General matching network for acoustic wave filters and acoustic resonators

• US 20080042778A1
• Filed: 08/17/2006
• Published: 02/21/2008
• Est. Priority Date: 08/17/2006
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies Wireless IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Bradley, Paul, Frank, Michael, Jamneala, Tiberiu
• Granted Patent: US 7,501,912 B2
• Time in Patent Office: Days
• US Class Current: 333/133
• CPC Class Codes: H03H 9/0004 Impedance-matching networks H03H9/145 takes precedence
• CPC Class Codes: H03H 9/706 Duplexers

Abstract

A method and circuit matches a device to n filters, wherein each filter is a SAW filter, BAW filter, or FBAR filter. The method and system: (a) provide an inductor or transmission line connected between a common terminal and ground; (b) provide a plurality of capacitance values (C_1m, C_2m, . . . , C_nm) each corresponding to one of the n filters; and (c) for each of the n filters, directly connect a first terminal of the filter to either: (1) the common terminal, or (2) a first terminal of a corresponding capacitor having the correspondence capacitance value calculated in step (b), where a second terminal of the corresponding capacitor is directly connected to the common terminal.

Claims

1. A radio frequency (RF) signal processing device, the device comprising:

a common terminal;

a plurality of filters, wherein each of the filters is one of a surface acoustic wave (SAW) filter, a bulk acoustic wave (BAW) filter, and a thin film bulk acoustic resonator (FBAR) filter;

a plurality of matching capacitors corresponding to the plurality of filters, each capacitor having a first electrode directly connected to the corresponding filter and having a second electrode, wherein the second electrodes of all of the matching capacitors are directly connected together to the common terminal; and

one of an inductor and a transmission line connected between the common terminal and ground.

2. The RF signal processing device of claim 1, further comprising an antenna connected to the common terminal.

3. The RF signal processing device of claim 2, wherein each of the matching capacitors is adapted to match an impedance of the antenna to an impedance of the corresponding filter.

4. The RF signal processing device of claim 1, wherein the matching capacitors isolate a signal in a corresponding passband of each of the filters from all of the other filters.

5. The RF signal processing device of claim 1, wherein the device includes a single layer printed circuit board on which are provided the common terminal, the plurality of filters, the plurality of matching capacitors, and the inductor or transmission line.

6. The RF signal processing device of claim 1, wherein there are n filters and n matching capacitors,

wherein capacitance values (C_1m, C_2m, . . . , C_nm) of the n matching capacitors solve the equations:

(2π

F₁)²L(0+C₂+C₃+ . . . +C_n-1+C_n)=1;

(2π

F₂)²L(C₁+0+C₃+ . . . +C_n-1+C_n)=1;

. . . (2π

F_n)²L(C₁+C₂+ . . . +C_n-1+0)=1,

wherein C_i=(C_im*C_i0)/(C_im+C_i0),

wherein C_i0 is the equivalent capacitance value of filter i outside of its passband, and

wherein (F₁, F₂, . . . F_n) are center frequencies of the n filters.

7. The RF signal processing device of claim 1, wherein there are n filters and n matching capacitors, where n>

2.

8. A radio frequency (RF) signal processing device, the device comprising:

a common terminal;

n filters, where n>

2, wherein each of the filters is one of a surface acoustic wave (SAW) filter, a bulk acoustic wave (BAW) filter, and a thin film bulk acoustic resonator (FBAR) filter, each filter having first and second terminals, wherein the first terminal of each filter is directly connected to either;

(1) the common terminal, or (2) a first terminal of a corresponding matching capacitor, where a second terminal of the corresponding matching capacitor is directly connected to the common terminal;

one of an inductor and a transmission line connected between the common terminal and ground.

9. The RF signal processing device of claim 8, further comprising an antenna connected to the common terminal.

10. The RF signal processing device of claim 9, wherein the device includes a single layer printed circuit board on which are provided the common terminal, the plurality of filters, and the inductor or transmission line.

11. A method of matching a device to a plurality (n) of filters each having first and second terminals, wherein each of the filters is one of a surface acoustic wave (SAW) filter, a bulk acoustic wave (BAW) filter, and a thin film bulk acoustic resonator (FBAR) filter, the method comprising:

(a) providing one of an inductor and a transmission line connected between a common terminal and ground;

(b) determining a plurality of capacitance values (C_1m, C_2m, . . . , C_nm) each corresponding to one of the n filters; and

(c) for each of the n filters, directly connecting the first terminal of the filter to either;

(1) the common terminal, or (2) a first terminal of a corresponding matching capacitor having the correspondence capacitance value calculated in step (b), where a second terminal of the corresponding matching capacitor is directly connected to the common terminal.

12. The method of claim 11, wherein the capacitance values (C_1m, C_2m, . . . , C_nm) of the n capacitors solve the equations:

(2π

F₁)²L(0+C₂+C₃+ . . . +C_n-1+C_n)=1;

(2π

F₂)²L(C₁+0+C₃+ . . . +C_n-1+C_n)=1;

. . . (2π

F_n)²L(C₁+C₂+ . . . +C_n-1+0)=1,

wherein C_i=(C_im*C_i0)/(C_im+C_i0),

wherein C_i0 is the equivalent capacitance value of filter i outside of its passband, and

wherein (F₁, F₂, . . . F_n) are center frequencies of the n filters.

13. The method of claim 11, wherein when the first terminal of a filter is directly connected to the common terminal, and an input characteristic of the filter includes the corresponding capacitance value calculated in step (b).

14. The method of claim 11, where n>

2.