Programmable surface acoustic wave (SAW) filter

• US 20020047494A1
• Filed: 06/04/2001
• Published: 04/25/2002
• Est. Priority Date: 02/02/2000
• Status: Active Grant

• Current Assignee: Rutgers University
• Original Assignee: Rutgers University
• Inventors: Kosinski, John, Pastore, Robert, Zhu, Jiahua, Lu, Yicheng
• Granted Patent: US 6,541,893 B2
• Time in Patent Office: Days
• US Class Current: 310/313B
• CPC Class Codes: H03H 9/6403 Programmable filters

Abstract

A novel programmable SAW filter with switchable multi-element interdigital transducers (IDTs) controlled by a microprocessor or a computer is provided that realizes the tunability of both center frequency and bandwidth of the SAW filter. The filter possesses the feature of the programmability of both center frequency and 3 dB bandwidth. As an example design, the center frequency of the SAW filter ranges from 126.8 MHz to 199.1 MHz while the 3 dB bandwidth ranges from 18.8 MHz to 58.9 MHz. The multi-input configuration increases the programmability of the device and improves insertion loss. A matching network for the programmable SAW filter further improves insertion loss level and stopband attenuation. A resistance weighting method has been applied to improve in band ripple with the passband ripple being reduced from 6.44 dB to 1.37 dB after resistance weighting. The prototype of programmable SAW filter simplifies the device structure and fabrication process by eliminating the tap weighting and summing circuits, resulting in a smaller device and lower costs. Moreover, frequency response shaping is realized without apodization.

Claims

1. A surface acoustic wave device having, on a piezoelectric substrate, an input interdigital transducer for transforming an electric signal into a surface acoustic wave and an output interdigital transducer disposed in opposite orientation relative to said input interdigital transducers, for transforming the surface acoustic wave resulting from the transformation by said input interdigital transducer into an electric signal, wherein each of said input and output transducers comprise overlapping electrodes of quarter wavelength each, the wavelength being the wavelength of the surface acoustic wave, selected ones of said overlapping electrodes being of different widths but having the same aperture length.

2. A surface acoustic device according to claim 1, wherein said piezoelectric substrate comprising lithium niobate.

3. A surface acoustic wave device according to claim 1, wherein said device comprises eleven constant overlapping interdigital transducers.

4. A surface acoustic device according to claim 3, wherein said device comprises at least one RF switch for switching between different filter configurations by charging the input and output interdigital transducers.

5. A surface acoustic wave device according to claim 3, wherein groups of selected electrodes have widths differing from widths of electrodes of other groups.

6. A surface acoustic wave device according to claim 5, wherein electrodes designated as 1, 4 and 7 each have an electrode width of approximately 5 μ

m;

electrodes designated as 0, 2, 5 and 10 each have an electrode width of approximately 6 μ

m; and

electrodes designated as 3, 6 and 9 each have an electrode width of approximately 8 μ

m.

7. A surface acoustic wave device according to claim 2, wherein said electrodes are comprised of aluminum.

8. The surface acoustic wave device in combination with a package with conductive leads.

9. The combination of claim 8, wherein said package comprises a ceramic dual-in-line package.

10. The combination of claim 9, wherein the electrodes of said surface acoustic wave device are wire bonded conductively to said leads.

11. A surface acoustic wave device, comprising:

a piezoelectric substrate;

a plurality of interdigital transducers defined by overlapping electrodes disposed on said piezoelectric substrate, each of said electrodes being of width approximately equal to a quarter wavelength of said surface acoustic wave device, selected ones of said electrodes being of different widths.

12. A surface acoustic wave device according to claim 11, wherein selected ones of said electrodes define an input interdigital transducer and other selected ones of said electrodes define an output interdigital transducer.

13. A surface acoustic wave device, according to claim 12, wherein selected ones of said electrodes define plural input interdigital transducers.

14. A surface acoustic wave device, according to claim 12, further comprising at both ? RF switch for charging the input and output interdigital transducers.

15. A surface acoustic wave device according to claim 12, wherein said piezoelectric substrate comprises lithium niobate.

16. A surface acoustic wave device according to claim 12, wherein said electrodes define eleven interdigital transducers.

18. A surface acoustic wave device according to claim 17, wherein said means to change the weighting factor comprises a resistor.

19. A surface acoustic wave device according to claim 18, wherein said resistor is connected in series with said one transducer.

17. A surface acoustic wave device, comprising:

a piezoelectric substrate;

a plurality of interdigital transducers defined by overlapping electrodes disposed on said piezoelectric substrate, each of said electrodes being of width approximately equal to a quarter wavelength of said surface acoustic wave device, selected ones of said electrodes being of different widths, selected ones of said electrodes defining an input interdigital transducer and other selected ones of said electrodes defining an output interdigital transducer, and

means connected to one of said input transducers or said output transducers to change the weighting factor of said one transducer.