Soc Design Often Includes Analog and Mixed-signal Circuits. Understanding Some of the Challenges of These Devices Helps Engineers Develop a Successful Soc-design Strategy

CMOS was developed as a digitally friendly process. Now, thanks to high levels of system integration and the emergence of SOC (system-on-chip) design, CMOS has also become the process of choice for mixed-signal applications. However, cutting-edge CMOS has limitations in these applications. Process restrictions, inaccurate simulation models, wide parametric variance, and noisy application environments require special efforts in circuit design, architecture, and layout techniques and in making optimal use of a limited process. Addressing these issues provides a systemdevelopment strategy for mixed-signal circuitry on CMOS. A DCP (digital-CMOS process) optimizes logic functions, including switching speed, low-voltage power supplies, submicron geometry, and high component density. Considerations that address analog and mixed-signal circuits are not emphasized in the definition of process parameters. Full process characterization and analog-circuit elements get left out. High CMOS volumes and the preference for digital-signal-processing methods motivate engineers to seek viable CMOS-SOC designs. Bipolar and other non-CMOS processes now find use primarily in applications that require special performance characteristics. To implement successful mixed-signal designs, you must use several strategies to get the most out of a restrictive process, reduce noise, use design techniques for process and environment robustness, and decide between digital and analog architectures. You must develop strategies for circuit elements and their models, circuit architecture, layout, and mask design.