Flexible Constraint-Management Drives Next-Generation Mixed-Signal Design

AMS Challenges

Advanced manufacturing technologies present AMS designers with greater challenges in managing parasitic behavior complexity, thermal and process variations, and noise interactions. In advanced designs using multiple power supply regions, IC designers require greater precision in transistor optimization and layout as they address growing concerns in high-speed I/O, noise control and significant IR drop due to parasitics. At the same time, increasing design and manufacturing requirements drive a growing array of design and manufacturing parameters that must be addressed early in design to avoid costly respins. The need for greater accuracy requires improved characterization of analog IP and libraries " each of which is becoming more sensitive to process variation and circuit interaction effects with each new product generation and advance in manufacturing technology.

For AMS semiconductor companies, the combined effect of growing technical issues and increasing business challenges impacts all phase of the AMS market. In mainstream AMS design, IC manufacturers expect designers working in 130nm technologies to maximize both design performance and manufacturing yield. For these designers, achieving the optimal balance requires greater accuracy in modeling and simulation to reduce guard bands without compromising yield. In addition, the ability to achieve an effective co-design of analog circuitry and packaging has become critical, particularly as speeds approach radio-frequency.

As design complexity mounts, so do the technical requirements and associated challenges (Figure 1). At 90nm, signal integrity and timing closure issues require engineers to adopt more effective means to identify and fix these problems, while still addressing yield concerns prior to manufacturing.

Furthermore, designers creating advanced system-in-package (SiP) and next-generation 65nm system-on-chip (SoC) designs need to combine complex digital blocks with RF components for wireless consumer devices. As clock frequencies increase and IC feature sizes shrink, these engineers must address the increasing analog behavior from digital blocks while coping with a combination of analog, digital and packaging requirements in these complex designs. For companies moving to 45nm technologies, these emerging challenges magnify in importance as designers work to characterize cell libraries quickly and accurately.

Design realities

With traditional approaches, AMS design teams have simply lacked the tools and methodologies needed to explore design alternatives early in design. Decisions made early in design have largely "locked in" the result, too often forcing wholesale redesigns and costly respins to untangle problems arising from early design decisions.

In the design phase, inefficient verification methods have complicated engineers' ability to optimize sensitive designs. In the face of shrinking product schedules, designers have been forced to limit verification runs, potentially compromising coverage for the sake of time-to-market. At the extremes of design complexity, SiP and SoC designers must work around traditional limitations in their ability to verify analog or RF circuits in the context of the full system.

With the increasing impact of physical effects on design performance, these problems extend and expand in layout phase, too often leading to further delays as engineers rework layouts or even completely redo physical designs to accommodate a growing list of design and manufacturing constraints. Here, the gap between modeling accuracy and silicon performance becomes sharply evident, leading to ICs that fail to achieve expected levels of performance, manufacturing yield or both.

Yet, more effective design methodologies, tools and models remain only supporting elements in AMS design. The custom nature of AMS design inherently requires continual manual guidance and careful tuning, depending on the knowledge, experience and talent of engineers to transform design specifications into high-yield, high-performance silicon. Indeed, AMS design can never be fully automated, but an effective design platform can significantly assist the process of custom design. By providing capabilities able to enhance the productivity of design teams, more effective methodologies, tools and models can help AMS manufacturers achieve their silicon objectives in a minimal amount of time with the minimum number of engineering resources.