Surface acoustic wave filter

• US 20030098756A1
• Filed: 10/21/2002
• Published: 05/29/2003
• Est. Priority Date: 10/26/2001
• Status: Active Grant

• Current Assignee: Intellectual Ventures Holding 81 LLC (Intellectual Ventures LLC)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Ohashi, Wataru, Komazaki, Tomokazu, Ehara, Hisanori
• Granted Patent: US 6,861,925 B2
• Time in Patent Office: Days
• US Class Current: 333/133
• CPC Class Codes: H03H 9/6483 Ladder SAW filters

Abstract

A surface acoustic wave filter includes an antenna terminal, an antenna, a transmitting filter, a variable branching line and a receiving filter. The antenna is coupled to the antenna terminal. The transmitting filter is coupled to the antenna terminal for receiving an electrical power. The variable branching line is coupled to the antenna terminal. The variable branching line has a first length when the antenna terminal is opened and has a second length that is longer than the first length when the antenna terminal is terminated so that the electrical power received by the transmitting filter when the antenna terminal is opened is smaller than it when the antenna terminal is terminated. The receiving filter is coupled to the variable branching line.

Claims

1. A surface acoustic wave filter comprising:

an antenna terminal;

an antenna coupled to the antenna terminal;

a transmitting filter coupled to the antenna terminal, the transmitting filter receiving an electrical power;

a variable branching line coupled to the antenna terminal, the variable branching line has a first length when the antenna terminal is opened and has a second length that is longer than the first length when the antenna terminal is terminated so that the electrical power received by the transmitting filter when the antenna terminal is opened is smaller than it when the antenna terminal is terminated; and

a receiving filter coupled to the variable branching line.

2. A surface acoustic wave filter as claimed in claim 1, further comprising a power amplifier coupled to apply the electrical power to the transmitting filter.

3. A surface acoustic wave filter as claimed in claim 1, further comprising a low noise amplifier coupled to the receiving filter.

4. A surface acoustic wave filter as claimed in claim 1, wherein the transmitting filter has a plurality of resonators.

5. A surface acoustic wave filter as claimed in claim 4, wherein the transmitting filter is a T-type ladder filter.

6. A surface acoustic wave filter as claimed in claim 1, wherein the receiving filter has a plurality of resonators.

7. A surface acoustic wave filter as claimed in claim 6, wherein the receiving filter is a π

-type filter.

8. A surface acoustic wave filter comprising:

an antenna terminal;

a front end open line coupled to the antenna terminal;

an antenna coupled to the antenna terminal;

a transmitting filter coupled to the antenna terminal, the transmitting filter receiving an electrical power;

a variable branching line coupled to the antenna terminal, the variable branching line has a first length when the antenna terminal is opened and has a second length that is longer than the first length when the antenna terminal is terminated so that the electrical power received by the transmitting filter when the antenna terminal is opened is smaller than it when the antenna terminal is terminated; and

a receiving filter coupled to the variable branching line.

9. A surface acoustic wave filter as claimed in claim 8, further comprising a power amplifier coupled to apply the electrical power to the transmitting filter.

10. A surface acoustic wave filter as claimed in claim 8, further comprising a low noise amplifier coupled to the receiving filter.

11. A surface acoustic wave filter as claimed in claim 8, wherein the transmitting filter has a plurality of resonators.

12. A surface acoustic wave filter as claimed in claim 11, wherein the transmitting filter is a T-type ladder filter.

13. A surface acoustic wave filter as claimed in claim 8, wherein the receiving filter has a plurality of resonators.

14. A surface acoustic wave filter as claimed in claim 13, wherein the receiving filter is a π

-type filter.

15. A surface acoustic wave filter comprising:

an antenna terminal;

an antenna coupled to the antenna terminal;

a transmitting filter coupled to the antenna terminal, the transmitting filter receiving an electrical power;

a branching line coupled to the antenna terminal;

an electrical power control adjuster for adjusting the electrical power received by the transmitting filter so that the electrical power when the antenna terminal is opened is smaller than it when the antenna terminal is terminated; and

a receiving filter coupled to the variable branching line.

16. A surface acoustic wave filter as claimed in claim 15, wherein the electrical power control adjuster changing a length of the branching line so that the branching line has a first length when the antenna terminal is opened and has a second length that is longer than the first length when the antenna terminal is terminated.

17. A surface acoustic wave filter as claimed in claim 15, further comprising a power amplifier coupled to apply the electrical power to the transmitting filter.

18. A surface acoustic wave filter as claimed in claim 15, further comprising a low noise amplifier coupled to the receiving filter.

19. A surface acoustic wave filter as claimed in claim 15, wherein the transmitting filter is a T-type ladder filter.

20. A surface acoustic wave filter as claimed in claim 15, wherein the receiving filter is a π

-type filter.