JPH07288443A - Communication system using demodolator - Google Patents

Abstract

PURPOSE:To easily demodulate a signal subjected to spread spectrum modulation with simple circuit configuration. CONSTITUTION:The spread-spectrum-modulated signal is transmitted from a transmitter and received at a receiver. The demodulator for this receiver is provided with a reference signal generator 3 for generating a code for reference corresponding to a received signal 1 and a surface acoustic wave(SAW) element 5 for inputting the received signal 1 and the output signal from the reference signal generator 3, and this SAW element is provided with two comb-like exciting electrodes 102 and 103 for exciting SAW and an acoustic/electric converter 104 composed of a comb-like electrode provided between these two exciting electrodes on a piezoelectric substrate 101. The pitch of the comb-like electrodes at the acoustic/electric converter 104 is almost half as long as the pitch of the comb-like exciting electrodes 102 and 103 and the SAW with double waves as many as the waves of SAW excited from two exciting electrodes 102 and 103 is selectively converted to an electric signal by the acoustic/electric converter 104.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system using a device for demodulating an information signal, and more particularly to a communication system using a demodulation device suitable for demodulating a spread spectrum modulated signal.

[0002]

2. Description of the Related Art Spread spectrum communication is a communication in which an information signal to be transmitted is spread over a sufficiently wider bandwidth and transmitted, and code division multiplexing is possible, resistant to interference and highly confidential. There is a feature of.

In the reception processing in this spread spectrum communication, the information signal is demodulated by performing so-called despreading processing, in which the spread code assigned to each channel is used to obtain correlation with the received signal. The receiving unit of spread spectrum communication is conventionally divided into a synchronizing unit and a demodulating unit. In the synchronizing unit, synchronization is achieved by, for example, a sliding correlation method that detects a correlation with a reference spreading code having a bit rate slightly different from that of the receiving spreading code.

As a method capable of high-speed synchronization acquisition, there is a method using a convolver. The convolver is a convolution operation element, and when one of the two input signals is a time-reversal signal, it functions as a correlator. That is, when the received signal is input to one of the convolver input signals and the signal obtained by temporally inverting the received signal is input to the other as the reference signal, the two signals match at a certain point,
It produces a sharp peak output. In particular, if the spreading code used here is a code having a good autocorrelation characteristic, a sharp peak output is generated only when the two signals match, and almost no output appears in other cases. One of the convolvers is the surface acoustic wave convolver. The surface acoustic wave convolver is an analog arithmetic element and can perform signal processing in real time, so it is effective for high-speed transmission.

FIG. 11 shows a spread spectrum demodulator using a conventional surface acoustic wave convolver. In the figure, 1
Is a received signal, 2 and 4 are frequency converters, 5 is a surface acoustic wave element (convolver), 6 is a filter (F), 10 is a detector (D), 8 is a peak detection circuit (PD), and 3 and 9 are A code generator (CG). The received signal 1 is converted to an intermediate frequency by the frequency converter 2 and input to the surface acoustic wave element 5. Further, the code generator 3 generates a code obtained by inverting the spread code of the received signal as a reference spread code,
Input to the surface acoustic wave element 5 through the frequency converter 4.

The surface acoustic wave element 5 includes a first excitation electrode 102, a second excitation electrode 103 for exciting surface acoustic waves on the piezoelectric substrate 101, and the first excitation electrode 102 and the second excitation electrode. It has a rectangular output electrode 105 between 103 and 103.

The first frequency converter 2 and the second frequency converter 4 each include an oscillator 15, a multiplier 13 and a filter (F) 14.

When the received signal 1 is input to the first excitation electrode 102 and the output from the code generator 3 is input to the second excitation electrode 103, the first excitation electrode 10 is placed on the output electrode 105.
The first surface acoustic wave excited from 2 and the second excitation electrode 1
The second surface acoustic wave excited from 03 overlaps while propagating in opposite directions. Due to the parametric mixing phenomenon of the two surface acoustic waves overlapping on the substrate 101, the displacement and the potential of the product of the two surface acoustic waves occur at a frequency of twice the input signal and a wave number of 0, so that at the output electrode 105, It can be integrated as an electric signal within the range of the output electrode. Therefore, in the surface acoustic wave element 5, when two surface acoustic waves coincide on the output electrode 105, a sharp peak output is generated at the center frequency 2f (where f is the center frequency of the input signal). This output is taken out through a filter 6, envelope-detected by a detector 10, and then a peak is detected by a peak detection circuit 8. Based on this peak information, a reference spread code generated by a code generator 3 and a received signal are detected. Code generation is performed by adjusting the generation timing of the reference spreading code generated from the code generator 3 so that the surface acoustic wave elements 5 match in a desired state.

Further, the above-mentioned peak information is also inputted to the code generator 9 for generating the same spread code as the received signal, the spread code is generated from the code generator 9 in synchronization with the received signal, and received by the multiplier 11. By multiplying with the signal,
The received signal that has been spread spectrum modulated is despread. Since the despread signal is a commonly used modulation signal such as frequency modulation or phase modulation, this signal is demodulated through a commonly used demodulator (DM) 12.

[0010]

However, in the above-mentioned conventional example, the output of the surface acoustic wave element is used only for code synchronization, and a demodulation section must be provided separately, which results in a large circuit scale. there were.

On the other hand, Nakagawa et al. "Dc effects in e
lastic surface waves ", Applied Physics Letters, Vo
l.24, No.4, pp.160-162, 15 February 1974, Figure 1
A surface acoustic wave device as described in No. 2 is disclosed. In FIG. 12, input interdigital transducers 17 and 18 and an output interdigital transducer 19 are formed on a piezoelectric substrate 16. Transducer 1
When a pulse signal of wave number k and frequency ω is input to 7 and a pulse signal of wave number -k and frequency ω is input to transducer 18, surface acoustic waves propagating in opposite directions are generated from each transducer 17, 18. These surface acoustic waves cause an interaction in the region between the transducer 17 and the transducer 18, and the wave number 2 from the output transducer 19 is caused by the nonlinear effect.
A signal of k and frequency 0 is taken out.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a communication system using a demodulator capable of demodulating a signal modulated by a spread code with a simple structure. That is, the present invention facilitates data demodulation by using the element disclosed in the material of Nakagawa et al. In a demodulator.

[0013]

According to the present invention, in order to achieve the above object, a code generating means for generating a reference code corresponding to a received signal, and the received signal and the output from the code generating means. In a communication system including a receiver including a demodulation device including a surface acoustic wave element for inputting a signal and a transmitter for transmitting a signal to the receiver, the surface acoustic wave element is elastic on a piezoelectric substrate. At least two excitation electrodes that excite surface waves, and an acoustoelectric converter that is provided between the two excitation electrodes and that converts a surface acoustic wave into an electric signal are provided. There is provided a communication system, which is configured to selectively convert a surface acoustic wave having a wave number twice as large as that of the surface acoustic wave excited from the excitation electrode into an electric signal.

In one aspect of the present invention, the excitation electrode and the acoustoelectric transducer are both comb-shaped electrodes, and the pitch of the comb-shaped electrodes constituting the acoustoelectric converter is the excitation electrode. Is approximately half the pitch of the comb-shaped electrodes that form the.

In another aspect of the present invention, each of the excitation electrode and the acoustoelectric converter is a comb-shaped electrode, and the comb-shaped electrode forming the excitation electrode is a double electrode. The comb-shaped electrodes forming the converter are single electrodes, and the electrode pitch of the excitation electrodes and the electrode pitch of the acoustoelectric converter are substantially equal.

According to another aspect of the present invention, there is provided a phase shift means for changing the phase of at least one of the received signal and the output signal from the code generating means.

According to still another aspect of the present invention, two surface acoustic wave elements described above are provided. Here, the means for branching the received signal into two, the means for branching the output signal from the code generating means into two, and the phase of the two outputs of at least one of the two branching means are made different. And means. Further, the arrangement of the acoustoelectric converter with respect to the excitation electrode in one of the two surface acoustic wave elements is different from the arrangement of the acoustoelectric converter with respect to the excitation electrode in the other of the two surface acoustic wave elements. The surface acoustic wave may be shifted by v / 8f (where v is the surface acoustic wave propagation velocity and f is the center frequency of the signal input to the first and second surface acoustic wave elements) in the propagation direction of the surface acoustic wave. it can. Further, the arrangement of the one excitation electrode with respect to the acoustoelectric converter in one of the two surface acoustic wave elements is the arrangement of the one excitation electrode with respect to the acoustoelectric converter in the other of the two surface acoustic wave elements. On the other hand, v / 4f (v is the propagation velocity of the surface acoustic wave, and f is the center frequency of the signal input to the first and second surface acoustic wave elements) is shifted in the propagation direction of the surface acoustic wave. Can be

In the present invention, the two surface acoustic wave devices can be integrally formed on the same substrate.

In the present invention, a spread spectrum modulated signal can be used as the received signal.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 shows a block diagram of a first embodiment of a demodulator used in a communication system of the present invention.
In the figure, 1 is a received signal, 2 is a first frequency converter for converting the frequency of the received signal 1, 3 is a reference signal generator (RG) for generating a reference signal including a reference code, and 4 is It is a second frequency converter that converts the frequency of the output signal from the reference signal generator 3. The first frequency converter 2 and the second frequency converter 4 each include an oscillator 15, a multiplier 13, and a filter (F) 14.

Reference numeral 5 inputs the output signal from the first frequency converter 2 and the output signal from the second frequency converter 4,
A surface acoustic wave element (convolver) that outputs a baseband convolution signal of the two signals. The surface acoustic wave element 5 includes a piezoelectric substrate 101 and the piezoelectric substrate 101.
The first excitation electrode 102 and the second excitation electrode 103, which are formed on the first excitation electrode 102 for exciting the first surface acoustic wave and the second surface acoustic wave, for exciting the second surface acoustic wave, The acoustoelectric transducers 104 are formed on the propagation paths that propagate in opposite directions.

The first excitation electrode 102 and the second excitation electrode 103 are so-called interdigital transducers (comb electrodes), which are formed on the piezoelectric substrate 101 by a conductive film of aluminum, silver, gold or the like. The array pitch p i of the electrode fingers of the interdigital transducer (hereinafter referred to as “IDT”) is v /, where f is the center frequency of the input signal and v is the propagation velocity of the surface acoustic wave.
Make it substantially equal to 2f.

The acoustoelectric transducer 104 is a so-called IDT.
(Comb-shaped electrode), which is formed of a conductive film of aluminum, silver, gold, or the like on the piezoelectric substrate 101. The arrangement pitch p0 of the electrode fingers of the IDT is v / 4f, that is, the arrangement pitch p of the electrode fingers of the first and second excitation electrodes 102 and 103.
It should be substantially equal to 1/2 of i.

Reference numeral 6 is a filter (F) for extracting a desired signal from the output of the surface acoustic wave element 5.

The details will be described below.

The received signal 1 received from the antenna or cable is input to the first frequency converter 2 through a filter, an amplifier, etc., if necessary, and is set to the operating frequency (input center frequency f) of the surface acoustic wave element 5. It is converted and input to the first excitation electrode 102 of the surface acoustic wave element 5.
On the other hand, the reference signal generator 3 generates a code sequence in which the code sequence of the desired reception signal is time-reversed in accordance with the desired reception signal, and the operation of the surface acoustic wave element 5 is performed through the second frequency converter 4. It is converted to a frequency (input center frequency f) and input to the second excitation electrode 103 of the surface acoustic wave element 5.

In the surface acoustic wave element 5, the first surface acoustic wave having the component of the received signal 1 is excited from the first excitation electrode 102, and the second surface acoustic wave having the reference signal component is excited by the second excitation. Excited from the electrode 103, the first surface acoustic wave and the second surface acoustic wave propagate in opposite directions between the first excitation electrode 102 and the second excitation electrode 103. In the region where the two surface acoustic waves overlap, the product component of the two surface acoustic wave signals becomes due to the parametric mixing effect.
The wave number is twice as high as that of the first and second surface acoustic waves and is generated as the baseband frequency. This is due to the Nak
This is as reported in the material of agawa et al. That is, the first surface acoustic wave is F (t−x / v) exp (2πjf (t−x / v)), and the second surface acoustic wave is G (t + x / v) exp (2πjf (t + x / v)). ), In the region where the first surface acoustic wave and the second surface acoustic wave overlap, F (t−x / v) · G (t + x / v) exp (4πjf
x / v) component displacement and potential are generated. this is,
The signal has a carrier frequency of 0 and a wave number of 4πf / v. Therefore,
In the region where the first surface acoustic wave and the second surface acoustic wave overlap, the acoustoelectric transducer 104 is set to the pitch p of the comb-shaped electrodes.
By forming so that 0 becomes substantially v / 4f, the component of ∫F (t−x / v) · G (t + x / v) dx, that is, the convolution signal of the signal F and the signal G becomes the base. Acoustoelectric transducer 10 as band signal
It occurs in 4. This signal is extracted through the filter 6. Since the output of the filter 6 is a baseband signal, the data can be easily demodulated.

Here, spread spectrum communication, particularly spread spectrum communication of the direct spread system will be described. In direct spread spectrum spread communication, a plurality of bits are assigned to one bit of data by using a high-speed spread code. When a spread spectrum signal is input as the received signal 1, the reference signal generator 3 outputs a code obtained by time-reversing the spread code of the received signal.
On the surface acoustic wave element 5, the code pattern of the received signal 1 and the code pattern output from the reference signal generator 3 periodically match, and at that time, a peak output is obtained in the acoustoelectric converter 104, and the peak output is obtained through the filter 6. Taken out. Here, when the received signal 1 is a two-phase modulation, the potential of the output signal becomes positive or negative depending on whether the data is "1" or "0", as shown in FIG. Therefore, the data can be easily “1” or “0” simply by checking whether the output signal of the filter 6 is positive or negative.
Can be determined.

[Second Embodiment] FIG. 3 shows a block diagram of a second embodiment of a demodulator used in the communication system of the present invention.
In this figure, the same members as those in FIG. 1 are designated by the same reference numerals. In this embodiment, a phase shifter (PS) 404 is provided between the oscillator 401 and the multiplier 402 inside the second frequency converter 4, and a part of the output of the filter 6 is a phase control circuit (PC). 7 and the phase control circuit 7 sends a control signal to the phase shifter 404, which is the difference from the first embodiment.

It goes without saying that this embodiment also has the same effects as the first embodiment, but in this embodiment, further, in accordance with the fluctuation of the output level of the filter 6,
Since the phase of the signal input to the multiplier 402 can be controlled, the acoustoelectric converter 104 of the surface acoustic wave element 5 can be controlled.
A stable output can be obtained by controlling the phase relationship between the first and second surface acoustic waves propagating above.

Although the phase shifter 404 is provided in the second frequency converter 4 in the present embodiment, the same effect can be obtained by providing the phase shifter in the first frequency converter 2.

[Third Embodiment] FIG. 4 shows a block diagram of a third embodiment of the demodulator used in the communication system of the present invention.
In this figure, the same members as those shown in FIGS. 1 and 3 are designated by the same reference numerals. In this embodiment,
The first excitation electrode 202 and the second excitation electrode 203 of the surface acoustic wave element 5 are double electrodes (split electrodes), and the electrode pitch pi is substantially equal to v / 4f, that is,
The difference from the first embodiment is that it is substantially equal to the electrode pitch of the acoustoelectric converter 104.

In this embodiment, the first excitation electrode 202 and the second excitation electrode 203 of the surface acoustic wave element 5 are double electrodes, and the electrode pitch pi is v / 4f.
Therefore, the input center frequency is f, which is the same as that in the first embodiment, and the same operational effect as the first embodiment is obtained.
Further, in this embodiment, due to the double electrode structure, the reflection of the surface acoustic wave is suppressed at the first and second excitation electrodes 202 and 203, and the spurious signal is reduced.

The first and second excitation electrodes may have any structure as long as they efficiently convert an electric signal of the input center frequency f into a surface acoustic wave, and may be, for example, a one-way electrode.

[Fourth Embodiment] FIG. 5 shows a block diagram of a fourth embodiment of the demodulator used in the communication system of the present invention.
In this figure, the same members as those in FIGS. 1, 3 and 4 are designated by the same reference numerals. In the present embodiment, a first surface acoustic wave element 51 and a second surface acoustic wave element 52 are provided, and the output from the code generator 3 is divided into two, which are respectively a second frequency converter 41 and a second frequency converter 41. Of the first surface acoustic wave element 51 through the frequency converter 42 of FIG.
Input to the second excitation electrode 113 of the second surface acoustic wave element 52. Third frequency converter 42
Then, the signal from the oscillator 401 common to the second frequency converter 41 is input to the multiplier 422 through the 90-degree phase shifter (PS) 424. The received signal 1 is frequency-converted by the first frequency converter 2 and then is divided into two to be divided into the first excitation electrode 112 of the first surface acoustic wave element 51 and the first excitation electrode 112 of the second surface acoustic wave element 52. It is input to the excitation electrode 122.

In the present embodiment, the received signal 1 is input in phase to the first excitation electrode 112 of the first surface acoustic wave element 51 and the first excitation electrode 122 of the second surface acoustic wave element 52. On the other hand, the output from the reference signal generator 3 has a phase of 9 between the second excitation electrode 113 of the first surface acoustic wave element 51 and the second excitation electrode 123 of the second surface acoustic wave element 52.
It is entered 0 times differently. Therefore, a signal having a carrier frequency of 0 and a wave number of 4πf / v generated on the substrate 111 of the first surface acoustic wave element 51 and a wave number of 4πf at a carrier frequency of 0 generated on the substrate 121 of the second surface acoustic wave element 52. Since the / v signal has a 90-degree phase difference, the outputs from the acoustoelectric transducers 114 and 124 have a 90-degree phase difference, and have a relationship between the SIN component and the COS component.

Therefore, the output of the acoustoelectric transducer 114 of the first surface acoustic wave element 51 and the output of the acoustoelectric transducer 124 of the second surface acoustic wave element 52 are passed through filters (F) 61 and 62, respectively. Then, the data can be easily demodulated.

In the present embodiment, the output from the reference signal generator 3 is divided into two and the phase is changed by 90 degrees, but the received signal 1 may be divided into two and the phase is changed by 90 degrees. The first and second surface acoustic wave devices 51 and 52 may be formed on the same substrate, and the first excitation electrodes 112 and 122 or the second excitation electrodes 113 and 123 may be integrally formed. You may.

[Fifth Embodiment] FIG. 6 is a block diagram of a fifth embodiment of a demodulator used in the communication system of the present invention.
In this figure, the same members as those in FIGS. 1 and 3 to 5 are designated by the same reference numerals. In this embodiment, the first surface acoustic wave element 51 and the second surface acoustic wave element 52 are provided, and the array of electrode fingers of the IDT that constitutes the acoustoelectric converter 114 of the first surface acoustic wave element 51 is arranged. On the other hand, the array of electrode fingers of the IDT forming the acoustoelectric transducer 124 of the second surface acoustic wave element 52 is formed by shifting v / 8f in the surface acoustic wave propagation direction (that is, | d1 −
d2 .vertline. = v / 8f).

In the present embodiment, the received signal 1 is frequency-converted by the first frequency converter 2 and is then halved to the first excitation electrode 112 and the second surface of the first surface acoustic wave element 51.
Input to the first excitation electrode 122 of the surface acoustic wave element 52. The output from the reference signal generator 3 is frequency-converted by the second frequency converter 4 and then divided into two to be divided into the second excitation electrode 113 of the first surface acoustic wave element 51 and the second surface acoustic wave element. 52 to the first excitation electrode 123. Acoustoelectric transducer 114 of first surface acoustic wave element 51
Since the acoustoelectric converter 124 of the second surface acoustic wave element 52 is formed by shifting v / 8f in the surface acoustic wave propagation direction, the carrier frequency 0 generated on the substrate is 4πf.
The signal of / v will be taken out by shifting a quarter wavelength.
Just extract the SIN and COS components.

Therefore, the output of the acoustoelectric transducer 114 of the first surface acoustic wave element 51 and the second surface acoustic wave element 5
The output of the second acoustoelectric converter 124 and the output of the acoustoelectric converter 124 can be easily demodulated after passing through the filters 61 and 62, respectively.

In this embodiment, as shown in FIG.
And the second surface acoustic wave elements 51 and 52 on the same substrate 131.
It may also be formed on top and also further integrates the two first excitation electrodes of these elements into electrode 132 and / or integrates the two second excitation electrodes of these elements into electrode 133. You can also do it.

[Sixth Embodiment] FIG. 8 shows a block diagram of a sixth embodiment of a demodulator used in the communication system of the present invention.
In this figure, the same members as those in FIGS. 1 and 3 to 7 are designated by the same reference numerals. In this embodiment, the first surface acoustic wave element 51 and the second surface acoustic wave element 52 are provided on the same substrate 131, and the two first surface acoustic wave elements 51 and 52 are provided. Excitation electrodes are integrated into an electrode 132, and two second excitation electrodes are integrally formed into an electrode 143. Further, with respect to the arrangement of the second excitation electrodes of the first surface acoustic wave element 51, As a result, the array of the second excitation electrodes of the second surface acoustic wave element 52 is formed by shifting by v / 4f in the propagation direction of the surface acoustic wave.

In this embodiment, the received signal 1 is frequency-converted by the first frequency converter 2 and then the first and second signals are converted.
Is input to the first excitation electrodes 132 of the surface acoustic wave elements 51 and 52. The output from the reference signal generator 3 is frequency-converted by the second frequency converter 4 and then input to the second excitation electrodes 143 of the first and second surface acoustic wave elements 51 and 52. Since the second excitation electrode of the first surface acoustic wave element 51 and the second excitation electrode of the second surface acoustic wave element 52 are formed by being shifted by v / 4f in the surface acoustic wave propagation direction, The phase of the surface acoustic wave generated at the excitation electrode of the element 51 differs from that of the surface acoustic wave generated at the excitation electrode of the element 52 by 90 degrees. Therefore, the first surface acoustic wave element 51
The signal having a wave number of 4πf / v at the carrier frequency 0 generated on the side and the signal having a wave number of 4πf / v at the carrier frequency 0 generated on the side of the second surface acoustic wave element 52 are different in phase by 90 degrees, and these signals are respectively transmitted. When it is taken out by the electric converters 114 and 124, just the SIN component and the COS component are taken out.

Therefore, the output of the acoustoelectric transducer 114 of the first surface acoustic wave element 51 and the second surface acoustic wave element 5
The output of the second acoustoelectric converter 124 and the output of the acoustoelectric converter 124 can be easily demodulated after passing through the filters 61 and 62, respectively.

In this embodiment, the first surface acoustic wave element 51 is used.
Although the second surface acoustic wave element 52 and the second surface acoustic wave element 52 are formed on the same substrate, they may be formed on different substrates. Further, in the present embodiment, the arrangement of the second excitation electrodes of the first and second surface acoustic wave elements is shifted by v / 4f, but the arrangement of the first excitation electrodes may be shifted by v / 4f. Further, the arrangement of the first and second excitation electrodes is appropriately shifted to change the first surface acoustic wave element 51.
The phase of the signal having the wave number of 4πf / v generated at the carrier frequency of 0 on the substrate may be different by 90 degrees between the side and the second surface acoustic wave element 52 side.

In the first to sixth embodiments described above, piezoelectric single crystals of lithium niobate or the like can be used as the substrates 101, 111, 121 and 131, but the present invention is not limited to this. For example, any material and structure having a parametric mixing effect may be used, such as a structure in which a piezoelectric film is added on a semiconductor or glass substrate. Further, a surface acoustic wave waveguide may be formed on the substrate so that the surface acoustic wave can easily propagate.

In the fourth to sixth embodiments, the excitation electrodes 112, 122, 113, 123, 13 are used.
2, 133, 143 may be formed by double electrodes or unidirectional electrodes.

FIG. 9 is a schematic diagram showing an embodiment of the spread spectrum communication system of the present invention. In FIG.
The information signal output from the terminal 301 is transmitted by the transmitter 3
In the spread modulator 302 in 04, the spread code generator 3
The spread code generated by 03 is used for spread modulation. The spread-modulated signal is transmitted from transmitter 304 via antenna 305.

The signal transmitted from the transmitter 304 is received by the receiver 308 via the antenna 306. The received signal is demodulated by the demodulation device 307 in the receiver 308, and the demodulated information signal is input to the terminal 309. Here, the demodulation device 307 has the configuration of any of FIG. 1 and FIGS. 3 to 8 described above.

FIG. 10 is a schematic diagram showing another embodiment of the spread spectrum communication system of the present invention. 10, the same members as those shown in FIG. 9 are designated by the same reference numerals, and detailed description thereof will be omitted. The communication system of FIG.
Only the point of transmitting the signal from the transmitter 304 to the receiver 308 through the cable 310 instead of the antenna of FIG.
Unlike the above example, the signal modulation / demodulation is performed in exactly the same manner as in the example of FIG.

The present invention can be applied in various ways other than the embodiment described above. The present invention includes all such application examples without departing from the scope of the claims.

[0054]

As described above, according to the present invention,
The spread spectrum signal can be easily demodulated with a simple structure, and the circuit scale of the demodulator can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a demodulation device used in a communication system of the present invention.

FIG. 2 is a diagram showing an example of an output signal.

FIG. 3 is a configuration diagram of a second embodiment of a demodulation device used in the communication system of the present invention.

FIG. 4 is a configuration diagram of a third embodiment of a demodulation device used in the communication system of the present invention.

FIG. 5 is a configuration diagram of a fourth embodiment of a demodulation device used in the communication system of the present invention.

FIG. 6 is a configuration diagram of a fifth embodiment of a demodulation device used in the communication system of the present invention.

FIG. 7 is a configuration diagram of a modified example of the fifth embodiment of the demodulation device used in the communication system of the present invention.

FIG. 8 is a configuration diagram of a sixth embodiment of a demodulation device used in the communication system of the present invention.

FIG. 9 is a schematic diagram showing an embodiment of a communication system of the present invention.

FIG. 10 is a schematic view showing another embodiment of the communication system of the present invention.

FIG. 11 is a schematic diagram showing a configuration example of a conventional demodulation device.

FIG. 12 is a schematic perspective view showing an example of a surface acoustic wave element.

[Explanation of symbols]

 1 Received Signal 2, 4, 41, 42 Frequency Converter 3 Reference Signal Generator 5, 51, 52 Surface Acoustic Wave Element 6, 61, 62 Filter 102, 112, 122 First Excitation Electrode 103, 113, 123 Second Exciting Electrodes 104, 114, 124 Acoustoelectric Converters

Claims (10)

[Claims] 1. A reception comprising a demodulation device comprising code generation means for generating a reference code corresponding to a reception signal, and a surface acoustic wave element for inputting the reception signal and an output signal from the code generation means. In a communication system comprising a transmitter and a transmitter for transmitting a signal to the receiver, the surface acoustic wave element comprises at least two excitation electrodes for exciting surface acoustic waves on a piezoelectric substrate, and the two excitation electrodes. And an acoustoelectric converter for converting a surface acoustic wave into an electric signal, the acoustoelectric converter having an acoustic wave having a wave number twice the wave number of the surface acoustic wave excited by the two excitation electrodes. A communication system configured to selectively convert a surface wave into an electric signal. 2. The excitation electrode and the acoustoelectric converter are both formed of comb-shaped electrodes, and the pitch of the comb-shaped electrodes forming the acoustoelectric converter is set to that of the comb-shaped electrodes forming the excitation electrode. Communication system according to claim 1, characterized in that it is approximately half the pitch. 3. The excitation electrode and the acoustoelectric transducer are both comb-shaped electrodes, and the comb-shaped electrode constituting the excitation electrode is a double electrode, and the comb-shaped electrode constituting the acoustoelectric transducer is formed. The communication system according to claim 1, wherein the electrode is a single electrode, and the electrode pitch of the excitation electrode and the electrode pitch of the acoustoelectric converter are substantially equal. 4. The communication according to claim 1, further comprising a phase shift means for changing the phase of at least one of the received signal and the output signal from the code generation means. system. 5. The communication system according to claim 1, further comprising two surface acoustic wave elements. 6. A means for branching a received signal into two and a means for branching an output signal from the code generating means into two and the two.
6. The communication system according to claim 5, further comprising: a means for changing the phase of two outputs of at least one of the two branching means. 7. The arrangement of the acoustoelectric converter with respect to the excitation electrode in one of the two surface acoustic wave elements is the same as the arrangement of the acoustoelectric converter with respect to the excitation electrode in the other of the two surface acoustic wave elements. On the other hand, v / 8f (v is the propagation velocity of the surface acoustic wave, f is the center frequency of the signal input to the first and second surface acoustic wave elements) is shifted in the propagation direction of the surface acoustic wave. Communication system according to claim 5, characterized in that 8. The arrangement of one excitation electrode for the acoustoelectric converter in one of the two surface acoustic wave elements is such that one excitation electrode is arranged for the other of the two surface acoustic wave elements in the acoustoelectric converter. For placement of electrodes,
It is characterized in that it is shifted by v / 4f in the propagation direction of the surface acoustic wave (v is the propagation velocity of the surface acoustic wave, and f is the center frequency of the signal input to the first and second surface acoustic wave elements). The communication system according to claim 5. 9. The surface acoustic wave device according to claim 5, wherein the two surface acoustic wave devices are integrally formed on the same substrate.
The communication system according to any one of 1. 10. The communication system according to claim 1, wherein the received signal is a spread spectrum modulated signal.