PATENT DOCUMENT

Publication Number: US-8786384-B2
Application Number: US-200913125362-A
Country: US
Kind Code: B2

Title: Self-matched band reject filter

Abstract:
The present application describes a radio frequency band reject filter including an input port, an output port, a plurality of acoustic resonators and an inductor for matching the impedance of the plurality of acoustic resonators. The inductor is positioned within the band reject filter in respect of the plurality of acoustic resonators such that a static capacitance between the input port and the inductor is substantially equivalent to a static capacitance between the output port and the inductor. The plurality of acoustic resonators may be a plurality of parallel resonators, a plurality of series resonators or a combination of series and parallel resonators. The radio frequency band reject filter is fabricated using any of surface acoustic wave (SAW) technology, thin film bulk acoustic resonator (FBAR) technology, and bulk acoustic wave (BAW) technology.

Claims:
The invention claimed is: 
     
       1. A radio frequency band reject filter comprising:
 an input port; 
 an output port; 
 a plurality of acoustic resonators coupled between the input port and the output port, wherein the plurality of acoustic resonators comprise a first plurality of acoustic resonators and a second plurality of acoustic resonators; and 
 an inductor positioned within the band reject filter, and comprising:
 a first terminal coupled to ground; and 
 a second terminal coupled to a common node between the first plurality of acoustic resonators and the second plurality of acoustic resonators, wherein a static capacitance between the input port and the common node is substantially equivalent in value to a static capacitance between the output port and the common node; 
 
 wherein a combined impedance of the inductor and the plurality of acoustic resonators is equivalent in value to at least one of:
 an impedance of the radio frequency band reject filter from the input port to ground; or 
 an impedance of the radio frequency band reject filter from the output port to ground. 
 
 
     
     
       2. The radio frequency band reject filter of  claim 1  wherein the plurality of acoustic resonators are one of:
 a plurality of parallel acoustic resonators; 
 a plurality of series acoustic resonators; and 
 a combination of series acoustic resonators and parallel acoustic resonators. 
 
     
     
       3. The radio frequency band reject filter of  claim 2 , wherein the combination of series acoustic resonators and parallel acoustic resonators comprises:
 N, where N&gt;2, series acoustic resonators; and 
 M, where M≧2, parallel acoustic resonators. 
 
     
     
       4. The radio frequency band reject filter of  claim 3 , wherein N is an even number and there are N/2 series acoustic resonators between the input port and the common node and N/2 series acoustic resonators between the output port and the common node. 
     
     
       5. The radio frequency band reject filter of  claim 3  or  claim 4 , wherein M is an even number and there are M/2 parallel acoustic resonators between the input port and the common node and M/2 parallel acoustic resonators between the output port and the common node. 
     
     
       6. The radio frequency band reject filter of  claim 1  wherein the radio frequency band reject filter is fabricated using one of: surface acoustic wave (SAW) technology; thin film bulk acoustic resonator (FBAR) technology; and bulk acoustic wave (BAW) technology. 
     
     
       7. The radio frequency band reject filter of  claim 1  wherein the inductor is a short stub on-chip inductor. 
     
     
       8. The radio frequency band reject filter of  claim 7  wherein the inductor has an inductance that is equal to or less than 0.1 nH. 
     
     
       9. The radio frequency band reject filter of  claim 1  cascaded with one or more other radio frequency band reject filters. 
     
     
       10. The radio frequency band reject filter of  claim 9 , wherein at least one of the one or more other radio frequency band reject filters has an inductor for matching impedance of the respective at least one other radio frequency band reject filters. 
     
     
       11. The radio frequency band reject filter of  claim 1 , wherein the plurality of acoustic resonators comprise a combination of series acoustic resonators and parallel acoustic resonators, and wherein each series acoustic resonator of the series acoustic resonators and each parallel resonator of the parallel acoustic resonators is formed by a set of interdigital electrodes extending from a pair of parallel conductive elements. 
     
     
       12. The radio frequency band reject filter of  claim 11 , wherein for the parallel acoustic resonators, at least one of the pair of parallel conductive elements is coupled to ground. 
     
     
       13. The radio frequency band reject filter of  claim 11 , wherein for at least one series acoustic resonator or at least one parallel acoustic resonator, or both, at least one of the pair of parallel conductive elements forming the respective acoustic resonator is coupled to the inductor. 
     
     
       14. The radio frequency band reject filter of  claim 13 , wherein the inductor is a short stub element located between the at least one of the pair of parallel conductive elements and ground. 
     
     
       15. The radio frequency band reject filter of  claim 1  wherein the inductance of the inductor can be fabricated accurately enough that external matching circuits are not used with the filter. 
     
     
       16. A telecommunication base station comprising:
 at least one antenna; 
 transmit circuitry configured for modulating one or more carrier signals having a desired transmit frequency or frequencies; 
 receiving circuitry configured for receiving a radio frequency signal bearing information from one or more remote transmitters; 
 a baseband processor configured for:
 processing a received signal received by the receiving circuitry; and 
 encoding a signal for transmission by the transmit circuitry; 
 
 at least one of the transmit circuitry or receiving circuitry comprising the radio frequency band reject filter of  claim 1 . 
 
     
     
       17. A telecommunication wireless terminal comprising:
 at least one antenna; 
 transmit circuitry configured for modulating one or more carrier signals having a desired transmit frequency or frequencies; 
 receiving circuitry configured for receiving a radio frequency signal bearing information from one or more remote transmitters; 
 a baseband processor configured for:
 processing a received signal received by the receiving circuitry; and 
 encoding a signal for transmission by the transmit circuitry; 
 
 at least one of the transmit circuitry or receiving circuitry comprising the radio frequency band reject filter of  claim 1 . 
 
     
     
       18. A duplexer comprising the radio frequency band reject filter of  claim 1 . 
     
     
       19. A method of impedance matching during the fabrication of a radio frequency band reject filter comprising:
 fabricating an input port; 
 fabricating an output port; 
 fabricating a plurality of acoustic resonators between the input port and the output port, comprising fabricating a first plurality of acoustic resonators and a second plurality of acoustic resonators; 
 fabricating an inductor that comprises a first terminal configured to couple to ground, and further comprises a second terminal; 
 wherein fabricating the inductor comprises coupling the second terminal of the inductor to a common node between the first plurality of acoustic resonators and the second plurality of acoustic resonators, wherein a static capacitance between the input port and the common node is substantially equivalent in value to a static capacitance between the output port and the common node; and 
 wherein a combined impedance of the inductor and the plurality of acoustic resonators is equivalent in value to at least one of:
 an impedance of the radio frequency band reject filter from the input port to ground; or 
 an impedance of the radio frequency band reject filter from the output port to ground. 
 
 
     
     
       20. The method of  claim 19 , wherein fabricating the inductor comprises fabricating a short stub on-chip element that has a desired inductance. 
     
     
       21. The method of  claim 20  wherein fabricating a short stub on-chip element that has a desired inductance comprises controlling at least one of the length, width, and thickness of the short stub on-chip element.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of and is a National Phase Entry of International Application Number PCT/CA2009/001564 filed Nov. 2, 2009, and claims the benefit of U.S. Provisional Patent Application No. 61/110,147 filed on Oct. 31, 2008, which are both hereby incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to acoustic resonator band reject filters. 
     BACKGROUND OF THE INVENTION 
     There is a strong need in the telecommunications market, particularly in the area of 4 G wireless communication systems, as well as in existing wireless systems, for miniature type filters with improved performance from current levels. As 4 G systems target a very high speed data transfer, they need much wider bandwidth than existing systems such as GSM, CDMA and UMTS. On the other hand, limited frequency resources in 4 G systems require wireless carrier companies to set guard-bands as narrow as possible to enable maximum user capacity. Combining these two issues means that the 4 G wireless systems require miniature RF filters for their wireless terminal devices. 
     Due to their miniature size and low cost, acoustic materials-based RF filters such as surface acoustic wave (SAW), thin film bulk acoustic resonator (FBAR) and/or bulk acoustic wave (BAW) filters are widely used in compact and portable type terminal devices of various wireless systems. However, the current level of filter performance of these filters is still far from 4 G wireless system filter requirements. 
     Some non-acoustic microwave technology type filters, such as metal-type cavity filters or dielectric filters can be designed to meet filter performance requirements for these applications, but these types of designs have an ultra-high cost and result in physically large filters. As a result, metal-type cavity filters and dielectric filters are undesirable, particularly for applications in wireless terminals, for which size and weight are of considerable importance. 
     A lower cost and smaller size filter would be desirable for many purposes in communication systems. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a radio frequency band reject filter comprising: an input port; a plurality of acoustic resonators; an inductor for matching the impedance of the plurality of acoustic resonators; an output port; the inductor being positioned within the band reject filter in respect of the plurality of acoustic resonators such that a static capacitance between the input port and the inductor is substantially equivalent to a static capacitance between the output port and the inductor. 
     In some embodiments, the plurality of resonators is one of: a plurality of parallel resonators; a plurality of series resonators; and a combination of series and parallel resonators. 
     In some embodiments, the radio frequency band reject filter is fabricated using one of: surface acoustic wave (SAW) technology; thin film bulk acoustic resonator (FBAR) technology; and bulk acoustic wave (BAW) technology. 
     In some embodiments, the inductor is a short stub on-chip inductor. 
     In some embodiments, the inductance of the inductor is equal to or less than 0.1 nH. 
     In some embodiments, the radio frequency band reject filter is cascaded with one or more other radio frequency band reject filters. 
     In some embodiments, at least one of the one or more other radio frequency band reject filters has an inductor for matching impedance of the respective at least one other radio frequency band reject filters. 
     In some embodiments, the combination of series and parallel resonators comprises: N, where N≧2, series resonators; and M, where M≧2, parallel resonators. 
     In some embodiments, N is an even number and there are N/2 series resonators between the input port and the inductor and N/2 series resonators between the output port and the inductor. 
     In some embodiments, M is an even number and there are M/2 parallel resonators between the input port and the inductor and M/2 series resonators between the output port and the inductor. 
     In some embodiments, each series and parallel resonator is formed by a set of interdigital electrodes extending from a pair of parallel conductive elements. 
     In some embodiments, for the parallel resonators, at least one of the pair of parallel conductive elements is coupled to ground. 
     In some embodiments, for at least one series resonator or at least one parallel resonator, or both, at least one of the pair of parallel conductive elements forming the respective resonator is coupled to the inductor. 
     In some embodiments, the inductor is a short stub element located between the at least one of the pair of parallel conductive elements and ground. 
     In some embodiments, the inductance of the inductor can be fabricated accurately enough that external matching circuits are not used with the filter. 
     According to another aspect of the invention, there is provided a telecommunication base station comprising: at least one antenna; transmit circuitry configured for modulating one or more carrier signals having a desired transmit frequency or frequencies; receiving circuitry configured for receiving a radio frequency signal bearing information from one or more remote transmitters; a baseband processor configured for: processing a received signal received by the receiving circuitry; and configured for encoding a signal for transmission by the transmit circuitry; at least one of the transmit circuitry or receiving circuitry comprising the radio frequency band reject filter as described above or herein below. 
     According to another aspect of the invention, there is provided a telecommunication wireless terminal comprising: at least one antenna; transmit circuitry configured for modulating one or more carrier signals having a desired transmit frequency or frequencies; receiving circuitry configured for receiving a radio frequency signal bearing information from one or more remote transmitters; a baseband processor configured for: processing a received signal received by the receiving circuitry; and configured for encoding a signal for transmission by the transmit circuitry; at least one of the transmit circuitry or receiving circuitry comprising the radio frequency band reject filter as described above or herein below. 
     According to another aspect of the invention, there is provided a duplexer comprising the radio frequency band reject filter of as described above or herein below. 
     According to another aspect of the invention, there is provided a method of impedance matching during the fabrication of a radio frequency band reject filter comprising: fabricating an input port; fabricating a plurality of acoustic resonators; fabricating an inductor for matching the impedance of the plurality of acoustic resonators; fabricating an output port; wherein fabricating the inductor comprises positioning the inductor in the band reject filter in respect of the plurality of acoustic resonators such that a static capacitance between the input port and the inductor is substantially equivalent to a static capacitance between the output port and the inductor. 
     In some embodiments, fabricating the inductor comprises fabricating a short stub on-chip element that has a desired inductance. 
     In some embodiments, fabricating a short stub on-chip element that has a desired inductance comprises controlling at least one of the length, width, and thickness of the short stub on-chip element. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the attached drawings in which: 
         FIG. 1  is a schematic illustration of a conventional band reject filter; 
         FIGS. 2A and 2B  are schematic illustrations of additional conventional band reject filters; 
         FIGS. 3A and 3B  are schematic illustrations of further conventional band reject filters; 
         FIG. 4  is a schematic illustration of an embodiment of a self-matched band reject filter; 
         FIG. 5  is a schematic illustration of another embodiment of a self-matched band reject filter; 
         FIG. 6  is a schematic illustration of a further embodiment of a self-matched band reject filter; 
         FIGS. 7A and 7B  are schematic illustrations of further embodiments of a self-matched band reject filter; 
         FIG. 8A  is a schematic illustration of yet another embodiment of a self-matched band reject filter; 
         FIG. 8B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 8A ; 
         FIG. 9A  is a schematic illustration of a further embodiment of a self-matched band reject filter; 
         FIG. 9B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 9A ; 
         FIG. 10A  is a schematic illustration of yet a further embodiment of a self-matched band reject filter; 
         FIG. 10B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 10A ; 
         FIG. 11A  is a schematic illustration of another embodiment of a self-matched band reject filter; 
         FIG. 11B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 11A ; 
         FIG. 12A  is a schematic illustration of a further embodiment of a self-matched band reject filter; 
         FIG. 12B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 12A ; 
         FIG. 13A  is a schematic illustration of another embodiment of a self-matched band reject filter; 
         FIG. 13B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 13A ; 
         FIG. 14A  is a schematic illustration of a further embodiment of a self-matched band reject filter; 
         FIG. 14B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 14A ; 
         FIG. 15A  is a schematic illustration of a yet another embodiment of a self-matched band reject filter; 
         FIG. 15B  is a representative illustration of an implementation of the self-matched band reject filter of  FIG. 15A ; 
         FIG. 16  is a flow chart illustrating a method according to an embodiment of the invention; 
         FIG. 17  is a block diagram of an example base station that might be used to implement some embodiments of the present 5 application; and 
         FIG. 18  is a block diagram of an example wireless terminal that might be used to implement some embodiments of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION 
     Due to the desire for miniature sizing and low cost, surface acoustic wave (SAW), thin film bulk acoustic resonator (FBAR) and/or bulk acoustic wave (BAW) technology filters have became much utilized components in compact and portable type terminal devices for various modern wireless communication systems. Bandpass type and band-reject type filters can be designed using SAW, FBAR and BAW technologies. 
     An acoustic resonator-based ladder type band reject filter (BRF) usually needs a plurality of parallel inductors connected to the internal nodes of the filer for matching purpose. Also, if these internal matching inductors are not selected correctly, external matching circuits on both of input and output sides are necessary. Generally, such internal matching inductors have values over 2 nH and some of them could be as large or larger than 10 nH. A discrete component type inductor or printed circuit board (PCB) short stub type inductor is the common conventional choice to achieve this kind of internal matching. 
     However, in the real world, it is very difficult to find the correct inductance values for the internal matching on the PCB level, especially for a case that the BRF filter needs a plurality of parallel inductors for the internal matching. This may be due to the electromagnetic (EM) properties of a package body selected to house the BRF and bonding wires utilized to providing electrical coupling. In addition, the PCB itself may affect the values of such internal inductors. Also, when the operational frequency becomes larger than 2 GHz, the BRF itself becomes very small, and it is therefore unlikely that there is sufficient space for a plurality of such parallel type internal matching inductors as well as the input and output matching circuits surrounding the device. 
     One attempt to solve this problem is to directly make the short-stub transmission line on the die. However, as long as the value of the inductance is over 2 nH, any attempt of making an on-chip type short-stub inductor is impractical for actual device design, because an on-chip type inductor with such a value will require a huge footprint that could be 10 or more times bigger than the space occupied by the acoustic resonators of the BRF. 
     A technique is disclosed herein that allows internal matching inductors in a BRF device design to be in the range of 0.1 nH, which is a suitable value for the on-chip type short-stub inductor design. In some embodiments the dimension of the short-stub inductor in the range of 0.1 nH on a die containing a BRF can be of the same order as the acoustic resonator. 
     BRF devices can play a very important role in the RF front end of a wireless system for both a base station and a terminal device. It is a useful device for some wireless systems to aid in meeting power emission requirements or eliminate undesired signals such as the harmonic frequency signals and some spurious signals. 
     As the on-chip type short-stub inductor may be fabricated with the same accuracy as the acoustic resonator, the inductance value can be fabricated quite accurately, thus external input and output matching circuits may not be needed. Therefore, a self-matched and very small footprint BRF device becomes possible. 
     Due to the lack of a need for external input and output matching circuits on the PCB in some embodiments of the invention, the BRF may be easy to incorporate in some device implementations, such as wireless terminals and/or telecommunication base stations. Also, BRF devices can be used in a duplexer design that may provide improved power handling capability. 
     Some embodiments of the present invention can be applied to radio frequency (RF) band acoustic resonator-based BRF (Band Reject Filters), such as but not limited to those fabricated using surface acoustic wave (SAW), thin film bulk acoustic resonator (FBAR) and/or bulk acoustic wave (SAW) techniques. In some implementations, BRFs fabricated consistent with methods and devices disclosed herein are well suited for high frequency applications, for example over 1 GHz. 
     Some embodiments of the invention minimize the value of the single matching inductor L in a BRF design to a value that enables easier integration of the inductor into a BRF package design. 
     Some embodiments of the invention enable a high yield for mass-production, resulting in a potential reduced cost for fabricating the BRF device. 
     Referring to the drawings,  FIG. 1  is a schematic circuit illustration of a conventional band reject filter. In  FIG. 1 , a BRF  100  is shown including a first matching circuit  110  at an input port of the BRF  100  and a second matching circuit  140  at an output port of the BRF  100 . The BRF  100  includes multiple acoustic resonators  120 ,  122 ,  124 ,  126  in series, multiple acoustic resonators in parallel  130 ,  132 ,  134 , and multiple discrete inductors L 1 , L 2  L 3 . 
     Series resonator  120  is coupled to matching circuit  110  and a node to which inductor L 1 , parallel resonator  130  and series resonator  122  are coupled. Parallel resonator  130  and inductor L 1  are connected to ground  150 . Series resonator  122  is coupled to a node to which inductor L 2 , parallel resonator  132  and series resonator  124  are coupled. Parallel resonator  132  and inductor L 2  are connected to ground  150 . Series resonator  124  is coupled to a node to which inductor L 3 , parallel resonator  134  and series resonator  126  are coupled. Parallel resonator  134  and inductor L 3  are connected to ground  150 . Series resonator  126  is coupled to matching circuit  140 . 
     In general, the values of L 1 , L 2  and L 3  are typically over 2 nH and thus it may not be practical to fabricate the inductors on-chip by using short-stub type microwave transmission line techniques because the dimension of a short-stub on-chip inductor for such an inductance value may be quite large. Other disadvantages of this type of matching for a band reject filter may include one or more of (1) a large number of inductors may be needed for matching the overall filter; and (2) external matching circuits for both input and output ports may be needed, as shown in  FIG. 1 . 
       FIGS. 2A and 2B  are schematic circuit illustrations of additional conventional band reject filters. In  FIG. 2A , a BRF  200  includes two series resonators  210  and  212  coupled together via a ¼ wave transmission line  220 . In  FIG. 25 , a BRF  250  includes two series resonators  260  and  262  coupled together via a ¼ wave transmission line  280  as well as two parallel resonators  270  and  272  located between the respective series resonators  260  and  262  and the ¼ wave transmission line  280 . Inductors L 4  and L 5  are located prior to series resonator  160  on the input port side of BRF  250  and subsequent to series resonator  162  on the output port side of BRF  250 , respectively. 
     Some disadvantages of such an impedance matching method may be: (1) a ¼ wave transmission line for some frequencies may be too long for on-chip design; (2) a large number of inductors may be needed for matching the overall filter; and (3) inductors may have large inductance values and consequently may be difficult to integrate onto the chip. 
       FIGS. 3A and 3B  are schematic circuit illustrations of yet another conventional band reject filter. In  FIG. 3A , a BRF  300  includes four parallel resonators  310 ,  312 ,  314 ,  316  and inductors L 6  and L 7  located prior to series resonator  310  on the input port side of BRF  300  and subsequent to series resonator  316  on the output port side of BRF  300 . In  FIG. 3B , a BRF  350  includes a first inductor L 8  at an input port side of BRF  350  followed by four parallel resonators  360 ,  362 ,  364 ,  366  and a second inductor L 9 . The four parallel resonators  360 ,  362 ,  364 ,  366  and first and second inductors L 8  and L 9  are also coupled to ground  300 . A transmission line or impedance inverter  380  is coupled to the second inductor L 9 . A third inductor L 10  is coupled to transmission line  380 . Four more parallel resonators  370 ,  372 ,  374 ,  376  are coupled to third inductor L 10 . A fourth inductor L 11  is coupled to the four parallel resonators on the output port side of the BRF  350 . The four parallel resonators  370 ,  372 ,  374 ,  376  and third and fourth inductors L 10  and L 11  are also coupled to ground  300 . 
     Some of the disadvantages of this third type of impedance matching are similar to disadvantages of the previously described examples. Some of the disadvantages may include: (1) too many inductors may be needed for matching; (2) inductors may have large inductance values and consequently may be difficult to integrate onto the chip; (3) a ¼ wave transmission line for some frequencies may be too long for on-chip design; and (4) the designs of  FIGS. 3A AND 3B  utilize only parallel, also known as shunt, resonators, thus it may be difficult to achieve a high performance BRF. 
       FIG. 4  is a schematic circuit illustration of an embodiment of a self-matched BRF according to the present invention. In  FIG. 4 , a BRF  400  is comprised of a total of six series acoustic resonators  410 ,  412 ,  414 ,  416 ,  418 ,  420  and a single internal matching inductor L 12 . Inductor L 12  is coupled to ground  430  as well. The BRF  400  is also considered to have an input port  405  and an output port  425 . In the example of  FIG. 4 , the single matching inductor L 12  is located at a “midpoint” of the six series resonators. There are three series resonators on between the matching inductor L 12  and the input port  405  and the matching inductor L 12  and the output port  425 . Inductor L 12  is coupled to ground  430 . For the purposes of this application, the expression “coupled to ground” is used in the sense that each circuit element “coupled to ground” has two ports, a first port which is coupled to a given location in a circuit and the other port which is “coupled to ground”. 
     In some embodiments an inductor is utilized to match a plurality of series resonators as long as the total static capacitances of resonators on each side of inductor L 12  i.e. between the inductor L 12  and the input port  405  and between the inductor L 12  and the output port  425 , are close to equivalent in value. Therefore in some embodiments, the number of resonators on each side of the parallel inductor does not have to be equal, but the static capacitance should be close to equivalent in value. The BRF design of this embodiment minimizes the number of matching inductors. Reducing the number of matching inductors may improve rejection performance. 
     In some embodiments of the invention a single inductor is capable of impedance matching the BRF due to the manner in which the single inductor is fabricated in conjunction with the acoustic resonators that collectively form the BRF. Examples of this will be shown in greater detail in  FIGS. 8B to 15B . 
     While the specific example of  FIG. 4  illustrates six series resonators in the BRF, it is to be understood that the particular number of resonators that are included in the BRF is specific to the implementation, and is not to be limited to the example case of six resonators. 
       FIG. 5  is a schematic circuit illustration of another embodiment of a self-matched BRF. In  FIG. 5 , BRF  500  is comprised of a total of five parallel acoustic resonators  510 ,  512 ,  514 ,  516 ,  518  and an internal matching inductor L 13 . Inductor L 13  and the five parallel resistors are coupled to ground  520  as well. The BRF  500  is also considered to have an input port  505  and an output port  525 . 
     In some embodiments a single parallel inductor is utilized to match a plurality of parallel resonators as long as the total static capacitance of resonators on each side of inductor L 13  are close to equivalent in value. 
     While the specific example of  FIG. 5  illustrates five parallel resonators in the BRF, it is to be understood that the particular number of resonators that are included in the BRF of such an implementation is specific to the implementation. 
       FIG. 6  is a schematic circuit illustration of a third embodiment of a self-matched radio frequency band BRF.  FIG. 6  illustrates a BRF  600  having an input port  605  and an output port  625 . The BRF  600  includes a first group of three series resonators  610 ,  612 ,  614  on an input port side of BRF  600  and a second group of three series resonators  620 ,  622 ,  624  on an output port side of BRF  600 . Located between the first and second groups of series resonators is a third group of resonators that is similar to BRF  500  of  FIG. 5 . The third group of resonators includes a group of five parallel resonators  630 ,  632 ,  634 ,  636  and  638  and a matching internal inductor L 14 . Each of the five parallel resistors and inductor L 14  are also coupled to ground  640 . 
     In some embodiments, the BRF needs only a single inductor for matching a large number of series and/or parallel resonators. In some embodiments, the BRF does not need external matching circuits at the input and output ports. In some embodiments, the parallel inductance can be minimized to be as small as 0.1 nH, which is a value that can be easily integrated onto the BRF package design, for example for a printed circuit board (PCB) device. In some embodiments the self matching BRF device has a very small size, for example 2 mm 2  at an operation frequency of 5.6 GHz. 
       FIGS. 7A and 7B  are schematic circuit illustrations of a further embodiment of a self-matched band reject filter.  FIGS. 7A and 7B  show examples of cascading multiple BRFs.  FIG. 7A  illustrates a first example of a BRF  700 , which includes BRFs  400 ,  500  and  600 , from  FIGS. 4 ,  5  and  6 , respectively, cascaded together.  FIG. 7B  illustrates a second example of a BRF  750 , which includes multiple BRFs, corresponding to BRF  600  of  FIG. 6 , cascaded together. 
       FIGS. 7A and 7B  are merely two examples of how self-matched BRFs may be cascaded together. In particular the two examples shown are a first example in which different structural types of BRFs are being cascaded together to form a BRF with a different set of operational parameters than any of the individual BRFs and a second example in which two or more BRFs having a same structure, but not necessarily the same operating parameters for the elements in the structures, are cascaded together. It is to be understood that multiple self-matched BRFs, which are internally matched according to aspects of the invention disclosed herein, may be cascaded together. The specific number of BRFs, the orientation of the BRFs, and the properties and/or parameters of the particular components in the BRFs, are all implementation specific. 
       FIG. 8A  is a schematic circuit illustration of another embodiment of a self-matched band reject filter. In  FIG. 8A , BRF  800  is considered to have an input port  805  and an output port  825 . BRF  800  includes a single series resonator  810  and a single parallel resonator  830  on an input port side of the BRF  800 , which are coupled to a matching inductor L 15 . A single parallel resonator  840  and a single series resonator  820  on an output port side of the BRF  800  are coupled to the matching inductor L 15 . The two parallel resonators  830  and  840  and the matching inductor L 15  are also coupled to ground  850 . 
       FIG. 8B  is a representative illustration of an implementation of BRF  800  of  FIG. 8A  as an acoustic resonator interdigital transducer. Each resonator of the series resonators and the parallel resonators of  FIG. 8A  includes a plurality of consecutive interdigital transducer electrodes. Series resonator  810  is formed by electrodes of transducer element  803  and a first set of electrodes of transducer element  805 . Series resonator  820  is formed by electrodes of transducer element  826  and a first set of electrodes of transducer element  824 . Parallel resonator  830  is formed by electrodes of transducer element  807  and a second set of electrodes of transducer element  805 . Parallel resonator  840  is formed by electrodes of transducer element  822  and a second set of electrodes of transducer element  824 . Element  860  of the transducer is a short stub component that provides the desired inductance for inductor L 15 . Element  850  of the transducer is a ground bar. 
     In some embodiments of the invention the thickness, width and length of transducer element  860  are controlled during fabrication of the BRF to control the value of the inductance of inductor L 15 . 
       FIG. 9A  is a schematic circuit illustration of another embodiment of a self-matched band reject filter.  FIG. 9A  shows an example of cascading multiple BRFs.  FIG. 9A  illustrates a BRF  900  that includes three BRFs  800 A,  800 B,  800 C cascaded together. These three BRFs substantially correspond to the structure of BRF  800  of  FIG. 8A . As described above, while the structure of the elements of BRFs  800 A,  800 B,  800 C may be substantially the same as that of BRF  800 , the physical parameters of the various elements is not necessarily the same. 
       FIG. 9B  is a representative illustration of an implementation of BRF  900  of  FIG. 9A  as an acoustic resonator interdigital transducer. Three transducers  800 A, 800 B, 800 C of the type illustrated in  FIG. 8B  are shown. 
     Although only three cascaded BRFs are shown in  FIGS. 9A and 9B , the specific number of cascaded BRFs is implementation specific. Furthermore, while three BRFs of the same structure are cascaded together, it is to be understood that when multiple BRFs are cascaded together to form a new BRF, the multiple BRFs can be the same structure, with similar or different parameters, or can be different structures. 
       FIG. 10A  is a schematic circuit illustration of a further embodiment of a self-matched band reject filter. In  FIG. 10A , a BRF  1000  includes a portion of the BRF  1000  that is similar to the structure of BRF  800  of  FIG. 8A . The numbering from  FIG. 8A  has been maintained in  FIG. 10A  for convention purposes. Multiple series resonators  1010 , only one being shown, are coupled to an input side of the portion that is similar to BRF  800 . Multiple series resonators  1020 , only one being shown, are coupled to the output side of the portion that is similar to BRF  800 . 
       FIG. 10B  is a representative illustration of an implementation of BRF  1000  of  FIG. 10A  as an acoustic resonator interdigital transducer. A transducer similar to  800  of  FIG. 8B  is shown together with additional series resonator elements  1010  and  1020 . 
     In some embodiments the use of connection bus bars can be minimized resulting in a compact size of the BRF. For example, this may include controlling any of the length, width and thickness of transducer elements that for the BRF. 
       FIG. 11A  is a schematic circuit illustration of a further embodiment of a self-matched band reject filter. In  FIG. 11A , a BRF  1100  includes three cascaded portions  1000 A,  1000 B,  1000 C that are similar to BRF  1000  of  FIG. 10A . 
       FIG. 11B  is a representative illustration of an implementation of BRF  1100  of  FIG. 11A  as an acoustic resonator interdigital transducer. Three transducers  1000 A,  1000 B,  1000 C of the type illustrated in  FIG. 10B  are shown. 
     In some embodiments the use of connection bus bars can be minimized resulting in a compact size of the BRF. In some embodiments such a cascaded design enables enhanced BRF performance. 
       FIG. 12A  is a schematic circuit illustration of a further embodiment of a self-matched band reject filter. In  FIG. 12A , BRF  1200  is considered to have an input port  1205  and an output port  1275 . BRF  1200  includes a first series resonator  1210  and a second series resonator  1220  of multiple series resonators on an input port side of BRF  1200 . A first parallel resonator  1230  is coupled to the second series resonator  1220 . A matching inductor L 16  is coupled to the first parallel resonator  1230 . A second parallel resonator  1240  and a third parallel resonator  1250  are coupled to the matching inductor L 16 . Third series resonator  1260  and fourth series resonator  1270  of multiple series resonators on an output port side of BRF  1200  are coupled to the third parallel resonator  1250 . The three parallel resonators  1230 ,  1240  and  1250  and the matching inductor L 16  are also coupled to ground  1280 . 
       FIG. 12B  is a representative illustration of an implementation of BRF  1200  of  FIG. 12A  as an acoustic resonator interdigital transducer. Elements for implementing the first, second, third and fourth series resonators  1210 ,  1220 ,  1260  and  1270  and first, second and third parallel resonators  1230 ,  1240  and  1250  as well as matching inductor L 16  are shown. 
     In some embodiments the use of connection bus bars can be minimized resulting in a compact size of the BRF. For example, this may include controlling any of the length, width and thickness of transducer elements that for the BRF. 
       FIG. 13A  is a schematic circuit illustration of a further embodiment of a self-matched band reject filter. In  FIG. 13A , BRF  1300  is considered to have an input port  1305  and an output port  1385 . BRF  1300  includes a first series resonator  1310  and a second series resonator  1320  of multiple series resonators on an input port side of BRF  1300 . A first parallel resonator  1330  and a second parallel resonator  1340  are coupled to the second series resonator  1320 . A matching inductor L 17  is coupled to the second parallel resonator  1340 . A third parallel resonator  1350  and a fourth parallel resonator  1360  are coupled to the matching inductor L 17 . Third series resonator  1370  and fourth series resonator  1380  of multiple series resonators on an output port side of BRF  1300  are coupled to the fourth parallel resonator  1360 . The four parallel resonators  1330 ,  1340 ,  1350  and  1360  and the matching inductor L 16  are also coupled to ground  1390 . 
       FIG. 13B  is a representative illustration of an implementation of BRF  1300  of  FIG. 13A  as an acoustic resonator interdigital transducer. Elements for implementing the first, second, third and fourth series resonators  1310 ,  1320 ,  1370  and  1380  and first, second, third and fourth parallel resonators  1330 ,  1340 ,  1350  and  1360  as well as matching inductor L 17  are shown. 
     In some embodiments the use of connection bus bars can be minimized resulting in a compact size of the BRF. For example, this may include controlling any of the length, width and thickness of transducer elements that for the BRF. 
       FIG. 14A  is a schematic circuit illustration of a further embodiment of a self-matched band reject filter. In  FIG. 14A , BRF  1400  is considered to have an input port  1405  and an output port  1492 . BRF  1400  includes a first series resonator  1410  and a second series resonator  1420  of multiple series resonators on an input port side of BRF  1400 . A first parallel resonator  1430  and a second parallel resonator  1440  are coupled to the second series resonator  1420 . A matching inductor L 18  is coupled to the second parallel resonator  1440 . A third parallel resonator  1450 , a fourth parallel resonator  1460  and a fifth parallel resonator  1470  are coupled to the matching inductor L 18 . Third series resonator  1480  and fourth series resonator  1490  of multiple series resonators on an output port side of BRF  1400  are coupled to the fifth parallel resonator  1470 . The five parallel resonators  1430 ,  1440 ,  1450 ,  1460  and  1470  and the matching inductor L 18  are also coupled to ground  1495 . 
       FIG. 14B  is a representative illustration of an implementation of BRF  1400  of  FIG. 14A  as an acoustic resonator interdigital transducer. Elements for implementing the first, second, third and fourth series resonators  1410 ,  1420 ,  1480  and  1490  and first, second, third, fourth and fifth parallel resonators  1430 ,  1440 ,  1450 ,  1460  and  1470  as well as matching inductor L 18  are shown. 
     In some embodiments the use of connection bus bars can be minimized resulting in a compact size of the BRF. For example, this may include controlling any of the length, width and thickness of transducer elements that for the BRF. 
       FIG. 15A  is a schematic circuit illustration of a further embodiment of a self-matched band reject filter. In  FIG. 15A , BRF  1500  is considered to have an input port  1505  and an output port  1592 . BRF  1500  includes a first series resonator  1510  and a second series resonator  1515  of multiple series resonators on an input port side of BRF  1500 . A first parallel resonator  1520 , a second parallel resonator  1530  and a third parallel resonator  1540  are coupled to the second series resonator  1515 . A matching inductor L 19  is coupled to the third parallel resonator  1540 . A fourth parallel resonator  1550 , a fifth parallel resonator  1560  and a sixth parallel resonator  1570  are coupled to the matching inductor L 19 . Third series resonator  1580  and fourth series resonator  1590  of multiple series resonators on an output port side of BRF  1500  are coupled to the sixth parallel resonator  1570 . The six parallel resonators  1520 ,  1530 ,  1540 ,  1550 ,  1560  and  1570  and the matching inductor L 19  are also coupled to ground  1595 . 
       FIG. 15B  is a representative illustration of an implementation of BRF  1500  of  FIG. 15A  as an acoustic resonator interdigital transducer. Elements for implementing the first, second, third and fourth series resonators  1510 ,  1515 ,  1580  and  1590  and first, second, third, fourth, fifth and sixth parallel resonators  1520 ,  1530 ,  1540 ,  1550 ,  1560  and  1570  as well as matching inductor L 19  are shown. 
     In some embodiments the use of connection bus bars can be minimized resulting in a compact site of the BRF. For example, this may include controlling any of the length, width and thickness of transducer elements that for the BRF. 
     By using saw, FBAR and/or BAW design technologies, some embodiments of the invention result in economically low cost devices having a compact physical size. 
     Some aspects of the invention may find uses in applications such as U.S. patent application Ser. No. 12/424,068 filed Apr. 15, 2009, assigned to the assignee of the present application. 
     According to a broad aspect of the invention, a radio frequency band reject filter (BRF) includes an input port and an output port. The radio frequency BRF includes a plurality of acoustic resonators and an inductor for matching the impedance of the plurality of acoustic resonators. The inductor is positioned in the BRF in respect of the plurality of acoustic resonators such that a static capacitance between the input port and the inductor is substantially equivalent to a static capacitance between the output port and the inductor. 
     In some embodiments, the four acoustic resonators are one of: a plurality of parallel resonators; a plurality of series resonators; and a combination of series and parallel resonators. 
     In some embodiments, the combination of series and parallel resonators comprise: N, where N≧2, series resonators; and M, where M≧2, parallel resonators. 
     In some implementations when N is an even number, there are N/2 series resonators between the input port and the inductor and N/2 series resonators between the output port and the inductor. 
     In some embodiments, when M is an even number there are M/2 parallel resonators between the input port and the inductor and M/2 series resonators between the output port and the inductor. 
     In some embodiments, each series and parallel resonator that is part of a BRF is part of a transducer formed by a set of interdigital electrodes extending from a pair of parallel conductive elements. 
     In some embodiments, in the case of the parallel resonators, at least one of the pair of parallel conductive elements is coupled to ground. 
     In some embodiments, when at least one series resonator or at least one parallel resonator, or both, are coupled to at least one of the pair of parallel conductive elements, the at least one conductive element is coupled to a inductor. 
     In some embodiments the inductor is a short stub element located between the at least one of the pair of parallel conductive elements and ground. 
     In some embodiments the inductor is equal to or less than 0.1 nH. 
     In some embodiments the BRF is one of multiple radio frequency BRFs cascaded together with other radio frequency BRFs. 
     In some embodiments, some or all of the other BRFs each have a single inductor for matching the impedance of the respective radio frequency BRFs. 
     Referring to  FIG. 16 , a method for matching an impedance in a radio frequency BRF will now be described. In a first step  16 - 1 , the method involves fabricating an input port for the BRF. A second step  16 - 2  involves fabricating a plurality of acoustic resonators. A third step  16 - 3  involves fabricating an inductor for matching the impedance of the plurality of acoustic resonators. A fourth step  16 - 4  involves fabricating an output port. 
     The inductor is positioned in the band reject filter in respect of the plurality of acoustic resonators such that a static capacitance between the input port and the inductor is substantially equivalent to a static capacitance between the output port and the inductor. 
     In some embodiments, the plurality of acoustic resonators is at least four acoustic resonators. 
     It is to be understood that the steps of the method do not necessarily need to be performed in the specific order described above. Depending on how the BRF is fabricated, for example different materials are layered upon one another, the input port, output port, acoustic resonators and the inductor may be fabricated simultaneously, in the order described above, or in a different order altogether. 
     Fabricating the BRF may be performed according to known SAW, FBAR and BAW technologies, wherein fabricating the inductor is controlled to provide a desired inductor. 
     With reference to  FIG. 17 , an example of a base station  14  is illustrated. The base station  14  generally includes a control system  20 , a baseband processor  22 , transmit circuitry  24 , receive circuitry  26 , multiple antennas  28 , and a network interface  30 . The receive circuitry  26  receives radio frequency signals bearing information from one or more remote transmitters provided by mobile terminals  16  (illustrated in  FIG. 11 ) and relay stations  15  (illustrated in  FIG. 12 ). A low noise amplifier and a filter (not shown) may cooperate to amplify and remove broadband interference from the signal for processing. A BRF filter of the type described herein may be an example of a filter included in the receive circuitry  26 . Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  22  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  22  is generally implemented in one or more digital signal processors (DSPs) or application-specific integrated circuits (ASICs). The received information is then sent across a wireless network via the network interface  30  or transmitted to another mobile terminal  16  serviced by the base station  14 , either directly or with the assistance of a relay  15 . 
     On the transmit side, the baseband processor  22  receives digitized data, which may represent voice, data, or control information, from the network interface  30  under the control of control system  20 , and encodes the data for transmission. The encoded data is output to the transmit circuitry  24 , where it is modulated by one or more carrier signals having a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signals to a level appropriate for transmission, and deliver the modulated carrier signals to the antennas  28  through a matching network (not shown). Modulation and processing details are described in greater detail below. A BRF filter of the type described herein may also be included in the transmit circuitry  24 . 
     With reference to  FIG. 18 , an example of a mobile terminal  16  is illustrated. Similarly to the base station  14 , the mobile terminal  16  will include a control system  32 , a baseband processor  34 , transmit circuitry  36 , receive circuitry  38 , multiple antennas  40 , and user interface circuitry  42 . The receive circuitry  38  receives radio frequency signals bearing information from one or more base stations  14  and relays  15 . A low noise amplifier and a filter (not shown) may cooperate to amplify and remove broadband interference from the signal for processing. A BRF filter of the type described herein may be an example of a filter included in the receive circuitry  36 . Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  34  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. The baseband processor  34  is generally implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs). 
     For transmission, the baseband processor  34  receives digitized data, which may represent voice, video, data, or control information, from the control system  32 , which it encodes for transmission. The encoded data is output to the transmit circuitry  36 , where it is used by a modulator to modulate one or more carrier signals that is at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signals to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  40  through a matching network (not shown). A BRF filter of the type described herein may also be included in the transmit circuitry  24 . Various modulation and processing techniques available to those skilled in the art are used for signal transmission between the mobile terminal and the base station, either directly or via the relay station. 
     The above-described embodiments of the present application are intended to be examples only. Those of skill in the art may effect alterations, modifications and variations to the particular embodiments without departing from the scope of the application. 
     Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practised otherwise than as specifically described herein.

Metadata:
Filing Date: 20091102
Publication Date: 20140722
Grant Date: 20140722
Priority Date: 20081031
Inventors: JIAN CHUN-YUN
Assignee: APPLE INC
CPC Classifications: [{"code": "H03H9/542", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03H9/6409", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T29/4902", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H9/547", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0278", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B1/48", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/50", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03H9/542", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T29/4902", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H9/6409", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0278", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H9/547", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/48", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0278", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03H9/542", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03H9/547", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03H9/6409", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/50", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 42128166