There are two fundamental characteristics of CMOS that, in the long run, will carry it to win out over GaAs as the technology of choice for power amplifiers (PAs): integration and supply chain. Of course, these happen to be the same characteristics that have carried CMOS in the past, but let's take a closer look at how they are particularly relevant now.
Black Sand Technologies
First is integration. If a PA designer from 20 years ago were to look at what's shipping in today's handsets, he'd see PAs that look all-too familiar in architecture and function. While GaAs technology has changed little in the last two decades, a mind-boggling array of bill-of-materials reductions, performance improvements and feature integrations have been implemented elsewhere in the mobile phone.
Now that a 3G PA can be implemented in CMOS, the RF front end will be on a new technology trajectory that is aligned with the rest of the phone (what we all know as Moore's Law). We will soon see massive improvements in battery life and real-world performance.
Advanced polar and envelope tracking technologies will improve 3.5G and 4G output power and battery life. Pre-distortion loops will push PAs far into saturation, drastically increasing efficiency and battery life. On-chip tuning technologies will allow PAs to adapt to the real world, changing characteristics as the user walks along.
All or most of these technologies have been implemented in basestations. CMOS is the key to getting them into the handset.
Second there is supply chain. If every 1.3 billion handsets that ship next year include only CMOS PAs, it wouldn't make a dent in the supply chain, even considering that 3G phones have four or five PAs while 2G phones only had two. Meanwhile, leading GaAs PA vendors run 70-80 percent of their capacity solely for the handset market. Where will the GaAs suppliers get the capital they need to grow capacity to meet this exploding demand?
The massive R&D investment that occurs every year in the CMOS supply chain dwarfs all other semiconductor technologies combined.
How many times have we seen this movie before? Does anyone remember Cray? The GaAs supercomputer company. It took a while, but Intel's CMOS eventually did them in, and that's just one example.
In the early '90s it was Crystal (now Cirrus Logic) and ADI in audio converters putting an end to laser trimmed bipolar devices, while the late '90s had Cirrus and Marvell completely upend the read-channel market. Who knows who the players were before that?
And early in this decade, we saw Silicon Labs and Infineon take cellular transceivers into CMOS without looking back. Today we see the final stages of this progression in WiFi, with Broadcom, Atheros, and others offering single-chip radios. The scale of the CMOS supply chain is simply unstoppable once the technology aligns to take advantage of it.