JPS6065638A - Demodulator - Google Patents

Abstract

PURPOSE:To demodulate a pseudo noise code at high speed with simple constitution by dividing the pseudo noise code into a prescribed time interval and supplying the code to a surface acoustic wave correlation device while giving a delay by the time interval to add the outputs of the correlation device. CONSTITUTION:A carrier wave to phase modulation is branched into four at an input terminal 40 according to the spectral pseudo noise (PN) code, and after they pass through delay elements 41-44 respectively, the result is inputted to surface acoustic wave correlation devices 51-54, and its output signal is synthesized at an output terminal 50. Electrodes corresponding to the time interval of the PN codes T1-T4 divided into four are arranged respectively to the correlation devices 51-54. A delay time Ti (i=1-n) of the delay elements 41-44 is set to satisfy Equation, when T0 is an optional time. Thus, a code start point corresponding to the PN codes 61-64 reaches the correlation devices 51-54 after the PN codes are applied to the terminal 40, they are processed individually at each correlation device and the correlation of the entire PN code having the time interval of T1+T2+T3+T4 is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a demodulator using a surface acoustic wave element. - [Technical background of the invention and its problems] With the development of communications, various communication methods have been developed. In particular, spread spectrum communication systems have been attracting attention recently.

This modulates the spectrum pseudo noise (PN code) of the signal to be transmitted and transmits it. In particular, the confidentiality of communications,
It is expected to be a future communication method because it has excellent resistance to interference waves and can be expected to make effective use of frequencies. The signal modulated by the PN code in this way is demodulated and reproduced into the original signal, and various methods have been considered for the demodulator. For low-speed transmission signals, demodulators using LSI or CCD are generally used; however, for high-speed signal transmission, the processing speed of the above-mentioned devices is currently too low.1 It is difficult to put this into practical use because the circuit is complicated.

Another demodulator uses surface acoustic waves.

An outline of the principle of a post-tuner using a surface acoustic wave element will be explained below. FIG. 1 schematically shows a PN code. The original signal is modulated with this PN code, and the carrier wave is further phase-modulated with this signal. That is, 1. -1, the phase of the carrier wave is switched by 1800 degrees. This signal is a spread spectrum signal. FIG. 2 shows a schematic diagram of the configuration of a correlator using a surface acoustic wave element that demodulates this signal into an original signal. The electrode wire pitch of the input/output quadrature transducer 1°3 is determined so that the center frequency matches the carrier wave, and the twisted output quadrature transducer 3 has a plurality of electrodes 31 separated by a distance matching the bit period shown in FIG.
It consists of These plurality of electrodes correspond to 1. of the above-mentioned PN code. According to -1, for example, in 1, the left electrode line is connected to the upper common electrode (bus bar) 32, and in -1, the left electrode line is connected to the lower common electrode 33.

Incidentally, the crowd displacement transducers 1 and 3 are each formed on a pressurized substrate. Further, numeral 2 in the figure indicates a surface acoustic wave excited by the input transducer 1. According to such a configuration, the code of the output transducer 3 and the PN code of the aforementioned transmitting side completely match, and
When the code matches the output side transducer 3, the maximum output is generated, and only a small output is generated at other codes or times. A demodulator using a surface acoustic wave element having such a configuration has a simple structure and is characterized by high speed signal processing.

However, in a demodulator where the PN code corresponds to a code with a long period, for example, 255 pits or more.

The output signal from the output center near the input side and the far output
The mismatch in signal strength and phase with the output signal from the electrode section cannot be ignored, and a normal PN code correlation cannot be established. This leads to a reduction in process gain, which is important in so-called spread spectrum, and demodulation with good S/H cannot be expected.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and is based on the long-period P
The object of the present invention is to provide a demodulator that can demodulate an N-code modulated signal at high speed and with a simple configuration.

[Summary of the invention]

The present invention divides the surface acoustic wave element for demodulation into a plurality of parts, and separately connects all the surface acoustic wave delay lines to have the same function as the surface acoustic wave element shown in FIG. 2 in an isometric manner. Configure the demodulator.

〔Effect of the invention〕

According to the present invention, it is possible to achieve a circuit that demodulates a long-period PN code with a simple configuration and without deteriorating the theoretically determined process gain. It's good, P
Since one period of the N code is divided into a plurality of surface acoustic wave elements, a substrate with a long surface acoustic wave propagation path is not required. This indicates that long-period correlation, which was conventionally limited by the length of the surface acoustic wave substrate, becomes possible.

Furthermore, since a long surface acoustic wave substrate is not required, there is also a practical RC advantage in that costs can be reduced.

[Embodiments of the invention]

Embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing the overall configuration. The carrier wave that has undergone phase modulation according to the PN code is branched into four at the input terminal 40. Delay elements 41 to 44 with multiple signal branches branched into four
After passing through the surface acoustic wave correlators 51 to 54 as illustrated in FIG.
Synthesized at 0. FIG. 4 shows a long-period PN code in time series.

Divide the PN code into 4 and calculate P corresponding to the time interval 61 of T1.
5 surface acoustic wave correlators with electrodes corresponding to the N code
1. Elastic surface 'l+' corresponding to time interval 62 of T2
Surface acoustic wave correlators 51 to 54 corresponding to the PN codes corresponding to the time intervals 61 to 64 of T1 to T4 are respectively disposed, such as a P correlator 52. The delay times 1 to T4 of the running spreading elements 41 to 44 are selected as follows.

T1 =-TO+ 1. '1. + 'l”2 + T
aT2=To+TI+T2'r3=To+'i'I T42T.

Here, To is an arbitrary delay time. That is, the delay time is set so as to be expressed by the general formula: 1-1 Zi=Σ Tj i=1.2.3·middle-0.

By configuring the delay elements 41 to 44 in this way,
After time To + T 1 + T 2 + T 3 after the PN code shown in FIG. 4 is applied to the input terminal 40, the starting point of the code corresponding to 61 of the PN code is displayed at the input terminal of the surface acoustic wave correlator 510. Also, the surface acoustic wave correlator 52
The starting point of the code corresponding to 62 reaches the input terminal of , and so on, the starting point of the code corresponding to 61 to 64 of the PN code reaches the surface acoustic wave correlators 51 to 54, respectively. Thereafter, correlation within cycles 61 to 64 is performed by surface acoustic wave correlators 51 to 54 during time T.

Each correlation output is combined at an output terminal 50. the result,
It is divided into four at the input terminal 40 and processed separately at the correlators 51 to 54, making it possible to correlate the entire PN code having a time interval of TI+T2+T3+T4.

According to this actual Mti example, the surface acoustic wave correlator is approximately
It is possible to have a substrate length K of /4.

Further, the number of taps of output electrodes provided on the surface acoustic wave propagation path can be reduced to about 1/4 in each surface acoustic wave correlator. This is extremely important for surface acoustic wave correlators. Generally, as a matter of course, a part of the energy of the surface acoustic wave that has passed through the output electrode section is converted into electrical energy and is slightly attenuated. Moreover, a slight reflection phase shift occurs at the electrode portion. For this reason, the surface acoustic waves that have passed through a large number of output electrodes have a non-negligible attenuation of energy and a shift in one phase, resulting in PN
The autocorrelation of the codes is no longer ideal. In particular, when the codes do not match, the output increases and the ratio to the peak power decreases, leading to a so-called deterioration of process gain.

By dividing the PN code into several parts and manually inputting them to each correlator as in the present invention, the number of output electrode taps can be reduced. Therefore, the influence of the output electrode is reduced as a whole, and the exchange from surface acoustic waves to electrical energy at the output electrode portions can be sufficiently large without deteriorating the process gain of the first correlator, and the efficiency of the surface acoustic wave correlator is can be raised.

The delay elements 41 to 44 can be constructed of, for example, surface acoustic wave delay lines. At this time, each delay element has the same input/output electrode pattern, and only the input/output electrode spacing needs to be designed so that the above-mentioned relationship is satisfied.

At this time, the delay elements 41 to 44 can be formed on the same piezoelectric substrate, which is extremely effective in this embodiment where the accuracy of each delay time difference is important.

[Other embodiments of the invention]

In the above embodiment, the delay element was composed of surface acoustic wave delay lines, but when the period of the PN code is long, for example, delay lines such as T1 and T2 in FIG. The wave propagation path becomes longer. Therefore, a method can be considered to achieve the required delay time by dividing the sound into several parts and connecting them in series.

However, in this method, the transfer function of a system in which multi-stage delay lines are connected changes from the transfer function of a system in which multi-stage delay lines are connected. and make the shapes of the input and output electrodes of each delay line the same. With such a configuration, the transfer functions of groups having different delay times can be made the same, and deterioration of process gain can be avoided. Moreover, since the surface acoustic wave substrate can be short, it can be constructed at low cost. In particular, if T1 to T3 in FIG. 4 are all equal to T, the surface acoustic wave delay line 41 in FIG.
With a delay time of 2 total ΔT, it can be configured with only two types of surface acoustic wave delay lines. Surface acoustic wave elements are easy to produce in large numbers with the same characteristics, so they are inexpensive and good quality.
l PN code correlator is possible.

Furthermore, a 4-wave surface wave correlator is not necessarily composed of fixed tap electrodes as shown in Figure 2.For example, if a programmable correlator is used, The configuration consists of nine surface acoustic wave delay lines of two types and four programmable correlators VCrr.The tap polarity of each correlator is electrically switched according to the PN codes 61 to 64 in Fig. 4. For example, only one type of surface acoustic wave correlator is required.

The structure is very simple and it is extremely advantageous for manufacturing a long-period PN code demodulator.

Furthermore, even if the PN code is changed, the tap polarity is electrically variable, so there is an advantage that it can be handled at high speed.

Similarly, a surface acoustic wave memory correlator may be used instead of a programmable correlator. This makes it easy to use because a demodulator that functions as a correlator for the reference signal can be constructed by simply inputting all the reference signals without changing the polarity of the taps.

Furthermore, in this system, for example, as shown in FIG. 6, each branch of the dividing section of the input end and the output end.

Alternatively, a method of inserting an amplifier, which is a non-reciprocal element, into each delay element and the input/output terminal of the surface acoustic wave correlator is extremely effective in obtaining an accurate correlator in any of the above embodiments. That is, a signal received at the output electrode of any surface acoustic wave correlator is applied again to the output electrode of another surface acoustic wave correlator, causing multiple interference and making it impossible to obtain an accurate correlation. Specifically, for example, This results in an increase in side lobes in the pulse waveform of the correlation output and deterioration in process gain.

In order to prevent this, it is important to prevent the once-received signal from being applied again to other surface acoustic wave elements. For this reason, a circuit that makes the signal flow unidirectional is required. Since the amplifier can be made unidirectional and has the effect of compensating for the insertion loss of the surface acoustic wave element, it is very advantageous for the above purpose, and a highly sensitive and accurate correlator can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a pseudo-noise (PN) code. Fig. 2 is a diagram showing an example of a surface acoustic wave correlator for demodulating a PN code, Fig. 3 is a block diagram of the structure of the demodulator of the present invention, and Fig. 4 is a long frequency diagram for explaining the present invention. I)
FIGS. 5 and 6 showing examples of N code waveforms are diagrams showing other embodiments of the present invention, respectively. 40...Input terminal 44, 42.43.44...
・Delay element 51, 52, 53, 54...Surface acoustic wave correlator 50...Output terminal Patent attorney Kensuke Norichika (one person)

Claims (6)

[Claims] (1) Pseudo-noise code is divided into time intervals Tl, T2, ...Tn, and n surface acoustic wave correlations are formed in which electrodes are formed so that correlations can be taken corresponding to the codes in each time interval. a delay element that supplies the SiI pseudo-noise to these surface acoustic wave correlators with a delay of T1, T2, . . . Tn, and means for adding the correlation outputs of the surface acoustic wave correlators. and a delay time Ti of a delay element that supplies a signal to the surface acoustic wave correlator configured to be correlated with a code corresponding to a time Ti of the pseudo noise code is set to an arbitrary time j... A demodulator characterized by: (2) The demodulator according to claim 1, wherein the delay element is constituted by a surface acoustic wave element. (3) The delay line is characterized in that a plurality of surface acoustic wave delay lines are connected in series, and the number of stages of the series connection is equal in all signal-like paths divided into one. The demodulator according to item 1 or 2. (4) When dividing the entire period of the pseudo-noise code into n time intervals, all the time intervals except the last time interval are made to have the same time and are treated as one surface acoustic wave delay line. 2. The demodulator according to claim 1, wherein a plurality of demodulators having two types of delay times are connected in series. (5) A programmable surface acoustic wave correlator that can electrically control codes as a surface acoustic wave correlator configured to take correlations corresponding to codes in each time interval obtained by dividing the pseudo-noise code into n. A demodulator according to claim 1, characterized in that the demodulator uses: (6) The surface acoustic wave correlator is configured with a memory correlator, and before being used as a demodulator. Claim 1, characterized in that the reference signal is manually generated, memorized, and then used as a pseudo-noise signal demodulator.
Demodulator as described in section.