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RF Designers Favor Which Processes and PAs?

Data from Globalfoundries and an independent CDT survey confirm growth in RF silicon designs, III-IV challenges, and trends in power-amplifier techniques.

Earlier, I reported how RF devices benefit from overall low-power mobile trends and increased digitalization. Now, a recent paper and survey reveal which digital implementation processes are gaining popularity and which specific low-power amplification techniques are favored by semiconductor intellectual-property (IP) designers.

A few months back, Globalfoundries engineers Fayyaz Singaporewala and Peter A. Rabbeni provided a Chipestimate.com Techtalk presentation entitled, “Data at the Center of RF Foundry Growth.”

In their paper, the engineers discussed the flexibility of silicon-based RF chips: “Although the Johnson limit dictates the limitation of silicon in comparison to more traditional RF technologies like III-V’s, the ability to integrate RF with digital control provides designers the capability to innovate in ways never thought of and approach or even exceed the performance of these traditional technologies (see Figure 1).

The recently completed “Chip Design Trends” (CDT) RFIC survey confirms the popularity of the silicon implementation of RF devices (see Figure 2). For current designs, more respondents listed silicon (66%) followed in order by GaAs (32%), SiGe (27%), GaN (23%), and InP (10%). For future designs, more respondents listed silicon (66%) followed in order by SiGe (31%), GaN (28%), GaAs (16%), and InP (13%). [The “Chip Design Trends” 2013 RF-MW tools survey targeted developers of products in RF and analog/mixed-signal (AMS) ICs. A total of 129 qualified designers responded to this survey.]

From both the Globalfoundries data and CDT survey, it’s clear that silicon remains a popular implementation choice for RF and microwave IC designs. Also evident from the Globalfoundries data – although not queried in the CDT survey – is that many fabs and fabless companies are looking at alternative device implementations, such as silicon-on-insulator (SOI) for both analog RF and digital apps.

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Figure 1: Integrating RF with digital control is a growth trend at Globalfoundries.
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Figure 2: Favored high frequency PDK processes.

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Figure 3: Ranking of favored PA techniques.

Predistortion trends offered another point of comparison between the Globalfoundries paper and the CDT survey. The engineers from the foundry noted that the application of DSP concepts to RF applications is not new, “but the advancements in digital processing have reached a point where the benefits of these concepts can be efficiently realized.” Some emerging examples of these concepts include envelope tracking, tuning, and predistortion. Again, these are not new concepts, but it is only now that silicon technologies have advanced to a point which makes the application of these concepts to RF possible.

The CDT survey asked the following question: “If a discrete power amplifier (PA) is part of the RF front-end subsystem, then please rank the techniques that you would use to improve the efficiency of the PA.” As the results show (see Figure 3), digital pre-distortion is still the preferred technique for improving PA efficiency. Even though envelope tracking has received a lot of attention in the media, it ranks low in terms of priorities for PA development.

Low-power trends in high-growth areas like the mobile consumer market are driving the popularity of specific RF implementation processes and power-amplification techniques. The explosion of analog-digital smart sensor (or sensor fusion) devices should also accelerate these trends. ◆

References:

  • RF Circuit Design by Bowick, Blyler, and Ajluni, 2nd Edition, Elsevier
  • RF and Microwave Systems magazine
  • Semiconductor Growth Turns Wireless – IP Insider blog
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