PATENT DOCUMENT

Publication Number: US-8462755-B2
Application Number: US-201213450152-A
Country: US
Kind Code: B2

Title: Duplexer/multiplexer having filters that include at least one band reject filter

Abstract:
A wireless communications device includes an antenna, a multi-port path selection structure having an antenna port connected to the antenna, and plural ports connected to respective one or more receive and transmit paths of the wireless communications device. The multi-port path selection structure has a transmit band reject filter connected to the transmit path and a second filter connected to the receive path.

Claims:
What is claimed is: 
     
       1. A wireless communications device, comprising:
 an antenna; 
 a receiver; 
 a receive path connected between the antenna and the receiver and configured to couple the antenna to the receiver; 
 a transmitter; and 
 a transmit path connected between the transmitter and the antenna, wherein the transmit path includes a single transmit path filter device, and wherein the transmit path filter device comprises an acoustic resonator based band reject filter device; 
 wherein the receive path includes a single receive path filter device comprising an acoustic resonator based band reject filter device; and 
 wherein each of the transmit path filter device and the receive path filter device provides multiple reject bands. 
 
     
     
       2. The wireless communications device of  claim 1 , wherein the receive path comprises a band pass filter. 
     
     
       3. The wireless communications device of  claim 2 , wherein the band pass filter comprises an acoustic resonator based band pass filter. 
     
     
       4. The wireless communications device of  claim 1 , wherein the transmit path is coupled to the receive path in a duplexer, the acoustic resonator based band reject filter being part of the duplexer. 
     
     
       5. The wireless communications device of  claim 1 , wherein the wireless communications device comprises:
 a plurality of receivers; 
 a plurality of receive paths, each receive path connected between the antenna a respective receiver and configured to couple the antenna to the respective receiver; 
 a plurality of transmitters; and 
 a plurality of transmit paths, each transmit path connected between a respective transmitter and the antenna and coupled to a respective receive path, wherein each transmit path includes a single respective transmit path filter device, and wherein each transmit path filter device comprises an acoustic resonator based band reject filter. 
 
     
     
       6. The wireless communications device of  claim 5 , wherein the transmit paths are coupled to the receive paths in a multiplexer, the acoustic resonator based band reject filters being part of the multiplexer. 
     
     
       7. The wireless communications device of  claim 1 , wherein the wireless communications device comprises a wireless mobile station. 
     
     
       8. The wireless communications device of  claim 1 , wherein the wireless communications device comprises a wireless base station. 
     
     
       9. The wireless communications device of  claim 8 , wherein the receive path comprises a receive path band reject filter. 
     
     
       10. The wireless communications device of  claim 1 , wherein the acoustic resonator based band reject filter device is based on at least one of surface acoustic wave (SAW) resonators, thin film bulk acoustic resonators (FBAR), and bulk acoustic wave (BAW) resonators. 
     
     
       11. The wireless communications device of  claim 1 , wherein the acoustic resonator based band reject filter device comprises acoustic resonators arranged in a ladder-type configuration. 
     
     
       12. The wireless communications device of  claim 1 , wherein the transmit path band reject filter device has relatively weak acoustic vibration outside of a reject band of the transmit path band reject filter device, and relatively strong acoustic vibration inside the reject band of the transmit path band reject filter device. 
     
     
       13. A method comprising:
 coupling a transmitter of a wireless communications device to an antenna via a transmit path that includes a single transmit path filter device, wherein the transmit path filter device comprises an acoustic resonator based band reject filter device that rejects multiple frequency bands; 
 coupling a receiver to the antenna via a receive path, wherein the receive path includes a single receive path filter device comprising an acoustic resonator based band reject filter device that rejects multiple frequency bands; and 
 wherein the transmit path filter device isolating the receive path from one or more particular frequencies transmitted by the transmitter. 
 
     
     
       14. The method of  claim 13 , wherein the transmit path is coupled to the receive path in a duplexer, the acoustic resonator based band reject filter being part of the duplexer. 
     
     
       15. The method of  claim 13  further comprising:
 coupling a plurality of additional receivers to the antenna via a plurality of respective receive paths; 
 coupling a plurality of additional transmitters to the antenna via a plurality of respective transmit paths; 
 wherein each respective transmit path includes a single transmit path filter device, wherein each transmit path filter device comprises an acoustic resonator based band reject filter. 
 
     
     
       16. The method of  claim 15 , wherein the transmit paths are coupled to the receive paths in a multiplexer, the acoustic resonator based band reject filters being part of the multiplexer. 
     
     
       17. The method of  claim 13 , wherein the wireless communications device comprises a wireless mobile station. 
     
     
       18. The method of  claim 13 , wherein the wireless communications device comprises a wireless base station.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 12/237,098 filed on Sep. 24, 2008, published as U.S. 2010/0074240 A1, and entitled “Duplexer/Multiplexer Having Filters That Include At Least One Band Reject Filter,” which is hereby incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to a duplexer/multiplexer that has filters including at least one band reject filter. 
     BACKGROUND 
     Wireless communications devices, such as wireless terminals or wireless base stations, include wireless transceivers to perform wireless communications, such as radio frequency (RF) communications. A wireless communications device can include a duplexer (or multiplexer) to allow simultaneous transmission and reception in different frequency bands using the same antenna while ensuring that relatively high power transmit signals transmitted by the wireless transceiver do not swamp relatively low power receive signals received by the wireless transceiver. 
     A duplexer has an antenna port (for connection to an antenna), a receive port (to receive a signal from the antenna port) and transmit port (to transmit a signal to the antenna port). A multiplexer has an antenna port and one or more receive ports and one or more transmit ports. Note that a duplexer is a type of multiplexer. 
     A duplexer or multiplexer can include bandpass filters implemented with acoustic-type resonators. Conventional duplexers/multiplexers including bandpass filters implemented with acoustic-type resonators have relatively limited maximum power handling capabilities, which can prevent use of such conventional duplexers/multiplexers in high-power, high-frequency applications, such as in Worldwide Interoperability for Microwave Access (WiMax) applications or Long-Term Evolution (LTE) applications. WiMax is based on the IEEE (Institute of Electrical and Electronics Engineers) 802.16 Standard (as amended by the IEEE 802.16e or IEEE 802.16e-005). WiMax is able to provide broadband wireless connectivity for mobile stations at relatively high data rates. LTE is a technology that provides an enhancement to the Universal Mobile Telecommunications System (UMTS) technology. LTE is described in 3GPP TS 23.401 and 23.402. 
     In conventional duplexers/multiplexers that employ bandpass filters with acoustic-type resonators, high-power and high-frequency communications can cause ultrasonic vibration in metallic electrodes of the acoustic-type resonators, which can lead to a phenomenon referred to as acousto-migration, in which metal grain boundaries in the resonators migrate. The acousto-migration phenomenon can reduce the lifetime of the filters. Therefore, such filters may not survive for a desirable length of time at desired power levels and frequencies that may be required in certain types of wireless networks. 
     SUMMARY 
     In general, according to an embodiment, a wireless communications device includes an antenna and a multi-port path selection structure (e.g., a duplexer or multiplexer) having an antenna port connected to the antenna, and plural ports connected to respective receive and transmit paths of the wireless communications device. The multi-port path selection structure has a band reject filter connected to the transmit path and a second filter connected to the receive path. 
     Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a wireless communications device that includes a duplexer or multiplexer according to an embodiment. 
         FIG. 2  is a schematic diagram of a conventional duplexer that includes bandpass filters connected to a receive port and a transmit port of the duplexer. 
         FIG. 3  is a graph illustrating the transmit and receive bands provided by the bandpass filters of  FIG. 2 . 
         FIG. 4  is a schematic diagram of a duplexer that includes a receive filter connected to a receive port, and a band reject filter connected to a transmit port, according to an embodiment. 
         FIG. 5  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 4 . 
         FIG. 6  illustrates acoustic-type resonators arranged in a ladder-type configuration for implementing a band reject filter for use in a duplexer or multiplexer according to an embodiment. 
         FIG. 7  is a graph illustrating the resonance and anti-resonance frequencies of the resonators of  FIG. 6 . 
         FIG. 8  is a schematic diagram of a duplexer according to another embodiment that includes a band reject filter connected to a receive port, and a band reject filter connected to a transmit port. 
         FIG. 9  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 8 . 
         FIG. 10  is a schematic diagram of a multiplexer that includes bandpass filters connected to receive ports, and band reject filters connected to transmit ports, according to another embodiment. 
         FIG. 11  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 10 . 
         FIG. 12  is a schematic diagram of a multiplexer that includes bandpass filters connected to receive ports, and a band reject filter connected to a transmit port, according to a further embodiment. 
         FIG. 13  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 12 . 
         FIG. 14  is a schematic diagram of a band reject filter formed of cascaded band reject filter units to provide multiple reject bands, according to an embodiment. 
         FIG. 15  is a graph illustrating the multiple reject bands provided by the band reject filter of  FIG. 14 . 
         FIG. 16  is a schematic diagram of a duplexer according to a further embodiment that includes a bandpass filter connected to a receive port, and a band reject filter connected to a transmit port. 
         FIG. 17  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 16 . 
         FIG. 18  is a schematic diagram of a duplexer according to yet a further embodiment that includes a band reject filter connected to a receive port, and a band reject filter connected to a transmit port. 
         FIG. 19  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 18 . 
         FIG. 20  is a schematic diagram of a multiplexer that includes a band reject filter connected to a receive port, and a band reject filter connected to a transmit port, according to a further embodiment. 
         FIG. 21  is a graph illustrating the transmit and receive bands provided by the filters of  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of some embodiments. However, it will be understood by those skilled in the art that some embodiments may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     In accordance with some embodiments, a multi-port path selection structure for use in a wireless communications device is provided that has an antenna port connected to an antenna of the wireless communications device, and plural ports connected to respective receive and transmit paths of the wireless communications device. Examples of the wireless communications device include a wireless terminal (mobile station), a wireless base station, and other devices that are capable of performing wireless communications. 
     A multi-port path selection structure can be a duplexer or a multiplexer. Generally, a multi-port path selection structure includes circuitry to selectively route signals that are communicated along transmit and receive paths of the wireless communications device. Such circuitry can receive a signal from the antenna of the wireless communications device, and route the received signal to the receive path of the wireless communications device. Similarly, the multi-port path selection structure can route a transmitted signal from transmission circuitry in the transmit path of the wireless communications device to the antenna. The “routing” of the received and transmitted signals is accomplished by use of filters provided in the multi-port path selection structure, where the filters are designed to pass signals in respective receive and transmit frequency bands. In accordance with some embodiments, the filter connected to the transmit path is a band reject filter, and the filter connected to the receive path can either be a bandpass filter or band reject filter. 
     A duplexer has an antenna port connected to the antenna of the wireless communications device, and a single receive port and a single transmit port for connection to respective receive and transmit paths of the wireless communications device. A multiplexer includes an antenna port for connection to the antenna of the wireless communications device, and two or more ports connected to respective receive and transmit paths. Note that a duplexer is a type of multiplexer. 
     A multiplexer can have plural receive ports (corresponding to different receive frequency bands) and/or plural transmit ports (corresponding to different transmit frequency bands). The multiple receive ports can be connected to one or plural receive paths in the wireless communications device. The multiple transmit ports can be connected to one or plural transmit paths in the wireless communications device. Note that it is possible for multiple receive frequency bands and/or multiple transmit frequency bands to share just one receive path or transmit path, respectively, since a wireless communications device normally operates at just a single receive or transmit frequency band at any given time. Alternatively, separate paths in the wireless communications device can be provided for different receive frequency bands or different transmit frequency bands. 
       FIG. 1  illustrates an exemplary wireless communications device  100  that includes a duplexer or multiplexer  102  according to an embodiment. In the ensuing discussion, reference is made to “multiplexer”  102 , although it is to be understood that the discussion applies equally to a duplexer. The wireless communications device  100  has an antenna  104  for communicating radio frequency (RF) signals with another communications device. For example, the wireless communications device  100  can be a wireless terminal (e.g., mobile station) to communicate wirelessly with a wireless base station. Alternatively, the wireless communications device  100  can be base station for communicating with a wireless terminal. 
     The wireless communications device can be used in a wireless communications network, such as a WiMax (Worldwide Interoperability for Microwave Access) network, a Long-Term Evaluation (LTE) network, or any other type of network. Reference to LTE is to any technology based on LTE, such as defined by current standards 3GPP TS 23.401 and 23.402 or any subsequent standard. Reference to LTE can also refer to any subsequent standard derived from an evolution of LTE, whether or not such subsequent standard is referred to as “LTE” by name. 
     The multiplexer  102  has an antenna port  106  that is connected to the antenna  104 . The antenna port  106  of the multiplexer  102  is “connected” to the antenna  104  either directly or indirectly (through other circuitry). 
     The multiplexer also has a receive port  108  for connection to a receive path  110  of the wireless communications device  100 , and a transmit port  112  for connection to a transmit path  114  of the wireless communications device. The receive path  110  includes receive circuitry  116  to receive a signal from the antenna  104  through the multiplexer  102 . The transmit path  114  includes transmit circuitry  118  to generate a transmit signal to be sent through the multiplexer  102  onto the antenna  104 . 
     The multiplexer  102  has filters  120  and  122  for passing signals in the receive and transmit frequency bands, respectively. Also shown in dashed profile is another filter  124  and another port  126 , where the other filter  124  and port  126  can be connected to a transmit path or a receive path, depending upon the specific configuration of the wireless communications device  100 . 
     A conventional duplexer  10  is depicted in  FIG. 2 , where the conventional duplexer  10  has an antenna port  12 , a receive port  14  (that is connected to a receive path of a wireless communications device), and a transmit port  16  (that is connected to a transmit path of the wireless communications device). The conventional duplexer  10  uses bandpass filters (BPFs)  18  and  20  connected to the receive and transmit ports  14  and  16 , respectively. The bandpass filters  18  and  20  can be implemented with acoustic-type resonators. 
       FIG. 3  is a graph of the transmit frequency band  22  and receive frequency band  24  provided by the bandpass filters  20  and  18 , respectively. The graph of  FIG. 3  plots insertion loss (in terms of decibel or dB) as a function of frequency. Insertion loss is the decrease in signal power resulting from insertion of a device in a communications path. As discussed above, the bandpass filters  18  and  20  of a conventional duplexer such as duplexer  10  are subject to deterioration caused by the acousto-migration phenomenon at high power and high frequencies. 
     In accordance with some embodiments, instead of using bandpass filters  18  and  20  in the duplexer  10  as conventionally done, a duplexer  200  (depicted in  FIG. 4 ) can be provided that includes a band reject filter  202  connected to a transmit port of the duplexer  200 , and a receive filter  204  connected to a receive port of the duplexer  200 . Both the band reject filter  202  and receive filter  204  are connected to an antenna port. The receive filter  204  can either be a bandpass filter or a band reject filter, in accordance with some embodiments. 
     Typically, the transmit signals that are sent from the transmit port to the antenna port through the duplexer  200  are associated with relatively high power, while the receive signals communicated from the antenna port to the receive port through the duplexer  200  are associated with relatively low power. The receive filter  204  operates to protect the receive port (and receive circuitry connected to the receive port) against the high-power transmit signals communicated through the duplexer  200 . 
     Note that with the band reject filter  202 , the acoustic vibration is relatively strong in the reject band, but relatively weak in the pass band of the band reject filter. This enables the band reject filter  202  to handle relatively high power transmit signals with reduced acousto-migration issues. Moreover, another characteristic of a band reject filter is that it has lower phase distortion and less ripple in the pass band, as compared to a bandpass filter. 
     Assuming the receive filter  204  is implemented with a bandpass filter, then the receive and transmit frequency bands are depicted in  FIG. 5 , which plots insertion loss as a function of frequency. The bandpass filter  204  provides a pass band  302 —any signal having a frequency below or above the pass band  302  is attenuated or rejected by the bandpass filter  204 . The band reject filter  202  provides a reject band  304 —any signal having a frequency within the reject band  304  is attenuated or rejected, and any signal having a frequency above or below the reject band  304  is passed through the band reject filter  202 . The pass band  302  and reject band  304  of  FIG. 5  overlap. The pass band for the transmit path provided by the band reject filter  202  is represented by reference numerals  306 A and  306 B, which are on the two sides of the reject band  304  (and of the pass band  302  provided by the bandpass filter  204 ). 
     In the receive direction, the bandpass filter  204  passes a signal from the antenna port to the receive port of the duplexer  200  if the signal has a frequency within the receive band  302 . On the other hand, in the transmit direction, the band reject filter  202  passes a signal having a frequency outside the reject band  304  through the band reject filter  202  from the transmit port to the antenna port. 
     A band reject filter can be implemented with acoustic-type resonators RES 1  and RES 2  arranged in a ladder-type configuration, as depicted in  FIG. 6 . The ladder-type configuration includes a first acoustic-type resonator RES 1  (referred to as “series resonator”) connected in series between two ports PORT 1  and PORT 2 , and a second acoustic-type resonator RES 2  (referred to as “shunt resonator”) connected between PORT 2  and ground. Note that in the ladder-type configuration, there can be two (or more) series resonators between PORT 1  and PORT 2 , and two (or more) shunt resonators connected between nodes of the filter and ground. 
     Each of the resonators RES 1  and RES 2  can be any one of a surface acoustic wave (SAW) resonator, a thin film bulk acoustic resonator (FBAR), a bulk acoustic wave (BAW) resonator, or any other type of acoustic-type resonator. The BAW resonator can be a surface mounted resonator (SMR)-type BAW resonator. 
     The series resonator RES 1  of  FIG. 6  is designed to present a high impedance at the reject band  304  of interest. The series resonator RES 1  is configured to be anti-resonance at a reject band frequency (the anti-resonance frequency for the series resonator RES 1  is depicted in  FIG. 7 , according to one example), which means that the series resonator RES 1  presents a high impedance at the anti-resonance frequency. In contrast, the shunt resonator RES 2  is configured to provide a low impedance at a reject band frequency (a frequency within reject band  304 ). This is achieved by designing the shunt resonator RES 2  to be at or near resonance in the reject band  304 . The resonance frequency of the shunt resonator RES 2  is represented as  404  in  FIG. 7 . 
     The resonance frequency of series resonator RES 1  is represented as  406  in  FIG. 7 , while the anti-resonance frequency of the shunt resonator RES 2  is represented as  408  in  FIG. 7 . The resonance frequency  406  of the series resonator RES 1  is immediately below the reject band  304  and is between the pass band  306 A and the reject band  304  of the band reject filter—at the resonance frequency  406 , the series resonator RES 1  has a low impedance. In the pass band  306 A, the shunt resonator RES 2  simply presents a capacitive load to ground. 
     The anti-resonance frequency  408  of the shunt resonator RES 2  is immediately above the reject band  304  and is between the reject band  304  and the pass band  306 B—at the anti-resonance frequency  408 , the shunt resonator RES 2  presents a high impedance to ground. However, in the pass band  306 B, the series resonator RES 1  presents a capacitive series impedance. At frequencies much above or below the reject band  304 , the series and shunt resonators simply behave as high-Q capacitors. 
     In this manner, the overall effect of the filter provided by resonators RES 1  and RES 2  is to provide a high impedance for signals passing between ports PORT 1  and PORT 2  having frequencies in the reject band  304 . 
       FIG. 8  shows an implementation of the duplexer  200  in which the receive filter  204  is implemented with a band reject filter (instead of a bandpass filter as depicted in  FIG. 4 ). In this configuration, both the receive and transmit ports of the duplexer  200  are connected to band reject filters. 
     As depicted in  FIG. 9 , the band reject filter  202  for the transmit port is associated with the transmit reject band  304 , while the band reject filter  204  for the receive port has a receive reject band  402 . The band reject filter  204  allows a signal having a frequency outside the receive reject band  402  to be passed through the band reject filter  204 , whereas the band reject filter  202  allows a signal having a frequency outside the transmit reject band  304  to pass through the band reject filter  202 . 
       FIG. 10  shows a multiplexer  500  that has an antenna port, two receive ports (RX 1  port and RX 2  port), and two transmit ports (TX 1  port and TX 2  port). Note that the two receive ports can be connected to just one receive path (and the associated receive circuitry, such as circuitry  116  in  FIG. 1 ), or alternatively, the two receive ports can be connected to two different receive paths. Similarly, the transmit ports can be connected to just one transmit path (and the associated transmit circuitry, such as  118  in  FIG. 1 ), or alternatively, the transmit ports can be connected to multiple transmit paths. In other implementations, the multiplexer  500  can have more than two transmit ports and/or more than two receive ports. The different receive ports are associated with different receive frequency bands, and the different transmit ports are associated with different transmit frequency bands. 
     The receive ports of the multiplexer  500  are connected to corresponding bandpass filters  502  and  504 , whereas the transmit ports are connected to band reject filters  506  and  508 . Each of the bandpass filters and band reject filters  502 ,  504 ,  506 , and  508  is connected to the antenna port of the multiplexer  500 . 
     As depicted in the graph of  FIG. 11 , a receive pass band  602  corresponds to the pass band provided by the bandpass filter  502  for the RX 1  port, and a receive pass band  604  is provided by the bandpass filter  504  for the RX 2  port. 
     A transmit reject band  606  is provided by the band reject filter  506  for the TX 1  port, and a transmit reject band  608  is provided by the band reject filter  508  for the TX 2  port. 
     While  FIG. 10  shows separate band reject filters  506  and  508  to provide two respective reject bands  606  and  608  ( FIG. 11 ), note that a single band reject filter can be used instead, such as band reject filter  702  in a multiplexer  700  depicted in  FIG. 12 , to provide multiple reject bands. The multiplexer  700  has one transmit port connected to the band reject filter  702 . 
     The chart of  FIG. 13  depicts receive pass bands  602  and  604  and transmit reject bands  606  and  608  that are the same as those depicted in  FIG. 11 , except that the reject bands  606  and  608  of  FIG. 13  are provided by one band reject filter  702  ( FIG. 12 ), instead of two distinct band reject filters  506  and  508  ( FIG. 10 ). 
     The band reject filter  702  includes multiple cascaded band reject filter units to provide the multiple reject bands  606  and  608 . Cascading multiple band reject filter units means that the band reject filter units are connected in series. For example, as depicted in  FIG. 14 , three band reject filter units  802 ,  804 , and  806  are connected in series (cascaded) between PORT 1  and PORT  2 . Each of the band reject filter units  802 ,  804 , and  806  defines a respective reject band, as depicted in  FIG. 15 . The band reject filter unit  802  provides reject band  902 , the band reject filter unit  804  provides reject band  904 , and the band reject filter unit  806  provides reject band  906 . Each of the band reject filter units contains an arrangement of resonators; in the embodiment of  FIG. 14 , each band reject filter unit includes two series resonators and two shunt resonators arranged in the ladder-type configuration. To provide the two transmit reject bands  606  and  608  of  FIG. 13 , two band reject filter units (e.g., any two of  802 ,  804 , and  806 ) can be connected in series (cascaded) to form the band reject filter  702 . In other implementations, the resonators of all band reject filter units can be arranged in a mixed configuration for their locations in the ladder-type structure, namely each of the band reject filter units can have its resonators distributed in the entire filter structure and does not have to have all its resonators arranged together. 
       FIG. 16  shows an alternative embodiment of a duplexer  1000  that has a band reject filter  1002  for the transmit port that provides multiple reject bands  1102 ,  1104 , and  1106  ( FIG. 17 ). The band reject filter  1002  is thus able to block signals having frequencies in any of the reject bands  1102 ,  1104 , and  1106 . 
     A bandpass filter  1004  connected to the receive port of the duplexer  1000  provides a pass band  1108  ( FIG. 17 ). 
       FIG. 18  shows another embodiment of a duplexer  1200  that includes band reject filter  1202  connected to a receive port of the duplexer  1200 , and band reject filter  1204  connected to the transmit port of the duplexer  1200 . Each of the band reject filters  1202  and  1204  provides multiple reject bands, as depicted in  FIG. 19 . The band reject filter  1202  for the receive port provides reject bands  1312 ,  1310 , and  1314 , while the band reject filter  1204  for the transmit port provides reject bands  1304 ,  1302 , and  1306 . 
       FIG. 20  shows another embodiment of a multiplexer  1300  that includes a first band reject filter  1302  for the RX 1 , RX 2 , . . . , RXn port, and a second band reject filter  1304  for the TX 1 , TX 2 , . . . , TXn port. The band reject filter  1302  provides reject bands  1402 ,  1404 , and  1406 , whereas the band reject filter  1304  provides reject bands  1408 ,  1410 , and  1412 , as depicted in  FIG. 21 . 
     In the foregoing description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details. While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.

Metadata:
Filing Date: 20120418
Publication Date: 20130611
Grant Date: 20130611
Priority Date: 20080924
Inventors: JIAN CHUN-YUN
GAGNON ERIC
HU LAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B1/0057", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/0057", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 42037616