Abstract:
A tunable filter reduces the total number of filters used in TDD (Time-Division Duplex) communication circuitry. The communication circuitry may include a tunable filter and a first switch associated with the tunable filter. The tunable filter may include a tuning component and a filtering component. The tuning component may be located with the first switch on a first die. The filtering component may be located in a laminate underneath the first switch. Power amplifiers for amplifying transmission signals may be located on a second die, and the second die may be located on the laminate.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 61/812,454, filed Apr. 16, 2013, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The field of the disclosure is filtering signals in LTE-TDD (Long Term Evolution Time-Division Duplex) bands. Specifically, communication circuitry includes a tunable filter to reduce the total number of filters used and includes a switch to facilitate TDD operation of the tunable filter. The tunable filter may include a tunable element that is located on a same die as the switch. 
       BACKGROUND 
       [0003]    A conventional communication circuit may use 9 SAW (Surface Acoustic Wave) filters. These SAW filters facilitate split band coverage to avoid interference with a central ISM (Industrial Scientific and Medical, or WiFi) band. 
         [0004]    Filters in a conventional communication circuit are unidirectional, and thus either filter transmission (TX) signals or filter reception (RX) signals (but never both). 
         [0005]      FIG. 1  illustrates a conventional communication circuit with its major components. Specifically,  FIG. 1  illustrates: communication circuitry COMCKT including controller CKT 14 , transceiver CKT 2 , diversity filters CKT 4 , diversity switches CK 6 , high band pad CKT 8 , high band filters CKT 10 , high band switches CKT 12 , diversity antenna ANTDIV, and main antenna ANTMAIN. Additionally,  FIG. 2  illustrates details of transceiver CKT 2 , diversity filters CKT 4 , and diversity switches CKT 6 .  FIG. 3  illustrates details of high band pad CKT 8 , high band filters CKT 10 , and high band switches CKT 12 . 
         [0006]    Controller CKT 14  may control: transceiver CKT 2  through control line CL 2 , diversity filters CKT 4  through control line CL 4 , diversity switches CKT 6  through control line CL 6 , high band pad CKT 8  through control line CL 8 , high band filters CKT 10  through control line CL 10 , and ultrahigh band switches CKT 12  through control line CL 12 . Controller CKT 14  may include a processor and a non-transitory memory. 
         [0007]    A control line such as CL 2  may include (not shown) a voltage supply, a serial data line, parallel data lines, a clock signal, a ground, power amplifier control signals, switch control signals, and may also include return signals such as signal power measurements. 
         [0008]      FIGS. 2A and 2B  illustrate a conventional transceiver, diversity filters, and diversity switches from  FIG. 1 . Specifically,  FIGS. 2A and 2B  illustrate exemplary details of transceiver CKT 2 , diversity filters CKT 4 , and diversity switches CKT 6  from  FIG. 1 . 
         [0009]    Transceiver CKT 2  includes many nodes. The node names indicate what bands are transmitted or received by the specific node. Further, “TX” indicates that a main signal is being transmitted. “DRX” indicates that a diversity signal is being transmitted. “RX” indicates that a main signal is received. Thus, the top node is named “B 7  TX,” indicating that a main signal (S 2 ) in band  7  is transmitted. Further, bands such as band  40  may be referred to as “band B 40 ” for emphasis that the number “ 40 ” refers to a band. Additionally, a filter may be referred to as filtering “band B 40  RX” to emphasize that the signal being filtered is a received signal. 
         [0010]    From top to bottom, the nodes may be grouped as follows: transmitting main signals; receiving filtered diversity high band signals from switch SW 2  of diversity switches CKT 6 ; receiving filtered diversity low band signals from switch SW 4  of diversity switches CKT 6 ; and receiving other main signals. Each of these groups is discussed in sequence below. 
         [0011]    Two nodes transmit main signals (S 2  and S 4 ): B 7  TX transmits S 2 ; and B 38 / 40 / 41 /XGP TX transmits S 4 . 
         [0012]    Eight nodes receive high band diversity signals (S 6 , S 8 , S 12 , S 14 , S 16 , S 18 , and S 24 ) as follows: node B 41   a  DRX receives S 6 ; node B 1 / 4  DRX receives S 8 ; node B 40  receives S 10 ; node B 34  DRX receives S 12 ; node B 39  DRX receives S 14 , node B 3  DRX receives S 16 ; node B 2  DRX receives S 18 ; node B 7  DDRX receives S 24 ; 
         [0013]    Six nodes receive low band diversity signals (S 26 , S 28 , S 30 , S 32 , S 34 , and S 36 ) as as follows: node B 8 /D 28   a  DRX receives S 26 ; node B 20  DRX receives signal S 28 ; node B 26  DRX receives S 30 ; node B 13 /B 17  receives S 32 ; node B 29  DRX receives S 34 ; and node B 28   b  DRX receives S 36 . 
         [0014]    Four nodes receive main band signals (S 38 , S 40 , S 42 , and S 44 ): node B 40   a /B 41   a  RX receives S 38 ; node B 40   b  RX receives S 40 ; node B 38 /XGP/B 41   b  RX receives S 42 ; and node B 7 / 41   c  RX receives S 44 . 
         [0015]    Diversity filters CKT 4  include filters F 6 , F 8 , F 9 , F 11 , F 12 , F 14 , F 16 , F 18 , F 20 , F 22 , F 24 , F 25 , F 27 , F 28 , F 30 , F 32 , F 34 , and F 36 . 
         [0016]    Diversity switches CKT 6  include high band switch SW 2  and low band switch SW 4  located on a thin SOI (silicon on insulator) die DIE 2 . High band switch SW 2  may be a SP 10 T (single pole, ten throw) switch. Low band switch SW 4  may be a SP 7 T (single pole, seven throw) switch. 
         [0017]    High band switch SW 2  receives high band diversity signal S 46  at single pole SP 2 , and transmits high band diversity signal S 46  to a selected one of ten throws (T 6 , T 8 , T 9 , T 11 , T 13 , T 16 , T 18 , T 20 , T 22 , and T 24 ), to be transmitted towards diversity filters CKT 4  as signals S 6 , S 8 , S 9 , S 11 , S 13 , S 16 , S 18 , S 20 , S 22 , and S 24  respectively. 
         [0018]    High band switch SW 2  may include an additional throw (not shown) for grounding. 
         [0019]    Low band switch SW 4  receives low band diversity signal S 48  at single pole SP 4 , and transmits low band diversity signal S 48  to a selected one of seven throws (T 25 , T 27 , T 28 , T 30 , T 32 , T 34 , and T 36 ), to be transmitted towards diversity filters CKT 4  as signals S 25 , S 27 , S 28 , S 30 , S 32 , S 34 , and S 36  respectively. 
         [0020]    Three filters (F 6 , F 9 , and F 11 ) deserve special attention for future reference. Filter F 6  receives signal S 6  from throw T 6 , and transmits filtered signal S 6  to node B 41   a  DRX in transceiver CKT 2 . 
         [0021]    Filter F 9  receives signal S 9  from throw T 9  and transmits S 10  (filtered signal S 9 ) to node B 40  DRX. Filter F 11  receives signal S 11  and transmits signal S 10  (filtered signal S 11 ) to node B 40  DRX. If switch SW 2  is thrown to T 9 , then node B 40  DRX will receive signal S 9  filtered through filter F 9 . Alternatively, if switch SW 2  is thrown to T 11 , then node B 40  DRX will receive signal S 11  filtered through filter F 11 . In this fashion, diversity high band signal S 46  is filtered by either filter F 9  (if T 9  is thrown) or filter F 11  (if T 11  is thrown), and then transmitted as signal S 10  to node B 40  DRX. Of course, throws T 9  and T 11  may not be thrown (selected) simultaneously. 
         [0022]      FIG. 3  illustrates a conventional high band pad CKT 8 , high band filters CKT 10 , and high band switches CKT 12  from  FIG. 1 . 
         [0023]    In transmit mode for band  7 , high band pad CKT 8  receives signal S 2  (band  7  being transmitted from node B 7  TX), passes this signal through capacitor CAP 2  (to filter undesired very low frequency signals), amplifies this signal with amplifier PA 2 , and sends filtered amplified signal S 2  to duplexer DUPB 7 . 
         [0024]    Duplexer DUPB 7  sends the amplified signal towards main antenna ANTMAIN (not shown) as signal S 52  in transmit mode. 
         [0025]    Alternatively, in receive mode for band  7 , duplexer DUPB 7  receives signal S 52  from main antenna ANTMAIN, and sends this received signal as S 50  towards a transceiver (not shown). 
         [0026]    High band pad CKT 8  also receives signal S 4  (bands  38 ,  40  and  41  from node B 38 / 40 / 41 ), passes this signal through capacitor CAP 4  (to filter undesired very low frequency signals), amplifies this signal with amplifier PA 4 , and sends filtered amplified signal S 4  to single pole SP 6  of switch SW 6 . 
         [0027]    Switch SW 6  is an SP 4 T (single pole, four throw) having one pole (SP 6 ) and four throws (T 54 , T 56 , T 58 , and T 60 ). If switch SW 6  is thrown to throw T 54 , then filtered amplified signal S 4  (band B 41  or band B 38 ) is sent to filter F 54  in high band filters CKT 10 . Filter  54  sends filtered signal S 54  to high band switches CKT 12 , specifically to node TX B 41   b  and to throw T 54  in switch SW 8 . 
         [0028]    Similarly, throw T 56  sends signal S 56  (bands B 40   a  and B 41 ) to filters F 55  and F 57 . Filter  55  sends signal S 55  (band  40   a ) to high band switches CKT 12 . Filter  57  sends signal S 57  (band  41   a ). 
         [0029]    Throw T 48  sends signal S 58  (band B 41   c ) to filter F 58 . Filter F 58  sends filtered signal S 58  to high band switches CKT 12 . Throw T 60  sends signal S 60  to filter F 60 . Filter F 60  sends filtered signal S 60  to high band switches CKT 12 . 
         [0030]    High band filters CKT 10  includes 9 filters: transmission filters (F 54 , F 55 , F 57 , F 58 , and F 60 ), and reception filters (F 37 , F 39 , F 63 , and F 65 ). In TDD operation, one of the transmission filters is being used, or alternatively one of the reception filters is being used. Filter F 60  is a low pass filter, and the other filters shown in CKT 10  are band pass filters. 
         [0031]    High band switches CKT 12  include two switches: SP 6 T (single pole, six throw) switch SW 8  (including single pole SP 8  and throws T 62 , T 60 , T 54 , T 55 , T 57 , and T 58 ), and SP 3 T (single pole, triple throw) switch SW 10  (including single pole SP 10  and throws T 37 , T 39 , and T 64 ). Switch SW 8  and switch SW 10  may be placed on a single die DIE 4 . Die DIE 4  may be constructed of MEMS (microelectromechanical systems) or may be solid state SOI (silicon on insulator). 
         [0032]    Briefly referring back to  FIG. 2 , diversity filters CKT 4  include filters F 6  (band B 41   a  DRX), F 9  (band B 40  DRX), and  FIG. 11  (also band  40  DRX). These filters filter a signal received from the diversity or MIMO (Multiple Input Multiple Output) antenna ANTDIV. These bands are also received through the main antenna ANTMAIN, and filtered by high band filters CKT 10 . 
         [0033]    Switch SW 8  is a transmission switch, and transmits signal TX RF 1  to main antenna ANTMAIN (not shown). For example, switch SW 8  selects throw T 55  to transmit band B 40   a  TX through single pole SP 8  towards main antenna ANTMAIN (not shown) as signal TX RF 1 . 
         [0034]    In contrast, switch SW 10  is a reception switch, and receives signal RX RF 1  at single pole SP 10  from main antenna ANTMAIN (not shown). For example, switch SW 10  selects throw T 37 , then receives RX RF 1  at single pole SP 10  and transmits signal S 37  (band B 40   a  RX) towards filter F 37  in diversity switches CKT 10  in route to transceiver CKT 2 . 
         [0035]    TDD (Time-Division Duplex) alternately sends and then receives signals in a given frequency band. In this fashion, band B 40   a  may be alternately sent, and then received over main antenna ANTMAIN (not shown) through switch selections as discussed above. Similarly, band B 41   a  may be time-division duplexed using different switch settings. 
         [0036]    Conventionally, as shown in  FIGS. 2 and 3 , different filters are used for receiving and for transmitting in each band. This conventional approach requires large numbers of filters. For example, high band filters CKT 10  illustrates nine filters, and these nine filters are conventionally SAW (surface acoustic wave) or BAW (bulk acoustic wave) filters. 
         [0037]      FIG. 4  illustrates a conventional single filter used for transmission and reception of a single band. Specifically, filter F 114  is used (alternately, under TDD (Time-Division Duplex) procedures) for filtering a band  38  signal for transmission, and then for filtering a received band  38  signal. Filter F 114  is a “dual mode” filter because it filters the transmitted band  38  signal (in a first mode, see  FIG. 5C ) and also filters the received band  38  signal (in a second mode, see  FIG. 5D ). 
         [0038]    Conventionally (in  FIGS. 1 ,  2 , and  3 ), different filters are used for transmitting and for receiving because transmitted signals are high power (typically 25 dBm, with high insertion loss filters), whereas received signals are low power (typically 0 dBm, with low insertion loss filters). Thus, filters that are dedicated to received signals may use very little power during filtering. In contrast, dual purpose filters (reception or transmission) must be relatively large, and will consume relatively large amounts of power even when filtering received low power signals. 
         [0039]    However, there are some advantages to using a single dual purpose (or dual mode, or TX/RX) filter during LTE-TDD communications, such as reducing the number of filters, as shown in  FIG. 4 . 
         [0040]    Filtering circuit CKT 14  includes controller CONT 4  controlled by control lines CL 14 , capacitor CAP 6 , amplifier PA 6 , switch SW 14 , switch SW 12 , filters (F 114 , F 112 , and F 116 ), switch SW 16 , and capacitor CAPE. 
         [0041]    Controller CONT 4  may be controlled by control lines CL 14  that may include a bias voltage, a battery voltage, a clock signal, serial or parallel data signals, and enable signals. 
         [0042]    From left to right, signal S 100  includes a band  7  transmission signal or a band  38  transmission signal, is filtered by capacitor CAP 6 , amplified by amplifier PA 6 , received by single pole SP 110  of switch SW 14 , then switched to throw T 112  for the case of a band  7  transmission signal (or switched to throw T 114  for the case of a band  38  transmission signal). 
         [0043]      FIGS. 5A-5D  illustrate the use of a single filter (F 114 ) for transmitting and receiving in band  38  for LTE-TDD communications. Filter F 114  is a “dual mode” filter because it filters the transmitted band  38  signal (in a first mode, see  FIG. 5C ) and also filters the received band  38  signal (in a second mode, see  FIG. 5D ). 
         [0044]      FIG. 5A  illustrates the switches and filtering of circuit CKT 14  in  FIG. 4  for the case of transmitting band  7  (while omitting capacitors, amplifiers, and the controller for the sake of clarity). As discussed above, switch SW 14  throws the signal S 100  to throw  112 . This signal proceeds as signal S 102  to filter F 112 , is filtered, then proceeds as signal S 106  to throw T 126  of switch SW 16 . 
         [0045]    Signal S 106  proceeds from throw T 126  to single pole SP 120 , then exits as signal S 110  towards main antennal ANTMAIN. 
         [0046]      FIG. 5B  illustrates the switches and filtering for the case of receiving band  7  (omitting capacitors, amplifiers, and the controller for the sake of clarity). 
         [0047]    A band  7  signal is received by the main antenna ANTMAIN as S 110  (or B 7  RX), and is sent to single pole SP 120  of switch SW 16 . Single pole SP 120  throws the signal to throw T 126 , and the signal exits as S 106  towards filter F 116 . Filter F 116  filters the signal and sends the filtered signal as S 114  (B 7  RX) towards another location, such as towards a transceiver (not shown). Filter F 116  may include a balun (not shown), and may output the received and filtered band  7  signal S 114  as differential signals (a positive signal and a negative signal, not shown). 
         [0048]    The position of switch SW 14  is not shown in  FIG. 5B . Power amplifier PA 6  may be turned off when receiving the band  7  signal, or switch SW 14  may be thrown to throw T 114 , or switch SW 14  may be thrown to a ground (not shown). In other words, generally circuit CKT 14  would not simultaneously transmit and receive in band  7 , or else the high power transmission band  7  signal would tend to interfere with the relatively low power received band  7  signal. 
         [0049]      FIG. 5C  illustrates the switches and filtering for the case of transmitting band  38  (omitting capacitors, amplifiers, and the controller for the sake of clarity). Band  38  will be transmitted and received through the same filter F 114  (transmitted in  FIG. 5C , and received in  FIG. 5D ). 
         [0050]    Switch SW 14  throws signal S 100  (B 38  TX) from single pole SP 110  to throw T 114 . Throw T 114  send signal S 104  to filter F 114 . Filter F 114  sends filtered signal S 108  to throw T 124  of switch SW 16 , then to single pole SP 120  of switch SW 16 . Single pole SP 120  sends band  38  signal S 110  to main antenna ANTMAIN for transmission. 
         [0051]      FIG. 5D  illustrates receiving band  38  through filter F 114  (previously used for transmitting in the same band  38  in  FIG. 5C ).  FIG. 5D  is based on  FIG. 4 , but omits capacitors, amplifiers, and the controller for the sake of clarity). Thus,  FIGS. 5C and 5D  illustrate single filter F 114  being used for transmitting and receiving the same band  38  in TDD. 
         [0052]    In  FIG. 5D , a band  38  signal S 110  is received by main antenna ANTMAIN and sent to single pole SP 120  of switch SW 16 . Switch SW 16  throws the signal to throw T 124 , then throw T 124  sends signal S 108  to filter F 114 . As discussed above, filter F 114  now acts as a receiving filter in band  38 , instead of as a transmitting filter in band  38 . Switch SW 12  receives filtered signal S 104  at throw T 114 , and throws this signal to single pole SP 120 . Single pole SP 120  sends received and filtered band  38  signal S 112  upwards, possibly to a transceiver. Note that throw T 114  of switch SW 12  also serves as throw T 114  of switch SW 14 . 
         [0053]    Received and filtered band  38  signal S 112  may be transformed by a balun (not shown) into differential signals (a positive signal and a negative signal, not shown). 
         [0054]    Thus, single filter F 114  may alternately serve as a transmission filter (in  FIG. 5C ) and as a reception filter (in  FIG. 5D ) during time-division duplexing (TDD) in band  38 . 
         [0055]      FIG. 6  illustrates using single filters (to transmit and receive) for multiple LTE bands. In  FIG. 6 , filters F 210  and F 212  may each be used for filtering in a transmit mode (first mode) and then in a receive mode (second mode), similar to filter F 114  discussed above in  FIG. 4 ,  5 C, and  5 D. 
         [0056]    Specifically, circuit CKT 16  includes amplifier circuit CKT 18 , SP 2 T (single pole, double throw) switches SW 20  and SW 22 , and filters F 210  and F 212 . Solid signal lines indicate the paths of transmission signals, and dashed lines indicate the paths of reception signals. 
         [0057]    Starting at the top left, signal S 210  is a transmission signal for bands B 38 , B 40 , B 41 , and XGP. This signal is amplified by amplifier PA 10  and sent as signal S 212  to switch SW 20 . Switch SW 20  throws this signal to filter F 210  as signal S 214 . Filter F 210  transmits filtered signal S 216  towards an antenna (not shown. Filter F 210  may also filter reception signals (dashed lines) in these bands. 
         [0058]    Starting at the top right, filter F 210  may receive a signal (dashed line, S 218 ) from the antenna, and filter the signal and pass it to switch SW 20 . Switch SW 20  throws this filtered signal to the lower left pole, and this signal passes to the left and down as signal S 218 . Thus, switch SW 20  will be in a first position when transmitting, and in a second position when receiving signals in bands B 38  or B 41  or XGP. 
         [0059]    Similarly, switch SW 22  and filter F 212  may filter and transmit a signal in band B 40 , or may receive and filter a signal in band B 40  (depending upon the position of switch SW 22 . 
         [0060]    When transmitting a band B 40  signal S 220 , amplifier PA 8  amplifies the signal, filter F 214  filters the signal and sends filtered signal S 222  to switch SW 22 , switch SW 22  throws the signal to filter F 212  as signal S 224 , then filter F 212  filters the signal and sends signal S 226  towards an antenna (not shown, and not necessarily the same antenna that signal S 216  was sent to). 
         [0061]    Starting at the bottom right, filter F 212  may receive and filter a band  40  signal (dashed line S 228 )), then send the filtered signal to switch SW 22 . Switch SW 22  throws this signal to the left and downward as S 228 . 
         [0062]    The received signals S 218  and S 228  may be transformed into differential signals by baluns (not shown). 
         [0063]    Thus, conventional communication circuitry requires too many filters. These numerous filters consume power and take up valuable space. 
       SUMMARY 
       [0064]    A tunable filter reduces the total number of filters used in TDD (Time-Division Duplex) communication circuitry. 
         [0065]    In a first embodiment, communication circuitry may include a tunable filter and a first switch associated with the tunable filter. The tunable filter may include a tuning component and a filtering component. The tuning component may be located with the first switch on a first die. 
         [0066]    In a second embodiment, the filtering component may be located in a laminate underneath the first switch. 
         [0067]    In a third embodiment, power amplifiers for amplifying transmission signals may be located on a second die, and the second die may be located on the laminate. 
         [0068]    Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0069]    The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure. 
           [0070]      FIG. 1  illustrates a conventional communication circuit with its major components. 
           [0071]      FIG. 2  illustrates a conventional transceiver, diversity filters, and diversity switches from  FIG. 1 . 
           [0072]      FIG. 3  illustrates a conventional high band pad CKT 8 , high band filters CKT 10 , and high band switches CKT 12  from  FIG. 1 . 
           [0073]      FIG. 4  illustrates a conventional single filter used for transmission and reception of a single band. 
           [0074]      FIGS. 5A-5D  illustrate the use of a single filter (F 114 ) for transmitting and receiving in band  38  for LTE-TDD communications. 
           [0075]      FIG. 6  illustrates using single filters (to transmit and receive) for multiple LTE bands. 
           [0076]      FIG. 7  illustrates a power amplifier circuit associated with a dual mode tunable filter (also known as a combined tunable filter), with a first mode for transmitting and a second mode for receiving. 
           [0077]      FIG. 8  illustrates a manufacturing embodiment of  FIG. 7 . 
           [0078]      FIG. 9  illustrates some conventional bands of LTE-TDD (in MHz). 
           [0079]      FIG. 10  illustrates a conventional overlapping bandwidth approach for receiving signals in band B 40  by overlapping two SAW (Surface Acoustic Wave) filters (SAW 2  and SAW 4 ) to filter the entire range of band B 40 . 
           [0080]      FIG. 11  is similar to  FIG. 10 , but illustrates a dedicated filter F 510  for transmitting in band  41   c.    
           [0081]      FIG. 12  illustrates using one tunable filter in combination with two SAW filters to achieve split band coverage around the ISM band. 
           [0082]      FIG. 13  illustrates using a tunable filter and two narrow edge SAW filters to provide split band coverage around a central band. 
           [0083]      FIG. 14  is similar to  FIG. 13 , except that filters SAW 18  and SAW 20  from  FIG. 13  have been replace by (or “merged into”) diplexer DIP 2 . In this fashion, signal S 410  replaces signals S 404  and S 406  from  FIG. 13 . 
           [0084]      FIG. 15  is similar to  FIG. 12 , except that SAW 20  (2496 to 2565) has been replaced by a band  7  range (2496 to 2570) of band  7  duplexer DUPB 7 . 
           [0085]      FIG. 16  is similar to  FIG. 13 , except that band  41   a  (2496 to 2565) filter SAW 20  has been deleted. 
           [0086]      FIG. 17  is similar to  FIG. 12 , except that the left portion of the tunable filter band (band  40   a  (2300 to 2370)) has been replaced by an extended left portion of the tunable filter band (band  40  (2300 to 2400)). 
           [0087]      FIG. 18  illustrates circuitry implementing tuning component TUN 8  of  FIG. 17 , and illustrating a few additional features. 
       
    
    
     DETAILED DESCRIPTION 
       [0088]    The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
         [0089]      FIG. 7  illustrates an amplifier circuit CKT 20  including tunable filter and an associated switch. The tunable filter may include filtering component F 310  and tuning component TUN 2 . 
         [0090]    Tuning component TUN 2  may be a variable capacitor or an array of capacitors, and may be located with associated switch SW 24  on single die DIE 8 . The tuning component TUN 2  and the associated switch SW 24  may use the same manufacturing technology, facilitating their placement on a single die. For example (as shown in  FIG. 8 ), they may be manufactured by a single process such as SOI (Silicon-on-Insulator), or MEMS, or SiGe with high resistivity. This integration is not essential, but such integration will reduce size and cost. 
         [0091]    The upper portion of amplifier circuit CKT 20  is configured for band  7 , and is identical to the top portion of high band pad CKT 8  in  FIG. 3 . In transmit mode for band  7 , amplifier CKT 20  receives signal S 2  (band  7  being transmitted from node B 7  TX), passes this signal through capacitor CAP 2  (to filter undesired very low frequency signals), amplifies this signal with amplifier PA 2 , and sends filtered amplified signal S 2  to duplexer DUPB 7 . Duplexer DUPB 7  sends the amplified signal towards main antenna ANTMAIN (not shown) as signal S 52  in transmit mode. 
         [0092]    Alternatively, in receive mode for band  7 , duplexer DUPB 7  receives signal S 52  from main antenna ANTMAIN, and sends this received signal as S 50  towards a transceiver (not shown). 
         [0093]    Die DIE 8  includes tuning component TUN 2  and switch SW 24 . 
         [0094]    Starting at the lower left, capacitor CAP 8  receives signal S 320  (band B 38  or B 40  or B 41  for transmission), and sends signal S 322  to amplifier PA 12 . Amplifier PA 12  sends signal S 324  to throw T 304  of switch SW 24 . 
         [0095]    In a transmitting configuration, switch SW 24  throws signal  324  to single pole SP 300 . Then single pole SP 300  sends signal S 326  to filter F 310 . Filter F 310  (in a first mode, or transmission mode) transmits signal S 328  towards an antenna (not shown). 
         [0096]    Filter F 310  is tunable, so that it may filter a band B 38  signal, a band B 40  signal, band XGP signal, or band B 41  signal, depending upon how it is tuned. Tuning component TUN 2  is part of filter F 310 , and may be located on a die holding switch SW 24 . 
         [0097]    In a receiving configuration, received signals are indicated by dashed lines. Received signal S 328  (starting at the lower right, and moving towards the left) is received by tunable filter F 310  (in a second mode), sent to single pole SP 300  of switch SW 24 , thrown to throw T 302 , then sent downward as S 330  towards a transceiver (not shown). 
         [0098]    Thus, tunable filter F 310  may operate in a first mode transmitting in band B 38 , or (after switching from throw T 304  to throw T 302 ) in a second mode receiving band B 38 . After tuning to band B 40 , then tunable filter F 310  may operate in a first mode transmitting in band B 40 , or (after switching from throw T 304  to throw T 302 ) a second mode receiving in band B 40 . In this fashion, tunable filter F 310  serves the role of at least 4 different filters: transmit band B 38 , receive band  38 , transmit band B 40 , and receiver band B 40 . Further, if filter F 310  tunably filters for two bands, then the associated single switch SW 24  performs switching functions for two bands (replacing switch SW 20  and switch SW 22  in  FIG. 6 ). 
         [0099]    Coupled resonators (RES 2  and RES 4 ) act as a band pass filter, as shown in  FIG. 8  discussed below. In one embodiment (not shown), four resonators may be magnetically cross-coupled and may be symmetrically spaced in a square pattern. 
         [0100]      FIG. 8  illustrates a manufacturing embodiment of  FIG. 7 . In  FIG. 8 , circuit CKT 22  is an embodiment of power amplifier circuit CKT 20  of  FIG. 7 , and includes laminate (or substrate) LAM 2 , power amplifier die DIE 10  (including amplifiers PA 8  and PA 10 , not shown) on top of laminate LAM 2 , die DIE 8  (including switch SW 24  and tuning element TUN 2 , not shown) on top of laminate LAM 2 , resonator RES 2 , resonator RES 4  (magnetically coupled to RES 2 ), via VIA 2 , via VIA 4 , and bumps BUMP 1  through BUMP 4 . Bumps BUMP 1  through BUMP 4  may be solder, or may be rectangular copper pillars (with low resistance), or other known attachment structures. The resonators may be magnetically coupled, and may include additional resonators. 
         [0101]    Power amplifier die DIE 10  may be GaAs or CMOS or SiGe. Die DIE 8  may include switch SW 24  (not shown) for selecting between a first mode (transmitting or TX) and a second mode (receiving or RX), and may include a tunable component TUN 2  (not shown) of tuning filter F 310  (not shown). Tunable component TUN 2  may include a tunable array of capacitors for tuning filter F 310 . Tunable filter F 310  may be a bandpass TDD filter, may include RES 2  and RES 4 , and may include tunable component TUN 2  located on die DIE 8 . 
         [0102]    DIE 8  and DIE 10  may be a single package on a single laminate LAM 2 , as shown. 
         [0103]    The manufacturing embodiment of  FIG. 3  may be applied to any ASM (antenna switch module) where a single die includes band switching and tuning for LTE-TDD filters. 
         [0104]      FIG. 9  illustrates some conventional bands of LTE-TDD (in MHz). Band B 40  ranges from 2300 to 2400 (large bandwidth of 100 MHz). Band ISM (Industrial, Scientific, and Medical, including WiFi) ranges from 2401 to 2483 (bandwidth of 82 MHz). Band B 41  ranges from 2496 to 2690 (very large bandwidth of 194 MHz, for U.S.). Broadly speaking, these three bands may be referred to as a low band, a central band (or exclusion band), and a high band respectively. 
         [0105]    Together, bands B 40  and B 41  may be described as a “split-band” range, because the combined range is split into a low band (B 40 ) and a high band (B 41 ) by the central band ISM which must be avoided or excluded. 
         [0106]    Band B 41  encompasses bands XGP and B 38 . Band XGP (for Japan) ranges from 2545 to 2575 (bandwidth of 30 MHz). Band B 38  (for European Union) ranges from 2570 to 2620 (bandwidth of 50 MHz). 
         [0107]    It is difficult to build filters simultaneously having large bandwidths and having large attenuation at close offset frequencies (a “brick wall” at the end of the range of the filter). This difficulty also applies to tunable filters. 
         [0108]    Thus, it is difficult to build a single filter for receiving in band B 40  due to its large bandwidth (100 MHz) and its adjacency (at the high end, 2400 MHz) to the low end of the ISM band (2401 MHz). Similarly, it is difficult build a single filter for band B 41  due to its very large bandwidth (194 MHz) and its adjacency (at the low end, 2496 MHz) to the high end of the ISM band (2483 MHz). Thus, multiple filters may be used to cover band B 40 , as shown in  FIG. 10 . 
         [0109]      FIG. 10  illustrates a conventional overlapping bandwidth approach for receiving signals. This approach receives signals in band B 40  (low target band) and in band B 41  (high target band). The ISM band (exclusion band) is intentionally excluded from (filtered out of) the received signals. 
         [0110]    SAW filters provide good edge characteristics. The upper edge (at 2400 MHz) of SAW filter SAW 4  coincides with the upper edge of band B 40  (2400 MHz). SAW 4  passes signals at the upper edge of band B 40  (the low target band in this example), and excludes signals at the lower edge of the exclusion band. Alternatively, BAW (Bulk Acoustic Wave) filters also provide good edge characteristics, and may be used in place of (or in combination with) SAW filters throughout this specification. 
         [0111]    SAW 6  similarly (or symmetrically) provides good edge characteristics, passing signals at the lower edge of band B 41  (at 2496 MHz), and excluding signals at the high edge of the exclusion band (2483 MHz). 
         [0112]    Receiving (RX) in band B 40  is performed by using two overlapping SAW (Surface Acoustic Wave) filters (SAW 2  and SAW 4 ) to filter the entire range of band B 40 . 
         [0113]    Specifically, band B 40  is received by an overlapping combination of B 40   a  (2300 to 2370 MHz, using filter SAW 2 ) and band B 40   b  (2350 to 2400 MHz, using filter SAW 4 ). These two bands overlap by 20 MHz due to a 20 MHz maximum modulation bandwidth for SAW filters. 
         [0114]    Similarly, band B 41  is received by overlapping combinations of band B 41   a  (2496 to 2565 MHz, by SAW 6 ), band B 38   x  (2545 to 2640 MHz, by SAW 8 ), and band B 7  (2620 to 2690 MHz, by filter F 410 ). Band B 38   x  overlaps with band B 41   a  by 20 MHz, and overlaps with band B 7  by 20 MHz, due to a 20 MHz maximum modulation bandwidth for SAW filters. 
         [0115]    Filter F 410  may be a “reused” band  7  filter (not shown) from a duplexer (not shown), which is also being “reused” to filter the upper part of band B 41  (in addition to being used to filter band B 7 ) In other words, this filter may be defined as filtering band B 7  and band B 41   c.    
         [0116]      FIG. 11  illustrates a transmitting configuration similar to the receiving configuration of  FIG. 10 , and illustrates a dedicated filter F 510  for transmitting in band B 41   c . SAW filters SAW 10  and SAW 12  overlap to receive all of band B 40 . Filters SAW 14 , SAW 16 , and F 510  overlap to transmit all of band B 41 . 
         [0117]    Similar to  FIG. 10 , SAW filters are used at the high edge of the low target band and at the low edge of the high target band. 
         [0118]      FIG. 12  illustrates using one tunable filter in combination with two SAW filters to achieve split band coverage around the ISM band (the central or exclusion band). As shown in  FIGS. 9-11 , the three bands of interest for this embodiment are bands B 40  (low target band), ISM (to be avoided), and B 41  (high target band). As previously discussed, these filters may be used for receiving and for transmitting in TDD, with appropriate switching. 
         [0119]    A tunable filter TUNFILT 2  is configured to cover a low tunable band and a high tunable band. In  FIG. 12 , the low tunable band is labeled B 40   a  (2300 MHz to 2370 MHz, thus staying at least 20 MHz away from the lower edge of the exclusion band band). 
         [0120]    SAW filter SAW 4  (band B 40   b ) overlaps with the low tunable band (by 20 MHz), and combines with the low tunable band to completely cover low target band (B 40 , from 2300 to 2400 MHz). 
         [0121]    As discussed in previous figures, a SAW filter (SAW 4 ) is used to filter the upper edge of the low target band, adjacent to the lower edge of the exclusion band. 
         [0122]    Tunable filter TUNFILT 2  is also configured to cover most of the upper part of band B 41  (2545 to 2690, or Bands B 41   b , B 41   c , XGP, and B 38 ), thus staying at least 20 MHz away from the top of the exclusion band). See right portion of range of tuning component TUN 4 . 
         [0123]    As discussed above, in order to fully cover band B 40 , SAW filter SAW 4  filters band B 40   b  (2350 to 2400). This range overlaps with band B 40   a  by at least 20 MHz, and also provides a good cutoff at 2400 MHz to avoid interference with the lower edge of the ISM band (the central or exclusion band). Filter SAW 18  may be described as a narrow edge filter, because it has a relatively narrow range and because it filters the upper edge of band B 40 . 
         [0124]    Similarly, in order to fully cover band B 41  (a high band), SAW filter SAW 20  filters band B 41   a  (2496 to 2565). This range overlaps with TUNFILT 2  by at least 29 MHz, and provides a good cutoff at 2496 in order to avoid interference with the upper edge of the ISM band (the central or exclusion band). Filter SAW 20  may also be described as a narrow edge filter. 
         [0125]      FIG. 13  illustrates a switching configuration using a tunable filter and two narrow edge SAW filters to provide split band coverage around a central or exclusion band. Specifically, amplifier circuit CKT 24  is very similar to amplifier circuit CKT 20  in  FIG. 7 , but is modified to provide split band coverage. 
         [0126]    The use of SPDT (single pole double throw) switches to facilitate a single filter being used for transmitting and receiving in TDD was described in  FIG. 5C  and  FIG. 5D  respectively for band b 38 . 
         [0127]    For the purpose of this specification, the term “SPDT” should be interpreted broadly. For example, a SP 3 T (single pole triple throw) switch includes a SPDT switch, but merely has an additional throw available. In other words, adding an additional throw (or an additional pole) for some other purpose does not prevent infringement. 
         [0128]    Transmission signal S 324  (including bands B 38 , B 40 , and B 41 ) routes to three switches: SW 26 , SW 28 , and SW 30 . These switches are shown on the power amplifier side of the dual purpose filters, but may alternatively be located on the antenna side of the dual purpose filters (not shown) with a slightly different configuration (not shown). 
         [0129]    When transmitting in the tunable filter range (“split range”) of 2300-2370 or 2545-2690, then switch SW 26  receives signal S 324  at throw TbTX and routes this signal to single pole SPA. Single pole SPA sends this signal to tunable filter TUN 4 . Tunable filter TUN 4  filters signal S 324  to pass band B 40   a , or filters to pass bands B 41   b  and B 41   c , or filters to pass band B 38 , or filters to pass band XGP (depending upon how tunable filter TUN 4  is tuned). Tunable filter TUN 4  passes a tuned signal S 402  towards main antenna ANTMAIN (not shown). 
         [0130]    Tunable filter TUN 4  may include a tunable component TUN 6  that may be located on a die with switch SW 26 , similar to the discussions above for  FIGS. 7 and 8 . Alternatively, component TUN 6  may be a control portion that controls tunable filter TUN 4 . 
         [0131]    In the reverse direction, when receiving in the tunable filter range (“split range”) of 2300-2370 or 2545-2690, then tunable filter TUN 4  receives signal S 402  from main antenna ANTMAIN (not shown). Tunable filter TUN 4  filters signal S 324  to pass band B 40   a , or filters to pass bands B 41   b  and B 41   c , or filters to pass band B 38 , or filters to pass band XGP (depending upon the tuning of tunable filter TUN 4 ). 
         [0132]    Tunable filter TUN 4  passes a filtered signal S 408  to pole SPA of switch SW 26 . Pole SPA passes (not shown) the filtered signal S 408  to throw TARX. Throw TARX sends filtered signal S 408  to a transceiver (not shown). In  FIG. 13 , switch SW 26  is shown in the transmission position, but may be switched to throw TARX for receiving in TDD. 
         [0133]    For band B 41   a , switch SW 28  acts similarly to switch SW 26 . Filter SAW 20  filters transmission of signal S 324  or reception of signal S 404  in band B 41   a , depending upon the selection of switch SW 28 . 
         [0134]    For band b 40   b , switch SW 30  acts similarly to switch SW 28 . Filter SAW 18  filters transmission of signal S 324  or reception of signal S 406  in band B 40   b , depending upon the selection of switch SW 230 . 
         [0135]      FIG. 14  is similar to  FIG. 13 , except that filters SAW 18  and SAW 20  from  FIG. 13  have been replace by (or “merged into”) diplexer DIP 2 . In this fashion, signal S 410  replaces signals S 404  and S 406  from  FIG. 13 . 
         [0136]      FIG. 15  is similar to  FIG. 12 , except that SAW 20  (2496 to 2565) has been replaced by a band B 7  range (2496 to 2570) of band B 7  duplexer DUPB 7 . 
         [0137]      FIG. 16  is similar to  FIG. 13 , except that band  41   a  (2496 to 2565) filter SAW 20  has been deleted. The filtering duties of SAW 20  have been effectively shouldered by band  7  (2496 to 2570) duplexer DUPB 7 . 
         [0138]    To summarize,  FIG. 16  employs one tunable filter TUN 4  and one SAW filter SAW 18  to accomplish the filtering that previously required eight filters in  FIG. 3  (F 54 , F 55 , F 57 , F 58 , F 37 , F 39 , F 63 , and F 65 ). 
         [0139]      FIG. 17  is similar to  FIG. 12 , except that the left portion of the tunable filter band (band B 40   a  (2300 to 2370)) has been replaced by an extended left portion of the tunable filter band cover all of band B 40  (band B 40  (2300 to 2400)). Also, SAW  18  has been deleted, since it is no longer needed relative to  FIG. 12 . To document this change, the tuning component has been named TUNFILT 4  (instead of TUNFILT 2  as in  FIG. 15 ). This extension of the left portion of the tunable filter band eliminates the need for SAW 18  of  FIG. 12 . 
         [0140]      FIG. 18  illustrates filtering component F 506  and tuning component TUN 8  of tunable filter TUNFILT 4  of  FIG. 17 , and illustrates a few additional features. The bottom right portion of  FIG. 18  is new, but the remainder of the figure is identical to  FIG. 7 . As discussed above regarding  FIG. 17 , SAW 18  has been eliminated. 
         [0141]    Filter SAW 20  and switch SW 28  are retained from  FIG. 13  to handle band B 41   a . All other frequencies within bands B 40  and B 41  (excluding band B 41   a ) are filtered by filtering component F 506  and tuning component TUN 8 . 
         [0142]    Switch SW 32  is different from switch SW 26  in  FIG. 13 . Switch SW 32  is a SP 3 T switch, so that reception signals can be separated according to whether they are in the low portion of the tunable filter range (low band of the split band coverage), or in the high portion of the tunable filter range (high band of the split band coverage). If the received signal is in the low portion (B 40 ), then this is routed by switch SW 32  to RX 2  as signal S 504 . If the received signal is in the high portion (B 41   b , B 41   c , B 38 , XGP), then this signal is routed by switch SW 32  to RX 1  as signal S 502 . 
         [0143]    If the reception signal is in band B 41   a , then this signal is filtered by SAW 20 , and routed by switch SW 28  to RX 1  as signal S 502 . Thus, this reception signal in band B 41   a  is routed to RX 1 , the same as the reception signals in the high portion of the tunable filter range. All relatively high frequency reception signals are routed to RX 1 . 
         [0144]    In contrast, band B 40  is in the lower portion of the tunable filter range, and reception signals in this range are routed to RX 2  as signal S 504 . 
         [0145]    Thus,  FIG. 18  facilitates separate handling of received LTE TDD signals by a transceiver. This separate handling by the transceiver facilitates optimized matching by the transceiver, because the low portion is very different from the high portion (separated by almost 100 MHz). 
         [0146]    A single die may include duplexer DUPB 7 , switch SW 28 , switch SW 32 , tunable component TUN 8 , and switch SW 34 . Filter component FILT 506  may be located outside of the single die. This single die may be SOI (silicon on insulator). 
         [0147]    Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.