While the talk and boom about multimode multiband phone in CMOS is turning greener, there should be a natural question around it. How about doing all these in software? Rather add a level of programmability such that a great deal of issues from a hardwired implementation are shifted to more flexible firmware. Without contention, pros and cons with the idea of programmability still prevail. Clearly, one definite advantage I see with programmable design is the significant cost reduction and reuse. Additionally a migration or upgrade, which is imminent from a future gadget design point of view, can get done with relative ease with a programmable multimode chip. Building a suitable processor architecture to suit the modulations schemes (say an OFDM based scheme can have an inbuilt FFT engine or a WCDMA can have a correlator engine). Aren’t anyone working seriously in these directions? I am sure there are many, atleast startup ventures. Vaanu and Icera indeed are two things coming to my mind. How about the big boys? There were lot of furies about software programmable baseband chips being developed. Not quite sure what is the latest in that front. Isn’t it the next big thing in the offing? I am sure the EDA big houses have thought ahead for building tools for a heavily software oriented design, at least for years ahead. Or is it that, I am jumping the gun a little too far? However, I see some top level bottlenecks in making this programmable multimode chips realizable at an easier pace than a textbook concept. One of them is difficulty in getting away the analog front end. As a matter of fact, now I feel that, analog is going to stay.
So where are we heading to? Clearly, an all CMOS multiband multimode single chip (baseband and analog) with a near perfect RF and a software architecture would be the ultimate holy grail of cellular chip design. How many bands and how many modes to be incorporated becomes less important, if the programmability aspect is assured. Challenges within a single chip concept are themselves many. Clearly the RF portion is expected to take up lesser share of the overall chip size. An all digital front end is aimed in that direction. While a direct digitization of radio signal of high frequency eliminates analog life process significantly, there are several practical bottlenecks with this Utopian design model. We are not quite there to say good bye to analog entirely. Analog signal processing is still critical and inevitable, even for a programmable multimode dream. I will give you some numerical facts to substantiate my claim:
Suppose we decide to build programmable all digital zero if receiver for a 2GHz system (around the UMTS band). Then, Shannon Nyqusit sampling would demand at-least 4 G samples/second. Even with a processor which clocks 4Ghz and say 8 operations per cycle, our full steam purchase is going to be a maximum 32000000 operations per second. This theoretical figure is based on the assumption that processor memory is fully utilized. At the sampling rate of 4G samples/second, we only are going to get operations per sample. How are we going to have all the fancy radio algorithms shape life with this? Even to implement realistic functionality of a typical modern radio, this is inadequate. Another important thing is the imminent power dissipation to run a processor at . For a portable gadget, where these chip are targeted for, we still need more and more hand in hand optimization and integration with analog processing, software as well as digital processing, in addition to an optimized system architecture. My feeling is that, the analog front end is going to stay for some more time, if not for ever. At least on the immediate future, we need more inroads from analog processing, to realize the small size, cost effective multiband multi mode chip dream.