Jitter measurement built-in self-test circuit for phase locked loops

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 77-79).This paper discusses the development of a new type of BIST circuit, the (VDL)2, with the purpose of measuring jitter in IBM's phase locked loops. The (VDL)2, which stands for Variable Vernier Digital Delay Locked Line, implements both cycle-to-cycle and phase jitter measurements, by using a digital delay locked loop and a 60 stage Vernier delay line. This achieves a nominal jitter resolution of 10 ps with a capture range of +/- 150 ps and does so in real time. The proposed application for this circuit is during manufacturing test of the PLL. The circuit is implemented in IBM's 90 nm process and was completed in the PLL and Clocking Development ASIC group at IBM Microelectronics in Essex Junction, Vermont as part of the VI-A program.by Brandon Ray Kam.M.Eng

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data