System-on-Chip technology comes of age
The silicon transistor continues to be at the heart of post-PC era products like the smartphone and the tablet. The success metrics for the transistor, however, are quite different for these mobile consumer products than they have been in the past. Frequency (clock-speed) was the primary metric in the PC era and the central processing unit (CPU) was the primary chip that drove advancements in semiconductor technology for decades. Form-factor was hardly an influencer and there wasn’t as much of a drive to integrate system-level functionality either on-chip (SoC) or in-package (SiP).
Form-factor, cost and power for a given function are now critical drivers in the mobile market and that in turn has increased the importance of on-chip integration of functional hardware (e.g. power management, computing, audio/video, graphics, GPS and radio). This shift from mostly performance-centric chips to mostly power-constrained chips and the focus on lowering cost and increasing system-level integration is poised to disrupt the traditional semiconductor landscape. SoC technology has been used by fabless vendors and foundries for well over a decade. But it is the rapid proliferation of mobile post-PC products that is proving to be the catalyst for this technology to finally realize its full disruptive potential. Within the last five years, SoC technology has moved from being at the heart of smartphones to enabling tablets and full feature mobile computers like ultrabooks.
A post-PC world
With the advent of smartphones and tablets, the computing paradigm has begun to shift in such a way that the overall user experience is becoming a critical benchmark independent of the raw performance of the underlying technology. The Apple iPhone and iPad are great examples of this paradigm shift. Both devices provide a highly satisfactory user experience – not because they offer the fastest computing speed with the most advanced silicon but because they enable rich features at reasonable computing speed and reasonable price points.
The features of these devices collectively enhance the user experience – outstanding graphics rendering, wireless connectivity, instant-on, connected stand-by, long battery life and touch-screen apps. They may not offer the fastest raw computer performance, but they are perceived by the average consumer to be fast and provide a far superior user experience. The iPad represents the first of a wide array of post-PC products. Innovations like the Transformer (Asus), Surface (Microsoft), Nexus (Google), MacBook Air (Apple) and Ultrabook (Intel) are also aimed at redefining computing for the mobile age.
The key to the success of early post-PC products like the iPad is the fact that they were designed from the ground-up without the baggage of legacy PC-era software or hardware. Innovation around the sustaining silicon hardware technology would have called for higher performance standalone processors (CPUs) utilizing the abundance of logic transistors and even more complex layers of software to utilize the abundance of memory capacity. Instead, the new products utilize highly power constrained hardware and very lean software for accomplishing specific tasks (e.g. a video decoder to drive the display). In order to make power efficient systems for the mobile world, it is critical to shift as much of the burden on hardware while utilizing lean software. Simply force-fitting legacy PC hardware and software into a new form factor will not be as power efficient and hence will not lead to a superior user experience.
The emergence of tablets and smartphones does not herald the end of the traditional PC as we have come to know it. The PC will continue to find a place on every desk for the foreseeable future and banks of servers will continue to be used in data centers for compute-intensive applications. Yet, if history were a guide, it would suggest that the sustaining CPU semiconductor technology underlying traditional PC products is likely to be eventually displaced or at least substantially altered by the disruptive SoC technology underlying the smartphone. The rapid evolution of SoC based technology over the last few years supports this hypothesis.
Evolution – a look back
Since the advent of independent foundries at the end of the 1980s and early 1990s, the semiconductor industry has been segmented into three major entities – Integrated Device Manufacturers (e.g. Intel, AMD (pre-2009) and Samsung), fabless companies (e.g. Apple, Qualcomm, Broadcom, NVIDIA) and foundries which make chips for the fabless companies (e.g. TSMC, UMC, Samsung, GlobalFoundries).
Historically, Intel and AMD focused on making CPU-based chips (e.g. Core and Athlon) while NVIDIA focused on making standalone graphics chips (GPU) for the PC and server markets. All the other players in this landscape have utilized some form of on-chip system integration (SoC) to meet the diverse needs of their respective markets.
The generic definition of a SoC is the on-chip integration of a variety of functional hardware blocks to suit a specific product application. A SoC can thus be as simple as a basic connectivity chip which combines some mixed-signal and digital circuitry. A more complex SoC may include the on-chip integration of an application processor unit (APU) and a graphics processor unit (GPU). Even more functional SoCs further integrate various other hardware blocks (e.g. image processor, audio/video decoder and modem). It is this ability to continue to integrate disparate functionality on a chip that has enabled SoC technology to rapidly evolve from supporting a simple feature-phone to a smartphone and all the way to a tablet computer.
Qualcomm started out by designing chips for the growing connectivity market with the advent of cellular telephony and the internet. NVIDIA came to light as a maker of standalone graphics chips. Over time, each of these companies responded to an evolving technology trend and built upon their initial successes as they incorporated ever higher levels of functional integration into their chips. As a result, Qualcomm evolved its product line-up from standalone connectivity chips by adding an applications processor (Krait via ARM license), a GPU (Adreno via AMD Imageon buyout) and a power management unit. Qualcomm’s flagship products (Snapdragon family) now include all these blocks making it a highly functional mobile SoC product.
Similarly, NVIDIA evolved from a maker of standalone graphics chips by adding an applications core (via ARM license) and a connectivity block (via Icera acquisition). NVIDIA now offers highly integrated mobile SoCs (Tegra family) which power multiple tablet computers. Just a few years ago, Apple which was not even in the mobile chip design business started designing its own SoC based chips (A- family) using an application processor (via ARM license) and a graphics processor (via license from Imagination Technologies). Similarly, Samsung has also acquired all the SoC building blocks and is even taking early steps to extend this trend to server chips.
An indicator of the growing influence of the SoC is the consolidation trend within the industry. Apple acquired PA-Semi, enabling it to design its own application processors. Qualcomm recently acquired Atheros to strengthen its wireless connectivity suite and Summit Technology for enhanced power management capability. NVIDIA acquired Icera to strengthen its connectivity offering and Intel acquired Infineon Wireless to gain entry into the baseband connectivity market. These acquisitions point to a consolidating market in which only a few strong players have all the required functional blocks and are getting ready to fiercely compete in the growing mobile market.
The smartphone offered the first significant platform for SoC technology to demonstrate its potential and put the SoC on a collision course with the standalone CPU. The smartphone valued on-chip integration far more than a standalone desktop. Utilizing dedicated functional blocks has several advantages over general purpose processing cores – these blocks can operate at lower frequencies while delivering higher system-level performance and consuming much lower system-level power.
In addition, by moving more functionality to hardware, the SoC enables lean software which results in lower system-level power. Using dedicated cores enables the smartphone to only turn on specific blocks for specific tasks whereas a general purpose core would have to be on all the time regardless of the task being performed. A system-on-chip is thus far better suited for mobile devices compared to a standalone CPU.
Early leadership in SoC technology put the foundry ecosystem players at a significant advantage over incumbents like Intel and the technology also benefited immensely from rapid growth in smartphone shipments. Intel was unable to break into the smartphone market for the first five years (until 2012). The introduction of the iPad and the subsequent growth in the tablet market further solidified this trend.
An indicator of the disruptive potential of the SoC is the rapid rate of advancement – not only in terms of functionality and shipped volumes but also the proliferation of a robust design and software ecosystem to support it. In just five years, the SoC technology has catapulted from enabling basic computation/connectivity on a feature phone to being at the heart of all smartphones and early stage ultrabooks, capable of a wide range of functions including audio/video, gaming, communication and productivity.
Collision – present day
Early indications are that the SoC is very clearly on a collision course with the CPU. The Surface tablet from Microsoft highlights the choice that OEMs now have when choosing processor architecture. This tablet will be made in two versions – one using an ARM-based SoC processor (NVIDIA Tegra 3) and another using an Intel x86-based CPU processor (Ivy Bridge). Table 1 compares the relevant specs of these two versions while Figure 1 shows a die-photo and block diagram of the two chips. It is evident that the SoC based design is better suited for the ultra-mobile consumer form factor where light weight and long battery life are valued more than having the highest raw performance.
Click on image to enlarge.
Table 1 Comparison of SoC (NVIDIA) and CPU (Intel) based MS Surface tablets. It is clear that the tablet with SoC is more amenable for mobile use while the one with CPU would be less amenable as a mobile device. (Source: Microsoft Surface website)
The CPU based design relies on extra chips to achieve the necessary hardware integration and consumes more power, resulting in a 30% heavier and 40% thicker product form factor. It is also interesting to note that the NVIDIA SoC design is made using lagging 40nm lithography while the Intel CPU design is made using the two generation more advanced 22nm lithography. The comparison will only get more interesting next year when the SoC players move to 28nm technology with hi-k/metal gate transistors. The Surface tablet will serve as an important benchmark since it will provide a direct comparison between the incumbent/leading-edge CPU and the disruptive/trailing-edge SoC – not only in terms of functionality but also in terms of cost.
The unique cost structure enabled by the SoC has the potential to truly disrupt the business model in the semiconductor industry. The ASP for the NVIDIA Tegra SoC chip is in the range of $20 while the ASP for a leading edge Intel IvyBridge CPU chip is in the $150 range. The CPU chip will also need to be supported by other chips to provide the functionality that is provided by a single SoC. When OEMs compete on price, it will be very difficult for the CPU product to compete while retaining historically high profit margins. As the SoC gets better and encroaches into the ultrabook and laptop space, the cost differential will have an even larger impact. The rising influence of a low-cost, low-end technology (SoC) and its potential to eat into the profit margins of a high-cost, high-end technology (CPU) is an example of the classic segment-zero phenomenon articulated by Andy Grove (1).
The NVIDIA Tegra 3 SoC and the Intel Ivy Bridge CPU are both best-in-class products – but they are designed for different form factors and cost and value metrics. While it is conceivable that the low-margin SoC may be able to serve the high-end laptop market well, it seems unlikely that the high-margin CPU will be able to serve the low-end mobile market as well.
Click on image to enlarge.Figure 1 A typical CPU design (Intel Ivy Bridge) dominated by core/graphics compared to a highly integrated SoC (NVIDIA Tegra). The integrated SoC design has obvious advantages in the tablet and ultrabook formfactors (Source: Intel/NVIDIA websites).
The 32nm Medfield processor is expected to be replaced over the next year by an advanced 22nm processor (Merrifield) which is expected to sport a dual core Atom CPU for lower power. Even Intel’s flagship CPU products are seeing more on-chip integration. The GPU block grew significantly (an additional 400 million transistors) when Intel transitioned from the 32nm Sandy Bridge chip to the more advanced 22nm Ivy Bridge chip shown in Fig 1.
Intel has a significant lead in CPU process technology and is at the forefront of Moore’s Law. However, radical changes to architecture (e.g. Tri-Gate) may actually slow down the integration of on-chip functionality. In spite of acquiring baseband technology from Infineon in 2011, it is unclear when Intel will be able to integrate it with Tri-Gate transistors on Atom cores. Intel’s SoC product offering has traditionally lagged its mainstream CPU offering by 1-2 years. That gap is expected to narrow in the coming years as Intel addresses the growing need for on-chip integration and the growing threat from seemingly low-end product offerings which are rapidly becoming more competitive and cost-effective in the high-end.
Convergence – a look ahead
The present decade represents a period of strategic inflection in the evolution of the semiconductor industry – the next five years are likely to see a confluence of several technology and market forces which will collectively have a profound impact on the course of the industry. These trajectories are discussed below.
Trajectory #1: Ascendance of the SoC Functional integration is expected to continue making the SoC far more sophisticated and powerful. It will also evolve to consume less power and shrink in size as it moves from 40nm lithography to advanced geometries. Qualcomm, NVIDIA and Apple have demonstrated solid performance gains over successive iterations of their flagship SoCs (Snapdragon, Tegra and AX). There is likely to be fierce competition among these players as each tries to incorporate more functionality into their chips and win designs for new mobile products. The ascendance of the SoC will force disruptive changes to the traditional IDM cost structure and business model.
Trajectory #2: Ascendance of the GPU Usage models of the tablet and the smartphone indicate that the GPU is the most heavily used block within SoCs like the Tegra, Snapdragon and the A5X. Since the GPU is the largest block and also consumes most of the power on the chip, it is instructive that the silicon transistor be designed to optimize the performance and power of the GPU. It is likely that design houses and foundries will make the GPU the centerpiece for transistor design and manufacturing – historically all the blocks including the GPU had to adapt a transistor that had primarily been designed for the CPU. The rapid evolution of the SoC and the increasing role of the GPU are evident in Figure 2 which shows three successive generations of Apple A- family processors which were released within a two year period. The GPU on the latest A5X processor occupies almost half the die area.
Click on image to enlarge.
Trajectory #3: Diminishing returns from transistor scaling As the law of diminishing returns eventually catches up with Moore’s Law, there will be little economic incentive to scale transistor feature size. Companies at the leading edge of Moore’s Law may be able to compete effectively in high margin segments (servers and data centers) but will find it difficult to price their parts competitively for the low margin consumer markets. Design houses may find it more economical to scale orthogonally instead (e.g. adding more functionality and lower power per layer with 2.5D and 3D integration).
Trajectory #4: Accelerating product life-cycles Tablet and smartphone offerings are refreshed once every year – much faster than the historical PC refresh cycle. The semiconductor industry will need to adjust its technology development lifecycle to keep pace with the mobile product lifecycle. It is not feasible to scale-down transistor geometry every year – however it is quite feasible to rapidly incorporate increasing levels of functional integration into an existing geometry.
Trajectory #5: Dropping ASPs of mobile consumer products Already one is seeing the beginnings of a price war within the mobile space as companies like Google and Samsung offer tablets at half the price of the iPad. But as fabless vendors start competing from below for the high-end laptop and ultrabook markets, they will put significant pricing pressure on incumbents like Intel to price their parts competitively.
Trajectory #6: Growth in mobile SoC shipments Gartner predicts that total smartphone and tablet volumes may exceed 500 million units by 2015. At this rate, mobile SoC shipments will dwarf CPU shipments within the next few years.
The confluence of all of these vectors over the next 5 years is likely to put SoC technology at the heart of the semiconductor industry. Chip companies like Apple, Qualcomm, NVIDIA and Samsung are well positioned for this scenario and are likely to keep enhancing the functionality of their respective offerings. Design IP providers like ARM and Imagination Technologies are poised to benefit immensely as well. Foundries are well positioned to capitalize on this trend and will benefit from refocusing their efforts on transistor design in a way that is GPU-centric rather than being CPU-centric. Intel will continue to face increasing pressures to compete in the mobile market and Intel’s product mix may reflect a move toward more on-chip functional integration in the years to come. More importantly, Intel will be forced to also compete with SoC technology in the ultrabook and PC segments and doing so may necessitate a change not only in its technology direction but also in its business model.
If these trends continue, there is no reason why a SoC chip cannot displace a standalone CPU chip in a high-end laptop. The boundaries between the standalone CPU and the SoC are thus likely to erode in the years to come as the industry embraces and unleashes the full disruptive potential of the SoC.
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References
(1) Andrew S. Grove, Academy of Management, Annual Meeting, Aug 9 1998, https://www.intel.com/pressroom/archive/speeches/ag080998.htm
Pushkar Ranade is director of process integration at SuVolta. Prior to joining SuVolta in 2010, Ranade was with Intel Corp. where he contributed to transistor process integration and development of Intel’s 65nm, 45nm and 22nm logic technology. Ranade joined Intel in 2003 after graduating with a Ph.D. from the University of California, Berkeley. At Berkeley, his research was in the area of sub-70nm CMOS transistor design and involved the integration of novel gate materials and ultra-shallow junctions. Ranade has authored or co-authored over 40 technical publications and holds 9 U.S. patents.
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