Clocking scheme in nonlinear systems for distortion improvement

Systems and methods are provided for clocking scheme to reduce nonlinear distortion. An example system may comprise at least two processing paths, each comprising at least one circuit exhibiting nonlinear behavior. Nonlinearity may be managed during processing of signals, such as by assessing effects of the nonlinear behavior during the processing of signals, and controlling clocking applied via at least one path based on the assessed effects, to reduce the effects of the nonlinear behavior during the processing of signals, eliminating the need for post-processing corrections. The controlling of clocking may comprise adjusting timing of a clock applied in the at least path, such as by introducing a timing-delay adjustment to a clock when the clock is applied to a circuit after the circuit exhibiting nonlinear behavior. A timing-advancement may be applied to signals processed via the at least one path, particularly before the circuit exhibiting nonlinear behavior.

CLAIM OF PRIORITY

This patent application makes reference to, claims priority to and claims benefit from Indian Patent Application Serial No. 201711000734, filed Jan. 7, 2017. The above identified application is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

Aspects of the present disclosure relate to communications. More specifically, various implementations in accordance with the present disclosure relate to methods and systems for clocking scheme in nonlinear systems for distortion improvement.

BACKGROUND

Various issues may exist with conventional approaches for handling nonlinearity in communication systems. For example, conventional systems and methods, if any existed, for handling distortion in nonlinear systems may be costly, cumbersome, or inefficient—e.g., they may be complex, time consuming, require considerable power, and/or may fail to address distortion introduced by the nonlinearity and/or may introduce errors or distortion.

BRIEF SUMMARY

System and methods are provided for a clocking scheme in nonlinear systems for distortion improvement, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

DETAILED DESCRIPTION OF THE INVENTION

Various implementations in accordance with the present disclosure are directed to providing a clocking scheme in nonlinear systems for distortion improvement. An example method, in accordance with the present disclosure, may comprise managing nonlinearity in a system (e.g., transceiver) which may comprise at least two separate paths for use when processing signals, and with each path comprising at least one circuit exhibiting nonlinear behavior during the processing of signals. The managing of nonlinearity may comprise assessing effects of the nonlinear behavior during the processing of signals, and controlling clocking applied via at least one path used during the processing of signals, based on the assessed effects. The controlling may be configured to reduce the effects of the nonlinear behavior during the processing of signals, thus eliminating a need for post-processing corrections after completing the processing of signals.

In an example implementation, the controlling of clocking may comprise introducing a timing-advancement adjustment to signals processed in the at least one path.

In an example implementation, the method may comprise introducing the timing-advancement adjustment before the least one circuit exhibiting nonlinear behavior.

In an example implementation, the controlling of clocking may comprise adjusting timing of a clock applied in the at least one path. The adjusting of timing of the clock may comprise introducing a timing-delay adjustment to the clock when applied to at least one circuit that follows the least one circuit exhibiting nonlinear behavior.

In an example implementation, the at least two separate paths may comprise an in-phase (I) path and a quadrature (Q) path, and the processing of signals comprises processing I and Q components of processed signals via the I-path and Q-path, respectively.

In an example implementation, the effects of the nonlinear behavior may comprise effects of undesired tones or signals introduced because of the nonlinear behavior. The undesired tones or signals may comprise spurious components corresponding to processed signals and/or fold-back counterparts of the spurious components.

An example system, in accordance with the present disclosure, may comprise a first processing path that comprises at least one nonlinear circuit that exhibits nonlinear behavior and one or more other circuits, a second processing path that comprises at least one nonlinear circuit that exhibits nonlinear behavior, and one or more circuits configured for managing nonlinearity during processing of signals in the system. The managing of nonlinearity may comprise assessing effects of the nonlinear behavior during the processing of signals, and controlling clocking applied via one or both of the first processing path and the second processing path based on the assessed effects. In this regard, the controlling of clocking may be configured to reduce the effects of the nonlinear behavior during the processing of signals, thus eliminating a need for applying post-processing corrections after completing the processing of signals.

In an example implementation, one of the first processing path and the second processing path of the system comprises an in-phase (I) processing path operable to process I-components of the signals, and the other one of the of the first processing path and the second processing path comprises a quadrature (Q) processing path operable to process Q-components of the signals.

In an example implementation, the at least one nonlinear circuit, in each of the first processing path and the second processing path of the system, may comprise a digital-to-analog (DAC) circuit or a sample-and-hold (SAH) circuit.

In an example implementation, the one or more circuits, in each of the first processing path and the second processing path of the system, may comprise a sampler.

In an example implementation, the one or more circuits, in each of the first processing path and the second processing path of the system, may comprise a phase-shifter.

In an example implementation, one or both of the first processing path and the second processing path of the system may comprise a timing circuit operable to introduce, in conjunction with the controlling of clocking, a timing-advancement adjustment to signals processed via that path. The timing circuit may precede the least one nonlinear circuit exhibiting nonlinear behavior.

In an example implementation, controlling clocking in the system may comprise adjusting timing of a clock applied in the one or both of the first processing path and the second processing path. The adjusting of timing of the clock may comprise introducing a timing-delay adjustment to the clock when applied to one or more circuits that follows the least one circuit exhibiting nonlinear behavior.

In an example implementation, the system may comprise at least one combining circuit for combining outputs of the first processing path and the second processing path.

In an example implementation, the effects of the nonlinear behavior may comprise effects of undesired tones or signals introduced because of the nonlinear behavior. The undesired tones or signals may comprise spurious components corresponding to processed signals and/or fold-back counterparts of the spurious components.

FIG. 1illustrates an example system that may exhibit nonlinearity. Shown inFIG. 1is an electronic system100.

The electronic system100may comprise suitable circuitry for implementing various aspects of the present disclosure. In this regard, the electronic system100may support performing, executing or running various operations, functions, applications, and/or services. The electronic system100may be used, for example, in executing computer programs, playing video and/or audio content, gaming, performing communication applications or services (e.g., Internet access, browsing, email, text messaging, chatting, voice calling services, etc.), providing networking services (e.g., WiFi hotspot, Bluetooth piconet, Ethernet networking, cable or satellite systems, and/or active 4G/3G/femtocell data channels), etc.

In some instances, the electronic system100may be operable to handle or support communications, over wired and/or wireless connections, such as during executing, running, and/or performing of operations, functions, applications, and/or services in the electronic system100. For example, the electronic system100may be configured to support (e.g., using suitable dedicated communication components or subsystems) use of wired and/or wireless connections/interfaces, which may be configured in accordance with one or more supported wireless and/or wired protocols or standards, to facilitate transmission and/or reception of signals (carrying data) to and/or from the electronic system100. In this regard, the electronic system100may be operable to perform necessary processing operations to facilitate transmission and/or reception of signals (e.g., RF signals) over supported wired and/or wireless interfaces.

Examples of wireless standards, protocols, and/or interfaces which may be supported and/or used by the electronic system100for communication therebetween may comprise wireless personal area network (WPAN) protocols (e.g., as Bluetooth (IEEE 802.15) and ZigBee), near field communication (NFC) standards, wireless local area network (WLAN) protocols (e.g., such as WiFi (IEEE 802.11) standards), cellular standards (including 2G/2G+, such as GSM/GPRS/EDGE, IS-95 or cdmaOne, etc., and 3G/3G+, such as CDMA2000, UMTS, and HSPA, etc.), 4G standards (e.g., WiMAX (IEEE 802.16) and LTE), Ultra-Wideband (UWB), Extremely High Frequency (EHF, such as 60 GHz) Digital TV Standards (e.g., DVB-T/DVB-H, and ISDB-T), etc.

Examples of wireless standards, protocols, and/or interfaces which may be supported and/or used by the electronic system100for communication therebetween may comprise Ethernet (IEEE 802.3), Digital Subscriber Line (DSL), Integrated Services Digital Network (ISDN), Fiber Distributed Data Interface (FDDI), cable television and/or internet access standards (e.g., ATSC, DVB-C, DOCSIS, etc.), in-home distribution standards such as Multimedia over Coax Alliance (MoCA), Universal Serial Bus (USB) based standards/protocols/interfaces, etc.

In some instances, the electronic system100may be configured to support input/output (I/O) operations, to enable receiving input from and/or providing output to users. Accordingly, the electronic system100may comprise components or subsystems for obtaining user input and/or providing output to the user. For example, the electronic system100may support input/output (I/O) operations for allowing user interactions which may be needed for controlling the electronic system100or operations thereof—e.g., allowing users to provide input or commands, for controlling certain functions or components of the electronic system100, and/or to output or provide feedback pertaining to functions or components. The electronic system100may also support input/output (I/O) operations in conjunction with use of data (e.g., multimedia content). For example, the electronic system100may support generating, processing, and/or outputting of video and/or acoustic signals, such as via suitable output devices or components (e.g., displays, loudspeakers, etc.). In this regard, the output signals may be generated based on content, which may be in digital form (e.g., digitally formatted music or the like). Similarly, the electronic system100may support capturing and processing of video and/or acoustic signals, such as via suitable input devices or components (e.g., cameras, microphones, etc.), to generate (e.g., to store or communicate) corresponding data. The corresponding data may be in digital form (e.g., digitally formatted music, video, or the like).

Accordingly, the electronic system100may correspond to (at least portion of) such electronic devices as cellular and smart phones or similar handheld devices, tablets, personal computers, laptops or notebook computers, servers, personal media players, personal digital assistants, set top boxes, satellite receivers, wireless access points, cellular base stations, etc. The disclosure is not limited, however, to particular type of systems, and similar solutions as those described in this disclosure may apply to any suitable system where similar issues (e.g., nonlinearity) are encountered.

In operation, the electronic system100may perform various operations, functions, applications, and/or services supported therein. This may entail performing various processing functions, using suitable circuits, whereby signals and/or data may be processed, for example. In some instances, the electronic system100, and/or components thereof used during operations of the electronic system100, may exhibit nonlinear characteristics.

For example, components such as digital-to-analog-converters (DACs) and analog-to-digital-converters (ADCs) are particularly known to exhibit nonlinearity during operations (conversions of data or signals between analog and digital) thereof. This may pose significant issues to the operation of the system as a whole. For example, in instances where the electronic system100is performing communication operations (transmission and/or reception of signals), and circuit nonlinearity in such components as ADCs and/or DACs, may spawn spurious components related to the signals, called harmonics (or harmonic distortion (HD)) for narrow-band signals as well as their fold-back counterparts.

In the example implementation shown inFIG. 1, the electronic system100may be configured, in accordance with conventional approaches, for use of quadrature based communication (e.g., quadrature based encoding/decoding of signals), and such may comprise 2 paths—namely, an I-path and a Q-path (I=in-phase, Q=quadrature). Each of the I-path and the Q-path may comprise one or more circuits or components, including nonlinear (NL) components1101and1102, respectively, in each of the I-path and the Q-path, followed by samplers1201and1202, respectively, in each of the I-path and the Q-path, followed by phase-shifters1301and1302, respectively, in each of the I-path and the Q-path. The outputs of the I-path and Q-path may be combined (e.g., added or subtracted) via a mixer140.

An input signal being processed may be passed through the I-path and Q-path—e.g., through each of the NL components1101and1102, the samplers1201and1202, and the phase-shifters1301and1302. In the example use scenario shown inFIG. 1, the processed signal, s(t), is assumed to be a real signal. In conventional implementations, the same clocking is used in both paths—e.g., both samplers1201and1202are clocked using the same clock CLK=c(t).

The particular type and/or function of the blocks in each of the paths may differ from system to system and/or based on operations being performed. For example, in up-conversion system/operations, the NL component110may be a DAC. The sampler120after the NL component110may represent the sampling operation integrated in the DAC. The phase-shifters130may be implemented using I-Q mixers, that either up-convert or down-convert the signal(s), or poly-phase filters. In up-conversion, the input signal translates to a single side-band, either to a high-side band or to a low-side band, such as based on whether the mixer140following the phase-shifters130is a subtractor or an adder. Different harmonic components and their fold-back counter-parts, which may be generated and/or introduced in the NL components110, may be up-converted through the mixer140at the same side-band as that of the signal, causing such issues as poor signal-to-distortion ratio (SNDR) at the output.

In down-conversion system/operations, the NL component110may be a sample-and-hold (SAH) block/circuit, and the sampler120after the SAH may represent the sampling operation integrated in the SAH. The phase-shifters130may be implemented using analog-to-digital-converters (ADC) followed by discrete-time mixers or ADCs, followed by poly-phase filters. Similar to up-conversion scenarios, in down-conversion scenarios, undesired signals and their fold-back counterparts, which may be generated and/or introduced in the NL components110, may be down-converted to a frequency close to the desired signal, and as such may adversely affect the output signal (e.g., degrading SNDR).

Handling issues caused by system nonlinearity may be costly and/or ineffective. For example, a significant amount of power consumption during operations of conventional systems may be attributed towards reducing such effects (distortion components). Further, components (circuits) may need to be implemented in inefficient way (e.g., circuits sized up) so as to counteract possible issues (e.g., minimize the mismatch between them), to help reduce distortion components. This would have undesirable effect on the design of the system—e.g., inevitably resulting in larger die area.

Accordingly, in various implementations in accordance with the present disclosure, adaptive measures may be taken to alleviate nonlinearity in systems where nonlinearity-related issues would degrade performance (e.g., in I/Q-based transceivers), and do so in optimal and cost-effective manner resulting in lower power consumption and/or reduction of area in the system. This may be particularly done in sampling-based systems (comprising, e.g., DACs, ADCs, etc.) to relax linearity requirements in the system. Doing so in such systems, particularly ones that employ quadrature encoding of signals (I and Q components) may further allow maximizing bandwidth efficiency. Example implementations in accordance with the present disclosure are described below.

FIG. 2illustrates an example system that supports use of a clocking scheme for improving distortion when handling discrete-time signals, in accordance with the present disclosure. Shown inFIG. 2is an electronic system200.

The electronic system200may be substantially similar to the electronic system100ofFIG. 100, for example, and may operate and/or be used in a substantially similar manner. In this regard, as with the electronic system100, the electronic system200may also be configured for performing various operations, functions, applications, and/or services supported therein, and in doing so, the electronic system200, and/or components thereof, may exhibit nonlinear characteristics during these operations.

For example, as with the electronic system100, the electronic system200may also be configured for use of quadrature based communication (e.g., quadrature based encoding/decoding of signals), and such may comprise 2 paths—namely, an I-path and a Q-path. Each of the I-path and the Q-path may be substantially similar to the I-path and the Q-path, respectively, in the electronic system100. In this regard, each of the I-path and the Q-path in the electronic system200may comprise one or more circuits or components, including nonlinear (NL) components2101and2102, respectively, in each of the I-path and the Q-path, followed by samplers2201and2202, respectively, in each of the I-path and the Q-path, followed by phase-shifters2301and2302, respectively, in each of the I-path and the Q-path. The outputs of the I-path and Q-path may be combined (e.g., added or subtracted) via a mixer240.

The electronic system200may, however, incorporate certain changes for alleviating nonlinearity-related issues, particularly doing so in a cost-effective way. For example, the electronic system200may, for example, incorporate use of a modified clocking scheme for adjusting timing in each of the I-path and the Q-path, for mitigating nonlinearity related defects, particularly when handling discrete-time input signals. The clocking used in the system may be configured such that timing of processing functions applied in one or more of the paths (e.g., the I-path and/or the Q-path) may be adjusted to mitigate effects of nonlinearity exhibited in the system—e.g., HD distortion generated and/or introduced by the NL components2101and2102. This may be done, for example, by time-advancing the input signal in one path (e.g., the Q-path) and/or delaying certain functions applied during processing of the signal in that path (e.g., sampling), by applying certain time adjustment(s) that may be determined adaptively to optimize mitigating nonlinearity-related distortion.

In the example implementation shown inFIG. 2, the electronic system200, the input signal in Q-path is time-advanced by τ and the sampling-clock of the Q-path is delayed by τ. In this regard, the Q-path may comprise, in addition to the components already described, a time-advance block250, which may be operable to apply the time adjustment τ, before the NL component2101.

The clocking of the sampler2202may be adjusted using the same adjustment. Thus, while the sampler2201in the I-path is clocked using CLK=c(t), the sampler2201in the I-path is clocked using CLK=c(t−τ).

FIG. 3illustrates an example system that supports use of a clocking scheme for improving distortion, when handling continuous-time signals, in accordance with the present disclosure. Shown inFIG. 3is an electronic system300.

The electronic system300may be substantially similar to the electronic system100ofFIG. 100, for example, and may operate and/or be used in a substantially similar manner. In this regard, as with the electronic system100, the electronic system300may also be configured for performing various operations, functions, applications, and/or services supported therein, and in doing so, the electronic system300, and/or components thereof, may exhibit nonlinear characteristics during these operations.

For example, as with the electronic system100, the electronic system300may also be configured for use of quadrature based communication (e.g., quadrature based encoding/decoding of signals), and such may comprise 2 paths—namely, an I-path and a Q-path. Each of the I-path and the Q-path may be substantially similar to the I-path and the Q-path, respectively, in the electronic system100. In this regard, each of the I-path and the Q-path in the electronic system300may comprise one or more circuits or components, including nonlinear (NL) components3101and3102, respectively, in each of the I-path and the Q-path, followed by samplers3201and3202, respectively, in each of the I-path and the Q-path, followed by phase-shifters3301and3302, respectively, in each of the I-path and the Q-path. The outputs of the I-path and Q-path may be combined (e.g., added or subtracted) via a mixer340.

The electronic system300may also incorporate certain changes for alleviating nonlinearity-related issues, particularly doing so in a cost-effective way. For example, as with the electronic system200ofFIG. 2, the electronic system300may also incorporate use of modified clocking scheme for adjusting timing in each of the I-path and the Q-path, for mitigating nonlinearity related defects. In this regard, the clocking scheme used in the electronic system300is configured such that timing of processing functions applied in one or more of the paths (e.g., the I-path and/or the Q-path) may be adjusted to mitigate effects of nonlinearity exhibited in the system—e.g., HD distortion generated and/or introduced by the NL components3101and3102.

The clocking scheme used in the electronic system300is configured, however, for processing continuous-time signals. In this regard, because continuous-time signals do not incur any phase-shift due to sampling using a phase-shifted clock in the Q-path, no time-advancing (and thus no time-advance block/circuit) is used. Rather, the clocking scheme may include applying adjustment (e.g., delay) to a clock used in controlling the samplers3201and3202. Thus, while the sampler3201in the I-path is clocked using CLK=c(t), the sampler3201in the I-path is clocked using CLK=c(t−τ). The delay τ may be determined adaptively to optimize mitigating nonlinearity-related distortion.

However, while no time-advancing is used before the NL components3101and3102, in some instances additional measures may be taken after the NL components3101and3102, such as to account for the clocking variations based on implementation details of other components. For example, where the mixer350(e.g., adder/subtractor) that follows the phase-shifters3301and3302is implemented in the digital-domain, an interpolation-filter may be used to align both I and Q samples to the same clock.

FIGS. 4A-4Cillustrate charts for signals during operation of an example nonlinear system with clocking scheme for improving distortion, in accordance with the present disclosure.

FIG. 4Aillustrates fundamental and harmonics of signals in the I-path and the Q-path in a sampled nonlinear system incorporating clocking scheme for mitigating nonlinearity distortion (e.g., the electronic system200ofFIG. 2and/or the electronic system300ofFIG. 3), at different points in these paths, up to and before any phase shifting. In particular, shown inFIG. 4Aare diagrams corresponding to relative phases of fundamental at different nodes in the system (A); relative phases of undesired tones at outputs of NL components before sampling (B); and relative phases of undesired tones after sampling of outputs of NL components (C).

Diagram401illustrates the relative phases of fundamentals at different points in the I-path and Q-path up to the phase-shifters—e.g., I and Q (or I—finand Q—fin), corresponding to the inputs to the NL components; I1and Q1(or I1_finand Q1_fin), corresponding to the outputs of the NL components; and I2and Q2(or I2_finand Q2_fin), corresponding to the outputs of the samplers, where finis input frequency.

Diagrams411,413, and415illustrate the relative phases of undesired tones at outputs of NL components, before sampling. The undesired tones may be expressed as I1_(n*fin)and Q1_(n*fin)and I1_(Fs-n*fin)and Q1_(Fs-n*fin), where Fsis sampling frequency. Diagrams411illustrates the relative phases for these tones at outputs of NL components for n=2, 6, 10, . . . ; whereas diagram413illustrates the relative phases for these tones at outputs of NL components for n=3, 7, 11, . . . ; and diagram415illustrates the relative phases for these tones at outputs of NL components for n=4, 8, 12, . . . .

Diagrams421,423, and425illustrate the relative phases of undesired tones at outputs of samplers—i.e., after sampling. As noted above, the undesired tones may be expressed as I1_(n*fin)and Q1_(n*fin)and I1_(Fs-n*fin)and Q1_(Fs-n*fin). Diagrams421illustrates the relative phases for these tones at outputs of samplers for n=2, 6, 10, . . . ; whereas diagram421illustrates the relative phases for these tones at outputs of samplers for n=3, 7, 11, . . . ; and diagram425illustrates the relative phases for these tones at outputs of samplers for n=4, 8, 12, . . . .

As shown inFIG. 4A, linear phase-advance resulting from time-advance at input of Q-path NL-system is cancelled by linear phase-delay resulting from time-delay of the sampling clock of Q-path NL-system at all signal frequency. Thus the phase-shift may be ignored.

FIG. 4Billustrates relative positions of desired and undesired signals at the output (SOUT) of the mixer component (e.g., mixer250in the electronic system200, or mixer350in the electronic system300), in an example system implemented in accordance with the present disclosure and configured for up-conversion system—e.g., particularly where the phase-shifters are implemented using up-conversion quadrature mixers. In particular, as shown inFIG. 4B, the spurious tones (with diagrams431,433, and435corresponding, respectively, to n=2, 6, 10, . . . , n=3, 7, 11, . . . , and n=4, 8, 12, . . . ) appear at opposite side-band of LO (fLOis frequency of local oscillator) compared to fundamental tone as expressed in the following formulas:
Fs−nfinforn=2,6,10, . . . when τ=¼Fs(1)
nfinandFs−nfinforn=3,7,11, . . . when τ=½Fs(2)
Fs−nfinforn=4,8,12, . . . when τ=−¼Fs(3)

These tones may be attenuated, such as by use of a band-pass filter (BPF) at the output, or simply by limiting bandwidth of the blocks following the mixers. Since this technique increases the frequency-separation between the desired and undesired signals, the need for sharp bandpass filters to filter-out undesired signals may also be relaxed.

FIG. 4Cillustrates relative phases of desired and undesired signals at the input of a mixer block (e.g., mixer250in the electronic system200, or mixer350in the electronic system300) in an example system implemented in accordance with the present disclosure and configured for up-conversion system—e.g., where the mixer is implemented as adder/subtractor, and with phase-shifters implemented using down-conversion quadrature-mixers or poly-phase filters. In this regard,FIG. 4Cillustrates (A) relative phases of desired signals at fin(diagram461) and (B) relative phases of undesired spurious signals and their fold-back counterparts (with diagrams463,465, and467corresponding, respectively, to n=2, 6, 10, . . . , n=3, 7, 11, . . . , and n=4, 8, 12, . . . ). As shown inFIG. 4C, the spurious tones described above, with respect toFIG. 4B(as expressed using formula 1, 2, and 3, above) may be cancelled at output.