JPH10229320A - Delay line with surface-acoustic wave tap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the delay line with a surface-acoustic wave tap whose service life is long, regardless of high power. SOLUTION: An input side interdigital transducer 3 is made up of a plurality of tap electrodes 3a, 3b which are coded, an electrode finger pair number of the tap electrodes 3a, 3b corresponding to one code is more than one pair, and also a ratio of a carrier frequency to a half of a band width of the spread spectrum communication system in use or below. Total number of the electrode fingers of the input side digital transducer 3 is selected to be more than a total number of electrode fingers of an output interdigital transducer 4. Thus, the performance of components withstanding with respect to high power input is enhanced, and the service life of the components is prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a delay line with a surface acoustic wave tap, which is a correlator used in a demodulator for spread spectrum communication.

[0002]

2. Description of the Related Art In a direct spread system of spread spectrum communication, as shown in FIG. 4, a transmitting side spreads and modulates an information signal using a PN code (pseudo noise code) as a spread code. Then, the spread modulated signal is modulated by a carrier wave and transmitted from the transmitting antenna T. On the other hand, the reception side performs correlation detection by despreading the signal received by the reception antenna R using a PN code. In the despreading, an output is obtained when it matches the PN code on the transmitting side. The despread received signal is demodulated and information is output.

[0003] As the above-mentioned PN code, there are an M sequence, a Barker code sequence and the like.

In such spread spectrum communication, a demodulator for demodulating a transmitted spectrum requires a correlator for performing correlation detection with a spread code. One of the correlators is a correlator. A delay line with a surface acoustic wave tap is used.

FIG. 5 is a plan view showing a conventional delay line with surface acoustic wave taps. As shown in FIG. 5, a delay line 101 with a surface acoustic wave tap includes a piezoelectric substrate 102 and a piezoelectric substrate 102.
Input interdigital transducer 103 and output interdigital transducer 1 arranged above
04, a sound absorbing material 105.

[0006] The piezoelectric substrate 102 is made of quartz having a temperature coefficient of surface acoustic wave velocity of zero.

[0007] The input side interdigital transducer 103 is constituted by opposing comb-shaped electrodes having a plurality of electrode fingers, and converts an electric signal into a surface acoustic wave.

The output side interdigital transducer 104 is the input side interdigital transducer 1
The plurality of tap electrodes 104a and 104b, which are arranged at an interval from the reference numeral 03 and are composed of two electrode fingers that convert a surface acoustic wave into an electric signal. Further, the tap electrodes 104a and 104b are encoded by the arrangement of the electrode fingers, and when a pseudo noise code sequence having a 31-sequence length is used as the code sequence, the output interdigital transducer 104 corresponds to the pseudo noise code sequence. It has 31 tap electrodes 104a and 104b, and each tap electrode 104a and 104b is formed at a distance corresponding to the chip rate.

In FIG. 5, in order to clarify the shape of the electrode fingers in the drawing, the number of electrode fingers of the input and output interdigital transducers 103 and 104 is reduced. The side interdigital transducer 103 has 25 electrode fingers, and the output side interdigital transducer 104 has 62 electrode fingers.

The sound absorbing material 105 is arranged outside the input side interdigital transducer 103 and the output side interdigital transducer 104, and thereby absorbs unnecessary surface acoustic waves.

Next, the operation of the delay line with a surface acoustic wave tap shown in FIG. 5 will be described. The signal subjected to the spread spectrum modulation by the pseudo-noise code sequence is input from the input side interdigital transducer 103 and is transmitted to the output side interdigital transducer 104 as a surface acoustic wave. At this time, a large electric signal is obtained only when the sign of the transmitted surface acoustic wave matches the sign of the output side interdigital transducer 104, and the original information can be demodulated from this signal.

[0012]

However, in the conventional delay line 101 with a surface acoustic wave tap, the electrode fingers of the input interdigital transducer 103 are thin and small, and the electrode fingers used for the input interdigital transducer 13 are small. Therefore, when a high-power signal is input, the input-side interdigital transducer 103 cannot withstand the high-power signal and is quickly consumed. To solve this problem, the total number of electrode fingers of the input side interdigital transducer 103 may be increased. However, in the case of a delay line with a surface acoustic wave tap, since the bandwidth is determined by the number of electrode fingers of the input side interdigital transducer 103 which is the uncoded electrode, it is easy to increase the number of electrode fingers. , The desired bandwidth cannot be obtained.

The present invention has been made in view of these problems, and has as its object to provide a delay line with a surface acoustic wave tap that can be used for a long time at high power.

[0014]

According to a first aspect of the present invention, there is provided a delay line with a surface acoustic wave tap, comprising: a piezoelectric substrate; an input interdigital transducer formed on the piezoelectric substrate; An input-side interdigital transducer and an output-side transducer formed at an interval, the input-side interdigital transducer is configured by a plurality of encoded tap electrodes, and an electrode of a tap electrode corresponding to one code The number of finger pairs is more than one pair, the number of electrode finger pairs of the tap electrode corresponding to the one code is equal to or less than the ratio of the carrier frequency to half the bandwidth of the spectrum to be used, and the total number of electrode fingers constituting the output side interface is It is more than the electrode index of the digital transducer.

[0015] Thereby, the power durability of the component with respect to high power can be improved.

In the delay line with a surface acoustic wave tap according to a second aspect, the cross width is weighted so that the cross width of the input side interdigital transducer decreases toward the output side transducer.

Thus, the amplitude of a signal obtained when a pulse is input can be made constant.

In the delay line with a surface acoustic wave tap according to a third aspect, the output side interdigital transducer is weighted by the cross width.

Thus, the out-of-band spurious of the frequency characteristic can be reduced.

In the delay line with a surface acoustic wave tap according to the fourth aspect, the input or output interdigital transducer is constituted by a split electrode.

As a result, reflection at the electrode finger can be reduced.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A delay line with a surface acoustic wave tap according to the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a delay line with a surface acoustic wave tap according to a first embodiment of the present invention.

As shown in FIG. 1, a delay line 1 with a surface acoustic wave tap is composed of a piezoelectric substrate 2, an input interdigital transducer 3, an output interdigital transducer 4, and a sound absorbing material 5 arranged on the piezoelectric substrate 2. It is configured.

The piezoelectric substrate 2 is made of quartz, which is a material having a temperature coefficient of surface acoustic wave velocity close to zero.

The input-side interdigital transducer 3 is constituted by a plurality of tap electrodes 3a and 3b each composed of three electrode fingers for converting an electric signal into a surface acoustic wave. Further, the tap electrodes 3a and 3b are encoded by an arrangement of electrode fingers, and when a pseudo noise code sequence having a 31-sequence length is used as a code sequence, the input interdigital transducer 3 corresponds to the pseudo noise code sequence. It has 31 tap electrodes 3a, 3b, and each tap electrode 3a, 3b
b are formed at intervals corresponding to the chip rate.

The output-side interdigital transducer 4 is constituted by opposing comb-shaped electrodes having a plurality of electrode fingers on the input-side interdigital transducer, and converts a surface acoustic wave into an electric signal.

In FIG. 1, the number of electrode fingers of the input and output interdigital transducers 3 and 4 is reduced in order to clarify the shape of the electrode fingers in the drawing. The interdigital transducer 3 has 93 electrode fingers, and the output side interdigital transducer 4 has 25 electrode fingers.

The sound absorbing material 5 is disposed outside the input-side interdigital transducer 3 and the output-side interdigital transducer 4, thereby absorbing unnecessary surface acoustic waves.

Next, a second embodiment will be described with reference to the drawings. FIG. 2 is a plan view of a delay line with a surface acoustic wave tap according to a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description will be omitted.

This embodiment differs from the first embodiment shown in FIG. 1 in that the input side interdigital transducer and the output side interdigital transducer are weighted.

That is, as shown in FIG. 2, the input-side interdigital transducer 13 is designed such that the cross width of the electrode fingers of the tap electrodes 13a and 13b gradually decreases toward the output-side interdigital transducer 14. Cross-width weighting is performed.

Thus, the amplitude of a signal obtained when a pulse is input can be made constant.

As shown in FIG. 2, the output side interdigital transducer 14 has the smallest cross width of the electrode fingers at both end portions (at the input side interdigital transducer 13 side and the sound absorbing material 15 side). , The cross width is weighted such that the cross width becomes the largest.

With such a configuration, the out-of-band spurious of the frequency characteristic can be reduced.

Next, a third embodiment will be described with reference to the drawings. FIG. 3 is a plan view of a delay line with a surface acoustic wave tap according to a third embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description will be omitted.

The present embodiment is different from the first embodiment shown in FIG. 1 in that the electrode fingers constituting the input side interdigital transducer and the output side interdigital transducer are formed by split electrodes.

That is, as shown in FIG. 3, the input-side interdigital transducer 23 and the output-side interdigital transducer 24 are composed of a pair of electrode fingers and one split electrode. At this time, the number of electrode fingers is 93 in the input side interdigital transducer 23 and the output side interdigital transducer 2
4, the number of electrode fingers is set to 25.

With this configuration, it is possible to reduce the occurrence of reflection at the electrode finger.

[0039]

As described above, according to the present invention, the input side interdigital transducer is constituted by a plurality of encoded tap electrodes, and the number of electrode finger pairs of the tap electrode corresponding to one code is more than one pair. The number of electrode finger pairs of the tap electrode corresponding to one code should be equal to or less than the ratio of the carrier frequency to half the bandwidth of the spectrum to be used, and the total number of electrode fingers of the input interdigital transducer should be equal to the number of electrode fingers of the output interdigital transducer. Since the number is larger than the total number, it is possible to increase the power durability of the component with respect to a high-power input, and to prolong the component life.

In particular, in the invention according to the second aspect, the input side interdigital transducer is weighted so that the cross width decreases toward the output side transducer. The amplitude of the signal to be obtained can be made constant.

According to the third aspect of the invention, since the output side interdigital transducer is weighted by the crossover width, the out-of-band spurious of the frequency characteristic can be reduced.

Furthermore, in the invention according to claim 4, since the input or output interdigital transducer is constituted by the split electrode, reflection at the electrode finger can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a delay line with a surface acoustic wave tap according to a first embodiment.

FIG. 2 is a plan view of a delay line with a surface acoustic wave tap according to a second embodiment.

FIG. 3 is a plan view of a delay line with a surface acoustic wave tap according to a third embodiment.

FIG. 4 is a block diagram showing a spread spectrum communication system.

FIG. 5 is a plan view of a conventional delay line with a surface acoustic wave tap.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Delay line with surface acoustic wave tap 2 Piezoelectric substrate 3 Input side interdigital transducer 3a, 3b Tap electrode 4 Output side interdigital transducer 5 Sound absorbing material

Claims (4)

[Claims] A piezoelectric substrate, an input interdigital transducer formed on the piezoelectric substrate, and an output transducer formed on the piezoelectric substrate at a distance from the input interdigital transducer; The input side interdigital transducer is configured by a plurality of encoded tap electrodes, the number of electrode finger pairs of the tap electrode corresponding to one code is more than one pair, and the number of electrode finger pairs of the tap electrode corresponding to the one code. Is less than the ratio of the carrier frequency to half the bandwidth of the spectrum to be used, and the total number of constituting electrode fingers is larger than the electrode index of the output side interdigital transducer. line. 2. The surface acoustic wave tap according to claim 1, wherein the input side interdigital transducer is weighted with a cross width such that the cross width decreases toward the output side interdigital transducer. With delay line. 3. The delay line with surface acoustic wave tap according to claim 1, wherein the output side interdigital transducer is weighted by a cross width. 4. The delay line with a surface acoustic wave tap according to claim 1, wherein the input or output interdigital transducer is constituted by a split electrode.