From a standards point of view, the industry is transitioning from second-generation (2G) and variants of 2G (2.5G GPRS, 2.75G EDGE) systems to 3G air interfaces. The RF and baseband hardware and chips to support this transition are currently discrete, causing the phone's printed circuit board to get larger.
The 3G handsets available in the market today make us feel that we have regressed 10 years in cell phone size, form factor, and power consumption, states Alan Varghese, senior director of Semiconductors Research at ABI Research.
From a features and functions point of view, ABI Research notes that digital cameras have been a popular feature in cell phones. And it is projected that 150 million camera phones will be shipped in 2004. Functions such as Bluetooth, WiFi, and GPS are currently entering the high-tier models and will soon move down to the lower tiers.
What are the implications of these features and functions in terms of hardware and software? Cameras require a discrete module containing the lenses, image sensor, image processor and a few passives. Bluetooth, WiFi, and GPS all require additional hardware either in the form of one-chip or two-chip solutions. Moreover, all these features require additional software and processing power in the baseband and associated code and data memory as the industry moves from 2G and variants of 2G to 3G air interfaces, notes Varghese. Thus, according to Varghese, with the transition of standards, and with the addition of new functions, the handset will grow in size unless aggressive integration happens in the RF and baseband sections of the phone.
There are two trends happening as far as integration on the RF side is concerned. Until recently, the PA and its associated circuitry was always kept as a separate component from the rest of RF. The reason was twofold. First, it was designed in a technology such as GaAs, which was different from the other portions of the phone. Second, it dissipates a lot of heat so it is hard to integrate with anything else, without exceeding the thermal limits of chip packaging or causing secondary effects such as temperature drift in surrounding circuitry. But now, vendors that have deep skills in SiGe technology are using that process to design power amplifiers. Considering that the rest of the radio section has already been designed in SiGe, this opens up the intriguing possibility of integrating the PA and the RF transceiver (RFTCVR), asserts Varghese.
The other trend sees the PA and its associated circuits still kept as a discrete part, but the RFTCVR is designed in a RFCMOS process, which allows the possibility of integrating the RFTCVR with the baseband section — already done in CMOS. While the advantage of the first is that the sensitive RF/analog systems are all kept together, as well as the noise-inducing digital sections, the determining factor will be whether PAs in SiGe technology will meet the performance, cost and time-to-market requirements of the cell phone faster than the RFTCVR would in a RFCMOS process, adds Varghese.
Meanwhile, as the RF integration debate continues, software-defined radio (SDR) architectures are in preparation, bringing digitization of the signal closer to the antenna and allowing different communications standards and protocols to be implemented via software rather than through dedicated hardware. What this means is that the digital side will encroach more and more into the RFTCVR section, thus making RFTCVR a smaller and smaller section in the future.
Likewise, on the baseband front, there were two cores specialized in two functions. While the DSP core is specialized in the multiply-accumulate (MAC) number crunching, the microprocessor performs all the call processing software and interfacing to peripherals. Over time, both these cores found their way into the same package and then onto the same silicon die. The latest trend is where these two cores are collapsed into a single modem core that is reasonably optimized for both DSP and uP functions, according to ABI Research.
Plus, as new functions and features are added, the code and data space requirements have gone up by eight to 16 times the sizes common in the early days of cellular. Integration is in the form of System-in-Package (SIP) where the NOR FLASH, SRAM, Pseudo SRAM and maybe even NAND FLASH are stacked on top of each other, minimizing form factor, power consumption and cost. Finally, to do applications such as digital imaging, gaming, MMS, video calling, the high-tier phone models have a separate dedicated uP called the applications processor. But we notice a trend where the applications core is integrated with the baseband either as an SIP or on the same silicon die, or the applications code is absorbed into a slightly more powerful baseband processor. This relentless drive toward integration will continue, as the functions that are more stable go through consolidation, giving room for new features and new functions, concludes Varghese.