Conventional wisdom in consumer electronics, driven by Moore's law, calls for increasing functionality on single SoCs. But the laws of physics (heat, current leakage, crosstalk, etc.) have all but eliminated Moore's law as a gating factor for functional integration in consumer electronics. Modern microprocessors drain batteries like the engine of a Hummer drains a gas tank, while mixed-signal circuits stubbornly refuse to yield to microscopic digital design rules. Moore's law was fine for PCs that crunched masses of data and forced users to adapt to unnatural user interfaces like monitors and keyboards. It doesn't work, however, when terabytes of data, much of it audio, are constantly flowing back and forth wirelessly on a handheld device.
However, integration is still a demand from the consumer, so what's a digital designer to do? Not to worry. It's the analog designer's problem.
Integrated handheld devices need to be feature rich and small with long battery life. But consumer electronics feature sets are culturally driven. Asian customers look for multipurpose mobile phones with small form factors and long battery life. Europeans look for efficient communication devices but have traditionally been less concerned with games and video. Americans look for all of that, but in separate devices. For example, Treos are very popular in the US, but you won't see them in Japan or Korea because they don't like the form factor. While there may be convergence in the next decade, right now people want what they want.
So features and size, both directly connected to digital integration, are not common factors in consumer product success. But two factors are: power and analog signals.
No user wants to watch movies on a 1-inch square screen, so the size of the device is not as important as audio and video quality. Nor do they want the device to burst into flame. Quality of sound and battery life, especially when the user is watching a 2-hour film, are also of high importance. All of that is the specialty of analog and power-management design.
You can manage those features in a digital chip, but you need separate power management circuitry, which defeats the purpose of digital integration. When audio quality is important, digital processors just don't perform as well as dedicated, mixed-signal ICs.
Integrating mixed-signal and power-management functions into one IC, separate from digital logic, can be the best solution to make consumer products successful. This approach lowers chip count to as few as two in many systems and requires fewer compromises.
Mixed-signal and power management circuits have much in common. Both need detailed simulations based on accurate mathematical models of individual transistors. Some use characteristics that differentiate products, such as noise, harmonic distortion, and power efficiency, which are notoriously difficult to predict through simulations. Analog designers take this into account and often fine-tune the layout of circuit elements on their chips by hand.
Power efficiency in portable devices is often only possible with switched-mode power supplies, which generate switching noise. Since mixed-signal devices contain significant amounts of digital circuitry that produce switching noise, designers have already found ways to deal with this issue by protecting sensitive signals or using topologies that can deal with larger amounts of noise.
Giving mixed-signal designers control over the power supply has advantages for system-level design. Power management circuits are rarely affected by noise or interference from other circuit blocks, so power-management experts dabbling in mixed signal tend to dismiss noise abatement efforts out of ignorance or lack of understanding. Some of the most prevalent performance issues plaguing mixed-signal circuits today are directly related to the quality and stability of power supplies.
Integration of power management with audio functions enables the supply to react more quickly, or even anticipate, sudden increases in the system's power consumption. Shortening the power supply's reaction time reduces the need for storing a reserve of electrical charge in large costly capacitors and smaller, cheaper capacitors can be used.
Integrating power management and mixed-signal functions into a single-use IC clearly makes sense both economically and technologically. Overcoming the switching noise is key to the success of such combined ICs, and system-level design will help deliver solutions that do more than the sum of their parts. While the strategy of partial integration appears a more modest goal than all-in-one integration, it has a better chance of actually fulfilling its promise now. Multi-function ICs coming to market soon will allow digital designers the freedom to achieve expanded feature sets that give systems manufacturers significant market share in portable consumer electronics.