SU915225A1 - Retunable saw-filter - Google Patents

Description

The invention relates to acoustoelectronics and can find application in radio-technical devices. information processing, in particular, in filters on surface acoustic waves with smoothly tunable characteristics.

A device containing an electron gun, a piezoelectric evukoprovod made in the form of a plate, on one side of which two input and two output interdigital transducers, forming two parallel acoustic channels, is known; between the input and output converters deposited film of cadmium selenide. The re-radiation of surface acoustic waves from one channel to another is produced using a system of conducting bands formed on the film surface when it is irradiated with an electron beam by a scanning electron gun. The connection between the channels depends on the number of? 5 conductive bands [1].

The disadvantages of such a device are the complexity of the design, bulkiness, the need to place the device in a vacuum, limited to 30

service life due to wear of the electron gun.

It is also known a device containing a light source, a device projecting onto a substrate an image of a multiband directional coupler, a piezoelectric sound conductor, on one side of which two input and two output interdigital transducers are applied, forming two parallel acoustic channels, between the input and output transducers a photoconductive layer is applied. Reradiation of surface acoustic waves from one channel to another is produced using a system of conductive bands that make up a multi-strip directional coupler that form on the surface of a photoconductive film when irradiated with light 12].

The disadvantages of the device are relatively large dimensions and weight of the device due to the presence of a complex optical system for projecting the image of a multi-strip directional coupler, low reliability and short service life due to the presence of the Aoscine light source.

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915225

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The purpose of the invention is to simplify the design, increase reliability and increase service life.

This goal is achieved by the fact that in a tunable filter of surface acoustic waves containing a piezoelectric acoustic conduit with one input and two output interdigital transducers, forming two parallel acoustic channels, and a multi-band directional coupler located between the input and output transducers, on one side of a multi-strip directional coupler, parallel to its pins, two control electrodes are located, connected to the source voltage, and a semi-conductive film is applied to the surface of a multi-strip directional coupler and control electrodes.

The drawing shows a tunable filter.

The device contains a piezoelectric acoustic conductor 1, an inter-pin 25 input 2 and output 3 and 4 transducers, a multi-strip directional coupler 5, control electrodes b and 7 and a semiconductor film 8.

Piezoelectric conduit 1 is made in the form of a rectangular parallelepiped of a piezoelectric material, such as lithium niobate, piezoelectric ceramics, or some other piezoelectric crystal- * * ’tall, with a large electromechanical coupling coefficient. The surface of the piezoelectric duct is polished to reduce the loss of surface acoustic waves due to 40 scattering. .

The semiconductor film 8 should have a greater mobility of charge carriers to reduce the maximum value of the control voltage, 45 which is satisfied by semiconductors such as indium antimonide, gallium arsenide, etc.

The device works as follows. 50

Surface acoustic wave

is excited by the input transducer 2 and, propagating along the piezoelectric sound conduit 1, hits a multi-strip directional 55 otvetvitel 5. The step and number of pins of the multi-strip directional coupler are selected in such a way that in the absence of a control voltage, all the energy radiated by the input _p ^υ to converter 4. ·

The voltage applied to the control electrodes creates drift

charge carriers in the direction of propagation of an acoustic wave, while the effective electromechanical coupling coefficient is a function of the electric field strength in a semiconductor film.

In the presence of a control voltage, the condition under which all energy is re-emitted to converter 4 is violated for a given number of pins of a multi-strip directional coupler due to a change in the effective electromechanical coupling coefficient. Therefore, the energy emitted by the input transducer is redistributed between the output transducers 3 and 4 up to the full emission of the acoustic wave to the transducer 3.

Converters 3 and 4 have different frequency characteristics. The output signal is the sum of the signals taken from the converters 3 and 4; therefore, a change in the magnitude of the control voltage leads to a change in the resulting frequency response.

The use of lithium niobate and an antimonide-indium semiconductor film with a carrier mobility of 1250 cm '/ V-s and a thickness of 0.5 μm as a piezoelectric chute of 50 μm makes it possible to obtain a complete switching of the signal between the channels when the control voltage varies from 0 to 60 V.

Claims (1)

Claim Tunable surface acoustic wave filter containing a piezoelectric sound duct with one input and two output interdigital transducers applied to it, forming two parallel acoustic channels, and a multi-strip directional coupler located between the input and output transducers, characterized in that simplify the design and increase reliability, on both sides of the multi-strip directional coupler are control electrodes connected to voltage source, and on the surface of the multi-strip directional coupler and control electrodes applied semiconductor film.