Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
1999-03-18
2001-05-08
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S153000, C333S154000, C333S155000, C333S196000, C375S153000, C375S343000
Reexamination Certificate
active
06229409
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a surface acoustic wave matched filter comprising a substrate made of a piezo-electrical material, an input side electrode means formed on the substrate for receiving a spread spectrum signal, and an output side electrode means formed on the substrate to constitute a delay line with taps for receiving a surface acoustic wave propagated from the input side electrode means to generate a demodulated signal.
The spread spectrum signal thus transmitted is supplied to an input side electrode
2
of a surface acoustic wave matched filter
1
as shown in FIG.
1
D. The surface acoustic wave matched filter
1
further comprises an output side electrode
3
and a demodulate signal is derived therefrom. The output side electrode
3
constitute a delay line with taps, and includes an array of electrode fingers. Now it is assumed that a propagating velocity of the surface acoustic wave along the surface of the substrate of the surface acoustic wave matched filter is v, said array of electrode fingers has a period &lgr; equal to v/f
0
, a tap distance L equal to v/rN, and a tap pattern determined in accordance with the polarity of the PN code. In an ideal condition, the output side electrode
3
produces a demodulated signal having a strong correlation with an original base-band signal as shown in FIG.
1
E.
However, in actual surface acoustic wave matched filters, the propagating velocity of the surface acoustic wave is changed in accordance with temperature variation of the substrate, and the propagating velocity of the surface acoustic wave fluctuates for respective substrates. Furthermore, the propagating velocity of the surface acoustic wave fluctuates locally within a single substrate. When the propagating velocity of the surface acoustic wave varies in this manner, the correlation between the demodulated signal derived from the output side electrode and the base-band signal could not be attained and the spread spectrum signal could not be demodulated accurately.
To eliminate the above disadvantage, in JP Kokai-Hei 8-88535, there is proposed a surface acoustic wave matched filter, in which a variation in temperature of a substrate is suppressed by means of a temperature regulator. In JP Kokai-Hei 2-132938, there is described another surface acoustic wave matched filter, in which an output side electrode is divided into two parts viewed in the propagating direction of the surface acoustic wave, and these parts are arranged in parallel with each other also viewed in the propagating direction of the surface acoustic wave. An output signal from the rear half of the output side electrode is synthesized with an output signal from the front half of the output side electrode through a delay element. In JP Kokai-Hei 7-193478, there is proposed another surface acoustic wave matched filter, in which an output side electrode is divided into plural blocks, which are arranged in parallel each other viewed in the propagating direction of the surface acoustic wave, output signals from these blocks are converted into digital signals through respective comparators, and a demodulated signal is derived by supplying these digital signals to a calculator unit.
In the surface acoustic wave matched filter disclosed in the above JP Kokai-Hei 8-88535, a heater is provided for controlling the temperature of a piezo-electrical substrate such that the propagating velocity of the surface acoustic wave does not change due to the temperature characteristic of the substrate. Thus, the surface acoustic wave matched filter has an increased power consumption and has the complicated and expensive structure. Moreover, the local fluctuation in the propagating velocity of the surface acoustic wave within a single substrate could not be compensated for.
In the surface acoustic wave matched filter described in the above mentioned JP Kokai-Hei 2-132938, since the output side electrode is divided into two parts, the fluctuation in the propagating velocity of the surface acoustic wave due to the temperature characteristic could not be sufficiently corrected. Since the delay element is provided in the filter, additional fluctuation is disadvantageously introduced due to a fluctuation in a delay time of the delay element depending on the temperature change thereof. Like as the above explained conventional filter, the local change in the propagating velocity of the surface acoustic wave within a single substrate could not be compensated for.
In the surface acoustic wave matched filter disclosed in the above JP Kokai-Hei 7-193478, the degree of correcting the influence of the fluctuation in the propagating velocity of the surface acoustic wave due to the temperature characteristic changes depending on the number of the divided output side electrode parts. In the example shown in
FIG. 1
, the fluctuation is most highly corrected by dividing the output side electrode into N. However, in this case, a size of the filter becomes large and an output processing circuit requires comparators and calculators, and thus the filter is liable to be complicated in construction and the power consumption is increased.
It is an object of this invention to provide a surface acoustic wave matched filter, in which the above defects can be eliminated and a decrease in the correlation of the demodulated signal caused by the variation in the propagating velocity of the surface acoustic wave due to the temperature variation as well as by the fluctuation in the propagating velocity of the surface acoustic wave for respective substrates and the local fluctuation within a single substrate, and delay elements or complex circuit is not required, and thus the power consumption is low.
DISCLOSURE OF THE INVENTION
According to the invention, the surface acoustic wave matched filter comprising a substrate made of a piezo-electrical material, an input side electrode means formed on the substrate for receiving a spread spectrum signal, an output side electrode means formed on the substrate to constitute a delay line with taps for receiving a surface acoustic wave propagated from the input side electrode means to produce a demodulated signal, wherein said output side electrode means includes parts having different delay times between taps.
The surface acoustic wave matched filter of the present invention may be practiced in various configurations, which may be roughly classified into two groups. In one group, a plurality of parallel output side electrodes having different delay times between taps are arranged in parallel with each other viewed in the propagating direction of the surface acoustic wave, and in the other group, a single output side electrode includes parts having different delay times between taps. In the former group, plural input side electrodes designed for the same standard propagating velocity are arranged in parallel with each other viewed in the propagating direction of the surface acoustic wave and a plurality of output side electrodes having different scales viewed at least in the propagating direction of the surface acoustic wave or plural output side electrodes having different tap distances are provided correspondingly to the plural input side electrodes, respectively. In the latter group, said plural parts having different delay times between taps may be constructed by shaping electrode fingers of the output side electrode to be inclined with respect to a distance of an aperture length or into a dog-leg configuration, or covering the surface of the substrate between the electrode fingers of the output side electrode with thin films with different film covering ratio, or forming recessed portions in the substrate surface between the electrode fingers of the output side electrode such that a length of the recessed portions viewed in the propagating direction of the surface acoustic wave is varied in the direction of the aperture length or a size of the depressions viewed in the propagating direction of the surface acoustic wave and a depth of the recessed portions are changed.
REFERENCES:
pat
Imanishi Yuichiro
Shibata Tomohiko
Suetsugu Takumi
Tomabechi Shuichi
Tsubouchi Kazuo
Lee Benny
Parkhurst & Wendel LLP
Summons Barbara
Tsubouchi Kazuo
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