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SAW filter with unidirectional transducer and communication apparatus using the same

Imported: 23 Feb '17 | Published: 22 Oct '02

Shigeru Tsuzuki, Tsutomu Igaki, Kazunori Nishimura, Ken Matsunami

USPTO - Utility Patents

Abstract

A surface acoustic wave (SAW) filter is disclosed which comprises a piezoelectric substrate and at least two Interdigital Transducers (IDTs) having four fingered electrodes in a region corresponding to one-wavelength of SAW excited on the piezoelectric substrate. At least one IDT is formed of at least one pair of fingered electrodes having different electrode widths. By provision of the pair of fingered electrodes being different in electrode width, the IDT can be given unidirectionality. Thus, a SAW filter producing a low insertion loss and having good amplitude and phase characteristics in the pass-band can be realized. Further, by using such SAW filter, a high-performance and low-cost communication apparatus, such as a CDMA-system mobile telephone, can be realized.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a SAW filter according to embodiment 1 of the invention.

FIG. 2A is a top view of input IDT of the SAW filter shown in FIG.

1.

FIG. 2B is an enlarged top view of the portion surrounded by a broken line in FIG.

2A.

FIG. 3 is a characteristic curve showing relationship between electrode width ratio and insertion loss of the SAW filter according to embodiment 1 of the invention.

FIG. 4 is a characteristic curve showing relationship between metallization ratio and insertion loss of the SAW filter according to embodiment 1 of the invention.

FIG. 5 is a top view of a SAW filter according to embodiment 2 of the invention.

FIG. 6 is an enlarged top view of a main portion of FIG.

5.

FIG. 7A is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of the SAW filter according to embodiment 2 of the invention is strong.

FIG. 7B is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of the SAW filter according to embodiment 2 of the invention is weak.

FIG. 8A is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of a SAW filter of a comparison example is strong.

FIG. 8B is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of the SAW filter of the comparison example is weak.

FIG. 9 is a curve showing relationship between electrode width ratio and optimum position of fingered electrodes [(+)/(/16)] of the SAW filter according to embodiment 2 of the invention.

FIG. 10 is a top view of a SAW filter according to embodiment 3 of the invention.

FIG. 11 is an enlarged top view of a main portion in FIG.

10.

FIG. 12A is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of the SAW filter according to embodiment 3 of the invention is strong.

FIG. 12B is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of the SAW filter according to embodiment 3 of the invention is weak.

FIG. 13A is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of a SAW filter of a comparison example is strong.

FIG. 13B is a frequency characteristic curve of electromechanical transduction in the direction in which the directionality of the SAW filter of the comparison example is weak.

FIG. 14 is a curve showing relationship between electrode width ratio and optimum position of fingered electrodes [/(/16)] of the SAW filter according to embodiment 3 of the invention.

FIG. 15 is a curve showing relationship between electrode width ratio and optimum position of fingered electrodes [/(/16)] of the SAW filter according to embodiment 3 of the invention.

FIG. 16 is a top view of a SAW filter according to embodiment 4 of the invention.

FIG. 17 is a frequency characteristic curve of a SAW filter according to an embodiment of the invention used for IF filter in CDMA-system mobile telephone.

FIG. 18 is a frequency characteristic curve of a conventional SAW filter used for IF filter in CDMA-system mobile telephone.

FIG. 19 is a frequency characteristic curve of a SAW filter according to embodiment 6 of the invention used for IF filter in CDMA-system mobile telephone.

FIG. 20 is a frequency characteristic curve of a SAW filter, with unidirectionality thereof not controlled, according to an embodiment of the invention used for IF filter in CDMA-system mobile telephone.

FIG. 21 is a partly enlarged top view of a portion of IDT according to embodiment 7 of the invention.

FIG. 22 is a block diagram of a transmit-receive circuit in a general radio communication apparatus.

FIG. 23A is a top view of IDT of a conventional SAW filter.

FIG. 23B is an enlarged top view of a portion surrounded by an oblong solid line in FIG.

23A.

Claims

1. A Surface Acoustic Wave (SAW) filter comprising:

2. The SAW filter according to claim 1, wherein

3. The SAW filter according to claim 1, wherein

4. The SAW filter according to claim 1, wherein

5. The SAW filter according to claim 1, wherein

6. The SAW filter according to claim 1, wherein

7. A SAW filter according to claim 1, wherein said piezoelectric substrate is a 28°-42° rotated Y-cut quartz substrate.

8. A Surface Acoustic Wave (SAW) filter comprising:

9. A Surface Acoustic Wave (SAW) filter comprising:

10. A Surface Acoustic Wave (SAW) filter comprising:

11. A Surface Acoustic Wave (SAW) filter comprising:

12. A communication apparatus having a surface acoustic wave (SAW) filter disposed between the stages of a frequency mixer and an Intermediate Frequency (IF) amplifier, wherein