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Envelope Tracking Power Amplifiers
RF Cafe Quiz #63

RF Engineering Quizzes - RF CafeAll RF Cafe Quizzes make great fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job. Bonne chance, Viel Glück, がんばろう, buena suerte, удачи, in bocca al lupo, 행운을 빕니다, ádh mór, בהצלחה, lykke til, 祝你好運. Well, you know what I mean: Good luck!

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Note: Some material based on books have quoted passages.

Envelope Tracking Power Amplifiers for Wireless Communications - RF CafeThis quiz is based on the information presented in Envelope Tracking Power Amplifiers for Wireless Communications, by Zhancang Wang.

"Envelope tracking technology is seen as the most promising efficiency enhancement technology for RF PA for 4G and beyond wireless communications. More and more organizations are investing and researching on this topic with huge potential academic and commercial values. This is the first book on the market to give complete introduction, theory, and design considerations on envelope tracking for wireless communications. This resource presents microwave design engineers with a full introduction to the subject and covers underlying theory and practical design considerations.

Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway

I am continually amazed at the brilliance of people who work tirelessly to advance the state of the art of technology, medicine, transportation, and many other areas. They manage to succeed in spite of myriad obstacles placed in their collective way by infuriating levels of government regulation and government-imposed societal manipulation (e.g., political correctness). Scanning through the many engineering books I receive from Artech House, Cambridge University Press, et al, is a truly humbling experience as I witness the incredible talent and determination of my fellow humans. We owe them a great debt of gratitude. This book is a prime example of which I write.

On a comical note, I noticed that the translation to English while overall excellent, did produce some notable instances where similes did not come out quite right; e.g., on page 100 the description of something being 'the short pole' [in the tent] came out as "'the short board' to limit overall ..." Being the 'long pole' in the tent is often also used (but not in this book).


1. What happens to the power from an RF amplifier's DC power supply?

a)  It gets converted to heat

b)  RF amplifiers do not use DC

c)  It is unaffected

d)  It gets converted to RF power




2. What are the two types of efficiency definitions for an RF power amplifier?

a)  Thermal efficiency and layout efficiency

b)  Power added efficiency (PAE) and drain/collector efficiency

c)  RF efficiency and volume efficiency

d)  Time domain efficiency and frequency domain efficiency




3. Where did the Class S power amplifier get its name?

a)  It falls between the Class R and Class T amplifier topologies

b)  The 'S comes from its founder's (A.M. Sandman) last name

c)  The 'S' stands for 'sizzling' hot

d)  The 'S' emphasizes the plurality of the topology




4. What is the distinguishing feature of a Doherty amplifier?

a)  It operates in Class-D mode

b)  Low cost

c)  It doe snot require an external power source

d)  Load impedance varies according to the power level




5. What makes envelope tracking (ET) so attractive in mobile communications?

a)  High efficiency over a wide range of power levels

b)  It can operate on LiPo batteries

c)  Operates from DC to light

d)  It is popular amongst space alien believers




6. What is the name given to the diagram that portrays the parameter tradeoff in envelope tracking (ET) PAs?

a)  Eye diagram

b)  I-Q modulation plot

c)  Envelope tracking merit pyramid

d)  ETPTD (envelope tracking parameter tradeoff diagram)




7. What is the overall envelope tracking system efficiency most dependent upon?

a)  Accurate delay compensation between the RF signal and the envelope power supply

b)  Transistor efficiency

c)  Inductor 'Q'

d)  Ambient temperature




8. When is the nonsynchronous impedance transformer a good option for use?

a)  With synchronous communications systems

b)  When a synchronous transformer is too expensive

c)  In applications where a ¼-wave transformer is physically too long

d)  When cost is the primary design consideration




9. What is a common method used in digital front ends (DFEs) to mitigate efficiency degradation due to high peak-to-average-power-ratio (PAPR) signals?

a)  Software Defined Radio (SDR)

b)  Linear modulation

c)  Digital modulation

d)  Crest factor reduction (CFR) algorithms reduce PAPR before entering the RF power amplifier stage




10. How does envelope tracking (ET) boost RF PA efficiency?

a)  By using high capacity batteries

b)  By replacing a fixed DC supply with a dynamic supply voltage that tracks the RF envelope shape

c)  By assigning a location code for online data package tracking

d)  It doesn't



Need some help? Click here for the answers and explanations.

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