Acoustic Resonator Filter System

Abstract

One example includes an acoustic resonator filter system that includes a filter element disposed between a low voltage rail and a filter path node through which an RF input signal propagates to provide a filtered RF output signal, the filter element including an acoustic resonator and a capacitive network disposed in parallel with the acoustic resonator.

Description

[Technical field]

[0001] The present disclosure relates generally to communications, and more particularly to acoustic resonator filters. [Background technology]

[0002] Resonator circuits are implemented in a variety of different types of applications, such as for filtering frequency ranges. There are a variety of different types of resonators. One such type of resonator is an acoustic resonator that utilizes acoustic waves on an integrated circuit (IC). Acoustic resonators include bulk acoustic wave (BAW) resonators and standing acoustic wave (SAW) resonators. Acoustic wave resonators are designed to confine acoustic energy within the resonator to increase the quality factor (Q) of the resonator. As an example, a conventional acoustic resonator can provide effective filtering in a narrow band (e.g., about + / - 5 dB) around a center frequency. Summary of the Invention

[0003] One example includes an acoustic resonator filter system that includes a filter element disposed between a low voltage rail and a filter path node through which an RF input signal propagates to provide a filtered RF output signal, the filter element including an acoustic resonator and a capacitive network disposed in parallel with the acoustic resonator.

[0004] Another example includes an acoustic resonator filter system. The system includes a plurality of filter elements. Each of the filter elements may be disposed between a low voltage rail and one of a plurality of filter path nodes through which an RF input signal propagates to provide a filtered RF output signal. The acoustic resonator filter system is arranged as a resonator tank network. Each of the plurality of filter elements includes an acoustic resonator and a capacitive network disposed in parallel with the acoustic resonator.

[0005] Another example includes an integrated circuit (IC) that includes an acoustic resonator filter system. The system includes a plurality of filter elements. Each of the plurality of filter elements may be disposed between a low voltage rail and one of a plurality of filter path nodes through which an RF input signal propagates to provide a filtered RF output signal. The acoustic resonator filter system is arranged as a resonator tank network. Each of the plurality of filter elements includes an acoustic resonator and a capacitive network disposed in parallel with the acoustic resonator. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a block diagram of an example acoustic resonator filter system. [Diagram 2] FIG. 2 illustrates a dipole transformation of an example filter element. [Diagram 3] FIG. 1 is a circuit diagram of an example acoustic resonator filter system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present disclosure relates generally to communications, and specifically to acoustic resonator filter systems. The acoustic resonator filter systems may be implemented in various communication systems, such as in the transmit and / or receive paths of a wireless transceiver, or in various variable filter applications. The acoustic resonator filter systems include a plurality of filter elements, each including an acoustic resonator and a capacitive network. As an example, the acoustic resonators may be configured as combined overtone resonators (COR), bulk acoustic wave (BAW) resonators, or another type of acoustic resonator. As another example, the capacitive network may include at least one capacitor in parallel with the acoustic resonator. For example, the capacitors may include a fixed capacitor and a variable capacitor (varactor) (e.g., a barium strontium titanate (BST) varactor) configured to provide a variable capacitance.

[0008] As an example, the filter elements may each be disposed between one of the filter path nodes and a low voltage rail (e.g., ground). Thus, the acoustic resonator filter system may be arranged as a resonator tank network. As an example, each of the filter path nodes may be coupled by a plurality of filter path capacitors. The physical characteristics of the acoustic resonator, the capacitance of the capacitive network, and the capacitance of the filter path capacitor may be set to tune the filter characteristics of the acoustic resonator filter system. Thus, an RF input signal provided via a signal path including each of the filter path nodes and the plurality of filter path capacitors may be provided as a filtered RF output signal by the acoustic resonator filter system. Based on the arrangement of the filter elements including the acoustic resonator and the capacitive network in a parallel arrangement, the acoustic resonator filter system may achieve a significantly larger bandwidth (e.g., up to 25%) than a conventional acoustic resonator filter. Thus, by arranging the acoustic resonator filter system as a resonator tank network with respect to the plurality of filter elements, a filter system may be provided that is significantly improved over conventional filters including acoustic resonators in a ladder network.

[0009] 1 illustrates a block diagram of an example of an acoustic resonator filter system 100. Acoustic resonator filter systems may be implemented in various communication systems, such as in the transmit and / or receive paths of a wireless transceiver, or as a filter block for a larger selective filter system. As described herein, the acoustic resonator filter system, in the example of FIG. 1, filters a signal RF IN As an example, the acoustic resonator filter system 100 may be fabricated within an integrated circuit (IC).

[0010] The acoustic resonator filter system 100 includes N filter elements 102. Each of the filter elements 102 includes an acoustic resonator 104 and a capacitive network 106. By way of example, the acoustic resonator 104 may be configured as a coupled overtone resonator (COR), a bulk acoustic wave (BAW) resonator, or various other types of acoustic resonators. The capacitive network 106 may be arranged in parallel with the acoustic resonator 104. The arrangement and characteristics of the acoustic resonator 104 and the capacitive network 106 in each of the filter elements may provide a passband for an individual one of the filter elements 102 that may increase the bandwidth of the passband provided by the individual filter element 102 (e.g., up to about 25%). Thus, when an RF input signal RF IN are filtered in separate passbands to produce the RF output signal RF OUT It may be provided as:

[0011] As an example, the multiple filter elements 102 may each be disposed between one of the multiple filter path nodes and a low voltage rail (e.g., ground). Thus, the acoustic resonator filter system 100 may be disposed as a resonator tank network. As an example, each of the multiple filter path nodes may be coupled by multiple filter path capacitors. The physical characteristics of the acoustic resonator 104 and the capacitance values ​​of the capacitive networks 106 of the individual filter elements 102 may be set to tune the filter characteristics of the acoustic resonator filter system 100. Thus, disposing the acoustic resonator filter system 100 as a resonator tank network with respect to the multiple filter elements 102 may provide a significantly improved filter system over conventional filter systems that include acoustic resonators in a ladder network.

[0012] 2 shows a circuit diagram 200 of an example of dipole transforms of a plurality of filter elements. The diagram 200 shows a first dipole transform 202 and a second dipole transform 204. The dipole transforms 202 and 204 may correspond to a configuration of filter elements, such as one of the plurality of filter elements 102 of the example of FIG. 1. Accordingly, reference is made to the example of FIG. 1 in the following description of the example of FIG. 2.

[0013] The first dipole transformation 202 shows a first resonator dipole 206. The first resonator dipole 206 includes an inductor L1 in parallel with a capacitor C1, and the parallel arrangement of the inductor L1 and the capacitor C1 is in series with a capacitor C2. The first dipole transformation 202 shows a second resonator dipole 208 that is equivalent to the first resonator dipole 206. The second resonator dipole 208 includes an inductor L2 in series with a capacitor C3, and the series arrangement of the inductor L2 and the capacitor C3 is in parallel with a capacitor C4. For example, the equivalence between the first resonator dipole 206 and the second resonator dipole 208 can be based on approximately the same performance (e.g., including poles and zeros) over frequency based on adjusting the values ​​of the inductors L1 and L2 and the capacitors C1-C4.

[0014] The second dipole transformation 204 shows a second resonator dipole 208 and a third resonator dipole 210 that is approximately equivalent to the second resonator dipole 208. The third resonator dipole 210 is arranged similarly to the second dipole 208, but the capacitor C4 is split into a parallel set of capacitors C5 and C6. As described above in the second dipole transformation 204, the equivalence between the second resonator dipole 208 and the third resonator dipole 210 can be accommodated for nominal performance (e.g., including polarity and zero) across frequency based on adjusting the values ​​of the inductors L1 and L2 and the capacitors C1, C5, and C6. However, by adjusting the capacitance values ​​of the parallel set of capacitors C5 and C6, the bandwidth of the third resonator dipole 210 can be adjusted in terms of frequency poles to a much greater extent than by implementing only the capacitor C4.

[0015] The second dipole transformation 204 also shows a fourth resonator dipole 212 that is approximately equivalent to the third resonator dipole 210. The fourth resonator dipole 212 is arranged similarly to the third dipole 210, but with a capacitor C5 arranged in parallel with the series arrangement of inductor L2 and capacitor C5. The arrangement of inductor L2 and capacitors C3 and C5 may therefore correspond to an acoustic resonator dipole equivalent circuit shown at 214. The arrangement of the acoustic resonator dipole 214 may represent the operating characteristics of the associated acoustic resonator. For example, the inductance value of inductor L2, the capacitance value of capacitor C3, and the capacitance value of capacitor C5 may be based on the physical characteristics of the associated acoustic resonator (e.g., the dimensions of the substrate).

[0016] Thus, by incorporating capacitor C6 in parallel with an acoustic resonator (e.g., acoustic resonator dipole 214) in a manner similar to that described above with respect to third resonator dipole 210, an associated fourth dipole 212 can achieve a bandwidth having a significantly greater percentage of poles at associated frequencies than acoustic resonator dipole 214 alone. Thus, fourth resonator dipole 212 can be implemented as a filter element in an acoustic resonator filter system, such as acoustic resonator filter system 100 in the example of FIG. 1, to provide significantly higher performance than conventional filter systems implementing acoustic resonators.

[0017] Figure 3 shows a circuit diagram of an example acoustic resonator filter system 300. Acoustic resonator filter system 300 may correspond to acoustic resonator filter system 100 in the example of Figure 1. Accordingly, the following description of the example of Figure 3 will refer to the example of Figure 1.

[0018] The acoustic resonator filter system 300 includes a plurality of filter elements 302, N in number, where N is a positive integer. Each of the plurality of filter elements 302 includes an acoustic resonator 304, a capacitor C S , and another capacitor C V The plurality of filter elements 302 may be arranged similarly to the fourth resonator dipole 212 in the example of FIG. S and capacitor C V may correspond to capacitor C6. In the example of FIG. 3, the capacitor is shown as a variable capacitor (varactor) and has a voltage V TN is the capacitor C V Alternatively, a capacitor C V can have a fixed capacitance or be a capacitor C S and capacitor C V may be combined into a single equivalent capacitance (eg, similar to capacitor C6).

[0019] The acoustic resonator 304 is, in the example of FIG. 3, a first capacitor C R1 and inductor L R , and a first capacitor C R1 and inductor L R The series arrangement of the second capacitor C R2 . Thus, the acoustic resonator 304 is configured similarly to the acoustic resonator dipole 214 in the example of FIG. 2. The configuration of the acoustic resonator 304 can represent the operating characteristics of the acoustic resonator 304. For example, the first capacitor C R1 , the second capacitor C R2 , and inductor L R The value of may be based on the physical characteristics (e.g., substrate dimensions) of the acoustic resonator 304. The multiple filter elements 302 may be symmetrically positioned with respect to the first filter element 302, the last filter element 302, and the middle filter element 302 to provide proper impedance matching and filter matching characteristics.

[0020] As an example, the acoustic resonator 304 may be configured as a COR (e.g., an aluminum nitride (AlN) COR). Thus, the acoustic resonator 304 receives an RF input signal, RF IN The COR may exhibit a high quality factor (Q) at frequencies both above and below a particular frequency range (e.g., Ka band). For example, the COR may operate in a Q range of about 400 to about 1000. Additionally, acoustic resonator 304 configured as a COR may be configured to receive an RF input signal RF IN A shape factor selectivity of about 1.03 can be provided to substantially reject out-of-band components and interferences. Such selectivity can achieve about 60 dB of attenuation at about 50 MHz on either side of the 3.5 GHz bandwidth, thus providing significantly greater attenuation than conventional acoustic resonator filters (e.g., which exhibit a selectivity of about 1.5).

[0021] Acoustic resonator 304, capacitor C S , and capacitor C VThe parallel arrangement of the capacitors C in parallel with the acoustic resonator 304 can provide significantly improved filter characteristics over conventional filters. S and C V The split capacitance provided by the capacitor C can provide the ability to tune the filter element 302 over a wide frequency range with minimal impact on the quality factor Q and insertion loss. V can be configured as a barium strontium titanate (BST) varactor, which allows a tuning range of about 33%, with a loss tangent of about 0.006 and a quality factor Q of about 40 at a frequency of about 18 GHz. Thus, a capacitor C in parallel with acoustic resonator 304 S and C V The split capacitor configuration can provide a wide range of frequency tuning without performance degradation of the acoustic resonator filter system 300 .

[0022] In the example of Figure 3, each of the plurality of filter elements 302 is disposed between a filter path node 306 and a low voltage rail, shown as ground in the example of Figure 3. Each of the plurality of filter path nodes 306 is connected to a capacitor C FP_1 ~C FP_N+1 Therefore, the filter path capacitor C FP_1 ~C FP_N+1 is one more than the N filter elements 302. Thus, the acoustic resonator filter system 300 receives an RF input signal RF IN The RF input signal, RF IN is the multiple filter path capacitor C FP_1 ~C FP_N+1 and provided to a signal path through a plurality of filter path nodes 306 to provide an RF output signal RF OUT Therefore, multiple filter path capacitors C FP_1 ~C FP_N+1Based on the arrangement of the multiple filter elements 302 between the , the acoustic resonator filter system 300 is configured to provide one or more passbands (e.g., harmonically related passbands). As an example, a particular passband of the acoustic resonator filter system 300 may have a bandwidth of up to about 25%. In contrast, a conventional filter system including an acoustic resonator may have a bandwidth of less than 5%. Thus, the acoustic resonator filter system 300 may provide significant advantages over conventional filter systems including acoustic resonators.

[0023] The above are examples of the present invention. Of course, it is not possible to describe every conceivable combination of elements or methods for purposes of describing the present invention, but one skilled in the art will recognize that many more combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. In addition, when the disclosure or claims recite "a," "an," "a first," or "another" element, or the equivalent thereof, it should be construed as including one or more such elements, and does not require or exclude two or more such elements. As used herein, the term "includes" means including but not limited to, and the term "including" means including but not limited to. The term "based on" means based at least in part on.

Claims

1. 1. An acoustic resonator filter system comprising: a filter element disposed between a low voltage rail and a filter path node through which an RF input signal propagates to provide a filtered RF output signal, the filter element comprising: An acoustic resonator; a capacitive network disposed in parallel with the acoustic resonator.

2. The capacitive network comprises: a first capacitor disposed in parallel with the acoustic resonator; 10. The system of claim 1, further comprising: a second capacitor disposed in parallel with the acoustic resonator and the first capacitor.

3. The system of claim 2 , wherein the second capacitor is arranged as a varactor configured to provide a variable capacitance in response to a control voltage.

4. The system of claim 3 , wherein the varactor is arranged as a barium strontium titanate (BST) varactor.

5. 2. The system of claim 1 , wherein the filter element is a first filter element of a plurality of filter elements, each of the plurality of filter elements being disposed between one of a plurality of filter path nodes and the low voltage rail such that the acoustic resonator filter system is arranged as a resonator tank network.

6. 6. The system of claim 5, further comprising a plurality of filter path capacitors, each of the plurality of filter path capacitors coupled between a pair of filter path nodes of the plurality of filter path nodes such that the RF input signal propagates through each of the plurality of filter path capacitors and each of the plurality of filter path nodes.

7. 10. The system of claim 1, wherein the acoustic resonator includes a physical property and the capacitive network includes a capacitance value, the physical property and the capacitance value being selected to set a filter characteristic associated with the acoustic resonator filter system.

8. The system of claim 1 , wherein the acoustic resonator is arranged as a coupled harmonic resonator (COR).

9. 10. An integrated circuit (IC) comprising the acoustic resonator filter system of claim 1.

10. 1. An acoustic resonator filter system comprising a plurality of filter elements, each of the plurality of filter elements disposed between a low voltage rail and one of a plurality of filter path nodes through which an RF input signal propagates to provide a filtered RF output signal such that the acoustic resonator filter system is arranged as a resonator tank network, each of the plurality of filter elements comprising: An acoustic resonator; a capacitive network disposed in parallel with the acoustic resonator.

11. The capacitive network comprises: a first capacitor disposed in parallel with the acoustic resonator; The system of claim 10 comprising a second capacitor disposed in parallel with the acoustic resonator and the first capacitor.

12. The system of claim 11 , wherein the second capacitor is arranged as a varactor configured to provide a variable capacitance in response to a control voltage.

13. 12. The system of claim 11, further comprising a plurality of filter path capacitors, each of the plurality of filter path capacitors coupled between a pair of filter path nodes of the plurality of filter path nodes such that the RF input signal propagates through each of the plurality of filter path capacitors and each of the plurality of filter path nodes.

14. 11. The system of claim 10, wherein the acoustic resonator includes a physical property and the capacitive network includes a capacitance value, the physical property and the capacitance value being selected to set a filter characteristic associated with the acoustic resonator filter system.

15. An integrated circuit (IC) comprising the acoustic resonator filter system of claim 10.

16. 1. An integrated circuit (hereinafter IC) comprising an acoustic resonator filter system, the acoustic resonator filter system comprising a plurality of filter elements, each of the plurality of filter elements being disposed between a low voltage rail and one of a plurality of filter path nodes through which an RF input signal propagates to provide a filtered RF output signal such that the acoustic resonator filter system is arranged as a resonator tank network, each of the plurality of filter elements comprising: An acoustic resonator; a capacitive network disposed in parallel with the acoustic resonator.

17. The capacitive network comprises: a first capacitor disposed in parallel with the acoustic resonator; 17. The IC of claim 16, further comprising: a second capacitor disposed in parallel with the acoustic resonator and the first capacitor.

18. 20. The IC of claim 17, wherein the second capacitor is arranged as a varactor configured to provide a variable capacitance in response to a control voltage.

19. 17. The IC of claim 16, wherein the acoustic resonator includes a physical property and the capacitive network includes a capacitance value, the physical property and the capacitance value being selected to set a filter characteristic associated with the acoustic resonator filter system.

20. The IC of claim 16 , wherein the acoustic resonator is arranged as a coupled harmonic resonator (COR).

Images