Abstract
One of the most critical design considerations during the planning of any large VLSI structure is the definition and implementation of the clocked storage elements (CSEs) and the circuitry which drives the local clocks to these elements [1–4]. The nature of the solutions adopted will affect almost every aspect of the design, including its manufacturability, testability, reliability, power consumption, and operating frequency, while the complexity and style of latches and flip-flops employed will affect almost every design automation tool, from high level logic simulation methodology and logic synthesis engines, to circuit tools for detailed device tuning, timing, and testability analyses. A modern microprocessor chip may contain from 0.75 to 1.5M latches and flip-flops [5, 6], and clocked elements may account for 30–40% of the total chip AC power dissipation [7, 8]. Furthermore, the delay overhead or latency of these elements is typically in the range of 2–3 FO4 for modern high-speed designs [5, 9] which may account for 10–25% of the design cycle time for designs spanning the range from 10 FO4 (performance-only optimization) up to about 30 FO4, typically the upper end of the range for power performance optimized designs [10]. Thus the CSE definition is of fundamental importance to any VLSI project; the correct selection, optimization, and implementation will be a basic part of the global design strategy. The goal of this chapter is first to provide a high level overview of the design space of these elements covering the basic design metrics, issues, and trade offs, and second to look at several families of CSEs. This will be followed by a more detailed discussion on aspects of test and testability, design robustness against variability, reliability and soft error rate (SER) considerations.
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Warnock, J. (2009). Clocked Elements. In: Xanthopoulos, T. (eds) Clocking in Modern VLSI Systems. Integrated Circuits and Systems. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-0261-0_3
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