WO2017041814A1

WO2017041814A1 - Filter super-positioning for carrier aggregation

Info

Publication number: WO2017041814A1
Application number: PCT/EP2015/070339
Authority: WO
Inventors: Dror Regev; Shimi Shilo; Doron Ezri; Genadiy Tsodik; Junping Zhang; Gengen HU; Dong Liang; Yannan MIAO
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2015-09-07
Filing date: 2015-09-07
Publication date: 2017-03-16
Also published as: CN107949987B; CN107949987A

Abstract

A receiver system for generating filtered signals includes a frequency converter and a filter unit. The frequency converter includes a local oscillator. The frequency converter receives radio frequency signals within a first frequency bandwidth and shifts the radio frequency signals to a second frequency bandwidth. The filter unit filters the shifted signals by applying a derived band-pass filter (BPF). The derived BPF is generated by superpositioning at least one BPF and at least one band-stop BSF.

Description

FILTER SUPER-POSITIONING FOR CARRIER AGGREGATION

BACKGROUND The present invention, in some embodiments thereof, relates to processing carrier aggregated signals and, more specifically, but not exclusively, to filtering carrier aggregated signals.

Carrier aggregation (CA) in wireless communications is becoming a key approach to increasing the bandwidth and data rate as well as utilizing an optimally fragmented spectrum available in wireless communications (e.g., LTE, Wi-Fi).

The following types of CA are supported in modern wireless communications standards'.

i) Intra-band contiguous CA;

ii) Intra-band non-contiguous (NC) CA; and

iii) Inter-band CA.

The aggregated component carriers may all be of a different bandwidth and each may be transmitted using a different power level. Fig. 1 illustrates the three types of CA.

Non-Contiguous carrier aggregation (NC CA) presents many challenges for several reasons:

i) Wide total processing bandwidth (BW) of the aggregated carriers, possibly spanning an entire band with interfering signals between desired carriers. ii) Data rate and Error Vector Module (EVM) requirements for LTE and 802.1 lac employing high order QAMs are already stringent and CA influence further enhances requirements for higher EVM performance.

iii) EVM requirements for transceivers supporting CA target full performance per each component carrier with minimal mutual interference degradations. iv) CA in receive mode must consider blockers in-band and out-of-band as well as carriers with different received bandwidths and amplitudes.

Fig. 2 illustrates the difficulties of wide processing bandwidth, mutual interference and in-band blockers. CA includes both multiple local oscillator (LO) and single LO receiver solutions. Single LO implementations have the advantage of requiring only one LO synthesizer circuitry, without LO pulling and/or coupling risks.

Some prior-art processing methods for aggregating different receiver channels span the entire frequency band to process multiple carriers simultaneously, as shown in Fig. 3. Down-conversion units may employ one of the conventional topologies:

1) Super-heterodyne;

2) Low intermediate frequency (IF); or

3) Direct conversion with in-phase and quadrature (IQ) orthogonal channels. Wide -band direct conversion has several disadvantages. The wideband filter does not reject in-band blockers (as shown in Fig. 4), which may degrade signal purity and/or saturate baseband (BB) circuitry and the analog to digital converter (ADC). A wideband ADC having high dynamic rage and a large number of received bits is required.

The article "Reconfigurable blocker-resilient receiver with concurrent dual- band carrier aggregation" by Run Chen and Hashemi H. of Univ. of Southern California, Los Angeles, CA, USA, presents a technique for shifting filter center frequency symmetrically by ± Af to yield two low selectivity C filters (as shown in Fig. 5).

A second article, Reconfigurable SDR Receiver with Enhanced Front-end Frequency Selectivity Suitable for Intra-Band and Inter-Band Carrier Aggregation" by Run Chen and Hashemi H. of Univ. of Southern California, Los Angeles, CA, USA presents a schematic technique for aggregating three component carriers to different frequency shifts. Second order RC filters are shifted in frequency to three different positive and negative frequencies, as illustrated in Figure 6A. Band-pass filter (BPF) selectivity is enhanced to second order. A second order notch filter is used at DC. Additionally, a known technique was used to invert the impedance of the shifted filters and aggregate the BPFs in the current domain, as shown in Fig. 6B.

In both of the above solutions, the filters are narrow band and may not be wide enough for advanced wireless communication techniques such as CA. The frequency shift Af is limited in frequency, and increasing Af increases power consumption. Additionally, low rejection/selectivity filters (e.g. second order band-pass filters) are not adequate for strong blockers within and without aggregated channels. Therefore, although these prior art approaches are intended to reject blockers, the effective close blocker rejection is not sufficient.

Additional background art includes "Carrier Aggregation for LTE-Advanced: Design Challenges of Terminals " by Chester Sungchung Park, Konkuk University & Lars Sundstrom at all, Ericsson Research, Lund, Sweden.

SUMMARY Direct conversion receivers usually employ low pass filters (LPFs) or complex

BPFs that are centered at 0 Hz. (DC). The bandwidth of such filters is usually tunable to receive various BW component carriers and block nearby potential blockers. If two non-contiguous equal BW component carriers are to be aggregated, then potential blockers in between should be rejected with high selectivity band-pass filters.

In order to obtain high selectivity band-pass filters, embodiments herein superposition two or more filters to generate a derived filter with the desired transfer function. The filters may be superpositioned in parallel and/or in series in accordance with the requirements of the receiver domain (e.g. impedance matched, high impedance, low impedance, etc.). Some embodiments utilize impedance transformers to create BPFs or BSFs using impedance inversion techniques.

According to a first aspect of some embodiments of the present invention there is provided receiver system for generating filtered signals. The receiver system includes a frequency converter which includes a local oscillator (LO) and a filter unit. The frequency converter receives radio frequency signals within a first frequency bandwidth and shifts the radio frequency signals to a second frequency bandwidth. The filter unit filters the radio frequency signals in the second frequency bandwidth by applying a derived band-pass filter (BPF) generated by superpositioning at least one BPF and at least one band-stop filter (BSF) to generate filtered signals.

In a first possible implementation form of the system according to the first aspect the receiver system includes a controller for tuning a bandwidth of at least one BPF and/or at least one BSF, thereby changing center frequencies and/or bandwidth of the derived BPF. In a second possible implementation form of the system according to the first aspect the at least one BPF and the at least one BSF are centered at a DC frequency and the derived BPF is shifted around targeted positive and negative frequencies in relation to the DC frequency.

In a third possible implementation form of the system according to the first aspect the at least one BPF and the at least one BSF are integrated circuit components of an integrated circuit implementing a Carrier Aggregation (CA) receiver filter for the receiver system.

In a fourth possible implementation form of the system according to the first aspect the at least one BPF includes multiple complex BPFs and the at least one BSF is implemented by transforming the impedance of at least one of the derived BPFs.

In a fifth possible implementation form of the system according to the first aspect the receiver system is implemented as integrated circuit components in a voltage mode.

In a sixth possible implementation form of the system according to the first aspect the at least one BSF and the at least one BPF are connected in parallel. In a second possible implementation form of the system according to the sixth

implementation form of the first aspect the at least one BPF is wider than the at least one BSF. In a third possible implementation form of the system according to the sixth implementation form of the first aspect the at least one BSF and the at least one BPF generate two symmetrically shifted complex BPFs.

In a seventh possible implementation form of the system according to the first aspect the receiver system includes at least one impedance transformer for converting the derived BPF from a voltage mode to a current mode.

In an eighth possible implementation form of the system according to the first aspect the at least one BPF and the at least one BSF are defined according to transfer functions in an impedance domain, such that the derived BPF defines a configurable transfer function in the impedance domain.

In a ninth possible implementation form of the system according to the first aspect the filtered signals encode component carriers defined for Carrier aggregation (CA) and have a narrower bandwidth than the first frequency bandwidth.

In a tenth possible implementation form of the system according to the first aspect the at least one BPF includes a first complex BPF covering the second frequency bandwidth and a second complex BPF covering a narrower frequency bandwidth narrower than the second frequency bandwidth.

In an eleventh possible implementation form of the system according to the first aspect the at least one BPF and the at least one BSF are integrated circuit components, and the receiver system includes at least one impedance inverter connected to the second complex BPF and to the at least one BSF in a series scheme.

In a twelfth possible implementation form of the system according to the first aspect the at least one BPF and the at least one BSF are connected one to another in a series scheme. In a second possible implementation form of the system according to the twelfth implementation form of the first aspect the at least one BPF and the at least one BSF are impedance matched.

According to a second aspect of some embodiments of the present invention there is provided a method for receiving data transmitted via a combination of radio frequency (RF) signals. The method includes:

i) receiving radio frequency signals within a frequency bandwidth;

ii) superpositioning at least one band-pass filter (BPF) covering the frequency bandwidth and band-stop filter (BSF) to generate a derived BPF; and

iii) applying the derived BPF on the radio frequency signals to generate a plurality of filtered signals.

In a first possible implementation form of the method according to the second aspect the multiple radio frequency signals are received via a frequency converter comprising a single local oscillator (LO).

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 illustrates the three carrier aggregation techniques;

FIG. 2 illustrates the difficulties of wideband CA signal processing;

FIG. 3 is a simplified block diagram of a system for wideband CA signal processing;

FIG. 4 illustrates the results of wideband filtering of CA signals;

FIGS. 5-6B are simplified transfer functions of prior art aggregated filters;

FIG. 7 is a simplified diagram of the superpositioning of two filters, according to embodiments of the invention;

FIGS. 8A-8B are a simplified block diagrams of a receiver system for generating a plurality of filtered signals, according to first and second embodiments of the invention;

FIGS. 9A-9C are simplified diagrams illustrating the tuning of a derived BPF; FIG. 10 is a simplified block diagram of forming a BSF from a BPF using impedance inversion;

FIG. 1 1 is a simplified block diagram of a direct conversion system, in accordance with some embodiments of the invention;

FIG. 12 is a simplified block diagram of an impedance matched derived BPF, according to exemplary embodiments of the invention;

FIG. 13A is a simplified block diagram of a derived BPF for high passband impedance, according to exemplary embodiments of the invention;

FIG. 13B is a simplified block diagram of a receiver system including a derived high passband impedance BPF, according to exemplary embodiments of the invention; FIG. 13 C which is a simplified block diagram of a derived high passband impedance BPF, according to exemplary embodiments of the invention;

FIG. 14 is a simplified block diagram of a derived low passband impedance BPF, according to exemplary embodiments of the invention;

FIG. 15 illustrates superpositioning of three filters to yield a derived bandpass filter transfer function, according to embodiments of the invention;

FIG. 16 is a simplified block diagram of a derived high passband impedance BPF, according to an exemplary embodiment of the invention;

FIG. 17 is a simplified flowchart of a method of receiving data transmitted via a combination of RF signals, according to embodiments of the invention;

FIG. 18 is a graph of simulation results illustrating blocker channel rejection obtained with derived filters of various orders; and

FIG. 19 shows the received signal constellations obtained with derived filters of various orders.

DETAILED DESCRIPTION The present invention, in some embodiments thereof, relates to processing carrier aggregated signals and, more specifically, but not exclusively, to filtering carrier aggregated signals.

Wireless communication systems and chips may have more than one baseband (BB) channel and use complex (IQ) band-pass filtering at baseband. Multiple baseband channels and IQ filters are especially common in receivers for CA.

Embodiments presented herein employ high selectivity BPFs and band-stop filters (BSFs) centered at DC, which are superpositioned to create wide band, high selectivity, scalable BPFs, at targeted positive and negative frequencies. Some embodiments are implemented using impedance inversion to enable operation with both high and low impedance baseband filters. Direct conversion CA is supported as detailed herein. Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing.

Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network.

The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention. Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

Embodiments herein superposition baseband filters to obtain to derive bandpass filters shifted in frequency from DC, with scalable center frequency and bandwidths.

Consider filter transfer functions Hi(S), H₂(S) H_n(S), where Hi(S) is a tunable BW BPF centered at DC (for direct conversion receivers) that may serve for receiving a component carrier as wide band as Hi(S). In embodiments described herein, a filter with a new transfer function Hi_;2;...n(S) is derived by superpositioning different configurations of Hi(S), H₂(S) H_n(S). The derived filter reflects multiple BPFs shifted from DC. Complex (IQ) filters may be superpositioned in series and/or parallel schemes to yield complex derived BPFs. The derived BPF may now serve for filtering several narrower component carriers for CA while rejecting potential blockers. As used herein the terms "derived band-pass filter" and "derived BPF" means a filter which is obtained by superpositioning at least one band-pass filter and at least one band-stop filter.

As used herein the terms "derived baseband band-pass filter" and "derived baseband BPF" mean a derived filter obtained by superpositioning at least one baseband band-pass filter and at least one baseband band-stop filter.

As used herein the terms "band stop filter" and "BSF" include configurations such as impedance inversion of a BPF and shunting which enable superpositioning other types of filters (e.g. band-pass or high-pass) to block a desired range of frequencies.

As used herein the term "BPF" means at least one band-pass filter and the term "BSF(s)" means at least one band-stop filter.

As used herein the term "bandwidth" means a frequency bandwidth.

Fig. 7 is a simplified graph illustrating the superpositioning of two filters, Hi(S)_BBi_q and Hi(S)_BBi_q, according to embodiments of the invention. Hi(S)_BBi_q is a baseband quadrature (BB IQ) BPF and H₂(S)BBi_q is a BB IQ bandstop filter. The result is Hi_;2(S)BBiq, which includes two complex passbands centered symmetrically at DC.

Some embodiments of the invention use a shunt (parallel) configuration of two IQ BPFs. The wider BPF has high impedance in-band and low impedance out-of- band, whereas the shunting narrower BPF has low impedance in-band and high impedance out-of-band. Alternate embodiments use a series configuration of an IQ BPF and an IQ BSF. Optionally, the configuration of the derived filter includes both parallel and series components.

Optionally, all BPFs forming the derived BPF are identical tunable filters. The BPFs may be tuned different bandwidths. Further optionally, the derived BPF includes one or more impedance inverters to invert the impedances of narrow tuned BPFs.

Some of the embodiments herein are presented for non-limiting embodiments of complex filters and signals. Similar embodiments may be implemented for simple (non-quadrature) filters and signals.

A band pass filter used to generate the derived filter may be implemented by any means known in the art. This includes, but is not limited to, implementing a BPF as an IQ low pass filter. Similarly, a band stop filter used to generate the derived filter may be implemented by any means known in the art. This includes, but is not limited to, implementing a BSF as an IQ high pass filter. Reference is now made to Fig. 8A, which is a simplified block diagram of a receiver system for generating a plurality of filtered signals, according to

embodiments of the invention. Receiver system 800 includes frequency converter 810 and filter unit 820.

Frequency converter 810, with local oscillator (LO) 830, receives radio frequency (RF) signals within a first frequency bandwidth and converts the received RF signals to a second frequency bandwidth with a different center frequency.

Filtering operations described herein are applied to the frequency converted signal at the output of frequency converter 810.

Optionally, frequency converter 810 downconverts the RF signals to baseband. Further optionally, receiver system 800 is a direct conversion receiver using a single LO.

Filter unit 820 generates filtered signals by applying derived band-pass filter 825 to the signal output by frequency converter 810. Derived BPF 825 is generated by superpositioning at least one BPF and at least one band-stop filter (BSF), optionally at baseband.

Optionally, receiver system 800 further includes controller 840. Controller 840 changes the center frequencies and/or bandwidths of derived BPF 825 by tuning the bandwidth of at least one of the BPFs and/or at least one of the BSFs in filter unit 820.

Reference is now made to Fig. 8B, which is a simplified block diagram of a complex receiver system for generating a plurality of filtered signals, according to embodiments of the invention. Receiver system 850 is structured and operates similarly to receiver system 800 in Fig. 8A, with the difference that frequency converter 870 and filter unit 860 operate in the complex plane and that LO 850 is an IQ local oscillator. Derived BPF 875 is generated by superpositioning at least one BPF and at least one band-stop filter (BSF), optionally at baseband.

Optionally, one or more of the filters which are superpositioned in order to generate the derived BPF are high order filters. Using high order filters may result in a derived BPF with steeper slopes, resulting in more effective suppression of blockers. Table 1 below shows simulation results demonstrating dramatic improvement in EVM when higher order filters are used.

Optionally, the filtered signals encode component carriers defined for CA, each having a narrower bandwidth than the frequency bandwidth of the RF signal. Superpositioning filters with different center frequencies may result in a derived BPF which is not symmetrical with respect to DC.

Figs. 9A-9C are simplified diagrams illustrating how a derived BPF may be tuned by controller 840. Fig. 9A shows a tunable BPF and Fig. 9B shows a tunable BSF. Superpositioning the tunable filters results in a derived BPF with tunable bandwidths and central frequencies. For simplicity Figs. 9A-9B illustrate

superpositioning of two filters with the same center frequency Optionally, additional tunable BPF(s) and/or tunable BSF(s) are superpositioned to generate the tunable derived BPF by superpositioning three or more filters.

Optionally, the derived filter is tuned dynamically during CA signal reception and/or processing.

In some embodiments, controller 840 receives data from an external source, uses the data to determine which frequencies should be blocked and tunes the derived filter in order to block the undesired frequencies. For example, the data may identify desired frequency bands and/or desired carriers and/or frequencies to be blocked.

Alternately or additionally, the receiver system includes closed loop tuning of the derived filter. The receiver system analyzes the received signal, at RF and/or baseband frequencies, identifies frequency ranges to be blocked and tunes the derived filter to block the undesired frequency ranges.

Optionally, the BPF(s) and/or BSF(s) in filter unit 820 are centered at DC (0 Hz), and derived BPF 825 is shifted around targeted positive and negative frequencies in relation to the DC frequency.

Optionally, the BPF(s) and/or BSF(s) in filter unit 820 are connected one to another in a series scheme. Further optionally the receiver system is matched (e.g. exemplary embodiment Fig. 12).

Optionally, the BPF(s) and/or BSF(s) in filter unit 820 are integrated circuit components of an integrated circuit implementing a CA receiver filter for the receiver system. Optionally, receiver system 800 includes at least one impedance transformer. This enables using impedance inversion techniques in the receiver system, as described for embodiments below.

Optionally, filter unit 820 includes complex BPFs and at least one BSF is implemented by transforming the impedance of a complex BPF. Implementing an IQ BSF by inverting the impedance into an IQ BPF is illustrated in Fig. 10.

In some embodiments, receiver system 800 is implemented as integrated circuit components in voltage mode.

Optionally, at least one BSF and at least one BPF are connected in parallel (e.g. exemplary embodiment Fig.13 A).

In some embodiments, the BPF is wider than the BSF. Additionally or optionally, the BSF and BPF are adapted to generate two symmetrically shifted complex BPFs.

Optionally, receiver system 800 includes an impedance transformer for converting derived BPF 825 from a voltage mode to a current mode.

Optionally, the BPF(s) and BPF(s) are defined by transfer functions in an impedance domain, and derived BPF 825 defines a configurable transfer function in the impedance domain.

Optionally, the receiver system includes multiple BPFs. Further optionally, a first BPF is a complex BPF covering the frequency bandwidth of the signals at the output of frequency converter 810, and a second BPF is a complex BPF covering a narrower frequency bandwidth.

Further optionally, the receiver system includes at least one impedance inverter connected to the second complex BPF in a series scheme (e.g. exemplary embodiment Fig. 14).

In some embodiments voltage domain (high impedance within pass band and low impedance elsewhere) BPFs are transformed into voltage domain BSFs using impedance transformers. Furthermore, in some embodiments voltage domain BSFs are utilized as current domain BPFs (low impedance within pass band and high impedance elsewhere) using impedance transformers.

Optionally, the receiver system includes CA processing unit 845 or 890 (for Figs. 8A and 8B respectively). The CA processing unit performs carrier aggregation signal processing of the CA signal after filtering by filter unit 820 or 870 (for Figs. 8A and 8B respectively).

Exemplary Embodiments

Some embodiments described herein are directed at systems with direct conversion with a single LO. Direct conversion from RF to complex IQ baseband may include low pass filters. Such IQ LPFs are reflected to RF as a BPF if the mixer used for conversion is switch-based passive. Wide band span direct conversion provides schematic simplicity at the block level, and requires one LO and IF frequency band. Direct conversion is illustrated in Fig. 1 1 , which is a simplified block diagram of a direct conversion system in accordance with some embodiments of the invention. The RF signal is amplified by low noise amplifier (LNA) 1 100 and downconverted to baseband by mixer 1110 with a single complex LO. The downconverted signal is filtered by a complex low pass filter, IQ LPF 1 120.

A. Impedance matched derived BPF

Reference is now made to Fig. 12, which is a simplified block diagram of a 50 ohm impedance-matched derived BPF, according to exemplary embodiments of the invention.

Fig. 12 shows a derived BPF generated by connecting tunable IQ BPF 1210 in series with tunable IQ band-stop filter (BSF) 1250 using bypass switches 1230. The derived BPF may be 50 ohm matched and is suitable for passive applications.

B. Derived BPFs for high passband impedance

Reference is now made to Fig. 13 A, which is a simplified block diagram of a derived high passband impedance BPF, according to a exemplary embodiments of the invention. Fig. 13A shows derived BPF 1300 generated by configuring a BPF and BSF in parallel using switches. BSF 1310 shunts complex BPF 1320 through IQ switches 1330. BPF 1320 has a wider bandwidth than BSF 1310. This yields a derived BPF with two symmetrical tunable BPFs at the output of BPF 1320.

Optionally, BPF 1320 is a complex high impedance filter and BSF 1310 is implemented as a complex low impedance bandpass filter. Reference is now made to Fig. 13B which is a simplified block diagram of a receiver system including a derived high passband impedance BPF, according to exemplary embodiments of the invention. Derived BPF 1300 includes BSF 1310, BPF 1320 and IQ switches 1330 configured as described for Fig. 13 A. The RF signal (shown as a CA signal with inband blocker) is input to mixer 1340 which is connected to an IQ LO. The mixer quadrature output signal is provided to the derived BPF. At the output of derived filter 1300 the blocker has been significantly attenuated relative to the desired Chi and Ch2 signals. The filtered signals are input to ADC 1350 for further processing.

Reference is now made to Fig. 13C which is a simplified block diagram of a derived high passband impedance BPF, according to exemplary embodiments of the invention. Fig. 13C shows derived BPF 1301 generated by configuring two BPFs in parallel and using impedance inversion. Tunable IQ BPF 1 1350 is connected in parallel with impedance inverter A/Z 1360 by IQ switches 1370. A/Z 1360 connects in series with tunable IQ BPF2 1380. As shown in Fig. 10, the series combination of A/Z 1360 and BPF2 1380 yields a tunable BSF.

High impedance exemplary embodiments are typically suitable for voltage domain applications. C. Derived BPF for low passband impedance

Reference is now made to Fig. 14 which is a simplified block diagram of a derived low passband impedance BPF 1400, according to exemplaiy embodiments of the invention. IQ BPF 1420 is connected in parallel to IQ BSF 1430 by IQ switches 1440. Impedance inverter A/Z 1410 connects in series to the parallel BPF/BSF configuration. A/Z 1410 inverts the impedance of the voltage domain BPFs thereby obtaining current domain BPFs.

Optionally, BSF 1420 is an impedance inverted BPF as described above. Low impedance exemplary embodiments are typically suitable for current domain applications. D. Three-filter superpositioning

The above exemplary embodiments use two filters, however in other embodiments the derived BPF is generated by superpositioning more than two filters. Fig. 15 illustrates superpositioning a wide bandwidth BPF (Z_BBi_qi), narrower bandwidth BPF (Z_BBi_q2) and a BSF (Z_BBiq?) to yield a derived BPF with three passbands (Z_BBi_q).

Reference is now made to Fig. 16, which is a simplified block diagram of a derived high passband impedance BPF, according to an exemplary embodiment of the invention. Derived BPF 1600 is generated from three BPFs (1610-1630) shunted by A/Z 1640 and A/Z 1650. The bandwidth of the three BPFs narrows from BPF1 to BPF2, and then further to BPF3. The transfer function of the derived BPF has three passbands for Chi, Ch2 and Ch3 respectively.

This configuration may be extended to include four or more BPFs. Method of receiving data

Reference is now made to Fig. 17 which is a simplified flowchart of a method of receiving data transmitted via a combination of RF signals, according to embodiments of the invention.

In 1700 RF signals within a frequency bandwidth are received.

Optionally, the RF signals are received via a frequency converter which employs a single local oscillator (LO). Further optionally, the frequency converter performs direct conversion to baseband.

In 1710 at least one BPF covering the frequency bandwidth and at least one BSF are superpositioned to generate a derived BPF. Optionally the received signals are carrier aggregated and the derived BPF is designed to pass desired carrier bands and to filter out blockers between the desired bands.

In 1720, the derived BPF is applied on the RF signals to generate filtered signals. The filtering may be applied to RF, IF or baseband signals.

Superpositioning the filters to generate the derived BPF may be performed at least in any of the ways and configurations described herein. Simulation Results

Figs. 18 and 19 show simulation results obtained with differing orders of derived filters.

Fig. 18 is a graph with simulation results for a realistic receiver scenario, with the received channel centered on DC and an adjacent blocker channel that needs to be filtered. Fig.18 compares the rejection of the blocker channel for different filter orders, showing that first order filtering may not be sufficient.

Fig.19 illustrates the EVM performance of the receiver scenario for different orders of derived BPFs employed. Filter superpositioning supports CA with single LO direct conversion. Simulation results for fifth order filters demonstrate CA filtering selectivity higher than 20 dB/dec. Table 1 shows the EVM obtained at the output of the ADC.

Table 1

The derived filter described herein may utilize direct conversion baseband BPFs available on chip (e.g. for parallel reception) to reflect to IF BPFs with scalable BW and center frequency for NC CA reception. Embodiments support reception and processing of non-contiguous CA having two or more advanced wireless component carriers using a single LO signal, and provide robust selectivity and scalability of bandwidth and center frequency Frequency conversion of the CA signal may be performed with a single LO, and does not require an additional LO IF signal, IF BPF or harmonic rejection IF mixers.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

It is expected that during the life of a patent maturing from this application many relevant superpositioning techniques and configurations, filters, carrier aggregation methods, receivers, impedance inverters, impedance transformers, frequency conversion methods, mixers, local oscillators, signal domains and RF signals will be developed and the scope of the term superpositioning, filter, carrier aggregation, receiver, impedance inverter, impedance transformer, frequency conversion, local oscillator, domains and RP signal is intended to include all such new technologies a priori.

The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to". This term encompasses the terms "consisting of and "consisting essentially of.

The phrase "consisting essentially of means that the composition or method may include additional ingredients and/or steps, but only if the additional ingredients and/or steps do not materially alter the basic and novel characteristics of the claimed composition or method.

As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.

The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". Any particular embodiment of the invention may include a plurality of "optional" features unless such features conflict.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging/ranges between" a first indicate number and a second indicate number and "ranging/ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.

Claims

WHAT IS CLAIMED IS:

1. A receiver system for generating a plurality of filtered signals, comprising: a frequency converter comprising a local oscillator (LO), adapted to receive a plurality of radio frequency signals within a first frequency bandwidth and to shift said radio frequency signals to a second frequency bandwidth;

a filter unit adapted to filter said plurality of radio frequency signals in said second frequency bandwidth by applying a derived band-pass filter (BPF) generated by superpositioning at least one BPF and at least one band-stop filter (BSF) for generating a plurality of filtered signals.

2. The receiver system of claim 1, further comprising a controller for tuning a bandwidth of said at least one BPF and/or said at least one BSF for changing center frequencies and bandwidth of said derived BPF.

3. The receiver system of any of the preceding claims, wherein said at least one BPF and said at least one BSF are centered at a DC frequency and said derived BPF is shifted around targeted positive and negative frequencies in relation to said DC frequency.

4. The receiver system of any of the preceding claims, wherein said at least one BPF and said at least one BSF are integrated circuit components of an integrated circuit implementing a Carrier Aggregation (CA) receiver filter for said receiver system.

5. The receiver system of any of the preceding claims, wherein said at least one BPF comprises a plurality of complex BPFs and said at least one BSF is implemented by transforming an impedance of at least one of said derived BPFs.

6. The receiver system of any of the preceding claims, implemented as integrated circuit components in a voltage mode.

7. The receiver system of any of the preceding claims, wherein said at least one BSF and said at least one BPF are connected in parallel, in particular wherein said at least one BPF is wider than said at least one BSF and/or in particular adapted to generate two symmetrically shifted complex BPFs.

8. The receiver system of any of the preceding claims comprising at least one impedance transformer for converting said derived BPF from a voltage mode to a current mode.

9. The receiver system of any of the preceding claims, wherein said at least one BPF and said at least one BSF are defined according to transfer functions in an impedance domain such that said derived BPF defines a configurable transfer function in the impedance domain.

10. The receiver system of any of the preceding claims, wherein said plurality of filtered signals encode component carriers defined for Carrier aggregation (CA) and having a narrower bandwidth than said first frequency bandwidth.

11. The receiver system of any of the preceding claims, wherein said at least one BPF comprises a first complex BPF covering said second frequency bandwidth and a second complex BPF covering a narrower frequency bandwidth narrower than said second frequency bandwidth.

12. The receiver system of claim 1 1, wherein said at least one BPF and said at least one BSF are integrated circuit components; further comprising at least one impedance inverter connected to said second complex BPF and to said at least one BSF in a series scheme.

13. The receiver system of any of claims 1-3, wherein said at least one BPF and said at least one BSF are connected one to another in a series scheme in particular impedance matched.

14. A method of receiving data transmitted via a combination of a plurality of radio frequency (RF) signals, comprising:

receiving a plurality of radio frequency signals within a frequency bandwidth; superpositioning at least one band-pass filter (BPF) covering said frequency bandwidth and band-stop filter (BSF) for generating a derived BPF; and

applying said derived BPF on said plurality of radio frequency signals for generating a plurality of filtered signals.

1 . The method of claim 14, wherein said plurality of radio frequency signals are received via a frequency converter comprising a single local oscillator (LO).