Tunable filter for LTE bands

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.

Claims

1. Communication circuitry comprising: a tunable filter comprising a tuning component and a filtering component that collectively filter within a first band when tuned to the first band and filter within a second band when tuned to the second band; a first amplifier configured to amplify a first transmission signal; a first switch configured to: in a first mode, receive the amplified first transmission signal and pass the amplified first transmission signal to the tunable filter; and in a second mode, receive a first reception signal from the tunable filter and pass the first reception signal towards a transceiver; an LTE (Long Term Evolution) band 40b filter that is one of a SAW (Surface Acoustic Wave) filter and a BAW (Bulk Acoustic Wave) filter; a second switch configured to: in the first mode, receive the first transmission signal and pass the first transmission signal to the LTE band 40b filter; and in the second mode, receive a second reception signal from the LTE band 40b filter and pass the second reception signal towards the transceiver; a second amplifier configured to amplify an LTE (Long Term Evolution) band 7 transmission signal; and a duplexer configured to receive the amplified LTE band 7 transmission signal; and wherein the tuning component and the first switch are located on a first die and the filtering component is not located on the first die.

2. The communication circuitry of claim 1 wherein: the first amplifier is configured to amplify the first transmission signal before the first transmission signal reaches the first switch; and the second amplifier is configured to amplify the LTE band 7 transmission signal before the LTE band 7 transmission signal reaches the duplexer.

3. The communication circuitry of claim 1 further comprising a first SOI (Silicon On Insulator) die, wherein: at least a portion of the first switch, the second switch, and the tuning component are located on the first SOI die; and the filtering component is not located on the first SOI die.

4. The communication circuitry of claim 3 further comprising a second SOI die that is distinct from the first SOI die.

5. The communication circuitry of claim 4 wherein the second SOI die comprises the first amplifier, the duplexer, and the second amplifier.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) 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.

(2) FIG. 1 illustrates a conventional communication circuit with its major components.

(3) FIG. 2 illustrates a conventional transceiver, diversity filters, and diversity switches from FIG. 1.

(4) FIG. 3 illustrates a conventional high band pad CKT8, high band filters CKT10, and high band switches CKT12 from FIG. 1.

(5) FIG. 4 illustrates a conventional single filter used for transmission and reception of a single band.

(6) FIGS. 5A-5D illustrate the use of a single filter (F114) for transmitting and receiving in band 38 for LTE-TDD communications.

(7) FIG. 6 illustrates using single filters (to transmit and receive) for multiple LTE bands.

(8) 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.

(9) FIG. 8 illustrates a manufacturing embodiment of FIG. 7.

(10) FIG. 9 illustrates some conventional bands of LTE-TDD (in MHz).

(11) FIG. 10 illustrates a conventional overlapping bandwidth approach for receiving signals in band B40 by overlapping two SAW (Surface Acoustic Wave) filters (SAW2 and SAW4) to filter the entire range of band B40.

(12) FIG. 11 is similar to FIG. 10, but illustrates a dedicated filter F510 for transmitting in band 41c.

(13) FIG. 12 illustrates using one tunable filter in combination with two SAW filters to achieve split band coverage around the ISM band.

(14) FIG. 13 illustrates using a tunable filter and two narrow edge SAW filters to provide split band coverage around a central band.

(15) FIG. 14 is similar to FIG. 13, except that filters SAW18 and SAW20 from FIG. 13 have been replace by (or merged into) diplexer DIP2. In this fashion, signal S410 replaces signals S404 and S406 from FIG. 13.

(16) FIG. 15 is similar to FIG. 12, except that SAW20 (2496 to 2565) has been replaced by a band 7 range (2496 to 2570) of band 7 duplexer DUPB7.

(17) FIG. 16 is similar to FIG. 13, except that band 41a (2496 to 2565) filter SAW20 has been deleted.

(18) FIG. 17 is similar to FIG. 12, except that the left portion of the tunable filter band (band 40a (2300 to 2370)) has been replaced by an extended left portion of the tunable filter band (band 40 (2300 to 2400)).

(19) FIG. 18 illustrates circuitry implementing tuning component TUN8 of FIG. 17, and illustrating a few additional features.

DETAILED DESCRIPTION

(20) 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.

(21) FIG. 7 illustrates an amplifier circuit CKT20 including tunable filter and an associated switch. The tunable filter may include filtering component F310 and tuning component TUN2.

(22) Tuning component TUN2 may be a variable capacitor or an array of capacitors, and may be located with associated switch SW24 on single die DIE8. The tuning component TUN2 and the associated switch SW24 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.

(23) The upper portion of amplifier circuit CKT20 is configured for band 7, and is identical to the top portion of high band pad CKT8 in FIG. 3. In transmit mode for band 7, amplifier CKT20 receives signal S2 (band 7 being transmitted from node B7 TX), passes this signal through capacitor CAP2 (to filter undesired very low frequency signals), amplifies this signal with amplifier PA2, and sends filtered amplified signal S2 to duplexer DUPB7. Duplexer DUPB7 sends the amplified signal towards main antenna ANTMAIN (not shown) as signal S52 in transmit mode.

(24) Alternatively, in receive mode for band 7, duplexer DUPB7 receives signal S52 from main antenna ANTMAIN, and sends this received signal as S50 towards a transceiver (not shown).

(25) Die DIE8 includes tuning component TUN2 and switch SW24.

(26) Starting at the lower left, capacitor CAP8 receives signal S320 (band B38 or B40 or B41 for transmission), and sends signal S322 to amplifier PA12. Amplifier PA12 sends signal S324 to throw T304 of switch SW24.

(27) In a transmitting configuration, switch SW24 throws signal 324 to single pole SP300. Then single pole SP300 sends signal S326 to filter F310. Filter F310 (in a first mode, or transmission mode) transmits signal S328 towards an antenna (not shown).

(28) Filter F310 is tunable, so that it may filter a band B38 signal, a band B40 signal, band XGP signal, or band B41 signal, depending upon how it is tuned. Tuning component TUN2 is part of filter F310, and may be located on a die holding switch SW24.

(29) In a receiving configuration, received signals are indicated by dashed lines. Received signal S328 (starting at the lower right, and moving towards the left) is received by tunable filter F310 (in a second mode), sent to single pole SP300 of switch SW24, thrown to throw T302, then sent downward as S330 towards a transceiver (not shown).

(30) Thus, tunable filter F310 may operate in a first mode transmitting in band B38, or (after switching from throw T304 to throw T302) in a second mode receiving band B38. After tuning to band B40, then tunable filter F310 may operate in a first mode transmitting in band B40, or (after switching from throw T304 to throw T302) a second mode receiving in band B40. In this fashion, tunable filter F310 serves the role of at least 4 different filters: transmit band B38, receive band 38, transmit band B40, and receiver band B40. Further, if filter F310 tunably filters for two bands, then the associated single switch SW24 performs switching functions for two bands (replacing switch SW20 and switch SW22 in FIG. 6).

(31) Coupled resonators (RES2 and RES4) 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.

(32) FIG. 8 illustrates a manufacturing embodiment of FIG. 7. In FIG. 8, circuit CKT22 is an embodiment of power amplifier circuit CKT20 of FIG. 7, and includes laminate (or substrate) LAM2, power amplifier die DIE10 (including amplifiers PA8 and PA10, not shown) on top of laminate LAM2, die DIE8 (including switch SW24 and tuning element TUN2, not shown) on top of laminate LAM2, resonator RES2, resonator RES4 (magnetically coupled to RES2), via VIA2, via VIA4, and bumps BUMP1 through BUMP4. Bumps BUMP1 through BUMP4 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.

(33) Power amplifier die DIE10 may be GaAs or CMOS or SiGe. Die DIE8 may include switch SW24 (not shown) for selecting between a first mode (transmitting or TX) and a second mode (receiving or RX), and may include a tunable component TUN2 (not shown) of tuning filter F310 (not shown). Tunable component TUN2 may include a tunable array of capacitors for tuning filter F310. Tunable filter F310 may be a bandpass TDD filter, may include RES2 and RES4, and may include tunable component TUN2 located on die DIE8.

(34) DIE8 and DIE10 may be a single package on a single laminate LAM2, as shown.

(35) 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.

(36) FIG. 9 illustrates some conventional bands of LTE-TDD (in MHz). Band B40 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 B41 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.

(37) Together, bands B40 and B41 may be described as a split-band range, because the combined range is split into a low band (B40) and a high band (B41) by the central band ISM which must be avoided or excluded.

(38) Band B41 encompasses bands XGP and B38. Band XGP (for Japan) ranges from 2545 to 2575 (bandwidth of 30 MHz). Band B38 (for European Union) ranges from 2570 to 2620 (bandwidth of 50 MHz).

(39) 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.

(40) Thus, it is difficult to build a single filter for receiving in band B40 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 B41 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 B40, as shown in FIG. 10.

(41) FIG. 10 illustrates a conventional overlapping bandwidth approach for receiving signals. This approach receives signals in band B40 (low target band) and in band B41 (high target band). The ISM band (exclusion band) is intentionally excluded from (filtered out of) the received signals.

(42) SAW filters provide good edge characteristics. The upper edge (at 2400 MHz) of SAW filter SAW4 coincides with the upper edge of band B40 (2400 MHz). SAW4 passes signals at the upper edge of band B40 (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.

(43) SAW6 similarly (or symmetrically) provides good edge characteristics, passing signals at the lower edge of band B41 (at 2496 MHz), and excluding signals at the high edge of the exclusion band (2483 MHz).

(44) Receiving (RX) in band B40 is performed by using two overlapping SAW (Surface Acoustic Wave) filters (SAW2 and SAW4) to filter the entire range of band B40.

(45) Specifically, band B40 is received by an overlapping combination of B40a (2300 to 2370 MHz, using filter SAW2) and band B40b (2350 to 2400 MHz, using filter SAW4). These two bands overlap by 20 MHz due to a 20 MHz maximum modulation bandwidth for SAW filters.

(46) Similarly, band B41 is received by overlapping combinations of band B41a (2496 to 2565 MHz, by SAW6), band B38x (2545 to 2640 MHz, by SAW8), and band B7 (2620 to 2690 MHz, by filter F410). Band B38x overlaps with band B41a by 20 MHz, and overlaps with band B7 by 20 MHz, due to a 20 MHz maximum modulation bandwidth for SAW filters.

(47) Filter F410 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 B41 (in addition to being used to filter band B7) In other words, this filter may be defined as filtering band B7 and band B41c.

(48) FIG. 11 illustrates a transmitting configuration similar to the receiving configuration of FIG. 10, and illustrates a dedicated filter F510 for transmitting in band B41c. SAW filters SAW10 and SAW12 overlap to receive all of band B40. Filters SAW14, SAW16, and F510 overlap to transmit all of band B41.

(49) 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.

(50) 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 B40 (low target band), ISM (to be avoided), and B41 (high target band). As previously discussed, these filters may be used for receiving and for transmitting in TDD, with appropriate switching.

(51) A tunable filter TUNFILT2 is configured to cover a low tunable band and a high tunable band. In FIG. 12, the low tunable band is labeled B40a (2300 MHz to 2370 MHz, thus staying at least 20 MHz away from the lower edge of the exclusion band band).

(52) SAW filter SAW4 (band B40b) overlaps with the low tunable band (by 20 MHz), and combines with the low tunable band to completely cover low target band (B40, from 2300 to 2400 MHz).

(53) As discussed in previous figures, a SAW filter (SAW4) is used to filter the upper edge of the low target band, adjacent to the lower edge of the exclusion band.

(54) Tunable filter TUNFILT2 is also configured to cover most of the upper part of band B41 (2545 to 2690, or Bands B41b, B41c, XGP, and B38), thus staying at least 20 MHz away from the top of the exclusion band). See right portion of range of tuning component TUN4.

(55) As discussed above, in order to fully cover band B40, SAW filter SAW4 filters band B40b (2350 to 2400). This range overlaps with band B40a 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 SAW18 may be described as a narrow edge filter, because it has a relatively narrow range and because it filters the upper edge of band B40.

(56) Similarly, in order to fully cover band B41 (a high band), SAW filter SAW20 filters band B41a (2496 to 2565). This range overlaps with TUNFILT2 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 SAW20 may also be described as a narrow edge filter.

(57) 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 CKT24 is very similar to amplifier circuit CKT20 in FIG. 7, but is modified to provide split band coverage.

(58) 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 b38.

(59) For the purpose of this specification, the term SPDT should be interpreted broadly. For example, a SP3T (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.

(60) Transmission signal S324 (including bands B38, B40, and B41) routes to three switches: SW26, SW28, and SW30. 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).

(61) When transmitting in the tunable filter range (split range) of 2300-2370 or 2545-2690, then switch SW26 receives signal S324 at throw TbTX and routes this signal to single pole SPA. Single pole SPA sends this signal to tunable filter TUN4. Tunable filter TUN4 filters signal S324 to pass band B40a, or filters to pass bands B41b and B41c, or filters to pass band B38, or filters to pass band XGP (depending upon how tunable filter TUN4 is tuned). Tunable filter TUN4 passes a tuned signal S402 towards main antenna ANTMAIN (not shown).

(62) Tunable filter TUN4 may include a tunable component TUN6 that may be located on a die with switch SW26, similar to the discussions above for FIGS. 7 and 8. Alternatively, component TUN6 may be a control portion that controls tunable filter TUN4.

(63) In the reverse direction, when receiving in the tunable filter range (split range) of 2300-2370 or 2545-2690, then tunable filter TUN4 receives signal S402 from main antenna ANTMAIN (not shown). Tunable filter TUN4 filters signal S324 to pass band B40a, or filters to pass bands B41b and B41c, or filters to pass band B38, or filters to pass band XGP (depending upon the tuning of tunable filter TUN4).

(64) Tunable filter TUN4 passes a filtered signal S408 to pole SPA of switch SW26. Pole SPA passes (not shown) the filtered signal S408 to throw TARX. Throw TARX sends filtered signal S408 to a transceiver (not shown). In FIG. 13, switch SW26 is shown in the transmission position, but may be switched to throw TARX for receiving in TDD.

(65) For band B41a, switch SW28 acts similarly to switch SW26. Filter SAW20 filters transmission of signal S324 or reception of signal S404 in band B41a, depending upon the selection of switch SW28.

(66) For band b40b, switch SW30 acts similarly to switch SW28. Filter SAW18 filters transmission of signal S324 or reception of signal S406 in band B40b, depending upon the selection of switch SW230.

(67) FIG. 14 is similar to FIG. 13, except that filters SAW18 and SAW20 from FIG. 13 have been replace by (or merged into) diplexer DIP2. In this fashion, signal S410 replaces signals S404 and S406 from FIG. 13.

(68) FIG. 15 is similar to FIG. 12, except that SAW20 (2496 to 2565) has been replaced by a band B7 range (2496 to 2570) of band B7 duplexer DUPB7.

(69) FIG. 16 is similar to FIG. 13, except that band 41a (2496 to 2565) filter SAW20 has been deleted. The filtering duties of SAW20 have been effectively shouldered by band 7 (2496 to 2570) duplexer DUPB7.

(70) To summarize, FIG. 16 employs one tunable filter TUN4 and one SAW filter SAW18 to accomplish the filtering that previously required eight filters in FIG. 3 (F54, F55, F57, F58, F37, F39, F63, and F65).

(71) FIG. 17 is similar to FIG. 12, except that the left portion of the tunable filter band (band B40a (2300 to 2370)) has been replaced by an extended left portion of the tunable filter band cover all of band B40 (band B40 (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 TUNFILT4 (instead of TUNFILT2 as in FIG. 15). This extension of the left portion of the tunable filter band eliminates the need for SAW18 of FIG. 12.

(72) FIG. 18 illustrates filtering component F506 and tuning component TUN8 of tunable filter TUNFILT4 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, SAW18 has been eliminated.

(73) Filter SAW20 and switch SW28 are retained from FIG. 13 to handle band B41a. All other frequencies within bands B40 and B41 (excluding band B41a) are filtered by filtering component F506 and tuning component TUN8.

(74) Switch SW32 is different from switch SW26 in FIG. 13. Switch SW32 is a SP3T 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 (B40), then this is routed by switch SW32 to RX2 as signal S504. If the received signal is in the high portion (B41b, B41c, B38, XGP), then this signal is routed by switch SW32 to RX1 as signal S502.

(75) If the reception signal is in band B41a, then this signal is filtered by SAW20, and routed by switch SW28 to RX1 as signal S502. Thus, this reception signal in band B41a is routed to RX1, the same as the reception signals in the high portion of the tunable filter range. All relatively high frequency reception signals are routed to RX1.

(76) In contrast, band B40 is in the lower portion of the tunable filter range, and reception signals in this range are routed to RX2 as signal S504.

(77) 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).

(78) A single die may include duplexer DUPB7, switch SW28, switch SW32, tunable component TUN8, and switch SW34. Filter component FILT506 may be located outside of the single die. This single die may be SOI (silicon on insulator).

(79) 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.