Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/02535—Details of surface acoustic wave devices
  • H03H9/02543—Characteristics of substrate, e.g. cutting angles
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/02535—Details of surface acoustic wave devices
  • H03H9/02818—Means for compensation or elimination of undesirable effects
  • H03H9/02842—Means for compensation or elimination of undesirable effects of reflections
  • H03H9/0285—Means for compensation or elimination of undesirable effects of reflections of triple transit echo

Definitions

• This invention relates to surface wave acoustic de- vices and, more particularly, to an improved configuration for a filter substrate.
• SAW surface wave acoustic
• an input transducer in the form of a series of interdigitated conductive elements.
• a similarly arranged output tranducer also in ⁇ cluding a series of interdigitated conductive elements.
• a multi-strip coupler and a reflector are also included in the filter. The coupler causes signals launched by the transducer to be directed in quadrature to both the output transducer and the reflector. The phase relationship between the signals directed to the output transducer and the reflector results in substantial cancellation of "triple-transit" signals as thoroughly described in cited the patent. This is a highly desirable effect because
• SAW filter incorporating dummy transducers and an absorptive coating so as to similarly reduce reflections and enhance the filter frequency response.
• U.S. Patent 4,247,835 to Lewis depicts in Figure 1 a quartz crystal with various flat surfaces (that is, rhombohedral faces) lying in respective planes rotated about the crystal axes.
• the various planes, or "cuts" are distinquishable in that each may be characterized as providing resonators whose individual natural operating frequencies vary as a function of temperature in a predetermined, predictable fashion.
• the crystal cuts comprise a variety of irregularly perimetered surfaces.
• the subject invention is directed t an improved triangular substrate configuration that not onl attenuates the level of reflected signals but also significantly reduces the amount of substrate material required.
• the reduction in substrate surface area results • in a substantial reduction in the total cost of the device, largely because of the expense of the niobium component of, for example, a lithium niobate substrate.
• the invention is a surface wave acoustic filter com ⁇ prising aluminum transducers deposited on a triangularly configured lithium niobate substrate.
• the length of the sides of the substrate assume values eq ⁇ k-rst approximately 6.05, 9.25 and 11.05 milli ⁇ meters respectively.
• the sole drawing is a pictorial representation of the subject SAW filter.
• the subject surface wave acoustic filter includes, inter alia, a triangular substrate 1, which, in a preferred embodiment, is constructed from a piezoelectric material such as lithium niobate. Deposited on the substrate are an input transducer 5, an output transducer 2, a reflector 3 and a 3db coupler 4.
• the above elements are typically constructed from an electrically conductive material such as aluminum. The specific operation and configuration are
• the filter substrate is triangularly configured and comprises first, second and third sides 11, 12 and 13, respectively.
• the second side has a nominal dimension F, of 9.25 millimeters (mm).
• the third side of the substrate forms an angle, alpha, with an imaginary line that is perpendicular to the second side and has a length, J, nominally equal to 5.75 mm.
• alpha has a nominal value of 18 degrees. From the above it can be demonstrated that the nominal lengths of sides 11, 12 and 13 (given the nominal value of alpha) are 11.05, 9.25 and 6.05 mm respectively.
• the length, F, of the second side 12 may vary from 7 to 12 millimeters, the dimension J may vary from 3.0 to 10.0 mm, and the angle alpha may vary from 0 degrees to 36 degrees.
• the first side of the substrate may vary from approximately 7.6 to 17.2 mm, the second side from 7.0 to 12.0 mm, and the third side from 3.0 to 12.3 mm respectively.
• the thickness of the substrate may vary from approximately 0.1 to 1.0 mm, and again, may typically be constructed from lithium niobate, although other piezoelectric materials are certainly comtemplated by this invention.
• the input transducer 5 has -an eight-sided perimeter, four sides
• the reflector 3 has two sides 31 and 33 substantially parallel to the second side,- a side 32 substantially perpendicular to it and a side 34 substantially parallel to the third side.
• the 3db coupler has a side 41 substantially parallel to the second side, sides 42 and 44 substantially perpendicu ⁇ lar to it, and a side 43 substantially parallel to the first side.
• the relevant dimensions of the substrate, input and output transducers, 3db coupler and filter may be derived from the drawing and the table included therein. In practice those dimensions may vary, in millimeters, as follows:
• the triangularly configured substrate exhibits at least two salient advantages.
• the surface area of the substrate is the same.
• OMPI may be estimated at approximately one-half of the substrate required in other known structures.
• the surface wave reflections from the output transducer, and therefore the triple-transit reflections, are substantially reduced as a result of the triangular configura ion.
• the subject invention is useful as a signal process- n ing device in various types of electronic equipment and, i particular, as a surface acoustic wave filter for tele ⁇ vision receivers.

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• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Applications Claiming Priority (1)

Publications (2)

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ID=22182053

Family Applications (1)

Country Status (2)

Citations (2)

Family Cites Families (3)

• 1984
  • 1984-02-21 WO PCT/US1984/000248 patent/WO1985003816A1/fr not_active Application Discontinuation
  • 1984-02-21 EP EP19840901459 patent/EP0172811A4/fr active Pending

Patent Citations (2)

Non-Patent Citations (1)

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