Unbalanced saw filter

• US 5,093,638 A
• Filed: 11/05/1990
• Issued: 03/03/1992
• Est. Priority Date: 11/05/1990
• Status: Expired due to Fees

• Current Assignee: CTS Corporation
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Bickham, Richard S., Kinsman, Robert G.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/608,866
• Time in Patent Office: 484 Days
• Field of Search: 333/193-196, 333/150, 333/154, 333/133, 333/132, 333/129, 310/313 R, 310/313 B, 310/313 C, 310/313 D
• US Class Current: 333/195
• CPC Class Codes: H03H 9/009 Lattice filters

Abstract

An unbalanced surface acoustic wave (SAW) resonator-filter is achieved by using a predetermined length of unbalanced transmission line to define a ground potential and permit two SAW resonators and such transmission line to function together as an unbalanced filter.

Claims

1. An RF filter comprising:

A) a first SAW resonator having a first resonant frequency;

B) a second SAW resonator having a second resonant frequency; and

,

C) a grounded transmission line, having a length substantially equal to one half the average wavelength of the first and second frequencies, connected in series with the first SAW resonator;

an input and an output of the RF filter defined by opposing ends of a parallel circuit formed by interconnection of the second SAW resonator with opposing ends of the series connected first SAW resonator and grounded transmission line, and an RF filter ground defined by a ground of the grounded transmission line.

2. The RF filter as in claim 1 wherein the grounded transmission line has a length substantially equal to an odd-numbered multiple of one-half the average wavelength.

3. The RF filter as in claim 1 wherein the grounded transmission line comprises a meander line on a substrate and a ground plane on the opposite side of the substrate.

4. The RF filter as in claim 4 wherein the substrate comprises a piezoelectric material.

5. An RF filter comprising;

A) a first and second SAW resonator, each having a first resonant frequency, connected in series at a first midpoint to provide a first series circuit having opposing ends;

B) a third and fourth SAW resonator, each having a second resonant frequency, connected in series at a second midpoint to provide a second series circuit having opposing ends;

C) a grounded transmission line having a length substantially equal to one half the average wavelength of the first and second resonant frequencies, connected between the first and second midpoints,

an input and an output of the RF filter defined by opposing ends of a parallel circuit formed by interconnection of the opposing ends of the first series circuit with opposing ends of the second series circuit, and an RF ground defined by a ground of the grounded transmission line.

6. The RF filter as in claim 5 wherein the grounded transmission line has a length substantially equal to an odd-numbered multiple of one-half the average wavelength.

7. The RF filter as in claim 5 wherein the grounded transmission line comprises a meander line on a substrate and a ground plane on the opposite side of the substrate.

8. The RF filter as in claim 7 wherein the substrate comprises a piezoelectric material.