SU1170588A1 - Versions of filter based on surface acoustic waves - Google Patents

Abstract

Surface acoustic wave filter (SAW), containing a piezoelectric acoustic duct, on the surface of which are located input and output interdigital transducers (IDT), containing electrodes, which are different in order to increase the selectivity when working on odd harmonics From the IDT, each electrode is made in two stages with steps located in different acoustic channels; moreover, the ratio of the width of the first electrode step to the spatial step of the BSB is 0.55-0.7, and the width of the second The first step of the electrode is calculated by the formula, where a and q 2, respectively, are the widths of the first and second steps of the electrode; L is the spatial step of the IDP; in this case, in one of the acoustic channels between the IDP, there is a metallized coating, the length of which along the direction of propagation of the surfactant is calculated by the formula. .. where TI 2 L is the wavelength K is the coefficient of electromechanical communication of the duct material. S (L 2. A surface wave filter: capped waves containing a piezoelectric acoustic duct, on the surface of which an input is located; and output pinhole transducers containing electrodes, characterized in that, in order to increase the selectivity at odd in one of the IDTs, each electrode was made up of two stages with steps of 90 00 located in different acoustic channels, and the ratio of the width of the first electrode step to the spatial step of the IDT was 0.550, 7, and Torah electrode stage is calculated by a formula, where a and q., respectively the width of the first electrode and the second stages 1 spatial step. IDT,

Description

a, are offset relative to the steps of the electrodes with a, along a floor equal to half the length of this wave.

The invention relates to radio electronics and can be used in various devices for selecting high frequency signals. The purpose of the invention is to increase selectivity when working at odd harmonics. FIG. 1 and 2 show two variants of the constructive implementation of the filterJ in FIG. 3 shows the dependence of the intensity of the excitation of the surfactant on the frequency of acoustic synchronism o and its 3rd harmonic b on the metallization coefficient a. Each filter on the surfactant (Fig. 1) contains a piezoelectric duct 1, input and output counter-converters 2 and 3 of the surfactant, metallized coating 4. The filter on the surfactant works as follows. The amplitudes of the surfactant excited or received by VSHI 2 and 3 depend on the number of the excited harmonic and the ratio of the width of the IDT electrode to the spatial step a / L. So, for example, if the amplitude of the first harmonics (Fig. 3, curve b) in a wide range of O values (from 1.0 to 0.3) changes by only 30%, then the amplitude of the 3rd harmonic (curve c) same range of value. 01 takes the maximum possible antiphase value, zero crossing at a / L 0.5. Thus, the steps of electrodynamic transducer 2, located in acoustic channel 4, excite surfactants, the amplitude of which at frequency of acoustic synchronism is A, (Fig. 3), and at its 3rd harmonic A. Stages of electrodes located in acoustic Channel 5 of the same IDT 2, excites surfactants, the amplitudes of which are, respectively, A. and AZ. At the same time, in adjacent acoustic channels 4 and 5, surfactants at the frequency of acoustic synchronism will be excited in phase, and at the frequency of the 3rd harmonic in antiphase. Metallized coating 6, the length of which is equal, introduces an additional delay compared to channel 4 equal to / 2V at the frequency of acoustic synchronism, and at the third harmonic frequency, where L 3 is the length of the SAW at the 3rd harmonic-, V - surfactant speed under the metallized coating 6. As a result, an acoustic wave enters the transducer 3, the front of which contains the in-phase signals Aj and Aj and the antiphase signals A, tf A, which leads to the in-phase COMPLEX signals at the 3rd harmonic frequency and the signals cha Tote acoustic matching. In accordance with the second option (Fig. 2), the front of the surfactant emitted by IDT 2 contains antiphase amplitudes A and A at the frequency of acoustic synchronism and in-phase amplitudes Aj and at the frequency of the 3rd harmonic. LSI 3 provides in-house signal reception at the frequency of the acoustic synchronism of the filter and all its odd harmonics. The proposed filter allows suppressing the signal at an acoustic synchronism frequency of about 40 dB, which significantly increases its selectivity.

Oi

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FIG. i

14

/ /

I i a

 -y - “-

FIG. 2

/ 4, rel. units

0.1 a / L

Physical

Claims (2)

Filter on ^one surface acoustic waves iCal / surfactant / comprising piezoelectric acoustic line, the surface of which are arranged the input and output interdigital transducers (IDTs) having electrodes with otlichayuschiy- I that, in order to increase the selectivity at work on odd harmonics, in one of the IDTs, each electrode is made of two stages with steps located in different acoustic channels, and the ratio of the width of the first stage of the electrode to the spatial pitch of IDT is 0.55-0.7, and the width of the second tim electrode is calculated by the formula where a and q ₂ - respectively the width of the first electrode and second stages; L - spatial step IDT, while in one of the acoustic channels between IDT there is a metallized coating, the length of which along the direction of propagation of the surfactant is calculated by the formula B ^ ik ² where fl = 2 L is the wavelength; K is the coefficient of electromechanical coupling of the material of the sound duct. 2. A filter based on surface acoustic waves containing a piezoelectric sound duct, on the surface of which there are input and output interdigital transducers containing electrodes, characterized in that, in order to increase the selectivity when working on odd harmonics, each of the IDTs the electrode is made two-stage with steps located in different acoustic channels, and the ratio of the width of the first stage of the electrode to the space? At the actual step, the IDT is 0.550.7, and the width of the second electrode stage is calculated by the formula q ₂ = L-а,, where a ₍ and q. ₂ ^_ are the widths of the first and second electrode stages, respectively L is the spatial step. The IDT, in this case, the steps of electrodes with a width a, are displaced relative to the steps of electrodes with a width a ₂ along the propagation direction of the surfactant to a distance equal to half the length of this wave.