Linearised RF Power Amplifier Systems - Theory and Design

23rd to 27th April 2007. Cambridge, UK.

Venue: Kaetsu Centre, New Hall, University of Cambridge, England

PDF Format brochure


Dr. Steve C Cripps, Hywave Associates
Dr Chris Potter, Cambridge RF Ltd.


Introduction to Linearised PA Systems • Role of Linearisation, Review of Modulation Systems and Standards • Review of PA Techniques • Class A, AB, Class D,E,F, Kahn, Chireix, Doherty • Power Amplifier Linearity • Power and Volterra Series, AM-AM, AM-PM, Volterra Series Extraction, IM, Spectral Re-growth, Envelope Simulation, IM Asymmetry and Memory Effects • Predistortion Techniques , Basic Theory, Analog Predistortion •Digital Predistortion, Theory , Practice and Simulation, • Feedback Techniques • RF Feedback, Envelope Feedback, Cartesian and Vector Feedback • Feedforward • Feedforward Loop Analysis, EPA Power Tradeoffs, Adaption Issues, CAD Simulations • RF Component Design for Linearised Systems • Detectors, Vector Modulators, RF to DC Converters.


RF Transmitter linearity has become a topic of intensive research worldwide in the wireless communication era. The combination of fixed, narrow frequency bandwidth allocations and the growing demands for information throughput for rapidly evolving consumer wireless products has resulted in the implementation of RF modulation schemes, which have low tolerance for system non-linearity. This is in contrast to first generation wireless products, which used more traditional modulation schemes - such as OQPSK, GMSK.

These older systems were originally conceived with a primary goal of being tolerant of some moderate peak envelope clipping of the RF signal. Third generation, 3G-systems, have been forced to discard this concession to the RF designer, in the interests of much higher channel and signal bandwidth capacity.

The use of analog and digital techniques for linearisation of the transmitter, and especially the final power amplifier stage, has become not just desirable, but a key element in the success of 3G wireless products.


The objective of this course is to provide an up-to-date review of linearisation techniques for RF power amplifiers in wireless communications systems. This updated and extended course places a new emphasis on digital predistortion techniques, which are expected gradually to replace many of the existing analog methods over the new few years.Applications for all kinds of wireless systems are intended, and although there will be an emphasis on cellular base stations, other application areas such mobiles and satellite systems will be included. This course places an emphasis on the analysis and a priori design of PA linearisers, in addition to the CAD simulation of practical devices and systems. Various CAD tools will be used to illustrate the performance of practical designs.


PA Designers - PA designers at all levels will find this course an excellent update to their current knowledge and an opportunity to meet and discuss with others working in the same area.
System Level Engineers - Engineers who specify and use RF components, including PAs, in system design will obtain an understanding of what is possible, at what cost and system level tradeoff.
DSP Engineers - The growing role of DSP in RF PA systems is clear, and this course would serve as a good background for DSP designers who are, or are about to, become involved in the design of linearisation systems for RF PAs.


Day 1. The first day is mainly a review of PA design and non-linear PA effects. Classical PA modes (A, AB, B) will be briefly reviewed. The efficiency enhancement possibilities proposed by Khan, Chireix, and Doherty will be reviewed briefly. Different modulation schemes and specification standards will be reviewed, so that the linearity and efficiency requirements from each can be determined.

Day 2 begins with a study of PA non-linear effects, and behavioural modeling techniques will then be considered. This treatment will include the fitting of higher order polynomial models to measured PA characteristics, and the problem of IM asymmetry and memory effects. The rest of the day will be devoted to predistortion methods. Predistortion has become the most important developing linearisation technique in recent times due to the availability of faster DSP hardware. Nevertheless, analog predistortion still has value in some applications and it is also dealt with here. Basic predistortion theory, using polynomial series, will be presented.

Day 3 focusses on digital predistortion methods, applied either at the PA input, or as is becoming more standard practice, at the DSP signal synthesis system level. Tradeoffs between algorithmic, or LUT (Look-Up Table) implementations will be discussed. Memory effect correction will be described. Issues such as predistortion bandwidth, sampling rates, digital precision, for different specifications and standards will be given quantitative treatment. Illustrations using non-linear CAD simulations will be presented. Adaption issues and methodology are discussed. The requirement for power control and its impact on the system design is also assessed.

Day 4 will begin with a treatment of feedback techniques. The main emphasis will be on so-called indirect feedback techniques. The most familiar of these, the Cartesian and Polar Loop will be reviewed, but the vector loop will also be emphasised due to its possibilities as a stand-alone amplifier, rather than a transmitter, technique. Some quantitative and CAD analysis will be performed to illustrate the tradeoffs between baseband gain, bandwidth, stability, and linearisation effectiveness. Some novel approaches to vector PA feedback will be introduced, which may in the future lead feedback methods back into the forefront in linearised PA systems when newer RF transistor technologies become available.

Day 4 continues with feedforward, which in commercially available products still remains the mainstream linearisation technique. The feedforward loop will be analysed quantitatively in order to characterise the important tradeoffs between system performance and efficiency. The impact of different types of PA non-linearity on the feedforward system will be discussed. Tracking requirements, adaption, and error PA requirements will also be analysed quantitatively. A CAD simulator will be used to demonstrate some of the theoretical analysis, using both simple 2-carrier and also multicarrier signal environments. Some important variations on the basic feedforward loop will be discussed, including the so-called "digital feedforward" method, which is analogous to the digital derivative of analogue predistortion. The advantages and disadvantages of the two "DSP-era" PA linearisation techniques will be reviewed.

Day 5 considers practical implementation of linearised power amplifiers. First, the digital components of a predistortion system are discussed. This includes a review of currently available hardware, and considers the decision-making process in the selection of suitable parts for the predistorter. Next the theory and design of several microwave subsystem components are described, which are required in any linearisation scheme. This will include a more extensive analysis of various kinds of detectors, with the tradeoffs between speed and precision, and different detector technologies. Vector modulators will also be discussed. Finally, the intriguing concept of converting "wasted" RF energy back into useful DC supply will be reviewed and analysed as a possible efficiency enhancement technique.

Daily Schedule

Monday 9.30-12.30, 13.30-17.00

Part 1 - Introduction

Part 2 - RF Power Amplifiers Review

Part 3 - Review of Modulation Formats

Part 4 - Review of Regulatory Specifications for PAs

Tuesday 9.00-12.30, 13.30-17.00

Part 5 - Nonlinear Properties of RF PAs

Part 6 - Analog Predistortion

Wednesday 9.00-12.30, 13.30-17.00

Part 7 - Digital Predistortion

Hands-on Demonstration of Digital Predistortion

Thursday 9.00-12.30, 13.30-17.00

Part 8 - Feedback Techniques

Part 9 - Feedforward

Friday 9.00-12.30, 13.30-16.00

Part 10 - DSP and DPD hardware

Part 11 - RF Sensing and Control

Part 12 - Conclusions


Course Fee

Standard price £1,900
Early registration price (firm registration received 6 weeks before course start) £1,700

VAT at 17.5% will be added where applicable to these prices

The course fee includes tuition, course documents, lunches and break refreshments. Accommodation is not included in this price but we can arrange it for you or send you information. New Hall offers en-suite rooms which we can book for you (cost is £63+VAT per night inc full English breakfast), and many local hotels and guest houses are also available.

Preliminary Registration

We are happy to make a preliminary course reservation, until you are ready to confirm your booking. No payment or other financial commitment is required for a preliminary registration. To register, click here .

Firm Registration

When you confirm your registration we will send you information on the venue, accommodation and travel, and an invoice. If we receive a cancellation from you in writing up to 2 weeks before the course begins, we will refund your course fee less a 15% administration fee. After that date we cannot refund your fee. We can accept substitutions at any time until the course begins.

About your Tutors

Steve Cripps, Hywave Associates, Somerset, UK. Dr Cripps obtained his Ph.D. degree from Cambridge University, England. He worked for Plessey Research on GaAsFET hybrid circuit development. Later he joined Watkins-Johnson’s solid state division, Palo Alto, CA, and has held Engineering and Management positions at WJ, Loral, and Celeritek. During this period, he designed the industry’s first 2-8 Ghz and 6-18 Ghz 1 watt solid state amplifiers, and in 1983 published a technique for microwave power amplifier design, which has become widely adopted in the industry. In 1990 Dr. Cripps became an independent consultant and was active in a variety of commercial RF product developments, including the design of several cellular telephone power amplifier MMIC products. In 1996 he returned to England, where his consulting activities continue to be focused in the RF power amplifier area.

Chris Potter, Cambridge RF Ltd., Cambridge UK. Dr. Potter is presently a consultant with Cambridge RF Ltd. in Cambridge UK. Since 1998, he has been involved with linear PA designs for terminals and cellular infrastructure. His main research interests are in the field of adaptive linearisation. He is also active in RF system designs for terminals and cellular infrastructure, and tools for automation of the RF design process. Dr. Potter received the B.Sc. degree in Electronics in 1983 from the University of York, England and the Ph.D. degree in 1987 from the University of London, England. From 1983 to 1995, he designed a variety of microwave and RF test equipment at Marconi Instruments. From 1995 to 2002, he worked at Tality UK on RF architectures and product designs for GSM, EDGE, Bluetooth, 802.11a/b and WCDMA.

Getting in touch :

If you would like to find out more about our training courses or other services, why not send us an e-mail? Outline your requirement and we will be pleased to begin working with you.

Cambridge RF Ltd.,
10, Teversham Road,
United Kingdom
CB21 5EB

Telephone: +44 (0)1223 700497

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