Device incorporating a tunable thin film bulk acoustic resonator for performing amplitude and phase modulation

• US 5,714,917 A
• Filed: 10/02/1996
• Issued: 02/03/1998
• Est. Priority Date: 10/02/1996
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Ella, Juha
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US08/720,696
• Time in Patent Office: 489 Days
• Field of Search: 332/144, 332/146, 332/149, 332/174-176, 310/318, 310/345, 310/348, 310/349, 310/350, 310/365, 330/5, 330/5.5, 333/24 R, 333/147, 333/188
• US Class Current: 332/144
• CPC Class Codes: H03C 1/46 Modulators with mechanically-driven or acoustically-driven parts
• CPC Class Codes: H03C 3/42 by means of electromechanical devices H03C3/28 takes precedence
• CPC Class Codes: H03H 2003/0428 of an electrode
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/173 Air-gaps
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/175 Acoustic mirrors

Abstract

A method for amplitude modulating signals, and a circuit that operates in accordance with the method. The method includes a first step of applying a modulating low frequency signal having a time-varying voltage to a tunable resonator. The tunable resonator exhibits parallel and series resonances at frequencies which shift as a function of the time-varying voltage. A second step includes applying an RF carrier signal having a frequency that is between the parallel resonant frequency and the series resonant frequency to the tunable resonator. In response thereto, the tunable resonator causes the RF carrier signal to be attenuated as a function of the time-varying voltage of the modulating low frequency signal. Also provided is a method for phase modulating signals, and a circuit that operates in accordance therewith. A first step includes applying a modulating low frequency signal having a time-varying voltage to a tunable resonator. The tunable resonator yields a maximum phase shift at one of a parallel resonant frequency and a series resonant frequency in response to the modulating low frequency signal. The amount of phase shift yielded is a function of a variation of the modulating low frequency signal voltage. A further step includes applying an RF carrier signal having a frequency that is substantially equal to the one of a parallel resonant frequency and a series resonant frequency. In response thereto, the tunable resonator phase shifts the RF carrier signal by the amount of phase shift yielded by the tunable resonator.

Claims

1. A Bulk Acoustic Wave (BAW) resonator comprising:

a substrate;

resonating means;

a first electrode situated adjacent to a first surface of said resonating means;

a second electrode situated adjacent to a second surface of said resonating means;

a membrane situated between said second electrode and said substrate; and

a pair of etch windows; and

an air gap separating at least a portion of said substrate from at least a portion of said membrane, said air gap being formed by removing a portion of said substrate through said etch windows;

wherein said resonating means resonates in response to an electric field produced between said first and second electrodes as a result of a voltage that is applied therebetween, and wherein said air gap isolates vibrations produced by said resonating means from said substrate.

2. A Bulk Acoustic Wave resonator as set forth in claim 1, wherein said membrane comprises a first layer and a second layer.

3. A Bulk Acoustic Wave resonator as set forth in claim 2, wherein said first layer comprises at least one of poly-silicon (poly-si) and aluminum nitride (AlN), and wherein said second layer comprises at least one of silicon dioxide (SiO₂) and gallium arsenide (GaAs).

4. A Bulk Acoustic Wave resonator as set forth in claim 1, wherein said first and second electrodes are comprised of gold (Au).

5. A Bulk Acoustic Wave resonator as set forth in claim 1, wherein said resonating means comprises at least one of zinc-oxide (ZnO) and aluminum nitride (AlN).

6. A Bulk Acoustic Wave resonator as set forth in claim 1, wherein said substrate comprises at least one of silicon (Si), silicon dioxide (SiO₂), gallium arsenide (GaAs), glass, and a ceramic material.

7. An amplitude modulator circuit, comprising:

a variable voltage generator for generating a low frequency signal having a time-varying voltage;

a tunable resonator coupled to said variable voltage generator, said tunable resonator exhibiting parallel and series resonances at frequencies which shift as a function of voltage; and

means for generating an RF carrier signal having a frequency that is between a parallel resonant frequency and a series resonant frequency exhibited by said tunable resonator in response to a signal output by said variable voltage generator;

wherein, in response to both of a the low frequency signal being output by said variable voltage generator and an RF signal being output by said RF carrier signal generator, said tunable resonator causes the RF carrier signal to be attenuated by amounts that are a function of the time-varying voltage of the modulating low frequency signal, thereby amplitude modulating the RF carrier signal.

8. An amplitude modulator circuit as set forth in claim 7, wherein said resonator is connected within said circuit in one of a parallel configuration and a series configuration.

9. An amplitude modulator circuit as set forth in claim 7, wherein said RF carrier signal generator generates an RF carrier signal having a frequency which is within a range of frequencies over which said tunable resonator yields a minimum phase shift in response to a signal output by said variable voltage generator.

10. A phase modulator circuit, comprising:

a variable voltage signal generator for generating a low frequency signal having a time-varying voltage;

a tunable resonator, said tunable resonator yielding a maximum phase shift at one of a parallel resonant frequency and a series resonator frequency in response to a modulating low frequency signal output by said variable voltage signal generator; and

means for generating an RF carrier signal having a frequency that is substantially equal to said one of a parallel resonant frequency and a series resonant frequency;

wherein, in response to both of a modulating low frequency signal being output by said variable voltage signal generator and an RF carrier signal being output by said RF carrier signal generator, said tunable resonator causes the RF carrier signal to be phase shifted by an amount that is a function of a variation of the modulating low frequency signal voltage, thereby forming a phase-modulated signal.

11. A phase modulator circuit as set forth in claim 10, wherein said RF carrier signal generator generates a signal having a frequency that is substantially equal to said parallel resonant frequency for a case in which said resonator is connected within said tunable circuit in a parallel configuration, and wherein said RF carrier signal generator generates a signal having said series resonant frequency for a case in which said tunable resonator is connected within said circuit in a series configuration.

12. A method for amplitude modulating a signal, comprising the steps of:

applying a modulating low frequency signal having a time-varying voltage to a tunable resonator, the tunable resonator exhibiting parallel and series resonances at frequencies which shift by amounts that are a function of the time-varying voltage; and

applying an RF carrier signal having a frequency that is between the parallel resonant frequency and the series resonant frequency to the tunable resonator, wherein in response thereto, the tunable resonator causes the RF carrier signal to be attenuated as a function of the time-varying voltage of the modulating low frequency signal, thereby amplitude modulating said RF carrier signal.

13. A method as set forth in claim 12, wherein the RF carrier signal has a frequency which is approximately equal to one of which the resonator yields a minimum phase shift in response to the modulating low frequency signal.

14. A method for phase modulating a signal, comprising the steps of:

applying a modulating low frequency signal having a time-varying voltage to a tunable resonator, the tunable resonator yielding a maximum phase shift at one of a parallel resonant frequency and a series resonant frequency in response to the modulating low frequency signal, wherein the amount of phase shift yielded is a function of a variation of the voltage of the modulating low frequency signal; and

applying an RF carrier signal having a frequency that is substantially equal to said one of a parallel resonant frequency and a series resonant frequency, wherein in response thereto, the tunable resonator phase shifts the RF carrier signal by the amount of phase shift yielded by the tunable resonator, thereby phase modulating said RF carrier signal.

15. A method as set forth in claim 14, wherein the RF carrier signal has a frequency that is substantially equal to said series resonant frequency for a case in which the tunable resonator is connected in series, and wherein the RF carrier signal has a frequency that is substantially equal to said parallel resonant frequency for a case in which the tunable resonator is connected in parallel.