Evaluating Power Amplifier Performance for LTE and 802 ... · PDF fileEvaluating Power Amplifier Performance for LTE and 802.11ac Designs 3 LTE and 802.11ac: New Standards availability

© 2014 LitePoint, A Teradyne Company. All rights reserved.

Evaluating Power Amplifier Performance for LTE and 802.11ac Designs

WHITEPAPER

Evaluating Power Amplifier Performance for LTE and 802.11ac Designs 1

Table of ContentsLTE and 802.11ac: New Standards Influencing Power Amplifier Designs .................. 3

The Impacts of LTE and 802.11ac on PA Designs ....................................................... 3

Digital Predistortion and Envelope Tracking .............................................................. 4

Digital Predistortion ............................................................................................... 4

Envelope Tracking ................................................................................................... 4

Optimizing DPD and ET to Improve Power Amplifier Performance ........................... 5

Implementing and Optimizing DPD ....................................................................... 5

Implementing and Optimizing Envelope Tracking ................................................ 6

Essential Measurement Techniques for DPD and ET .................................................. 7

Error Vector Magnitude (EVM) Testing for 802.11ac Designs ............................... 7

Spectrum Mask Measurements for 802.11ac Designs .......................................... 8

ACLR for LTE PA Designs ........................................................................................ 8

Additional IEEE and 3GPP Test Specifications for PA Evaluations ......................... 9

Accelerating PA/FEM Testing and LitePoint’s Role ................................................... 10

Conclusion .................................................................................................................. 10

Learn More ................................................................................................................. 11

References .................................................................................................................. 12

More Information ...................................................................................................... 12


The wireless market’s insatiable demand for more bandwidth and faster data speeds is placing increased performance requirements on the components used in the RF front end of wireless devices, especially smartphones. New wireless standards such as LTE and 802.11ac employ advanced modulation schemes and signal processing to meet these performance demands, but these sophisticated techniques place stringent linearity and efficiency requirements on the RF PA.

PA component manufacturers are employing digital predistortion (DPD) and envelope tracking (ET) to manage PA linearity and efficiency, respectively, but DPD and ET are challenging to implement, test and optimize. Designers must have practical and reliable techniques to evaluate and manage these features under a wide range of potential operating conditions, before manufacture, to ensure that their PAs perform as intended and integrate properly with other components used in the transceiver.

The purposes of this paper are to highlight the implications LTE and 802.11ac have on PA designs; explain the use of DPD and ET to manage linearity and efficiency; and discuss three measurements that can be used to evaluate and optimize PAs that use these technologies. The measurements include error vector magnitude (EVM) and spectrum mask for 802.11ac PAs and adjacent channel leakage power ratio (ACLR) for LTE PAs.


LTE and 802.11ac: New Standards Influencing Power Amplifier DesignsThe LTE and 802.11ac standards are on the way to widespread adoption. LTE is being deployed in all global regions and by 2019 the standard is expected to provide commercial coverage for 65% of the world’s population.i Worldwide, subscriptions for this cellular technology are predicted to reach 2.6 billion by 2019.ii The new Wi-Fi standard, 802.11ac, is just now finding its way into handsets and it is expected to gain widespread acceptance in the handset market because it will help customers offload data from the cellular network. By 2015, 70% of mobile handset shipments will include this new technology.iii

Both LTE and 802.11ac use wider bandwidth, OFDMA modulation schemes, MIMO signal processing and other techniques to bolster data rates compared to earlier standards. The performance benefits are significant.

LTE, for example, can support transmission bandwidths of up to 20 MHz and use up to 4 MIMO channels to deliver high data rates. It offers theoretical peak speeds of 300 Mbps on the downlink and 75 Mbps on the uplink. An enhancement of the standard, LTE Advanced, can combine spectrum resources via carrier aggregation to increase transmission bandwidth to as much as 100 MHz to deliver theoretical peak speeds of up to 1Gbps on the downlink and 500 Mbps on the uplink.

The 802.11ac Wi-Fi standard can support bandwidths of up to 160 MHz with up to 8 spatial streams to dramatically increase data rates. A single stream, mandatory 80 MHz channel can support a 433 Mbps data rate, while the optional 160 MHz channel using 8 spatial streams can increase this sixteen-fold to 6.93 Gbps.

The cellular standard LTE, in particular, introduces a set of new operating features and conditions that will place additional responsibilities on the PA. LTE was standardized to support a wide variety of deployment configurations to ensure service

availability in any global market and provide roaming capabilities. In fact, version 11.0.1 of the standard provides specifications enabling manufacturers to use more than 40 frequency bands for LTE devices. LTE also offers six potential channel bandwidth options, the aforementioned carrier aggregation capability, and the opportunity to use FDD or TDD duplex schemes. LTE devices will be developed as multimode LTE/HSPA/GSM or LTE/CDMA products that can also use Bluetooth and GPS technologies, and most LTE devices will also be deployed along with Wi-Fi, which increasingly will use 802.11ac. In these contexts, it is reasonable to expect that an average device could require implementation of four RF paths and a high-end smartphone would need 12 or more RF paths to meet market needs.

LTE and 802.11ac therefore place many new demands on engineers, who must configure PAs, based on either of these technologies, to comply with the relevant standards and to also meet individual customers’ implementation and performance requirements.

The Impacts of LTE and 802.11ac on PA DesignsLTE and 802.11ac are forcing PAs to become increasingly complex. Rather than employing a single PA for each mode or band in a device, manufacturers must now employ multimode, multiband PAs that can help reduce costs and minimize board real estate. In addition, the increased use of mainstream CMOS processing methods for manufacturing PAs can exacerbate these problems, given the poor linearity of CMOS relative to GaAs and SiGe technologies.

One of the key PA design challenges is the need to amplify the signal to the required output level without introducing significant in-band distortion, harmonic distortion or out-of-band emissions or not burning excessive current, which sacrifices battery life. In addition to sophisticated biasing techniques, engineers must employ digital predistortion and envelope tracking to control linearity and efficiency trade-offs.


Digital Predistortion and Envelope Tracking Digital predistortion and envelope tracking techniques impact the processes used to design, simulate, characterize and validate PA operation. Simulations become increasingly more complex since some form of verification is required at the system level. Often a behavioral model is used for the PA for system level simulations that may not capture all the significant physical effects. This drives the need for extensive design validation in the lab where the PA is operated under realistic application conditions.

Digital Predistortion Many PA chipsets and front-end module technologies use DPD techniques to improve linearity (and therefore reduce distortions). The technique is especially important to companies that are using CMOS power amplifiers. For example, CMOS PAs designed for 802.11ac would likely need to employ DPD to achieve the required performance characteristics.

DPD is a signal processing technique that uses the transceiver’s digital signal processor (DSP) engine to mitigate amplifier nonlinearity. It works by estimating the nonlinearity of the PA, computing an inverse operation, and predistorting the RF input signal with the “inverse” of the amplifier nonlinearity. This effectively “linearizes” the PA to transmit the correct signal. There are many DPD algorithms in the published literature, but these can be broadly categorized as look up table (LUT), memoryless polynomial, and polynomial with memory.

In 802.11ac amplifiers, DPD is typically used to correct for both AM/AM and AM/PM distortion. This allows the PA to operate at a higher output power level for a given EVM level compared to the non-DPD case, thereby allowing extended range and higher quality connections for the end user. In LTE amplifiers that employ envelope tracking, DPD is typically used to correct for AM/PM distortions.

DPD can be challenging to deploy. While optimizing the DPD parameters for a given operating condition is useful, it is also important to understand over what range of conditions this correction can be applied. Again, this often drives extensive characterization efforts in the lab. Further, DPD also serves to increase the peak to average ratio (PAR) of the signal and thus crest factor reduction (CFR) techniques are often employed in conjunction with DPD. Finally, the processor in the host may impose limitations on the complexity of the DPD algorithms available. Thus PA characterization under DPD conditions requires the test instrumentation to support different algorithms with control over the various parameters and allow for a degree of automation to collect data under the numerous cases.

Envelope TrackingEnvelope tracking is a power modulation technique that improves control of power consumption in the RF power amplifier. It is considered an essential technology for improving the overall efficiency of the radio transmitter in wideband cellular devices to help preserve battery life.

ET it is expected to become a standard feature in LTE phones, which have a higher PAR than phones using earlier cellular standards. ET is gaining interest for its potential use in 802.11ac implementations as well.iv

Envelope tracking improves amplifier efficiency by varying the amplifier power supply, in accordance with the power requirements of the RF power envelope, so that unnecessary power dissipation is minimized. It requires dynamic tracking of the envelope and continuous, instantaneous adjustments of the supply voltage. This is achieved by monitoring the IQ signals, performing magnitude, scaling and shaping calculations and driving a power supply modulator accordingly.v

The efficiency benefits of ET are substantial. As the OpenET Alliance has demonstrated, ET can enable PAs to achieve practical, overall efficiencies of 50% or more compared to an efficiency of 25-30% that is typical when a fixed power supply is used. The inherent efficiency and superior broadband performance of envelope tracking transmitters are illustrated in Figure 1, which compares the envelope tracking and fixed supply efficiency of a handset PA fed with an 8.0 dB PAR LTE signal.vi

ET provides additional important benefits. As a broadband technique it enables manufacturers to offer multiband PAs. As such, it makes it more efficient for a single PA to operate over a range of frequencies, which will be especially necessary in LTE. Comparatively narrowband techniques, such as those offered by Doherty PAs, can’t deliver this capability.

Another ET benefit is that it can be effectively deployed in CMOS PAs. Due to the high levels of integration available with CMOS, designers can potentially integrate ET and the RF PA on the same die.

ET does have its challenges, however. The interface between the supply modulator and the PA is critical. The path between the two must have low impedance to maintain the wide bandwidth of the signal envelope. Further, any noise or spurious content from the modulator will be amplitude modulated onto the RF carrier, which can cause out-of-band emission issues and even desense issues in the FDD receive bands. More subtle effects such as LO leakage due to IQ offsets can give rise to image rejection issues. While the correct choice of shaping table can help mitigate AM/AM effects, DPD may be required to compensate for AM/PM distortion. Excellent performance results can be achieved at a single operating condition; the challenge is to maintain this level over the wide range of operating conditions.


Figure 1. Broadband Performance of Handset PA

Eff

icie

ncy

[%]

55

50

45

40

35

30

25

20

15

Frequency [GHz]

Efficiency of Final Stage

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

Fixed-Drain

Envelope Tracking

Source: OpenET

Optimizing DPD and ET to Improve Power Amplifier PerformanceIn order to optimize and verify PA performance, designers need to characterize their components under test conditions that represent deployment environments and customer use cases that are as realistic as possible. This section summarizes key considerations for implementing and optimizing DPD and ET technologies that are used to improve PA performance.

Implementing and Optimizing DPD DPD introduces substantial additional complexities to the PA design process that require careful engineering and testing. Designers must simulate their digital partners’ approaches to DPD, simulate the various operating conditions in which the components will be used, quantify essential performance characteristics, and adjust their designs to ensure overall system performance. Designers need high-performance instrumentation and software that can characterize and test the PA linearization, evaluate DPD for a given PA or transmitter design, and employ its sophisticated algorithms to predistort the signal to improve the linearity of the PA.

A typical DPD implementation comprises three key steps. First, the PA’s baseline performance is established by measuring the PA with its operating (non-DPD) waveform. Next, the PA is stimulated with a training waveform and the resulting output is measured. The input and output are then time-aligned and compared to build a nonlinear model of the PA. The “inverse” of this function is calculated and used to predistort the operational waveform. Finally, the PA is measured to evaluate the performance improvement.

Designers will employ one or more algorithms to predistort the waveform, depending on the system requirements. A lookup table (LUT) is the simplest technique for determining the needed signal level. However a single LUT cannot accommodate amplifier memory effects. A memoryless polynomial algorithm provides an equation to map input to output, but as with LUTs (and as its name suggests), this technique cannot accommodate memory effects. A memory-based polynomial is a more powerful algorithm because it determines the required output signal by considering not only the current input signal sample but also several previous samples. This type of algorithm can capture certain PA memory effects that are prevalent with wideband signals, but the technique does increase the complexity of the signal processing and hence the computational load in a real chipset implementation.


The training waveform can be an “operating” waveform, i.e., a waveform that is representative of the wireless communication system; a CW ramp; or a specifically designed waveform. Operating waveforms are realistic but they do not give the engineer control over the signal envelope distribution. Also, an operating waveform might not provide the best choice if the designer is using a memoryless model and the wideband signal stimulates memory effects in the PA. Some form of CW ramp training waveform can be useful because one can engineer its bandwidth and signal dynamics.

A vector signal generator (VSG) and vector signal analyzer (VSA) are used to deliver the complex modulated input and to correctly demodulate the output, respectively. To perform DPD without significant error, instruments with sufficiently low distortion are required. A wide measurement bandwidth is required for DPD tests, especially for WLAN devices. A VSG or VSA that does not have sufficient dynamic range will introduce nonlinear distortion and yield measurements that represent a combination of the PA nonlinearity and the system nonlinearity, creating erroneous results.

Wide bandwidth is necessary because DPD algorithms require the VSG/VSA instruments to source and capture multiple adjacent channels to measure and reduce adjacent channel leakage that occurs from PA distortion. A rule of thumb is that the equipment should provide 3 to 5 times the bandwidth of the original signal. DPD tests that are conducted with limited VSG bandwidth will not be able to accurately reproduce the predistorted waveform, which does not allow the adjacent and alternate channels to be properly corrected.

Testing tools must be able to represent the foregoing conditions realistically to ensure accurate measurements. In particular, to provide the most value to the designer, the test equipment should integrate VSA and VSG instrumentation as well as the algorithms and models needed to create and measure DPD. All of these capabilities should be easy to use for the evaluation of DPD as well as basic PA performance parameters.

Implementing and Optimizing Envelope Tracking There are two main tasks associated with implementing and optimizing ET: characterization of the PA and system design validation.

PA characterization involves measuring the PA efficiency and gain as a function of output power for a variety of supply voltages. From these measurements, a shaping table can be derived that relates the instantaneous signal envelope level to the PA supply voltage. The shaping table offers the opportunity for crest factor management, detroughing and the establishment of constant gain (minimizing AM/AM at the expense of slight efficiency degradation).

For system design validation, the goal is to establish that the overall system—the PA with envelope tracking—is operating correctly. In this case, the RF signal is fed from the RF generator directly to the PA input. The signal envelope from this waveform is then modified by the shaping table and used to drive the input of the envelope tracker using a second, baseband generator. The MIPI Alliance has standardized this interface as an analog 100-ohm differential input for cellular applications.vii One of the key tasks of the measurement system is to align the envelope signal with the RF prior to taking performance measurements. This requires baseband and RF signal generation modules capable of accurate time alignment with low jitter. For LTE applications, the timing error should be on the order of a nanosecond or less. See Figure 2.

Figure 2: IF and Signal Envelope


Essential Measurement Techniques for DPD and ETWhen evaluating effects on an 802.11ac PA or FEM, two of the most important requirements that the overall transceiver must meet include the IEEE test specifications for error vector magnitude (EVM) and spectrum mask. For evaluating LTE devices the 3GPP’s adjacent channel leakage power ratio (ACLR) specification is key, along with out-of-band emissions measurements.

Error Vector Magnitude (EVM) Testing for 802.11ac Designs Error vector magnitude (EVM) is a comprehensive and widely used metric for characterizing the transmit quality of the RF output. As such, it captures the impact of many implementation imperfections, including phase noise, IQ imbalance, spurs, nonconstant group delay, nonlinear distortion and temporal effects including thermally induced droop. EVM can verify the modulation accuracy of the transmitter with a convenient, “one number” indicator of its quality.viii

EVM requirements for the PA are much more stringent due to the small allocation from the overall EVM budget. Typically the requirement is expressed as a given EVM (usually in the region 1.5-1.8%) at a given average output power for a given channel bandwidth. This, in turn, requires the signal generator and analyzer to have excellent residual EVM floors to avoid significant error contribution to the measurements.ix

EVM should be evaluated under realistic operating conditions. For PA testing this requires enabling the PA only for the duration of the RF burst (plus some margin). This configuration is often referred to as Dynamic EVM (DEVM). Evaluating the PA under static conditions fails to capture the transient events associated with the real dynamic conditions and can yield overly optimistic EVM measurements. The time delay between the PA enable signal and the start of the RF burst is on the order of a few hundred nanoseconds to a few microseconds, thus requiring accurate synchronization between the PA control signal and the RF signal generation. See Figure 3.

Figure 3: Amplifier EVM Performance Under DPD With VHT80 Signal


Spectrum Mask Measurements for 802.11ac Designs A spectral mask describes the distribution of signal power across each channel and can be applied when evaluating DPD and ET.

The IEEE defines the permitted distribution of power for each 802.11 standard. For a product to comply with the standard, the transmitted distribution of power for the product’s transmitted signal must fall within the mask that the IEEE has specified for a given standard and channel bandwidth. The full plot must be checked. This can be done easily by analyzing the captured spectral plot against the spectral mask specified by IEEE. See Figure 4.

Spectral mask is one of a series of measurements for which the complete transmitter must be compliant and therefore its testing requirements can be more onerous than others. For example, an 802.11ac MCS9 signal places more stringent linearity requirements on the PA than it does for an MCS0 signal. However, an MCS0 signal is typically used at higher power so while it might pass the EVM requirement, it’s possible it would fail the spectral mask requirement.

Figure 4: Measured Spectral Mask for an 802.11ac Signal

ACLR for LTE PA DesignsAdjacent channel leakage power ratio (ACLR) is one of the key performance measurements for LTE power amplifiers that will be integrated into smartphones and other end-use devices. The ACLR characterizes the extent of undesired interference that leaks from a transmitted signal into an adjacent channel. ACLR is one of the 3GPP’s conformance test specifications for LTE end-use equipment and as such adjacent channel leakage must be evaluated to ensure compliance of LTE PA designs. See Figure 5.

Adjacent channel leakage is important to control in LTE PAs because the standard can be deployed with a variety of frequency bands, channel bandwidths and transmission schemes and the particular configuration used can impact performance. LTE can also be deployed in channels that are adjacent to W-CDMA channels, and therefore emissions from an LTE signal can affect the W-CDMA service.


Figure 5: ACLR Measurement

Additional IEEE and 3GPP Test Specifications for PA EvaluationsThis paper emphasizes the need to measure EVM and spectral mask to ensure that PAs based on 802.11ac conform to IEEE mandated specifications for the standard and the need to measure ACLR to ensure that devices based on LTE conform to the specifications for that standard issued by 3GPP.

In addition to these three measurement techniques, engineers will likely want to evaluate additional performance characteristics to meet internal or customer requirements. For example, P1dB, IP3, AM/AM and AM/PM measurements may be taken to correlate observed performance with analog simulation results.


Accelerating PA/FEM Testing and LitePoint’s RoleThe design validation process is fundamental to the success of a PA or FEM. And today, as manufacturers in the wireless industry compete to supply the global market with LTE and 802.11ac smartphones, tablets and other devices, RFFE component suppliers have a particular need for sophisticated technologies that can optimize the performance of their products. They also need specialized tools that can help them get well-designed and well-integrated products on the market as quickly as possible. Making accurate measurements, making them quickly, and evaluating a design’s performance over a wide range of operating conditions are all essential to this work.

LTE and 802.11ac technologies do place many new demands on the design and validation processes. These new procedural demands result from the complexities of these technologies, the many deployment options available and the opportunities to employ new techniques such as DPD and ET to optimize component performance and improve operating efficiencies. Devices based on these technologies must meet very stringent performance requirements to achieve their promised capabilities and ensure compliance and integration with other parts. System-level testing in the laboratory with equipment that can support DPD and ET is required to fully characterize the PA.

All of these technologies do impact the laboratory evaluation process. For example, the variety of frequency bands, power levels and test conditions available for an RFFE product can add time to the design process. Given the need for multimode devices in LTE and backward-compatibility in Wi-Fi, test equipment must support all of the relevant standards for the LTE or Wi-Fi implementation. And to expedite design, engineers need tools that can be used to quickly and easily set up test plans, collect data and efficiently analyze the results. A test executive or sequencer should be readily available to automate tests, especially when there are numerous test conditions and configurations under evaluation. In addition, the test instrumentation itself should offer sufficient performance so that it does not significantly impact the accuracy of the measurements.

Good performance can be achieved with bench-top instruments but new lower-cost, modular solutions based on the PXI form factor can accurately test the latest generation of RFFE components to help companies accelerate time to market with standards-compliant products that are optimized for their specific implementations. The compact PXI form factor reduces the equipment’s physical footprint compared to more traditional benchtop instruments. PXI equipment makes it relatively straightforward to achieve precise synchronization and timing between instruments since the devices can be triggered across a common backplane. A PXI solution can be readily expanded with additional power supplies for independent control of PA different stages, additional VSGs for coexistence testing and RF switching to facilitate single insertion multiple measurements on RFFEs.

Modular solutions are also ideally suited for MIMO applications, enabling designers who want to go beyond PA stimulus response testing to test a complete transceiver system that uses multiple antennas. Thus one platform for PA testing can be conveniently adapted, with additional hardware, to evaluate a chipset reference design that includes the PA.

To support companies in these efforts, LitePoint continually develops its tools to handle new wireless standards and it provides hardware that offers broad contiguous frequency coverage. LitePoint also manages the measurement science so engineers can focus their efforts on validating and getting their products to market quickly.

ConclusionWireless handsets and other end-use devices based on LTE and 802.11ac standards are on the way to widespread market adoption, but the PA technologies used in these devices have strict linearity and efficiency requirements that are hard to achieve. Component manufacturers are employing new techniques such as DPD and ET to manage PA linearity and efficiency, respectively, but DPD and ET are challenging to implement, test and optimize.

Modular test instrumentation and software can conveniently facilitate the required tests for these technologies, accelerate the validation process to shorten time-to-market, and give designers the flexibility they need to cost-effectively adapt the testing environment, as needed, to meet their customers’ specific implementation and performance requirements.

Note: The terms Wi-Fi and WLAN are used interchangeably throughout this document.


Learn MoreLitePoint looks forward to helping companies employ the latest methods and best practices to characterize and test PAs and FEMs. For more information about LitePoint’s PA/FEM test solutions, please visit www.litepoint.com.

Copyright © 2014 LitePoint, A Teradyne Company.

All rights reserved

CONTACT INFORMATIONLitePoint Corporation965 W. Maude Ave.Sunnyvale, CA 94085-2803United States of America Telephone: +1.408.456.5000Facsimile: +1.408.456.0106

LITEPOINT TECHNICAL SUPPORTwww.litepoint.com/supportTelephone: +1.408.456.5000Available: weekdays 8am to 6pm,Pacific Standard Time.E-mail: [email protected]

Doc: 1075-1016-001September 2014 Rev. 1

TRADEMARKSLitePoint and the LitePoint logo,IQxstream, IQview, IQflex, IQnxn, and IQmax are registered trademarks and IQnxnplus, IQsignal, IQwave, IQfact, IQcheck, IQdebug, IQmeasure, IQtest,IQexpress, IQturbo, IQultra, IQxel, IQ2015, IQ2012, IQ201X, IQ2011, IQ2011q IQ2010, TrueChannel, and TrueCable are trademarks of LitePoint Corporation. Microsoft Windows is a registered trademark of Microsoft Corporation in the United States and/ or other countries. All trademarks or registered trademarks are owned by their respective owners.

RESTRICTED RIGHTS LEGEND

No part of this document may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language or computer language, in any form or by any means, electronic, mechanical, magnetic, optical, chemical, manual, or otherwise, without the prior written permission of LitePoint Corporation.

DISCLAIMER

LitePoint Corporation makes no representations or warranties with respect to the contents of this manual or of the associated LitePoint Corporation products, and specifically disclaims any implied warranties of merchantability or fitness for any particular purpose. LitePoint Corporation shall under no circumstances be liable for incidental or consequential damages or related expenses resulting from the use of this product, even if it has been notified of the possibility of such damages.

If you find errors or problems with this documentation, please notify LitePoint Corporation at the address listed below. LitePoint Corporation does not guarantee that this document is error-free. LitePoint Corporation reserves the right to make changes in specifications and other information contained in this document without prior notice.


References

i “Ericsson Mobility Report: On the Pulse of the Networked Society,” June 2014, page 3. See http://www.ericsson.com/res/docs/2014/ericsson-mobility-report-june-2014.pdf

ii Ibid, page 6.

iii “Seventy Percent of Mobile Handset Shipments Will Use Wi-Fi (802.11ac) in 2015,” ABI Research, Press Release, Oct. 18, 2012. See https://www.abiresearch.com/press/seventy-percent-of-mobile-handset-shipments-will-u

iv “Qualcomm’s Envelope Tracking Bolsters its Position in LTE,” Strategy Analytics Advanced Semiconductor Applications blog, March 3, 2014. See http://blogs.strategyanalytics.com/GAAS/post/2014/03/03/Qualcomms-Envelope-Tracking-Bolsters-Its-Position-in-LTE.aspx

v “ET101: An Introduction to Envelope Tracking for RF Amplifiers,” a white paper by Steven Baker, the OpenET Alliance, Nov. 29, 2011, page 3. Visit the OpenET Alliance site at www.open-et.org.

vi Ibid, page 9.

vii “Analog Control Interface WG eTRAK® Specification,” the MIPI Alliance. See http://mipi.org/specifications/analog-control-interface-wg-etrak%C2%AE-specification

viii “Practical Manufacturing Testing of 802.11 OFDM Wireless Devices,” handbook published by LitePoint Corp., 2010, page 23. See http://www.litepoint.com/wp-content/uploads/2014/02/Testing-802.11-OFDM-Wireless-Devices_WhitePaper-1.pdf

ix “Power Amplifier Testing for 802.11ac,” an application note published by LitePoint Corp. 2014. See http://www.litepoint.com/wpcontent/uploads/2014/04/Power_Amplifier_Testing_802.11ac_Whitepaper_010814c.pdf

More Information Martins, João Paulo; Cabral, Pedro Miguel; Carvalho, Nuno Borges; and Petro, José Carlos. “A Metric for the Quantification of Memory Effects in Power Amplifiers,” in IEEE Transactions on Microwave Theory and Techniques, Vol. 54, No. 12, December 2006.

Pedro, Jose C. and Mass, Stephen A. “A Comparative Overview of Microwave and Wireless Power-Amplifier Behavioral Modeling Approaches,” in IEEE Transactions on Microwave Theory and Techniques, Vol. 53, No. 4, April 2005.

“Testing LTE – Where to Begin? Optimizing LTE Test for IQxstream,” white paper published by LitePoint, 2010.

Signals Research Group. “The LTE Standard: Developed by a Global Community to Support Paired and Unpaired Spectrum Deployments.” Study commissioned by Ericsson and Qualcomm. April 2014.

Wood, John. Behavioral Modeling and Linearization of RF Power Amplifiers. Artech House, 2014.

Yoon, Sang-Woong. “Static and Dynamic Error Vector Magnitude Behavior of 2.4-GHz Power Amplifier,” in IEEE Transactions on Microwave Theory and Techniques. April 2007.

Documents

Evaluating Power Amplifier Performance for LTE and 802 ... · PDF fileEvaluating Power Amplifier Performance for LTE and 802.11ac Designs 3 LTE and 802.11ac: New Standards availability