SURFACE ACOUSTIC WAVE DEVICE

• US 20100308936A1
• Filed: 06/08/2010
• Published: 12/09/2010
• Est. Priority Date: 06/09/2009
• Status: Active Grant

• Current Assignee: Taiyo Yuden Company Limited (Taiyo Yuden Co)
• Original Assignee: Taiyo Yuden Company Limited (Taiyo Yuden Co)
• Inventors: Takahashi, Naoki
• Granted Patent: US 8,461,942 B2
• Time in Patent Office: Days
• US Class Current: 333/195
• CPC Class Codes: H03H 9/0071 the balanced terminals being on the same side of the tracks
• CPC Class Codes: H03H 9/0085 having four acoustic tracks
• CPC Class Codes: H03H 9/6436 having one acoustic track only

Abstract

A surface acoustic wave device includes a first filter and a second filter, each of them being a surface acoustic wave (SAW) filter including an odd number of at least three InterDigital Transducers (IDTs); an unbalanced terminal to which an unbalanced signal is input; a first balanced terminal from which a signal having a same phase as the unbalanced signal is output; and a second balanced terminal from which a signal having an opposite phase to the unbalanced signal is output. One of electrodes of a first center IDT and one of electrodes of a second center IDT are commonly connected to the unbalanced terminal, the first center IDT and the second center IDT being one out of the odd number of IDTs and locating at a center in the first filter and the second filter respectively. The number of electrode fingers of the first center IDT is an odd number, and the number of electrode fingers of the second center IDT is an even number.

Claims

1. A surface acoustic wave device comprising:

a first filter and a second filter, each of them being a surface acoustic wave (SAW) filter including an odd number of at least three InterDigital Transducers (IDTs) respectively;

an unbalanced terminal to which an unbalanced signal is input;

a first balanced terminal from which a signal having a same phase as the unbalanced signal is output; and

a second balanced terminal from which a signal having an opposite phase to the unbalanced signal is output,

wherein one of electrodes of a first center IDT and one of electrodes of a second center IDT are commonly connected to the unbalanced terminal, the first center IDT and the second center IDT being one out of the odd number of IDTs and locating at a center in the first filter and the second filter respectively;

one of electrodes in each of two IDTs locating on either side of the first center IDT is commonly connected to the first balanced terminal;

one of electrodes in each of two IDTs locating on either side of the second center IDT is commonly connected to the second unbalanced terminal;

the number of electrode fingers of the first center IDT is an odd number; and

the number of electrode fingers of the second center IDT is an even number.

2. The surface acoustic wave device according to claim 1, wherein the number of electrode fingers of an electrode, which is one of electrodes constructing the first center IDT and is connected to the unbalanced terminal, is greater than the number of electrode fingers of another electrode.

3. The surface acoustic wave device according to claim 1, wherein at least one of the number of electrode fingers, an aperture length, and an electrode pitch is different from each other between two IDTs locating on either side of the first center IDT and two IDTs locating on either side of the second center IDT.

4. The surface acoustic wave device according to claim 1, wherein the first filter and the second filter is formed on a same piezoelectric substrate.

5. The surface acoustic wave device according to claim 1, further comprising:

a first resonator connected between the unbalanced terminal and the first filter, and between the unbalanced terminal and the second filter;

a second resonator connected between the first balanced terminal and the first filter; and

a third resonator connected between the second balanced terminal and the second filter.

6. The surface acoustic wave device according to claim 5, wherein each of the first resonator, the second resonator, and the third resonator includes an IDT, and resonators located on either side of the IDT.

7. The surface acoustic wave device according to claim 6, wherein at least one of the number of electrode fingers, an aperture length, and an electrode pitch of the IDT included in the second resonator is different from that of the third resonator.

8. The surface acoustic wave device according to claim 1, wherein the first filter and the second filter are a multimode filter.