JPH07254868A - Chirp type saw spread spectrum modem, its constituting method, communication equipment and system using the modem, chirp signal multiplexing method, and detection of correlation from multiplexed chirp signal - Google Patents

Abstract

PURPOSE:To suitably generate a chirp signal and to detect correlations between the chirp signal and a spread spectrum modulation signal by taking one electrode from electrodes constituting each of first and second SAW(surface acoustic wave) filters, which are formed on a piezoelectric substrate, as a common electrode and using the complex conjugate property of the frequency characteristic of the common electrode. CONSTITUTION:An input electrode 2 and an output electrode 4 are constituted on the surface of a piezoelectric substrate 1 where a SAW is propagated, and the first SAW filter which outputs the chirp signal from the output electrode 4 at the time of input of an impulse to the input electrode 2 and the second SAW filter which detects correlations between the chirp signal and a signal subjected to spread spectrum modulation at the time of input or this signal to the input electrode 2 are provided. One of electrodes 2 and 4 is constituted as a common electrode 3. That is, the complex conjugate property of frequency characteristics of the common electrode 3 is used to perform chirp signal generation and correlation detection on the single piezoelectric substrate 1.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to surface acoustic waves (SAW).
The present invention relates to a SAW spread spectrum demodulator that spread spectrum demodulates a spread spectrum modulated signal using a matched filter, and more particularly to a chirp SAW spread spectrum modulator / demodulator obtained by improving this. The present invention further relates to a chirp type spread spectrum communication device configured by using the chirp type SAW spread spectrum modulator / demodulator and a spread spectrum communication system configured by using the chirp type spread spectrum communication device. And the present invention is
The present invention relates to a method of constructing a chirp SAW spread spectrum modulator / demodulator according to the present invention. In addition, the present invention relates to a method of multiplexing a chirp signal using the chirp SAW spread spectrum modulator / demodulator of the present invention and detecting a correlation while separating the chirp signal from the multiplexed chirp signal.

[0002]

2. Description of the Related Art A spread spectrum system is a radio communication system which has high confidentiality of signals and is resistant to interference from other signal sources. Several methods are known as the spread spectrum method. For example, in the direct modulation method, the transmission signal is phase-modulated by the code modulator installed in the transmitter,
The received signal is demodulated by the code demodulator mounted on the receiver. The code used in this modulation / demodulation (spread spectrum modulation / demodulation) is called a pseudo noise (PN) code, and the spectrum distribution of the transmission signal is spread by performing modulation with this code. Therefore, even if another person receives the transmission signal subjected to the spread spectrum modulation, the P signal used for this modulation is used.
It cannot be demodulated without knowing the N code (signal confidentiality). Further, even if a radio signal in a close band is emitted from another signal source, the spectrum is spread, so that it is difficult to receive the interference.

Among the characteristics of the spread spectrum system, signal confidentiality is emphasized particularly in military-related communication equipment in which confidentiality of information is important. Furthermore, in addition to this confidentiality, the property of being resistant to interference is emphasized in various consumer devices. First, the frequency of wireless systems has been increasing in recent years, and the deterioration of received signal quality due to multipath interference has become a serious problem. This problem can be mitigated or solved by a spread spectrum method that is strong against interference. Secondly, a spread spectrum method for spreading the spectrum of a transmission signal is effective when it is desired to share a radio frequency with another radio system in order to effectively use frequency resources.

To implement the spread spectrum method,
It is necessary to mount a code modulator (spread spectrum modulator) on the transmitter and a code demodulator (spread spectrum demodulator) on the receiver. Further, the modulation rate in this spread spectrum modulator must be higher than the transmission rate of the signal (data) to be transmitted. Furthermore, the demodulation speed of the spread spectrum demodulator of the receiver must be as high as the modulation speed of the transmitter. Since such high-speed processing is required, designers and the like are required to consider the components related to spread spectrum modulation / demodulation more than the components related to data modulation / demodulation.

Further, in the spread spectrum demodulator, it is necessary to obtain synchronization with the code used in the transmitter. As a method of acquiring synchronization, for example, there is a method of repeating demodulation until synchronization is achieved, or a method of executing synchronization acquisition and spread spectrum demodulation in parallel. However, in these methods, there are problems that it takes time to acquire synchronization and that the configuration of the receiver becomes complicated. Especially, when the spread spectrum modulation signal is multiplexed and transmitted, the circuit configuration becomes more complicated.

As a spread spectrum demodulator which does not cause this kind of problem, there is a configuration using a SAW convolver. That is, the same code as that used in the spread spectrum modulator is time-inverted and input to the SAW convolver, the correlation with the received signal is obtained, and the data is demodulated when the correlation value reaches a peak. Spread spectrum demodulation can be performed without causing the problems described above. However, when such a configuration is used, a code obtained by time-reversing the code used in the spread spectrum modulator is required. Moreover, the efficiency of the SAW convolver is not so good and the insertion loss is large.

As another configuration of the spread spectrum demodulator, there is a configuration using a SAW matched filter. That is, a filter (matched filter) having a complex conjugate frequency response with respect to the frequency spectrum of the spread spectrum modulated transmission signal is realized by using the SAW delay line. By inputting the received signal to this filter, S
Signal (electrode) determined by AW matched filter configuration
The correlation between the pattern and the reception signal is obtained, and the reception signal can be subjected to spread spectrum demodulation by detecting the timing (phase) at which this correlation reaches a peak. When such a configuration is used, a time-reversed code as in the SAW convolver is not necessary and the insertion loss is relatively good.

[0008]

However, in the case of performing spread spectrum demodulation using the SAW matched filter, this filter must be designed according to the frequency spectrum of the spread spectrum modulated transmission signal. That is, the characteristics of the SAW matched filter must be designed according to the code used in the spread spectrum modulator.

Further, the temperature characteristics of the SAW matched filter must be stable over the entire temperature range in which the system is used, and this stability must be absolutely obtained on the basis of the ambient temperature.

Further, when two-way communication is required as in a local area network (LAN) arranged in an office, for example, when attempting spread spectrum communication between a server and a client, spread spectrum is spread to each device. Since the modulator and the spread spectrum demodulator must be mounted together, the size and complexity of the device configuration will increase, which will result in cost demerits.

Even if a chirp signal whose frequency changes with time is used as the spread spectrum modulation signal or the demodulation signal, it is difficult to obtain a good chirp signal. That is, it is difficult to obtain a chirp signal whose frequency smoothly changes with time in any conventionally known spread spectrum modulator.

In addition, when the chirp signals are multiplexed and transmitted, it is difficult to obtain a plurality of chirp signals to be multiplexed from a single signal source. In other words, the rate of frequency change of the chirp signal is high, and in order to generate a plurality of such chirp signals with a single signal source, it is necessary to accurately reproduce the amplitude and phase of the signal with respect to the signal source. Required. Answering such demands is often technically difficult. Therefore, in order to multiplex and transmit the chirp signal, it is necessary to provide a plurality of signal sources for generating the chirp signal and to add the outputs thereof, but this causes an increase in circuit cost and also the This causes deterioration of signal characteristics due to characteristic mismatch.

The present invention has been made to solve the above problems, and firstly, a spread spectrum modulator installed in a transmitter and a spread spectrum demodulator installed in a receiver. SA having exactly the same configuration
It is possible to realize by using W electrode, and by this,
The purpose is to easily match the characteristics of the spread spectrum demodulator with the characteristics of the spread spectrum modulator. Secondly, it is not necessary to absolutely secure the stability of the temperature characteristics based on the ambient temperature standard, but only the temperature difference (relative temperature) between the transmitter and the receiver is used as the standard. It is intended to be used in. Third, by configuring the spread spectrum modulator and spread spectrum demodulator as a single component, the spread spectrum modulator and spread spectrum can be combined into a single device, such as a system for bidirectional communication with spread spectrum. It is an object of the present invention to make it possible to reduce the size and weight of the device even if the demodulator must be installed together. Fourth
In addition, it is possible to suitably generate a chirp signal and use it as a spread spectrum modulation signal, and further to demodulate the data carried by this spread spectrum modulation signal on a device of the same configuration and the same specifications. To do.
Fifthly, an object is to obtain a modulator that realizes multiplexing of chirp signals with a simple circuit configuration and good characteristics, and to obtain a demodulator that can preferably separate correlation peaks from the multiplexed chirp signals. And

[0014]

In order to achieve such an object, the SAW spread spectrum modulator / demodulator of the present invention comprises:
A first SAW filter having a piezoelectric substrate capable of propagating SAW on its surface, an input electrode and an output electrode formed on the surface, and outputting a chirp signal from the output electrode when an impulse is input to the input electrode. And a second SAW filter having an input electrode and an output electrode formed on the surface, and detecting a correlation between a spread spectrum modulated signal and the chirp signal when the signal is input to the input electrode, And one of the input electrode and the output electrode of the first SAW filter is configured as a common electrode with the one of the input electrode and the output electrode of the second SAW filter, and the SAW is on the side of the first SAW filter. Complex conjugation of the frequency characteristics of the common electrode caused by the difference in whether the wave is transmitted or received to the second SAW filter or the wave is transmitted or received to the second SAW filter side. Used, and performs the generation and correlation detection of the chirp signal on a single piezoelectric substrate.

Further, the SAW spread spectrum modulator / demodulator of the present invention comprises an output electrode of the first SAW filter and a second SAW filter.
It is characterized in that the input electrode of the W filter is a common electrode. That is, the first structure of the SAW spread spectrum modulator / demodulator of the present invention is a piezoelectric substrate capable of propagating SAW on its surface, and a SAW generated in response to the input of an impulse to form a predetermined direction on the piezoelectric substrate. This SA
And an input electrode for transmitting W and formed on the surface at a first predetermined distance from the input electrode in the predetermined direction,
When the SAW transmitted by the input electrode is received, it has a characteristic of converting it into a chirp signal and outputting it. At the same time, the SAW is generated in response to the input of the spread spectrum modulation signal and the And a common electrode that is formed on the surface at a second predetermined distance in the opposite direction to the input electrode when viewed from the common electrode and receives the SAW transmitted by the common electrode. Whether the SAW is received from the input electrode side or transmitted to the output electrode side, and an output electrode having a characteristic of outputting a signal indicating the correlation between the spread spectrum modulated signal input to the input terminal and the chirp signal. It is characterized in that the chirp signal is generated and the correlation is detected on a single piezoelectric substrate by using the complex conjugate property of the frequency characteristic of the common electrode caused by the difference.

The SAW spread spectrum modulator / demodulator of the present invention comprises an output electrode of the first SAW filter and a second SAW filter.
The output electrode of the W filter is a common electrode. That is, the second configuration of the SAW spread spectrum modulator / demodulator of the present invention is the piezoelectric substrate capable of propagating SAW on the surface thereof, and the first substrate on the piezoelectric substrate which is formed on the surface and generates SAW in response to the input of an impulse. Of the first input electrode for transmitting the SAW in the predetermined direction and the first predetermined direction of the surface viewed from the first input electrode to generate the SAW in response to the input of the spread spectrum modulation signal. A second input electrode for transmitting the SAW in a second predetermined direction opposite to the first predetermined direction on the piezoelectric substrate, and a second predetermined direction on the surface viewed from the first input electrode in the first predetermined direction. When the SAW transmitted by the first input electrode is received at a first predetermined distance and a second predetermined distance from the second input electrode in the second predetermined direction. This is the chirp signal A common electrode having a characteristic of converting and outputting, and a characteristic of outputting a signal showing the correlation between the spread spectrum modulation signal and the chirp signal when receiving the SAW transmitted by the second input electrode. And using the complex conjugate property of the frequency characteristic of the common electrode caused by the difference between receiving the SAW from the first input electrode side or receiving the SAW from the second input electrode side. It is characterized in that the chirp signal is generated and the correlation is detected on the substrate.

Further, the SAW spread spectrum modulator / demodulator of the present invention comprises an input electrode of the first SAW filter and a second SAW filter.
It is characterized in that the input electrode of the W filter is a common electrode. That is, the third structure of the SAW spread spectrum modulator / demodulator of the present invention is the piezoelectric substrate capable of propagating SAW on the surface thereof, and the SAW generated on the surface thereof in response to the input of an impulse to generate the SAW. Common to transmit the SAW in a predetermined direction, while generating the SAW in response to the input of the spread spectrum modulation signal, and transmit the SAW in a second predetermined direction opposite to the first predetermined direction on the piezoelectric substrate. When the SAW transmitted from the electrode to the first predetermined direction in the first predetermined direction is separated from the common electrode on the surface by the common electrode, the SAW transmitted in the first predetermined direction is received. And a first output electrode having a characteristic of converting into a chirp signal and outputting the chirp signal and a second predetermined distance in the second predetermined direction when viewed from the common electrode on the surface. A second output electrode having a characteristic of outputting a signal indicating a correlation between the spread spectrum modulation signal and the chirp signal when receiving the SAW transmitted in the second predetermined direction, Is transmitted to the first output electrode side or to the second output electrode side by using the complex conjugate property of the frequency characteristic of the common electrode, which is generated on the single piezoelectric substrate. It is characterized by performing generation and correlation detection.

The chirp SAW spread spectrum modulator / demodulator according to the present invention is further characterized in that the time interval between the input impulses is not more than the duration of the generated chirp signal.

The chirp type SAW spread spectrum modulator / demodulator of the present invention is characterized in that the time interval of the input impulse is variable.

The chirp SAW spread spectrum modulator / demodulator according to the present invention is characterized in that the spread spectrum modulated signal to be inputted is a signal obtained by multiplexing a plurality of chirp signals.

The spread spectrum communication apparatus of the present invention comprises the SAW spread spectrum modulator / demodulator of the present invention, means for inputting impulses modulated by the data to be transmitted to the SAW spread spectrum modulator / demodulator, and output from the SAW spread spectrum modulator / demodulator. And a means for transmitting and outputting the chirp signal as a spread spectrum modulation signal.

The spread spectrum communication apparatus of the present invention receives the SAW spread spectrum modulator / demodulator of the present invention and a signal which carries data and is spread spectrum modulated by a chirp signal, and inputs the signal to the SAW spread spectrum modulator / demodulator. Means and means for reproducing data according to the timing when the correlation detected by the SAW spread spectrum modulator / demodulator has a peak.

The spread spectrum communication system of the present invention comprises:
A spread spectrum communication apparatus of the present invention that transmits a chirp signal as a spread spectrum modulation signal, and a spread spectrum communication apparatus of the present invention that receives a signal that is spread spectrum modulated by a chirp signal.

The chirp signal multiplexing method of the present invention is multiplexed by inputting a series of impulses to the SAW spread spectrum modulator / demodulator of the present invention at time intervals equal to or less than the duration of the generated chirp signal. It is characterized by generating a chirp signal.

In the correlation detection method from the multiplexed chirp signal of the present invention, the chirp signal multiplexed by the method of the present invention is input to the SAW spread spectrum modulator / demodulator as a signal subjected to spread spectrum modulation. By doing so, the correlation is detected while separating each of the multiplexed chirp signals.

Then, the SAW spread spectrum modulator / demodulator constructing method of the present invention is such that when the SAW transmitted from the input electrode of the first SAW filter is received by the output electrode of the first SAW filter, The pattern of the input electrode and the output electrode of the first SAW filter is determined so that a chirp signal obtained by spectrally spreading the impulse excited by is obtained, and the SAW transmitted from the input electrode of the second SAW filter is the second SAW filter. When the signal is received by the output electrode of the filter, one of the input electrode and the output electrode of the first SAW filter is connected to the second electrode so that a signal obtained by pulse-compressing the spread spectrum modulation signal that excites the input electrode is obtained. A second SAW filter while being used as a common electrode that also serves as either one of the input electrode and the output electrode of the SAW filter. The patterns of the input electrodes and the output electrodes and the arrangement intervals thereof are determined, and a total of three electrodes constituting the first SAW filter and the second SAW filter with the first SAW filter are formed on the surface of the piezoelectric substrate capable of propagating SAW on the surface. The SAW spread spectrum modulator / demodulator of the present invention is configured by forming the SAW spread spectrum modulator / demodulator with a predetermined arrangement interval and pattern.

[0027]

In the SAW spread spectrum modulator / demodulator of the present invention, the first and second SAW filters are formed on a single piezoelectric substrate. The first SAW filter is a filter for generating a chirp signal which is a spread spectrum modulation signal, and the second SAW filter is a filter for detecting a correlation peak of the spread spectrum modulation signal and the chirp signal (usually a matched signal). Filter). That is, when an impulse is input to the input electrode of the first SAW filter, a chirp signal is output from the output electrode of this filter. Further, when a spread spectrum modulated signal (spread spectrum modulated signal) is input to the input electrode of the second SAW filter, a signal indicating the correlation between the spread spectrum modulated signal and the chirp signal is output from the output electrode of this filter. Is output. Each electrode is designed so that such an action occurs.

In the present invention, either the input electrode or the output electrode of the first SAW filter and the second SW filter are used.
One of the input electrode and the output electrode of the AW filter is configured as a common electrode. That is, there are two SAW propagation directions (first direction and second direction) in the common electrode, and the frequency characteristic of the common electrode is the first direction.
The first SAW filter and the second SAW filter can be configured so as to realize the chirp signal generation by the former and the pulse compression by the latter, respectively, because they are complex conjugate with each other.

Therefore, by using the SAW spread spectrum modulator of the present invention, it becomes possible to perform chirp signal generation and pulse compression with complex conjugate characteristics except for time delay in the transmitter and the receiver. The spread demodulation characteristics match the spread spectrum modulation characteristics. Also,
Since the chirp signal is generated and the pulse compression (correlation detection) is performed on the same piezoelectric substrate, it is not necessary to absolutely ensure the stability of temperature characteristics based on the ambient temperature standard, and the temperature difference between the transmitter and the receiver ( Since it can be used only in a wide temperature range since it is only necessary to ensure the relative temperature) as a reference, it is not necessary to use a quartz substrate and insertion loss is reduced. Furthermore, since the spread spectrum modulator and spread spectrum demodulator are configured as a single component, the spread spectrum modulator and spread spectrum demodulator can be installed in a single device, such as a system for bidirectional communication involving spread spectrum. Even for applications that must be installed together, the device can be made compact and lightweight. Then, it becomes possible to generate a chirp signal whose frequency changes smoothly with time and use it as a spread spectrum modulation signal, and to demodulate the data carried by this spread spectrum modulation signal demodulation on the same device. Become.

Since the frequency characteristic of the SAW filter does not change even if the input and output are exchanged, the SAW spread spectrum modulator / demodulator of the present invention has the following structure: a) first SAW
A configuration in which the output electrode of the filter and the input electrode of the second SAW filter are used as common electrodes, b) a configuration in which the output electrode of the first SAW filter and the output electrode of the second SAW filter are used in common electrodes, and c) the first SAW filter input electrode and second
Of the configuration in which the input electrode of the SAW filter of the
Types are possible.

The present invention can also be applied to the multiplexing of chirp signals. That is, in the present invention, the time interval between the input impulses is further set to be equal to or less than the duration of the generated chirp signal, whereby a multiplexed chirp signal is obtained. Since the multiplexed chirp signals are signals generated by the same SAW filter based on the same principle, they have characteristics aligned with each other. As a result, it becomes unnecessary to use a plurality of signal sources and adder means for obtaining the multiplexed chirp signal, and the chirp signal can be multiplexed with a simple circuit configuration and good characteristics. Conversely, when a multiplexed chirp signal is input, it is possible to detect the correlation peak while separating the correlation peak from each chirp signal. This is because the correlation peaks are separated and obtained at the impulse time intervals. Also, if the time interval of the input impulses is changed according to the communication status, for example, the speed of data transmitted in spread spectrum transmission (data rate) can be changed as appropriate.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

(1) Configuration of Chirp SAW Spread Spectrum Modulator / Demodulator FIG. 1 shows the configuration of a chirp SAW spread spectrum modulator / demodulator 101 according to an embodiment of the present invention. The chirp SAW spread spectrum modulator / demodulator 101 shown in this figure has three types of electrodes 2 to 4 on the same surface of the piezoelectric substrate 1.
Is formed.

Of these electrodes, the impulse input electrode 2
The common electrode 3 is configured as a SAW filter that generates a spread spectrum modulation signal. That is, when an impulse is input to the electrode 2 via the terminal 5, the electrode 2 is excited by this impulse and SAW is generated on the surface of the substrate 1. This SAW propagates to the right and left in the figure when viewed from the electrode 2. Among them, the SAW propagating in the right direction is received by the electrode 3 and converted into an electric signal. Here, the electrode pattern of the electrodes 2 and / or 3 (for example, the pattern of the electrode width, the electrode pitch, the electrode length, etc.) is such that a chirp signal can be obtained from the electrode 3 when an impulse is input to the electrode 2. The chirp signal is designed to have a constant amplitude for a predetermined period (waveform shaping function) (weighting of electrodes 2 and 3). Therefore, by inputting an impulse modulated with data as an impulse, a chirp signal carrying data is output from the terminal 6. Since this chirp signal is a signal obtained by spreading the impulse in a spread spectrum, it can be transmitted as a spread spectrum modulation signal. Therefore, the terminals 5 and 6 are used as the input terminal of the impulse modulated by the data or the output terminal of the spread spectrum modulation signal (chirp signal), respectively, when the device of this figure is mounted on the communication device.

Further, the common electrode 3 and the demodulation signal output electrode 4
Constitute a SAW matched filter for demodulating a spread spectrum modulated signal. That is, when a signal is input to the electrode 3 via the terminal 6, the electrode 3 is excited by this signal and SAW is generated on the surface of the substrate 1. This SAW propagates to the right and left in the figure when viewed from the electrode 3. Among them, the SAW propagating in the right direction is received by the electrode 4 and converted into an electric signal. Here, the electrode pattern of the electrodes 3 and / or 4 (for example, the pattern of the electrode width, the electrode pitch, the electrode length, etc.) has complex frequency conjugate characteristics in the electrode 2 direction and the electrode 4 direction related to the electroacoustic conversion of the electrode 3. When a chirp signal is input to the electrode 3, the SAW filter composed of the electrodes 3 and 4 (reverses the SAW filter composed of the electrodes 2 and 3). Then, the chirp signal is pulse-compressed and the correlation peak is output. That is, when the chirp signal obtained from the SAW filter composed of the electrodes 2 and 3 is input to the electrode 3, the correlation between the signal and the electrode pattern reaches a peak at a predetermined timing.
Therefore, when the chirp signal which is the spread spectrum modulation signal is input to the electrode 3, the data carried by the chirp signal can be reproduced based on the signal (correlation peak) output from the electrode 4 through the terminal 7. . Therefore, the terminals 6 and 7 are used as a spread spectrum modulation signal input terminal or a spread spectrum demodulation signal output terminal, respectively, when the device of this figure is mounted in a communication device.

The operation and effects As described above, according to this embodiment, the electrodes 2 and / or 3 of the three kinds of electrodes 2-4 formed on a single piezoelectric substrate 1
Since a SAW filter for generating a chirp signal is formed by weighting the electrodes 2 and 3 with a predetermined weight,
By inputting an impulse to the signal, a chirp signal whose frequency smoothly changes with time and whose waveform is shaped can be obtained as a spread spectrum modulation signal. Further, by utilizing the fact that the frequency characteristic of the electrode 3 is a complex conjugate between the left and right propagation directions, it is possible to pulse-compress the chirp signal input to the electrode 3 as the spread spectrum modulation signal to obtain the correlation peak. Therefore, the data can be demodulated from the chirp signal generated by the SAW filter including the electrodes 2 and 3 described above. Furthermore, since these two types of SAW filters are formed on a single piezoelectric substrate 1 and a part of their configuration is shared, a chirp type spread spectrum modulation / demodulation that is compact and lightweight and stable in temperature. You get a bowl.

(2) Configuration of Chirp Spread Spectrum Communication Device FIG. 2 shows the configuration of a chirp spread spectrum communication device 201 constructed by using the chirp SAW spread spectrum modulator / demodulator 101 shown in FIG. . The chirp spread spectrum communication device 201 shown in this figure.
In addition to the chirp SAW spread spectrum modulator / demodulator 101, the impulse generator 102 and the transmission / reception switch 10
3, transmitting mixer 104a, receiving mixer 104b, local oscillator 105, high frequency power amplifier 106, distributor 1
07, an antenna 108, a low noise amplifier 109, and a data regenerator 110.

The impulse generator 102 generates an impulse modulated by the data to be transmitted and inputs it to the electrode 2 via the terminal 5 of the chirp type SAW spread spectrum modulator / demodulator 101. The electrode 2 excites the surface of the piezoelectric substrate 1 by this impulse to generate SAW. The generated SAW is received by the electrode 3 after a lapse of time corresponding to the distance between the electrode 2 and the electrode 3. The electrode 3 converts the received SAW into an electric signal. The obtained signal is a chirp signal whose frequency changes smoothly with time, and the chirp signal is waveform-shaped.
If the SAW filter on the transmitting side (for generating the chirp signal) is designed so that the amplitude of the chirp signal is constant within one cycle of the data to be transmitted, the amplitude modulated at the same speed as the data to be transmitted can be obtained. A chirp signal having is obtained. This chirp signal (chirp signal for transmission) is transmitted / received by the transmission / reception switch 1 via the terminal 6 as a spread spectrum modulation signal.
03, and further to the transmission mixer 104a. The transmission mixer 104a mixes the local oscillation signal generated by the local oscillator 105 with the spread spectrum modulation signal, and converts the mixed signal into a radio frequency (RF). The high frequency power amplifier 106 power-amplifies the signal converted into RF and supplies the amplified signal to the antenna 108 via the distributor 107.
As a result, a signal carrying data and spread spectrum modulated is wirelessly transmitted. Further, since the amplitude of each chirp signal is constant in one cycle of data, the chirp signal is less susceptible to the nonlinearity of the mixer 104a and the amplifier 106. Therefore, additional problems such as expansion of the frequency bandwidth do not occur.

On the contrary, when a spread spectrum modulation signal (chirp signal) carrying data is received from another communication device, the low noise amplifier 1 is first passed through the distributor 107.
This signal is supplied to 09, and is low-noise amplified by the low-noise amplifier 109. The low-noise amplified signal is mixed with the local oscillation signal by the reception mixer 104b, and R
Converted from F to intermediate frequency (IF). The signal converted into IF is input to the electrode 3 via the transmission / reception switch 103 and the terminal 6. The electrode 3 excites SAW on the surface of the piezoelectric substrate 1 by this signal. The generated SAW is electrode 3
Then, the wave is received by the electrode 4 after a lapse of time corresponding to the distance between the electrode 4 and the electrode 4. The electrode 4 converts the received SAW into an electric signal. The electrodes 3 and 4 are designed to output the correlation peak by pulse-compressing the chirp signal by utilizing the fact that the frequency characteristic of the electrode 3 is complex conjugate in the left and right propagation directions. Data can be reproduced based on the signal. This reproduction is performed by the data reproducer 110.

The operation and effect Hence, by mounting the chirp type SAW spread spectrum modulator-demodulator 101 according to this embodiment, L in the office
The chirp spread spectrum communication apparatus 201 that performs bidirectional communication involving spread spectrum, such as AN, can be made smaller and lighter.

(3) Chirp spread spectrum communication system FIG. 3 shows a chirp spread spectrum communication apparatus 2 of FIG.
01 and a chirp type spread spectrum communication device 201 ′ having the same configuration as that of the chirp type spread spectrum communication system. When the system is configured as shown in this figure, the chirp type SAW spread spectrum modulator / demodulator 101 mounted on each of the chirp type spread spectrum communication devices 201 and 201 ′ can have the same principle and the same characteristics. Therefore, modulation / demodulation with the same principle and the same characteristics can be realized in each of the chirp spread spectrum communication devices 201 and 201 '. At this time, since the complex conjugate property of the frequency characteristic of the electrode 3 related to the SAW propagation direction is used, the design of determining the characteristic of the spread spectrum demodulator in consideration of the characteristic of the spread spectrum modulator becomes unnecessary. Further, since the modulation and demodulation with the same principle and the same characteristics are performed in both the chirp spread spectrum communication devices 201 and 201 ', the temperature stability of the chirp spread spectrum demodulator is absolutely ensured on the basis of the ambient temperature. There is no need. That is, it suffices that the temperature characteristics are stable with respect to the difference between the operating temperature of the chirp type spread spectrum communication device 201 and the operating temperature of the chirp type spread spectrum communication device 201 ′. Generally, chirp spread spectrum communication devices 201 and 20.
When the operating temperature range of 1'is compared with the operating temperature difference between the two, the latter is smaller, so that the usable temperature range of the chirp spread spectrum communication devices 201 and 201 'is expanded.

(4) Method of Constructing Chirp SAW Spread Spectrum Modulator / Demodulator Next, the method of constructing the chirp SAW spread spectrum modulator / demodulator 101 shown in FIG. 1 will be described in more detail.

Design of Chirp Signal First, for simplification of explanation, a linear chirp signal whose frequency changes linearly with time is considered as the chirp signal. The characteristic h (t) of the linear chirp signal in the time domain can be expressed by the following equations (1) to (4).

[0044]

## EQU00001 ## h (t) = A (t) exp (j.phi. (T)) (1)

## EQU2 ## φ (t) = 2πf (t) t + φ ₀ (2)

F (t) = α / 2 · t + f ₀ (3)

A (t) = A ₀ (when t ₁ ≦ t ≦ t ₂ ) = 0 (when t <t ₁ or t ₂ <t) (4) where j is an imaginary unit and φ ₀ Is a phase offset, α is a frequency change rate, and f ₀ is a frequency offset.

As represented by the equation (3), the frequency f (t) of the chirp signal, and thus the phase φ, as the time t passes.
(T) changes linearly. The linear chirp signal is a chirp signal having such a property. Further, the amplitude A (t) of the linear chirp signal becomes A _{0 at} time t ₁ ≦ t ≦ t ₂ as represented by the equation (4). That is, the duration of the chirp signal is the period of t ₁ ≦ t ≦ t ₂ .

Further, this value A ₀ is preferably constant. This is because if A ₀ changes with time t, it is necessary to take into account the non-linearity of the circuits in the subsequent stage (the mixer 104a and the amplifier 106 in the case of transmission). When the generated chirp signal is used as the transmission signal, if the amplitude A ₀ is constant regardless of the time t, the transmission signal is defined regardless of the nonlinearity of the mixer 104a and the amplifier 106 and without any special processing. It is possible to meet the limited frequency bandwidth.

Chirp Signal and Spread Spectrum Communication Such a chirp signal can be used for spread spectrum communication.

First, the frequency offset is f ₀ to f ₀ ′.
When the frequency f changes to
(T) is represented by f ′ (t) represented by the following equation (5), and phase φ (t) represented by the equation (2) is represented by φ ′ (t) represented by the following equation (6). To each.

[0049]

F ′ (t) = α / 2 · t + f ₀ ′ (5)

Φ ′ (t) = 2πf ′ (t) t + φ ₀ = 2πf (t + 1 / α · (f ₀ ′ −f ₀ )) · (t + 1 / α · (f ₀ ′ −f ₀ )) + φ ₀ = Φ (t + 1 / α · (f ₀ ′ −f ₀ )) + φ ₀ ′ = φ (t + dt) + φ ₀ ′ (6) where φ ₀ ′ and dt are the following formulas (7) and (8). It is represented by.

[0050]

(7) φ ₀ ′ = π / α · (f ₀ ′ −f ₀ ) · (f ₀ ′ + f ₀ ) ... (7)

Dt = t + 1 / α (f ₀ ′ −f ₀ ) ... (8) Therefore, the frequency characteristic h ′ of the chirp signal in this case is obtained.
(T) is represented by the following equation (9).

[0051]

H ′ (t) = A (t) exp (jφ ′ (t)) = A (t) exp (j (φ (t + dt) + φ ₀ ′)) (9) On the other hand, the equation (1) Suppose that the linear chirp signal having the characteristic h (t) shown in is transmitted and the receiving side receives this signal at time t + dt, the received signal has the characteristic h ″ represented by the following equation (10). It can be expressed as (t).

[0052]

H ″ (t) = h (t + dt) = A (t + dt) exp (jφ (t + dt)) (10) Therefore, h ′ (t) of the equation (9) and h of the equation (10). ''
The difference in (t) is only the term φ ₀ ′ that does not change with time. This means that the received signal obtained when communication is performed using a linear chirp signal is a signal obtained by adding a change in frequency offset or phase offset to h (t) in addition to the delay due to dt. I mean. In general, the distance between the transmitting and receiving points is indefinite, and the transmitting and receiving clocks are asynchronous, so the influence of dt and the influence of changes in frequency offset or phase offset can be ignored. Also, if dt is sufficiently smaller than t ₂ −t ₁ , d
The effect of t becomes even smaller. In other words, by using the chirp signal, asynchronous communication can be realized between transmission and reception.

If spread spectrum communication using a chirp signal can be realized, confidentiality of information and strength against noise can be obtained. In order to demodulate the spread spectrum modulation signal which is a chirp signal, it is necessary to calculate the correlation with the chirp signal used at the time of modulation, and as a means for that, it is preferable to use a matched filter. If the received signal is demodulated at the timing when the correlation obtained by the matched filter has a peak, the signal having the signal propagation path difference can be separated, so that the interference caused by the multipath can be removed to some extent.

Source of chirp SAW spread spectrum modulation
Management will now be described the principle of chirp type spread spectrum modulation in the present invention.

First, regarding the frequency characteristics of the SAW filter, the terms of electroacoustic conversion by the input electrode and SAW on the piezoelectric substrate are used.
Is expressed by the product of the term indicating the time required for propagating and the term of acoustoelectric conversion by the output electrode. Therefore, the frequency characteristic relating to the electroacoustic conversion of the input electrode 2 in the example is S _I (ω), the frequency characteristic relating to the acoustoelectric conversion of the common electrode 3 is S _C (ω), and the frequency characteristic between the input electrode 2 and the common electrode 3 is SAW
When the propagation time is T ₁ , the frequency characteristic S ₁ (ω) of the SAW filter formed by the electrodes 2 and 3 is

[Number 11] _{S 1 (ω) = S I} (ω) S C (ω) exp (-jωT 1) ... is (11). When an impulse whose frequency characteristic is represented by I (ω) (provided that it is modulated by transmission data) is input to the electrode 2, the electrode 3 has the following frequency characteristic H (ω). An electric signal is obtained.

[0056]

H (ω) = I (ω) S ₁ (ω) = I (ω) S _I (ω) S _C (ω) exp (−jωT ₁ ) ... (12) Therefore, from the electrodes 2 and 3. In order to obtain the chirp signal by the configured SAW filter, when the Fourier transform of the chirp signal (time characteristic h (t)) is H (ω), the frequency characteristics S _I (ω) of the electrodes 2 and 3 and S
_C (ω) must satisfy the relationship of Expression (12). That is, the electrodes 2 and 3 have their frequency characteristics S _I
The weighting is designed so that (ω) and S _C (ω) satisfy the equation (12) and thus the chirp signal of the frequency characteristic H (ω) is obtained from the electrode 3.

Source of chirp SAW spread spectrum demodulation
In order to demodulate the spread spectrum modulated signal by the chirp signal using the electrode 3 designed in this way,
It is necessary to provide the electrode 4 on the side opposite to the electrode 2 when viewed from the electrode 3, and to design the electrode 4 as follows.

The principle underlying this design is that the relationship of equation (11) does not change even if the input / output relationship is exchanged. That is, the electrode 3 in the example
The frequency characteristic of the SAW filter using the electrode 2 as the input electrode and the electrode 2 as the output electrode is also the characteristic S ₁ (ω) represented by the equation (11).

Further, in the SAW filter, generally, when a certain electrode excites the surface of the piezoelectric substrate, the SAW generated thereby propagates in two directions on the piezoelectric substrate. Therefore, the SAW generated when the common electrode 3 is used as the input electrode propagates to the electrode 2 side while the SAW is generated.
Propagate to the side. When the frequency characteristic related to acoustoelectric conversion of the electrode 4 is S _O (ω) and the time required for SAW to propagate between the SAW electrodes 3 and 4 is T ₂ , the electrode 3 is used as an input electrode and the electrode 4 is output. The frequency characteristic S ₂ (ω) of the SAW filter used as the electrode is expressed by the following equation (13).
That is, for the SAW that transmits (or receives) in the opposite direction (direction of the electrode 4), the frequency characteristic of the electrode 3 is S _C ^* (ω) related to complex conjugation.

[0060]

S ₂ (ω) = S _C ^* (ω) S _O (ω) exp (−jωT ₂ ) ... (13) Therefore, the chirp signal whose frequency characteristic is represented by H (ω) is transmitted to the electrode 3. When input, an electric signal whose frequency characteristic is represented by the following P (ω) is obtained from the electrode 4.

P (ω) = H (ω) S ₂ (ω) = H (ω) S _C ^* (ω) S _O (ω) exp (−jωT ₂ ) ... (14) This signal P (ω) Is required to represent the correlation peak, the SAW filter composed of the electrodes 3 and 4 is a matched filter. For that purpose, the time T ₂ , that is, the interval between the electrodes 3 and 4 is set so as to satisfy the condition of the negative time required for forming the matched filter, and S ₂ (ω) has the following characteristic. , S
_It is sufficient to design _C ^* (ω) S _O (ω), that is, the structure (weighting) of the electrodes 3 and 4.

[0061]

S ₂ (ω) = H ^* (ω) exp (−jωT ₂ ) ... (15) Further, side lobes in the time domain (time side lobes)
In order to reduce the value, for example, the electrodes 4 (and 3) are humming-weighted so that the frequency characteristic P (ω) of the output signal from the electrode 4 is represented by the following equation (16). . Of course, other weightings are possible.

[0062]

Equation 16] _{P = 0.08 + 0.92cos (2π (} f-f c) / B) (f c -B / 2 ≦ f ≦ f c + if B / 2) = 0 (otherwise) ... (16 ) Where f _c is the center frequency of the received signal and B is the used frequency bandwidth.

Relationship between two SAW filters By designing the electrodes 2 to 4 as described above, it is possible to generate a chirp signal and demodulate a spread spectrum modulation signal obtained by using the chirp signal. . That is, since the frequency characteristic of the electrode 4 when transmitting the SAW from the electrode 3 to the electrode 4 is complex conjugate with that when transmitting the SAW to the electrode 2, the SAW filter including the electrodes 3 and 4 is used. The frequency characteristic S ₂ (ω) can be easily set as the matched filter characteristic. This makes it possible to realize the functions of chirp signal generation and chirp signal correlation detection on a single piezoelectric substrate 1.

In general, the electromechanical conversion coefficient of the SAW filter is small, so that the insertion loss of the SAW filter is large. Further, the piezoelectric material, which has a relatively large electromechanical conversion coefficient and therefore is likely to reduce the insertion loss, has poor temperature characteristics and a large temperature coefficient of the SAW propagation delay time (that is, T ₁ and T ₂ described above are large due to temperature changes). fluctuate). The temperature coefficient of the SAW filter is obtained by inverting the sign of the temperature coefficient of the SAW propagation delay time, so that the magnitude of the temperature coefficient of the propagation delay time is generally an important issue in designing the SAW filter. Therefore, in the past, a crystal substrate that is stable in temperature has been used as a piezoelectric substrate.

On the other hand, in this embodiment, the chirp signal is generated and its correlation is detected on the single piezoelectric substrate 1. Therefore, it is not necessary for the frequency temperature coefficient to be stable over the entire temperature range in which the communication device is used, and it is sufficient if there is no significant frequency difference between the two communication devices that transmit and receive signals. Become. This is the 2
This means that it is only necessary to consider the temperature difference of the table. Generally, the temperature difference between the two units is smaller in each stage than in the entire temperature range in which the communication device is used. Therefore, in the present embodiment, it is possible to use a material other than quartz as the piezoelectric substrate 1, and it is possible to reduce the insertion loss. It will be possible.

(5) Multiplexing The configuration of the above embodiment is suitable for spread spectrum multiplex communication. That is, in the impulse generator 102, if the impulses are generated at a time interval shorter than the duration of the chirp signal, the chirp signals carrying different data can be preferably multiplexed. Further, when the multiplexed chirp signal is received from another SAW spread spectrum communication device, the autocorrelation peak can be suitably separated from each multiplexed chirp signal.

Multiplexing Principle In general, piezoelectric substrates used in SAW devices are linear over a very wide range of power levels. RF
The reason why SAW devices are widely used in IF and IF is that a high-performance filter having high linearity can be realized by the linearity of the piezoelectric substrate. This linearity is also used when the present embodiment is applied to the multiplexed transmission of chirp signals.

Now, a single impulse input from the impulse generator 102 is represented by i (t) in the time domain and I (ω) in the frequency domain. Then, the response output from the SAW filter composed of the electrodes 2 and 3 is represented by h (t) of the equation (17) in the time domain and H (ω) of the equation (18) in the frequency domain. It In addition, in Formula (17), the operator * has shown convolution.

[0069]

H (t) = i (t) * s ₁ (t) (17)

[Equation 18] H (ω) = I (ω) · S ₁ (ω) (18) If two impulses are input to the electrode 2 from the impulse generator 102 at a time interval t ₁ , the time interval is Since the delay due to t ₁ is represented by exp (−jωt ₁ ), the frequency response to the second impulse becomes the response shown on the left side of the following equation (19).

[0070]

H (ω) · exp (−jωt ₁ ) = I (ω) · S ₁ (ω) · exp (−jωt ₁ ) ... (19) As described above, the SAW filter has good linearity. Therefore, it is possible to superimpose equations (18) and (19). That is, a SAW composed of electrodes 2 and 3
The frequency response of the filter is 2 input at time interval t _1.
For each impulse, the response is represented by the following equation (20), and the time response is represented by the equation (21) obtained by the inverse Fourier transform of the equation (20). This indicates that the output of the SAW filter composed of the electrodes 2 and 3 is a signal obtained by adding the correlation between the electrode pattern of the SAW filter and each impulse.

[0071]

H (ω) · {1 + exp (−jωt ₁ )} = I (ω) · S ₁ (ω) · {1 + exp (−jωt ₁ )} (20)

H (t) + h (t−t ₁ ) = {i (t) + i (t−t ₁ )} * s ₁ (t) (21) In equations (20) and (21), 2 When the time interval t ₁ of the impulses is set shorter than the duration of the chirp signal, the signal output from the electrode 3 is the chirp signal output in response to the first impulse and the second impulse. It becomes a signal obtained by multiplexing the chirp signal output in response. Further, the two chirp signals to be multiplexed are generated by the same SAW filter according to the same principle, and thus have mutually uniform amplitudes and phases. Therefore, according to the present embodiment, a plurality of chirp signals can be accurately generated by a single signal source (SAW filter composed of the electrodes 2 and 3 in this embodiment) when performing spread spectrum multiplex transmission. The circuit configuration becomes simple.

Principle of Decomposition In addition, the cross-correlation between signals that belong to the same frequency band and are spread spectrum with different codes is generally worse than the cross-correlation between signals that are spread spectrum with the same code. Therefore, among the signals appearing at the output of the SAW filter on the demodulation side (SAW filter composed of the electrodes 3 and 4 in this embodiment), the level of the time spurious generated by the input of the signals having the different signs is the same as the above. It is generally lower than the case of the signals related to the code. Therefore, as described above, the correlation peak can be preferably detected from the plurality of chirp signals generated by the same SAW filter by using the same matched filter. Furthermore, when the multiplexed chirp signal generated by such a principle is received from another spread spectrum communication device, the correlation peak obtained by inputting this to the electrode 3 was used when the chirp signal was generated. It is obtained separately for each chirp signal at an impulse time interval t ₁ . That is, the peak of the correlation between the electrode pattern of the SAW filter composed of the electrodes 3 and 4 and the chirp signal corresponding to the second impulse is the peak of the correlation between the electrode pattern of this SAW filter and the chirp signal corresponding to the first impulse. It occurs after the time interval t ₁ from the peak of the correlation with. As a result, the correlation peak can be detected while being separated from the plurality of multiplexed chirp signals. Since the impulse used to generate the chirp signal is modulated by the data, each data can be reproduced properly by detecting the correlation peak while separating the correlation peak from each chirp signal.

Variable Performance of Data Rate Further, according to this embodiment, the data rate can be changed by appropriately changing the time interval of impulses. For example, if the time interval is changed in consideration of the communication status (the degree of noise and the degree of interference from other systems) between the spread spectrum communication apparatuses 201 and 201 ′ shown in FIG. 3, the data rate becomes the communication status. The rate can be adjusted accordingly.

(6) Others The characteristics of the filter composed of the electrodes 3 and 4 are as follows.
It does not change whether the electrode 3 or the electrode 4 is used as an input electrode. Similarly, the characteristics of the filter composed of the electrodes 2 and 3 do not change regardless of which of the electrodes 2 and 3 is used as the input electrode. Therefore, the configuration of the present invention is not limited to the configuration in which the electrodes 2 and 3 are used as input electrodes and the electrodes 3 and 4 are used as output electrodes. Further, the number of chirp signals to be multiplexed is not limited to two and may be three or more. When the present invention is applied to multiplexing, the pattern of each electrode needs to be set so that the waveform can be shaped so that the multiplexed chirp signal has good characteristics.

[0075]

As described above, according to the present invention,
One of each of the electrodes forming the first and second SAW filters formed on a single piezoelectric substrate is taken out as a common electrode, and the complex conjugate property of the frequency characteristics of the common electrode depending on the SAW propagation direction is used. Therefore, the chirp signal can be suitably generated, the correlation between the chirp signal and the spread spectrum modulation signal can be detected, and in addition, these functions can be suitably realized on the single piezoelectric substrate. Therefore, by installing the chirp type SAW spread spectrum modulator / demodulator of the present invention, it is possible to make the spread spectrum modulator / demodulator that performs bidirectional communication involving spread spectrum, such as a LAN in an office, smaller and lighter. Further, according to the present invention, a chirp type S mounted on a plurality of spread spectrum communication devices.
Since the AW spread spectrum modulator / demodulator can have the same configuration according to the present invention, modulation / demodulation with the same principle and the same characteristics can be realized in each spread spectrum communication device.
In addition, according to the present invention, since the modulation and demodulation of the same principle and the same characteristics are performed in any of the plurality of chirp spread spectrum communication apparatuses that wirelessly communicate with each other, the temperature stability of the chirp SAW spread spectrum demodulator is improved. It is no longer necessary to secure the absolute temperature standard. As a result, the usable temperature range of the chirp spread spectrum communication device is widened, and it is not necessary to use a quartz substrate, and it is possible to reduce the insertion loss by using a material having good electroacoustic conversion characteristics.

In the present invention, a) a structure in which the output electrode of the first SAW filter and the input electrode of the second SAW filter are used as a common electrode, b) the output electrode of the first SAW filter and the second SAW A configuration in which the output electrode of the filter is used as a common electrode, c) the input electrode of the first SAW filter and the second SW filter
It can be realized by any of the configurations in which the input electrode of the AW filter is a common electrode.

Further, according to the present invention, the time interval of the input impulses is set to be less than or equal to the duration of the generated chirp signal, so that a multiplexed chirp signal can be obtained. Further, since the multiplexed chirp signals are signals generated on the same principle by the same SAW filter, they have characteristics aligned with each other, and a plurality of signal sources are used and addition means are used to obtain the multiplexed chirp signal. Is unnecessary, and multiplexing of chirp signals can be realized with a simple circuit configuration and good characteristics. Conversely, when a multiplexed chirp signal is input, it is possible to detect the correlation peak while separating the correlation peak from each chirp signal. Further, the data rate can be appropriately changed by changing the time interval of the input impulses, for example, according to the communication status.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a chirp type SAW spread spectrum modulator / demodulator according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a chirp type spread spectrum communication device realized by applying this embodiment.

FIG. 3 is a block diagram showing a configuration of a chirp type spread spectrum communication system including the chirp type spread spectrum communication device shown in FIG.

[Explanation of symbols]

1 piezoelectric substrate 2 impulse input electrode 3 common electrode 4 demodulation signal output electrode 5 impulse input terminal 6 spread spectrum modulation signal output and spread spectrum modulation signal input terminal 7 spread spectrum demodulation signal output terminal 101 chirp SAW spread spectrum modulator / demodulator 102 impulse generation Device 103 Transmission / reception switch 104a Transmission mixer 104b Reception mixer 105 Local oscillator 106 High frequency power amplifier 107 Distributor 108 Antenna 109 Low noise amplifier 201, 201 'Chirp spread spectrum communication device

 ─────────────────────────────────────────────────── --Continued from the front page (54) [Title of Invention] Chirp SAW spread spectrum modulator / demodulator, communication device and system using the same, chirp signal multiplexing method, correlation detection method from chirp signal and chirp SAW spread spectrum modulator / demodulator configuration method

Claims (13)

[Claims] 1. A piezoelectric substrate capable of propagating a surface acoustic wave on the surface thereof, and an input electrode and an output electrode formed on the surface, and when an impulse is input to the input electrode, a chirp signal is output from the output electrode. A first SAW filter for outputting, an input electrode and an output electrode formed on the surface, and when a spread spectrum modulated signal is input to the input electrode, the correlation between this signal and the chirp signal is detected. A second SAW filter, wherein one of the input electrode and the output electrode of the first SAW filter is configured as a common electrode with the one of the input electrode and the output electrode of the second SAW filter, and The common electric power generated by the difference between whether the surface wave is transmitted or received to the first SAW filter side or the second SAW filter side is transmitted or received. Of using the complex conjugate of the frequency characteristic, chirp type SAW spread spectrum modem which is characterized in that the generation and correlation detection of the chirp signal on a single piezoelectric substrate. 2. A piezoelectric substrate capable of propagating a surface acoustic wave on its surface, and a surface acoustic wave formed on said surface for generating a surface acoustic wave in response to an input of an impulse and transmitting the surface acoustic wave in a predetermined direction on the piezoelectric substrate. The first input electrode in the predetermined direction when viewed from the input electrode on the surface.
When the surface acoustic waves transmitted by the input electrodes are received, the surface acoustic waves are converted into chirp signals and output, and the surface acoustic waves respond to the input of the spread spectrum modulation signal. And a common electrode that generates a wave in the direction opposite to the input electrode on the piezoelectric substrate, and a second predetermined distance in the direction opposite to the input electrode when viewed from the common electrode on the surface, and is transmitted by the common electrode. An output electrode having a characteristic of outputting a signal showing the correlation between the spread spectrum modulation signal input to the common electrode and the chirp signal when receiving the surface acoustic wave Using the complex conjugate property of the frequency characteristics of the common electrode caused by the difference between receiving from the electrode side or transmitting to the output electrode side, the generation and phase of the chirp signal are generated on a single piezoelectric substrate. Chirp type SAW spread spectrum modem, characterized in that the detection. 3. A piezoelectric substrate capable of propagating a surface acoustic wave on its surface, and a surface acoustic wave formed on said surface for generating a surface acoustic wave in response to an input of an impulse, in the first predetermined direction on the piezoelectric substrate. Is formed on the surface in the first predetermined direction as viewed from the first input electrode, and a surface acoustic wave is generated in response to the input of the spread spectrum modulation signal on the piezoelectric substrate. A second input electrode for transmitting this surface acoustic wave in a second predetermined direction opposite to the first predetermined direction; and a first input electrode in the first predetermined direction on the surface when viewed from the first input electrode. A predetermined distance away from the second input electrode and a second predetermined distance in the second predetermined direction when viewed from the second input electrode, the surface acoustic wave transmitted by the first input electrode is received. The characteristic of converting this into a chirp signal and outputting it And a common electrode having a characteristic of outputting a signal indicating a correlation between the spread spectrum modulation signal and the chirp signal when the surface acoustic wave transmitted by the second input electrode is received, By using the complex conjugate property of the frequency characteristics of the common electrode caused by the difference between receiving the surface acoustic wave from the first input electrode side or receiving it from the second input electrode side, on a single piezoelectric substrate A chirp-type SAW spread spectrum modulator / demodulator characterized by performing generation of a chirp signal and correlation detection. 4. A piezoelectric substrate capable of propagating a surface acoustic wave on its surface, and a surface acoustic wave formed on said surface for generating a surface acoustic wave in response to an input of an impulse, in the first predetermined direction on the piezoelectric substrate. And a common electrode for generating a surface acoustic wave in response to the input of the spread spectrum modulation signal and transmitting the surface acoustic wave in a second predetermined direction opposite to the first predetermined direction on the piezoelectric substrate. When the surface acoustic waves that are formed on the surface at a first predetermined distance in the first predetermined direction from the common electrode and are transmitted by the common electrode in the first predetermined direction are received, And a first output electrode having a characteristic of converting into a chirp signal and outputting the chirp signal, and a second predetermined distance in the second predetermined direction when viewed from the common electrode on the surface, and the second electrode is formed by the common electrode. Sent in the specified direction A second output electrode having a characteristic of outputting a signal indicating the correlation between the spread spectrum modulation signal and the chirp signal when receiving the surface acoustic wave that has been oscillated, Generation and correlation detection of a chirp signal on a single piezoelectric substrate using the complex conjugate property of the frequency characteristics of the common electrode caused by the difference between transmitting to the output electrode side or transmitting to the second output electrode side A chirp SAW spread spectrum modulator / demodulator that performs the following. 5. The chirp SAW according to claim 1.
In the spread spectrum modulator / demodulator, a chirp SAW spread spectrum modulator / demodulator in which a time interval of input impulses is equal to or shorter than a duration of a generated chirp signal. 6. The chirp SAW spread spectrum modulator / demodulator according to claim 5, wherein the time interval of the input impulse is variable. 7. A chirp type SAW according to claim 1.
In the spread spectrum modulator / demodulator, the input spread spectrum modulated signal is a signal in which a plurality of chirp signals are multiplexed, and a chirp SAW spread spectrum modulator / demodulator. 8. A SAW spread spectrum modulator / demodulator according to claim 1, wherein the impulse modulated by the data to be transmitted is SA.
A spread spectrum communication device comprising: means for inputting to a W spread spectrum modulator / demodulator; and means for transmitting and outputting a chirp signal output from a SAW spread spectrum modulator / demodulator as a spread spectrum modulated signal. 9. A SAW spread spectrum modulator / demodulator according to any one of claims 1 to 8, means for receiving a signal which carries data and is spread spectrum modulated by a chirp signal, and inputs the signal into the SAW spread spectrum modulator / demodulator. A spread spectrum communication device comprising: means for reproducing data according to the timing at which the correlation detected by the SAW spread spectrum modulator / demodulator reaches a peak. 10. A spread spectrum communication apparatus according to claim 8, which transmits a chirp signal as a spread spectrum modulation signal, and a spread spectrum communication apparatus according to claim 9, which receives a signal spread spectrum modulated by the chirp signal. A spread spectrum communication system having. 11. A multiplexed chirp signal is generated by inputting a series of impulses to the SAW spread spectrum modulator / demodulator according to any one of claims 1 to 4 at time intervals equal to or less than the duration of the generated chirp signal. A chirp signal multiplexing method characterized by: 12. A chirp signal obtained by multiplexing the chirp signal obtained by the method according to claim 11 as a spread spectrum modulated signal to the SAW spread spectrum modulator / demodulator according to any one of claims 1 to 4. A method for detecting a correlation from a multiplexed chirp signal, wherein the correlation is detected while separating the signals from each other. 13. A chirp signal obtained by spectrally spreading an impulse that excites an input electrode when a surface acoustic wave transmitted from an input electrode of the first SAW filter is received by an output electrode of the first SAW filter. So that the pattern of the input electrode and the output electrode of the first SAW filter is determined so that the surface acoustic wave transmitted from the input electrode of the second SAW filter is received by the output electrode of the second SAW filter. In order to obtain a signal obtained by pulse-compressing the spread spectrum modulation signal that excites the input electrode, the first SAW
Either one of the input electrode and output electrode of the filter is
The second SAW filter is used as a common electrode that is also used as one of the input electrode and the output electrode of the SAW filter.
A total of three patterns are defined for the first and second SAW filters on the surface of the piezoelectric substrate capable of propagating surface acoustic waves on the surface, by defining the pattern of the input and output electrodes of the filter and their arrangement intervals. The SAW spread spectrum modulator / demodulator according to claim 1, wherein the SAW spread spectrum modulator / demodulator according to claim 1 is formed by forming the electrodes of (1) with a predetermined arrangement interval and pattern.