I’ve seen quite a few comments in this section along the lines of “What’s really new here?” Is there some new technological enabler that makes it now possible to integrate more analog than ever before? What’s analog’s equivalent of Moore’s law?
While there is no wand that I can wave that will cause a clear and decisive answer to appear, there are a number of factors that should help clarify. Some factors are technology based; others relate more to the culture and mindset of the company doing the integration. I will try to be specific about the enablers that I can enumerate.
Process technology innovations
While digital CMOS technology has been shrinking by regular factors of two every two years, it should be noted that digital CMOS contains only transistors and interconnects. This means that fully digital ICs can benefit fully from reduced line widths. This is in contrast to analog circuits that need a significant amount of capacitor and resistor area. Many analog IC layouts are dominated by capacitor area and may make use of on-chip inductors as well, which are also area-intensive.
Process technologies that can provide higher capacitance per square millimeter can obviously make a big difference here, and that’s an area where you can expect innovation from companies that have their own process technology research such as IBM, NXP, and Maxim Integrated.
The basic parameters that define capacitance (relative permitivity, total area, and distance between the “plates”) are all subject to innovation in IC process technology. In particular, the use of deep trench structures, as contrasted with traditional planar techniques, can dramatically increase the effective area per planar mm2 of capacitors.
A quick web search on this topic will reveal just how active an area of innovation this is. Another area of process innovation is the ability to handle high voltages and high logic gate densities on the same die, using bipolar, CMOS, or DMOS (BCD) technology at 180nm and below. This allows for new classes of devices such as the power SOCs that integrate a microcontroller along with efficient power-management functions, audio codecs, battery “fuel gauges,” and more.
Digitally assisted analog
Where analog circuits have inherent limitations such as non-linearity, gain variations, DC offset accumulation, and frequency response accuracy (to name a few), it is often the case that digital monitoring and control can substantially correct these deficiencies, with 100 percent repeatability and high precision. In this approach, the main signal path remains analog in nature, and the digital assistance is (ideally) made transparent to the user. From an application point of view, the IC may appear like a traditional analog function, but in terms of the key analog performance metrics, it outperforms a competitor that is purely analog.
Another approach lies in the aggressive digitization of previously analog signal paths, which rely on the availability of ADCs and DACs with sufficient bandwidth and dynamic range within the power budget of the application. This is becoming increasingly feasible as ADC technology improves, and should always be considered for new designs.
Nevertheless, it is rare that the entire signal path can be digitized and the appropriate partitioning largely determines the performance, power consumption, and cost tradeoff of the device. Judicious use of digital technology to enhance or partially replace analog signal paths is a key area for innovation and differentiation.
As we approach system level integration on mixed-signal SOC designs, we need new design methodologies to manage the resulting complexity and verify the solution does perform as intended (and that we have the correct intentions, i.e., requirements, in the first place). This involves systematic methods and tools for requirements capture and traceability, along with the use of top-down design and verification methodologies that encompass mixed signal designs.
We also need tools that eliminate the discontinuity (and redundancy) in requirements representation and design representation that cause unproductive work, hide errors, and separate the system designers from the circuit designers. This is known as “single-source” design information. These system-level approaches to the design flow require a considerable cultural shift in an organization and executive-level support to implement. Nevertheless, this whole topic is a key enabler and cannot be neglected.
A company can have technology coming out of its ears and methodologies galore, but may still not succeed commercially unless it has a “can do, will do” attitude to getting things done and always challenges the technological status quo. Innovation and value creation occur when we have the guts to challenge previous limitations, and the technical skills that allow us to succeed from time to time. I must also mention that the execution discipline (which is also an attitude) is mandatory to make sure innovation becomes a shipable product in a timely manner.