A sub-mA phase-locked loop fabricated in a 65nm standard digital CMOS process is presented. The impact of process variation is largely removed by a novel open-loop calibration that is performed only during start-up but is opened during normal operation. This method reduces calibration time significantly compared with its closed-loop counterpart. The dual-loop PLL architecture is adopted to achieve a process-independent damping factor and pole-zero separation. A new phase frequency detector embedded with a level shifter is introduced. Careful power partitioning is explored to minimize the noise coupling. The proposed PLL achieves 3. lps RMS jitter running at 1.6GHz while consuming only 0.94mA.
Although the design of many kinds of microprocessors has been under developing for several decades, the computer architecture R＆D community lacks well documented lessons and experiences about design decisions in the research literature. In this paper, we systematically present the design decisions we made during the designing and prototyping of Godson-2 series processors. The 250MHz Godson-2B, 450MHz Godson-2C, and 1GHz Godson-2E processors that implement 64-bit, four-issue, out-of-order architecture were taped out in 2003, 2004, and 2005, respectively. Each processor triples its predecessor in the SPEC CPU2000 rates. Our first-hand experiences and lessons gained from these designs would provide unique perspectives and insights that are not available in any existing text books and/or published papers. We summarize 10 critical lessons and experiences based on hundreds of our attempts at architectural and design optimizations for performance improvement of Godson-2 series processors. The issues include silicon-simulation correlation, design balancing, performance optimizing, and pico-architecture tuning. We conclude that persistent improvement, attitude towards work-on-silicon design, and insightful understanding of software and fabrication process are the three most important factors for designing a high performance processor with low energy consumption.
