter output weighted electrode 3 is four asymmetric on the encoding electrode 2 side and two on the delay line output weighted electrode 5 side. The number of side lobes of the weighted electrode 4 for delay line output is two asymmetrical with the weighted electrode 4 for matched filter output and four on the sound absorbing material 6 side, and the number of electrode pairs is appropriately designed accordingly. As a result, the frequency characteristic shown in FIG. 3 can be obtained by the matched filter output weighted electrode 3 and the delay line output weighted electrode 4 even at “T1” which is approximately ３ shorter than “T2”. Since the in-band ripple and the squareness ratio are improved as compared with the frequency characteristics of FIG. 5, a surface acoustic wave element output equivalent to an output electrode composed of four side lobes symmetrically can be obtained.

In the present embodiment, four side lobes and two left and right asymmetric weighted electrodes 3 and 4 are used, but the number of left and right side lobes depends on the frequency characteristics and the element size. It should be appropriately designed together with the logarithm, and is not limited to the number of side lobes described in the present embodiment. The distance between the electrodes indicated by “T1” varies depending on the data transfer rate and the surface acoustic wave velocity of the piezoelectric substrate used, and is suitable for transfer rates other than 3 Mbps and the used piezoelectric substrate. Must be designed.

In the above description, one input electrode is used.
Although the description has been given of the case where two output electrodes have a data rate of 3 Mbps, such a surface acoustic wave device is different in a modulation method such as a two-phase modulation method or a four-phase modulation method in SS communication at an arbitrary data rate. In addition, matched filters and delay lines with multiple structures arranged on the same substrate are used according to their respective purposes, such as code multiplexing for multi-channeling, etc., and they can be implemented similarly. Needless to say,

As described above, according to the present embodiment, the number of side lobes formed on the weighted electrodes 3 and 4 differs between the left and right sides of the weighted electrodes 3 and 4 with respect to the main lobe. ), The amplitude of the ripple is reduced by increasing the number of side lobes by making the left and right asymmetric, and the distance between the matched filter output weighted electrode 3 and the delay line output weighted electrode 4 is shortened. It is possible to obtain an output having a desired frequency characteristic.

(Embodiment 2) FIG. 6 is a block diagram showing a spread spectrum communication apparatus according to Embodiment 2 of the present invention, wherein a surface acoustic wave device according to Embodiment 1 is used in a spread spectrum demodulator. 1 shows a spread communication device. 6, reference numeral 9 denotes a spread spectrum modulation unit for converting an information signal to be transmitted into a spread spectrum signal with a predetermined code sequence, 10 denotes a transmission / reception frequency conversion unit for converting the frequency of the spread spectrum signal and the frequency of the transmission / reception signal, and 11
Is equipped with the spread spectrum demodulation circuit according to the present embodiment (that is, the spread spectrum demodulation circuit using the surface acoustic wave device according to the first embodiment as the surface acoustic wave matched filter 13 and the delay circuit 14 in FIG. 7). A spread spectrum demodulation unit 12 for demodulating the signal into the original information signal that has been transmitted, and an antenna 12 for transmitting and receiving the signal.

In the above description, the transmission / reception frequency converter 1
The configuration of one transceiver using one 0 has been described. However, the configuration is not limited to the circuit configuration. For example, a configuration in which a transmission / reception frequency conversion unit is divided into transmission / reception units,
The present invention can be implemented in an optional spread spectrum communication apparatus including a spread spectrum demodulation unit such as a configuration in which a transmitter and a receiver are separated.

As described above, according to the present embodiment, since the spread spectrum demodulation unit 11 having the surface acoustic wave device according to the first embodiment is used, the spread spectrum demodulation unit 11 has a surface having an appropriate frequency characteristic. Since the output of the elastic wave element can be obtained, a spread spectrum communication apparatus having a good S / N and a small error rate can be obtained.

[0033]

As described above, according to the surface acoustic wave device of the first aspect of the present invention, at least one surface acoustic wave element is provided on the piezoelectric substrate.
A surface acoustic wave device comprising one encoded electrode and at least two weighted electrodes, wherein the number of side lobes formed on the weighted electrode differs from left to right around the main lobe, The number of side lobes is made asymmetrical and the amplitude of the ripple is reduced, and for example, even if the distance between the weighted electrode for matched filter output and the weighted electrode for delay line output is short, the desired weighted electrode can be obtained using the weighted electrode. An advantageous effect that frequency characteristics can be obtained is obtained.

According to the spread spectrum communication apparatus of the present invention, there is provided a spread spectrum communication apparatus having at least a spread spectrum demodulation section for demodulating a signal subjected to spread spectrum modulation, wherein the spread spectrum demodulation section is provided. By having the surface acoustic wave device according to item 1, it is possible to obtain a surface acoustic wave device output having an appropriate frequency characteristic in the spread spectrum demodulation unit, so that a spread spectrum communication device having a good S / N and a small error rate is provided. Can be obtained.

[Brief description of the drawings]

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

FIG. 2 is an enlarged view of a coded electrode of the surface acoustic wave device of FIG. 1;

FIG. 3 is a graph showing frequency characteristics of the surface acoustic wave device of FIG. 1;

FIG. 4 is a graph showing frequency characteristics of a conventional surface acoustic wave device (the number of side lobes is four).

FIG. 5 is a graph showing frequency characteristics of a conventional surface acoustic wave device (two side lobes).

FIG. 6 is a block diagram showing a spread spectrum communication apparatus according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a conventional spread spectrum demodulation circuit.

FIG. 8 is a pattern diagram showing a conventional surface acoustic wave device.

9 is an enlarged view of an input / output electrode of the surface acoustic wave device of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Encoding electrode 3 Weighted electrode for matched filter output 4 Weighted electrode for delay line output 5 Ground pattern 6 Sound absorbing material 7 Envelope of main lobe 8 Side lobe envelope 9 Spread spectrum modulator 10 Transmission / reception frequency Conversion unit 11 Spread spectrum demodulation unit 12 Antenna 13 Surface acoustic wave matched filter 14 Delay circuit 15 Integration circuit L1, L2 Signal line

Claims (2)

[Claims] 1. A surface acoustic wave device comprising at least one encoding electrode and at least two weighted electrodes on a piezoelectric substrate, wherein the weighted electrode is a side lobe formed on the weighted electrode. The surface acoustic wave device is characterized in that the number is different on the left and right around the main lobe. 2. A spread spectrum communication apparatus having at least a spread spectrum demodulation unit for demodulating a signal subjected to spread spectrum modulation, wherein the spread spectrum demodulation unit has the surface acoustic wave device according to claim 1. Spread spectrum communication device.