Low-Jitter Clock Multiplication: a Comparioson between PLLs and DLLs

This paper shows that, for a given power budget, a practical phase-locked loop (PLL)-based clock multiplier generates less jitter than a delay-locked loop (DLL) equivalent. This is due to the fact that the delay cells in a PLL ring-oscillator can consume more power per cell than their counterparts in the DLL. We can show that this effect is stronger than the notorious jitter accumulation effect that occurs in the voltage-controlled oscillator (VCO) of a PLL. First, an analysis of the stochastic-output jitter of the architectures, due to the most important noise sources, is presented. Then, another important source of jitter in a DLL-based clock multiplier is treated, namely the stochastic mismatch in the delay cells which compose the DLL voltage-controlled delay line (VCDL). An analysis is presented that relates the stochastic spread of the delay of the cells to the output jitter of the clock multiplier. A circuit design technique, called impedance level scaling, is then presented which allows the designer to optimize the noise and mismatch behavior of a circuit, independently from other specifications such as speed and linearity. Applying this technique on a delay cell design yields a direct tradeoff between noise induced jitter and power usage, and between stochastic mismatch induced jitter and power usage

Optimising filtering parameters for a 3D motion analysis system

AbstractIn the analysis of movement data it is common practice to use a low-pass filter in order to reduce measurement noise. However, the choice of a cut-off frequency is typically rather arbitrary. The aim of the present study was to evaluate a new method to find the optimal cut-off frequency for filtering kinematic data. In particular, we propose to use rigid marker clusters to determine the dynamic precision of a given 3D motion analysis system, and to use this precision as criterion to find the optimal cut-off frequency for filtering the data. We tested this method using a model-based approach in a situation in which measurement noise is a serious concern, namely the registration of the kinematics of swimming using a video-based motion analysis system. For the model data we found that filtering the data with a single cutoff frequency of 6Hz under some conditions decreased the accuracy of the reconstruction of the kinematics compared to using the unfiltered data. If the cut-off frequency was used that yielded optimal dynamic precision, then the accuracy improved by 29% compared to using raw data irrespective of the cluster position, close to the optimal accuracy improvement of 30%. We confirmed in an experiment that the cut-off frequency at which optimal precision was found varied between cluster positions and subjects, similar to the results obtained with the model. We conclude that 3D motion analysis systems can be made more accurate by optimising the cut-off frequency used in filtering the data with regard to their precision. Furthermore, the dynamic precision method seems useful to evaluate the effect of various filtering procedures

Supercooling of the high field vortex phase in single crystalline BSCCO

Time resolved magneto-optical images show hysteresis associated with the transition at the so-called ``second magnetization peak'' at B_sp in single-crystalline Bi_2Sr_2CaCu_2O_8+d. By rapid quenching of the high-field phase, it can be made to persist metastably in the sample down to fields that are nearly half B_sp.Comment: 2 pages, 2 figures Submitted to the conference proceedings of M2S-VI, February 200, Housto

A free account or not? Its effect upon information yield in strategic interviews with suspects

Asking suspects for a free account (FA) at the start of an interview is considered good practice in a growing number of police organisations, whereas in others it still is not commonplace. This study explored whether interviews with or without such an invitation yielded more information from guilty suspects. Students in safety and security committed a mock crime and were then interviewed using a strategy of gradual disclosure of evidence, in the experimental condition preceded with an FA invitation (n = 20) and without such an invitation in the control condition (n = 17). On average, relatively little information was collected in the FA phase and far more in the subsequent gradual disclosure phase. However, the FA condition yielded seven confessions, four of which were given already in the FA phase. The No FA condition yielded only two confessions. Other differences in yield were not found. These findings indicate that an FA invitation could lead to some relevant and important information, such as a confession, being gathered already at an early stage of an interview, and that such an invitation does not hamper the gathering of further information later in the interview

Magnetization Decay due to Vortex Phase Boundary Motion in BSCCO

We identify a new regime of decay of the irreversible magnetization in clean Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ crystals, at induction values close to the ``second peak field'' at which the bulk critical current density steeply increases. A time window is identified during which the decay of the induction is controlled by the slow propagation of the phase transformation front across the sample.Comment: 2 pages, 3 figures Paper submitted to the conference proceedings of M2S-2000 Houston T

A web observatory for the machine processability of structured data on the web

General human intelligence is needed in order to process Linked Open Data (LOD). On the Semantic Web (SW), content is intended to be machine-processable as well. But the extent to which a machine is able to navigate, access, and process the SW has not been extensively researched. We present LOD Observer, a web observatory that studies the Web from a machine processor's point of view. We do this by reformulating the five star model of LOD publishing in quantifiable terms. Secondly, we built an infrastructure that allows the model's criteria to be quantified over existing datasets. Thirdly, we analyze a significant snapshot of the LOD cloud using this infrastructure and discuss the main problems a machine processor encounters