Switchless band separation for transceivers

A system includes a plurality of band pass filters to pass signals in separated frequency bands to or from an antenna. A matching network provides characteristic impedances. The system is designed such that the configuration of the matching network and BPFs provides high impedance to the band pass filters for those routing paths other than the band pass path as these routing paths do not transmit or receive the signals at this particular pass band. The system is further designed such that the configuration of the matching network and BPFs provides minimal insertion loss for the band pass path of for transmission and receipt of signals at this particular pass band, where each routing path has a corresponding pass band. The matching network is for coupling to an amplifier, when frequency separation is needed at the output of the amplifier to the BPFs. In one embodiment an impedance network tunes the impedance by using varying length transmission lines.

BACKGROUND

Conventional multiband transceivers use a single antenna for both transmit and receive signals. Several switches and/or duplexers are used to switch between multiple signal bands. In some transceivers, additional switches may be used for selecting transmit Tx and receive Rx paths. A duplexer in such as conventional system typically includes a pair of filters for Tx and Rx paths to transmit and process the Tx and Rx signals simultaneously.

DETAILED DESCRIPTION

As described herein, a system includes a plurality of Band Pass Filters (BPFs) to pass signals in separated frequency bands to or from an antenna. A first impedance network couples to the antenna and provides impedances to the band pass filters adapted to build high impedance for the paths of bands of the BPFs that do not transmit or receive the signals at the frequencies of interest. A second impedance network is for coupling to a power amplifier and provides impedances to the band pass filters adapted to build high impedance for the paths of bands of the BPFs that do not transmit or receive the signals at the frequencies of interest. Note that the first and second impedance networks may be considered different portions of a single impedance network.

Signals to be transmitted or received are provided separate impedance tuned paths with narrow band BPFs between signal processing circuitry and one or more antennas. Each impedance tuned path operates to provide low impedance to signals in a desired band, and high impedance to signals outside the desired band. Use of the impedance tuned paths in conjunction with the band pass filters provides the ability to use antennas for multiple bands without the need for switches or multiplexers.

In various embodiments, a transceiver includes separate Tx and Rx antennas and wideband power amplifiers, each supporting the multiple bands, without relying on switches for the signal path selection. Separated Tx and Rx antennas may provide better isolation between Tx and Rx paths than a single antenna with multiplexers. Further, embodiments allow for small frequency separations between the Tx bands.

In one embodiment, each impedance tuned path provides an impedance that transitions between an optimal impedance for transmitting signals having frequencies corresponding to the band pass filter band, and transitions to an open circuit for frequencies outside the band. The tuned impedance paths act as through transmission lines matched to a system characteristic impedance, e.g., 50Ω, thereby passing signals at desired frequencies without signal mixing but with maximum power transfer.

In one embodiment, a system includes a plurality of band pass filters and a matching network. The BPFs are to pass signals in separated frequency bands to or from an antenna. The matching network is structured to provide impedances to the plurality of BPFs. The matching network is also structured to route signals to each of the plurality of band pass filters as a function of signal frequency. In this way, each path has a pass frequency band, wherein frequencies outside that pass frequency band are routed to other paths. In some embodiments, the matching network includes a plurality of impedance tuned paths, wherein each of the impedance tuned paths provides characteristic impedance to signals in a pass frequency band, and high impedance to the paths outside the pass frequency band path, wherein each impedance tuned path having a different pass frequency band.

In various embodiments, the impedance paths may include a conventional microstrip having desired transmission line length to vary impedance, a phase shifter, such as a transmission line, a pi network, a T network, or a composite right/left hand (CRLH) structure which behaves as a Metamaterial, such structures are referred to as Metamaterial, MTM, or CRLH structures.

In some embodiments, a front end module and antenna system using wideband Power Amplifiers (PAs) and include a radio frequency integrated circuit (RFIC) with integrated Low Noise Amplifiers (LNAs) and the PAs and antennas are coupled to band pass filters by transmit and receive impedance matching networks respectively. Separate transmit and receive antennas may be coupled to the Band Pass Filter (BPF) or a single antenna multiplexed to the BPFs may be used. In various embodiments, Surface Acoustic Wave (SAW) filters, Bulk Acoustic Wave (BAW) filters and Film Bulk Acoustic Resonators (FBAR) are examples suitable to use as BPFs as they have sufficient quality factors to provide relatively small band separations. Out-of-band rejection and minimal insertion loss in the pass band are provided by SAWs, BAWs or FBARs. The combination of such BPFs together with the impedance matching network provides equivalent multiplexer functionality. In one embodiment, multiband Tx and Rx antennas may be physically separated to provide better isolation. Further, some embodiments may be configured to provide Tx-to-Rx isolation in the Tx band in the Rx side as well as Tx-to-Rx isolation in the Rx band in the Tx side in a full duplex system based on the band pass filters and impedance matching. Such wideband embodiments may cover various frequency bands associated with over-the-air protocols, such as Universal Mobile Telecommunications Systems (UMTS), Long Term Evolution (LTE), Code Division-Multiple Access (CDMA), and Global System for Mobile Communications (GSM) or others.

An example of a conventional multiband FEM and antenna system uses a single antenna for both transmit and receive signals covering the multi bands and multi-modes, and includes switches and an antenna switch module to select signal paths as well as duplexers to share one antenna coupled to the Tx and Rx paths.FIG. 1illustrates a prior art system10, having a wideband Power Amplifier (PA)12, Such a conventional system includes switching mechanisms, such as switches14,18, coupled to multiple duplexers16for Tx and Rx paths to transmit and process the Tx and Rx signals through one antenna20. Such a system processes multiple band frequencies, however, the configuration incurs excess cost adding to complexity, insertion loss, and space required to build such devices. In current wireless application, there is strong pressure to achieve smaller device size and reduced complexity.

Examples and implementations of multiband and multimode FEM with single antenna systems are given, for example, in the US patent Pub. No. US 2007/0243832 A1, entitled “MULTIMODE/MULTIBAND MOBILE STATION AND METHOD FOR OPERATING THE SAME,” published on Oct. 18, 2007, and in the Proceeding of the 2009 IEEE ISSCC (International Solid-State Circuits Conference), pp. 116-118, entitled “Single-Chip Multiband WCDMA/HSDPA/HSUPA/EGPRS Transceiver with Diversity Receiver and 3G DigRF Interface Without SAW Filters in Transmitter/3G Receiver Paths,” by Tirdad Sowlati, et al., published on Feb. 9, 2009. In contrast, the system ofFIG. 2includes separate Tx and Rx antennas and wideband Pas (Low Band and High Band), each supporting the multiple bands, without relying on switches for the signal path selection and replaces switches in a conventional system with separate band pass filters (BPFs). Separated Tx and Rx antennas may provide better isolation between Tx and Rx paths than a single antenna with duplexers. Examples and implementations of FEM and antenna systems with separate Tx and Rx antennas without switches are given, for example, in the U.S. patent application Ser. No. 12/640,969, entitled “RF Front-End Modules and Antenna Systems,” filed on Dec. 17, 2009.

FIG. 2illustrates a block diagram of an example of an RF front-end module (FEM) and antenna system50based on wideband power amplifiers (PAs) and multiple antennas according to example embodiments. The system50includes an RFIC74and is coupled to a transmit (Tx) antenna52and a receive (Rx) antenna80. The system50may be used to support a wide frequency band including multiple sub-bands, such as up to ten Long Term Evolution (LTE)/Universal Mobile Telecommunications System (UMTS) bands and four Global System for Mobile Communications (GSM) bands, for example. The RFIC74, the Tx antenna52, PA62, and PA72are configured to support a wideband frequency range for a variety of applications. For simplicity, four bands in the Tx path and four bands in the Rx path are considered in the example shown inFIG. 2. The multiband Tx and Rx antennas52,80used in the system ofFIG. 2may be designed based on Composite Right/Left Handed (CRLH) structures, such as described in the U.S. patent application Ser. No. 11/741,674 entitled “Antennas, Devices and Systems based on Metamaterial Structures,” filed on Apr. 27, 2007; U.S. Pat. No. 7,592,952 entitled “Antennas Based on Metamaterial Structures,” issued on Sep. 22, 2009; U.S. patent application Ser. No. 12/250,477 entitled “Single-Layer Metallization and Via-Less Metamaterial Structures,” filed on Oct. 13, 2008; U.S. patent application Ser. No. 12/270,410 entitled “Metamaterial Structures with Multilayer Metallization and Via,” filed on Nov. 13, 2008; and U.S. patent application Ser. No. 12/465,571 entitled “Non-Planar Metamaterial Antenna Structures,” filed on May 13, 2009. Examples of wideband PAs include class-J PAs and PAs with a distributed power architecture. Examples and implementations of metamaterial-based class-J PAs are given for example, in the U.S. patent application Ser. No. 12/708,437 entitled “Metamaterial Power Amplifier Systems” filed on Feb. 18, 2010 (claiming priority to the U.S. Provisional Patent Application Ser. No. 61/153,398 entitled “A Metamaterial Power Amplifier System and Method for Generating Highly Efficient and Linear Multi-Band Power Amplifiers,” filed on Feb. 18, 2009. Examples and implementations of PAs with a distributed power architecture, such as Adaptive Current-draw Envelop-detection PA (ACE PA), are given, for example, in the U.S. patent application Ser. No. 12/473,228 entitled “RF Power Amplifiers with Linearization,” filed on May 27, 2009.

Various embodiments may be extended to a multiport antenna configuration to separate the high band and low band without using switches, for example, for a wider band coverage. Examples and implementations of multiport antennas are given, for example, in the US Provisional Application Serial No. 61/259,589 entitled “Multiport Frequency band Coupled Antennas,” filed on Nov. 9, 2009.

In the system ofFIG. 2, the PA62is used to amplify signals in a high band (HB) that includes two sub-bands, Band1and Band2; the PA72is used to amplify signals in a low band (LB) that includes two sub-bands, Band3and Band4. The input signals in the sub-bands Band1and Band2may be sent to the PA62simultaneously or in different time intervals. The amplified HB signals are then sent to a dual band filter60for one of the HB Tx bands. The filter60includes two separate branches from the single input port coupled to PA62, wherein each branch has a BPF56and a Phase Shifter (PS)58on the input side of the BPF56and a PS54on the output side of the BPF56. The two BPFs56are configured to perform out-of-band rejections for respective bands, i.e., Band1and Band2, to remove unwanted signals. The two PSs58on the input side of the BPFs56are configured to provide frequency band selection and direct the signals in the respective bands to the right paths based on phase adjustments, as explained later in this document. These branches are then connected to a feed point so that the signals in the Band1and the signals in the Band2are sent to the Tx antenna52. The PS54is coupled between the output of each BPF56in the dual band filter60and the feed point to antenna52. The output side PS54in the dual band filter60is configured to direct the signals in the respective bands to the Tx antenna52and prevent signal leakages into wrong paths.

Similar to the HB processing, the amplified LB signals are sent to a dual band filter64for the LB Tx bands, which includes a BPF68and two phase shifters,66,70on each branch. Signals are processed in dual band filter64and then sent to the Tx antenna52.

The Rx antenna80is configured to receive signals in the Rx path over the four bands, Bandl (HB), Band2(HB), Band3(LB) and Band4(LB). The received HB signals are sent to dual band diplexer82, the received LB signals are sent to a dual band diplexer84, each having two separate branches to accommodate each of the different frequency bands. For example, each path of diplexer82(HB), has Rx BPFs88and PSs86on the input side of the BPF, coupled to the RFIC74to output the received signals. The BPFs88are configured to perform out-of-band rejections for the respective bands to remove unwanted signals. The PSs86are configured to provide frequency band selection and direct the signals in the respective bands to the proper paths based on phase, as explained later. Furthermore, the combination of BPFs88and PSs86is configured to provide adequate isolation to prevent power leakage among different paths. Examples and implementations of isolation circuits for FEM and antenna systems for multiband operations are given for example, in the U.S. patent application Ser. No. 12/640,969, entitled “RF Front-End Modules and Antenna Systems,” filed on Dec. 17, 2009. Similarly, the received LB signals are processed with a diplexer having two BPFs coupled with two phase shifters.

Configurations such as those ofFIG. 2, provide a solution which avoids the use of switching in handling multiple frequency bands with one transmit antenna and one receive antenna. Other configurations may be similarly configured to accommodate a variety of frequency bands and satisfy a variety of specifications.

FIG. 3illustrates a block diagram of another example of an RF FEM and antenna system based on wideband PAs and multiple antennas according to various embodiments. For instance, two antennas, one for transmit and the other for receive may be used. The system150ofFIG. 3is similar to system50ofFIG. 2, but is additionally configured to handle a fifth Tx band, Band5. In one example, Band5may be much higher than the Tx Band1and Band2, such as a 2.6GHz band. A PA190operable for Band5is coupled to RFIC174. The system ofFIG. 3is configured also to handle the corresponding fifth Rx band, Band5. In the illustrated example, both the Tx antenna152and the Rx antenna180are configured to have a tri-port coupling to the components of the FEM. For clarity of understanding the dual band filters160and164and diplexers182and184are shown as functional blocks, and may be configured as filters60and64and diplexers82and84ofFIG. 2.

FIG. 4illustrates a block diagram of a similar example of an RF FEM and antenna system150based on wideband PAs262,272, filters260,264, diplexers282,284, RFIC274and multiple Tx and Rx antennas252,280, according to example embodiments. In this case, Band5transmissions use designated Tx and Rx antennas,294,288, making the total number of antennas four. System250is similar to system150ofFIG. 3, with Band5having separate antennas and signal paths.

FIG. 5illustrates a block diagram of yet another example of an RF FEM and antenna system based on wideband PAs and multiple antennas according to to various embodiments. Here the HB includes two frequency bands, the LB includes three frequency bands and there is an additional Band6, which is processed individually. System350is similar to systems150,250, wherein dual filter360is similar to filter60ofFIG. 2, RFIC374is similar to RFIC74and diplexer382is similar to diplexer82ofFIG. 2. The HB signals are processed by Tx HB PA362, dual filter360and antenna352. The Band6signals are processed by the PA390, BPF392and antenna352. The LB Tx band has three sub-bands in this example. Accordingly, the LB PA372is configured to operate for the three bands, and is coupled to a tri-band filter364for the LB Tx band, which includes three paths, each having a BPF368positioned between two PSs366,370. All of the Tx bands are transmitted via antenna352.

Continuing withFIG. 5, the antenna380receives signals from the HB, LB and Band6. For the LB Rx band, a triplexer384is used in the system to handle the three sub-bands in the LB Rx band; the triplexer384includes a BPF390and a PS388on each branch. The diplexer382is similar to diplexer82ofFIG. 2and handles the two HB frequency bands. Band6is received and processed by BPF386.

FIG. 6illustrates a block diagram of yet another example of an RF FEM and antenna system450based on wideband PAs462,472, an RFIC474, and having a Tx antenna452, and a Rx antenna480according to an example embodiment. In this example, the input and output PSs are integrated with the BPF to form PS-integrated BPF456,468on each branch of each of the dual-band filters460,464for the Tx bands. Similarly, the PS is integrated with the BPF488on one branch in each of the diplexers482,484for the Rx bands. Alternatively, a BPF may be designed for the right phase adjustment to route the signal properly instead of using a dedicated phase shifter.

FIG. 7illustrates a block diagram of an example of an RF FEM and antenna system550based on wideband PAs562,570, an RFIC572, and a single antenna552according to an example embodiment. In this example, the single antenna552is used for the multiband operation for both Tx and Rx transmissions, and a duplexers556,558,564,566are used for the Tx and Rx transmissions in respective bands. Thus, the signal path selection is carried out by a switch denoted SPXT554configured between the duplexers and the antenna552. For the HB band, two PSs560along with duplexers556,558are used to split the signals from the HB PA562into two sub-bands. The PSs560are coupled to respective duplexers,556,558. The PSs may be integrated in the PA package, duplexer package, or both. The LB signals are processed in a similar manner, wherein Tx signals are provided from PA570to PS568, each coupled to one of duplexers564,566.

FIG. 8illustrates a block diagram of another example of an RF FEM and antenna system650based on wideband PAs662,670, an RFIC672and a single antenna652according to an example embodiment. In this example, the duplexers656,658,664,666in each of the HB and LB bands are integrated with the corresponding PA. The PSs may be already integrated in the PA package, duplexer package, or both. Furthermore, the Tx BPF of the duplexers may be designed for the right phase adjustment to route the signal properly instead of using a dedicated phase shifter.

FIG. 9schematically illustrates the signal routing scheme realized by the phase shifters in the systems described above. For simplicity, the Tx signal transmission associated with one PA is shown in this figure. The band includes two sub-bands, which are represented by frequencies f1and f2, in this example, but may include three or more sub-bands. The signals in this band are inputted from the port P1to the PA752, which is a wideband PA capable of handling the two sub-bands f1and f2. The input signals may be fed simultaneously or at different time intervals. However, to avoid inter-modulations associated with the PA752, the signals in the different sub-bands may be fed at different time intervals. Furthermore, service standards typically use only one sub-band at a time interval. However, with the possible advent of new technologies and new market demands, the transmission scheme may evolve to include simultaneous transmission of multiband signals from a single port. The amplified signals f1or f2are outputted from the PA204. In order to pass the signal with f1through the upper branch to the port P2, the phase of the phase shifter PS2756may be configured to transform an impedance (e.g., some value away from 50Ω) at Pt4to an open (or some high impedance) at Pt3at frequency f1, thereby acting as an impedance transformer. The impedance at Pt4at frequency f1is much different from the characteristic impedance of a phase shifter, i.e., some value way from 50Ω. Thus, it is possible for the phase shifter to transform the impedance from the impedance at Pt4to an open (or high impedance) at Pt3. In this configuration, the lower branch is decoupled from the signal path so that the phase shifter PS1754acts as a through transmission line matched to an characteristic impedance, e.g., 50Ω, thereby passing the f1signal without signal leaking but with maximum power transfer. Similarly, in order to pass the signal with f2through the lower branch to the port P3, the phase of the phase shifter PS1754may be configured to transform an impedance (e.g., some value different from 50 Ω) at the Pt2to an open (or some high impedance) at the Pt1at frequency f2. In this configuration, the upper branch is decoupled from the signal path so that the phase shifter PS2756acts as a through transmission line matched to an characteristic impedance, e.g., 50Ω, thereby passing the f2signal without signal leaking but with maximum power transfer. The phase shifter configured as above may be implemented using a conventional microstrip, a pi network, a T network, or a CRLH structure.

According to various embodiment, the FEM and antenna system including wideband PAs is structured by means of the frequency band selection scheme based on PSs, thereby eliminating active switches and associated drive circuitry. Surface Acoustic Wave (SAW) filters, Bulk Acoustic Wave (BAW) filters and Film Bulk Acoustic Resonators (FBAR) are examples suitable to use for the BPFs in systems having relatively small band separations. This is because good out-of-band rejection and insertion loss in the pass band are achievable using SAWs, BAWs or FBARs, which are capable of providing the multiplexer function in conjunction with the phase shifters. In the multiple-antenna systems described in this document, the multiband Tx and Rx antennas are physically separated and thus provide better isolation. Further, some of the present systems are configured to provide the Tx to Rx isolation in the Tx band and the Tx to Rx isolation in the Rx band in the full duplex system based on the BPFs and PSs. The wideband may cover UMTS, LTE, and GSM bands or various other communication bands.

It is possible to integrate the input and output phase shifters in a BPF package. The phase shifters on the input side may be integrated in a PA. The phase shifters on the output side may be integrated as a part of the antenna feeding point. The multiband multimode FEM system using wideband PAs and a combination of BPFs and PSs as a dual-band element may be extended to a tri-band element. For example, the tri-port multiband antenna having a low-band for 700-900MHz, a mid-band for 1700-1980MHz, and a high-band for 2300-2700MHz may allow this system to be extended to a tri-band platform.

FIG. 10further illustrates a block diagram of a transmit portion of a transceiver1100. The block diagram is part of a FEM including PA1110coupled to matching networks1130,1131,1135, and1137. The matching networks may incorporate impedance elements and are configured in pairs on each side of a filter. For example, the matching network elements1130,1131is configured for filter1140, while the matching network elements1135,1127are configured for filter1145. Signals in transceiver1100are transmitted by antenna1155. The PA1110receives signals to be transmitted, amplifies the signals, and provides them on an output line1115. The amplified signals on output line1115may contain two or more signals to be transmitted. Each signal resides within a separate frequency band. In the case of two signals, as illustrated, the signals follow two separate impedance paths1120and1125. Each path experiences an input impedance, which is configured to act as an open circuit for frequencies outside the pass band of a given filter. The transceiver components and conductive paths and connections may be incorporated in an integrated circuit, or may be printed on a circuit board.

The matching networks1130,1131and1135,1137are tuned to combine with the band pass filters to provide a tuned impedance path to provide low insertion loss for signals within the corresponding path of the pass band and high impedance for other paths. The tuned impedance paths act as transmission lines matched to a system characteristic impedance, e.g., 50Ω, thereby passing signals at desired frequencies without signal leaking but with maximum power transfer. Line1150provides a path for the output of networks1131,1137to antenna1155.

FIG. 11is a block diagram of a transceiver system1500with multiple paths (two are illustrated, but any number may be implemented) coupled to a multiplexer for use of a single radiating element or antenna1505. Each path coupled to the multiplexer includes a matching-integrated filter for processing signals. The system1500may be implemented in some of the examples described herein. Filters1515,1520input to multiplexer1510.

FIG. 12illustrates an example embodiment of a front end portion of a multiple band transceiver having separate high and low band paths. The circuit1600includes an RFIC1602which prepares transmission signals for communication over the air via the antennas1610,1612,1614,1616. The RFIC1602may include LNA(s), PA(s) and or other signal processing circuitry. The RFIC1602is configured to route both Tx and Rx signals as well as high band and low band signals. The Tx paths are routed through PAs1650,1652,1654and antennas1614,1616, according to frequency band. As illustrated, the circuit1600is configured and designed to process frequency bands identified as Band1through Band5, each band having a designated Tx and Rx portion. Band5signals are processed by PA1650and the amplified signals are filtered by a single band BPF1660, then provided to antenna element1616. The BPF1660according to one embodiment is configured with multiple BPFs (not shown) configured in parallel, and each having a pair of phase shifters (not shown) configured at each port, input and output.

Bands1and2are processed by PA1652and the amplified signals are filtered by a multi-band BPF1662, then provided to antenna element1614. The BPF1662according to one embodiment is configured with multiple BPFs (not shown) configured in parallel, and each having a pair of phase shifters (not shown) coupled at each port, input and output.

Bands3and4are processed by PA1654and the amplified signals are filtered by a multi-band BPF1664, then provided to antenna element1614. The signals in bands3and4share antenna1614with signals in band1and2. The BPF1664according to one embodiment is configured with multiple BPFs (not shown) configured in parallel, and each having a pair of phase shifters (not shown) coupled at each port, input and output. The embodiments and configurations discussed throughout this document may be combined and used in a variety of combinations to accommodate a variety of bands and operating criteria.

Receive processing is done by way of two antennas1612,1614. The circuit1600includes multiple BPFs1620,1622,1624,1626,1628, each filtering a desired frequency of a received signal for the associated frequency band of bands1,2,3,4, and5. Antenna1612is coupled directly to BPF1620which filters out band1signals. The filtered band1signals are provided to RFIC1602for further processing. Antenna1610is coupled to two paths, wherein a first path provides received signals to Phase Shifter (PS)1634and PS1630, and the second path provides received signals to PS1632and PS1634. The BPF1622filters band2signals; BPF1624filters band3signals; BPF1626filters band4signals; BPF1628filters band5signals. Each path further includes an LNA1670,1672,1674,1676,1678. Application of impedance elements is adapted to cause high impedance of routing paths for other paths at the pass frequencies of the BPF. In the Tx paths, the impedance matching networks may coupled to an amplifier, such as a PA. The impedances may be implemented as a network of components in some embodiments.

The matching networks and impedance elements are designed and configured according to the frequency bands and components of a given system. While various configurations are provided, there are a variety of others which may be used. The matching network may employ any of a variety of techniques and components which are adapted to provide an input impedance that provides high impedance for undesired routing paths.

Only a few implementations are disclosed. However, it is understood that variations and enhancements may be made. In some embodiments, CRLH and MTM components are incorporated to improve performance and reduce the footprint of the circuitry. For example, one or more antennas may be implemented using CRLH structures. The circuitry and examples described herein may be particularly applicable to devices supporting a variety of over-the-air protocols and services, such as a wireless device supporting cellular communications, Wi-Fi local communications, GPS, and Bluetooth, or combinations of these. Such devices may reuse antennas or other components by implementation of additional elements.