Bandpass filter with tunable resonator

• US 20050148312A1
• Filed: 02/16/2005
• Published: 07/07/2005
• Est. Priority Date: 04/11/2001
• Status: Active Grant

• Current Assignee: Kyocera Corporation
• Original Assignee: Kyocera Wireless Corporation (Kyocera Corporation)
• Inventors: Fabrega-Sanchez, Jorge, Toncich, Stanley S.
• Granted Patent: US 7,174,147 B2
• Time in Patent Office: Days
• US Class Current: 455/339
• CPC Class Codes: H03H 7/0161 Bandpass filters H03H7/12 takes precedence
• CPC Class Codes: H03H 7/1791 Combined LC in shunt or branch path
• CPC Class Codes: H03J 3/08 by varying a second parameter simultaneously with the tuning, e.g. coupling bandpass filter

Abstract

A tunable bandpass filter is provided that comprises a first shunt-connected ferroelectric (FE) tunable tank circuit having a first node to accept an input signal. A second shunt-connected FE tunable tank circuit has a second node to supply a bandpass filtered signal. A first capacitor is connected in series between the first and second nodes. In one aspect, the first tank circuit comprises a first resonator connected to the first node, and a fourth capacitor connected between the first resonator and a reference voltage. The fourth capacitor is a tunable FE capacitor. Typically, a fifth capacitor is connected between the first node and the reference voltage. Likewise, the second tank circuit comprises a second resonator connected to the second node, and a sixth (FE) capacitor connected between the second resonator and the reference voltage. A seventh capacitor is connected between the second node and the reference voltage.

Claims

1. A tunable bandpass filter, the filter comprising:

a first shunt-connected ferroelectric (FE) tunable tank circuit having a first node to accept an input signal;

a second shunt-connected FE tunable tank circuit having a second node to supply a bandpass filtered signal; and

a first capacitor connected in series between the first and second nodes.

2. The filter of claim 1 wherein the first tank circuit comprises:

a first resonator having an input connected to the first node and an output connected to a reference voltage; and

a second capacitor having an input connected to the first node, an output connected to the reference voltage, and an input to accept a control signal, the second capacitor including an FE material with a dielectric constant responsive to the control voltage;

wherein the second tank circuit comprises;

a second resonator having an input connected to the second node and an output connected to the reference voltage; and

a third capacitor having an input connected to the second node, an output connected to the reference voltage, and an input to accept a control signal, the third capacitor including an FE material with a dielectric constant responsive to the control voltage.

3. The filter of claim 1 wherein the first tank circuit comprises:

a first resonator having an input connected to the first node and an output;

a fourth capacitor having an input connected to the first resonator output, an output connected to a reference voltage, and an input to accept a control signal, the fourth capacitor including an FE material with a dielectric constant responsive to the control voltage; and

a fifth capacitor having an input connected to the first node and an output connected to the reference voltage;

wherein the second tank circuit comprises;

a second resonator having an input connected to the second node and an output;

a sixth capacitor having an input connected to the second resonator output, an output connected to the reference voltage, and an input to accept a control signal, the sixth capacitor including an FE material with a dielectric constant responsive to the control voltage; and

a seventh capacitor having an input connected to the second node and an output connected to the reference voltage.

4. The filter of claim 3 wherein the fifth capacitor has an input to accept a control signal, and includes an FE material with a dielectric constant responsive to the control voltage;

and

wherein the seventh capacitor has an input to accept a control signal, and includes an FE material with a dielectric constant responsive to the control voltage.

5. The filter of claim 4 wherein the first tank circuit further comprises an eighth capacitor having an input and output interposed between the fifth capacitor output and the reference voltage, and an input to accept a control signal, the eighth capacitor including an FE material with a dielectric constant responsive to the control voltage;

and

wherein the second tank circuit further comprises a ninth capacitor having an input and output interposed between the seventh capacitor output and the reference voltage, and an input to accept a control signal, the ninth capacitor including an FE material with a dielectric constant responsive to the control voltage.

6. The filter of claim 3 further comprising:

an input node to accept the input signal;

a tenth capacitor having an input connected to the input node and an output connected to the first node;

an output node to supply the filtered signal; and

an eleventh capacitor having an input connected to the second node and an output connected to the output node.

7. The filter of claim 3 wherein the fourth and sixth capacitors each have a quality factor greater than about 80 in the temperature range between −

50 and 100 degrees C.

8. The filter of claim 3 wherein the first and second resonators are resonator types selected from the group including coaxial, stripline, microstrip, and monoblock resonators.

9. The filter of claim 3 wherein the fourth and sixth capacitors are FE capacitor types selected from the group including interdigital capacitor (IDC), overlay, and gap capacitors.

10. The filter of claim 6 wherein the first capacitor has an input to accept a control signal, the first capacitor including an FE material with a dielectric constant responsive to the control voltage;

wherein the tenth capacitor has an input to accept a control signal, the tenth capacitor including an FE material with a dielectric constant responsive to the control voltage; and

wherein the eleventh capacitor has an input to accept a control signal, the eleventh capacitor including an FE material with a dielectric constant responsive to the control voltage.

11. The filter of claim 10 wherein the first, tenth, and eleventh capacitors each have a capacitance in the range of 0.5 and 0.7 picofarads (pF);

wherein the fourth and sixth capacitors each have a capacitance in the range of 2 and 4.1 pF;

wherein the fifth and seventh capacitors each have a capacitance in the range of 0.5 and 1 pF;

wherein the first and second resonators each have an inductance of about 2.6 nanoHenrys (nH);

wherein the first tank circuit further comprises an eighth capacitor having an input and output interposed between the fifth capacitor output and the reference voltage, and a capacitance of about 200 pF; and

wherein the second tank circuit further comprises a ninth capacitor having an input and output interposed between the seventh capacitor output and the reference voltage, and a capacitance of about 200 pF.

12. The filter of claim 11 wherein the first capacitor has a capacitance of 0.7 pF;

wherein the fourth and sixth capacitors each have a capacitance of 3.45 pF;

wherein the fifth and seventh capacitors each have a capacitance of 0.53 pF;

wherein the tenth and eleventh capacitors each have a capacitance of 0.65 pF; and

wherein the filter is tuned to optimally pass signals from the input node to the output node having a frequency of about 1750 megahertz (M Hz).

13. The filter of claim 11 wherein the first capacitor has a capacitance of 0.5 pF;

wherein the fourth and sixth capacitors each have a capacitance of 2 pF;

wherein the fifth and seventh capacitors each have a capacitance of 1 pF;

wherein the tenth and eleventh capacitors each have a capacitance of 0.59 pF; and

wherein the filter is tuned to optimally pass signals from the input node to the output node having a frequency of about 1850 MHz.

14. The filter of claim 11 wherein the first capacitor has a capacitance of 0.7 pF;

wherein the fourth and sixth capacitors each have a capacitance of 1.72 pF;

wherein the fifth and seventh capacitors each have a capacitance of 0.78 pF;

wherein the tenth and eleventh capacitors each have a capacitance of 0.59 pF; and

wherein the filter is tuned to optimally pass signals from the input node to the output node having a frequency of about 1910 MHz.

15. The filter of claim 11 wherein the first capacitor has a capacitance of 0.67 pF;

wherein the fourth and sixth capacitors each have a capacitance of 4.1 pF;

wherein the fifth and seventh capacitors each have a capacitance of 1 pF;

wherein the tenth and eleventh capacitors each have a capacitance of 0.65 pF; and

wherein the filter is tuned to optimally pass signals from the input node to the output node having a frequency of about 1700 MHz.

16. A method for bandpass filtering a signal, the method comprising:

providing a first tank circuit, with a resonator and parallel capacitor, capacitively coupled to a second tank circuit with a resonator and parallel capacitor;

accepting an input signal;

ferroelectrically tuning the resonators of the first and second tank circuits;

in response to ferroelectrically tuning the resonators, bandpass filtering the input signal.

17. The method of claim 16 wherein providing first and second tank circuits comprises providing a ferroelectric (FE) capacitor series connected with each resonator, each FE capacitor made with a ferroelectric material having a dielectric constant responsive to a control signal;

and

wherein ferroelectrically tuning the resonators of the first and second tank circuits comprises supplying control signals to the FE capacitors connected in series to the resonators.

18. The method of claim 16 wherein providing first and second tank circuits comprises providing a FE capacitor in parallel with each resonator, each FE capacitor made with a ferroelectric material having a dielectric constant responsive to a control signal;

and

wherein ferroelectrically tuning the resonators of the first and second tank circuits comprises supplying control signals to the FE capacitors connected in parallel with the resonators.

19. The method of claim 16 wherein providing first and second tank circuits comprises providing a FE capacitor in parallel with each resonator and in series with each resonator, each FE capacitor made with a ferroelectric material having a dielectric constant responsive to a control signal;

and

wherein ferroelectrically tuning the resonators of the first and second tank circuits comprises supplying control signals to the FE capacitors connected in parallel and in series with the resonators.

20. A wireless telephone device with a tunable duplexer, the device comprising:

a receiver having an input;

a transmitter having an output;

an antenna having an antenna port;

a duplexer comprising a first port connected to the antenna port, a second port connected to the transmitter ouptput, and a third port;

a tunable bandpass filter coupled between the duplexer third port and the receiver input, the tunable bandpass filter comprising;

a first shunt-connected ferroelectric (FE) tunable tank circuit having a first node to accept an input signal;

a second shunt-connected FE tunable tank circuit having a second node to supply a bandpass filtered signal; and

a first capacitor connected in series between the first and second nodes.