Our Nov article, Linearization and High-Efficiency RF Design Techniques for Small Cells,  by authors from Scintera and TriQuint stirred up the following comments:

RF Power Amplifiers Group

Matt Diessner•Thank you for your insight and a good article. Liked the part about pre distortion!

Lei Guan•Totally agree that, the standalone DPD chip/unit will help a lot on linearization of RF Power amplifiers. Thanks for this interesting paper.

Wassim El-Ahdab•Indeed, interesting paper!

Patrick Hindle•My understanding is that this technique uses analog predistortion as opposed to digital predistortion (DPD) so it is typically easier to implement. DPD requires switching back and forth in the domains taking feedback from the end signal while analog predistortion is done all in the analog region.

Junfeng Jie•Nowadays, techniques have been developed to use less than 1.5X BW for DPD observation path, so that the ADC can be more close to PA sampling and one simple FB path is possible. With such structure digital baseband DPD maybe also very good option due to its flexibility and power. After all, mobile or small cell usually take less carriers and show narrower BW

Larry (Nanlei) Wang•Patrick: good article.

When I saw AP561, my heart skipped a beat. I lead the team designed that part long time ago, like 2003 initially! The old horse still has the horse power!

Amplifier Frontier Research Group

Zhancang Wang•Scintera APD is becoming more and more popular and being accepted by manufacturers.

Daniel Huang•Seems PA efficiency is not quite a critical issue for small cells comparing to macro cells.

Zhancang Wang•@Daniel, seems the story as you said. But if we change our perspective to evaluate this issue, that is small cell targeted at hot spot and in large qty to provide enhanced coverage and capability. Although small cell low efficiency will not be significant, overall small cell in volume still need high efficiency solution to save OPEX for operators, I think.

Patrick Hindle•Zhancang Wang is correct as small cells seem to be the best way to solve current coverage problems and future capacity issues so the volume is expected to be very large.

Ed Takacs•Efficiency is always an issue, it just varies on how it compares with other design goals. Efficiency certainly is more of an issue for portable systems and handsets, while it is less of an issue for base stations, or any other gear that has access to the "infinite bus". However, it is still an issue, as electricity consumption is expensive, and will e increasingly so.

Zhancang Wang•@Ed, totally agree with u. Is that one of the reason why Nujira put more efforts on handset ET recently? If efficiency was as urgent as handset for 4G, GaN could be easier to be accepted and put into volume widely and easier. :D

The problem with the Nujira modulator circuit components is that is takes up board space. There is a maximum size that the consumer for the various handset radios will consider, and power consumption will always be at a premium, because of bigger and better screens and/or function in the handset. Nothing cramps a user’s style more than a quickly drained battery. The tradeoff between linearity and what will suffice in terms of EVM to achieve the type of BER's that the system guys want and battery power will be an ongoing effort. The handset designers will be given increasingly tough requirements from both sides-the linearity and efficiency teams, as both data content requirements and battery life requirements increase.

Zhancang Wang•@Ed, thanks for your deep insights! For handset it seems much more difficult to come up any break through to make big capacity battery with small size than improving PA efficiency :) Once new monster battery emerges, people may be back to love simple low efficiency PA for low cost again?

I understand that ET is a philosophy that transfers the difficulty of high frequency, low efficiency, simple, high cost thing into low frequency modulator, high efficiency, more complex, and low cost stuff. So from the trade-offs, we all see our benefits from different angles to decide to use it or not...

Ed Takacs•All techniques are in the design toolkit of a prescient designer. :)

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