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Abstract-This paper presents analyses and experimental results on the jitter transfer of delay-locked loops (DLLs). Through a -domain model, we show that in a widely used DLL configuration, jitter peaking always exists and high-frequency jitter does not get attenuated as previous analyses suggest. This is true even in a firstorder DLL and an overdamped second-order DLL. The amount of jitter peaking is shown to trade off with the tracking bandwidth and, therefore, the acquisition time. Techniques to reduce jitter amplification by loop filtering and phase filtering are discussed. Measurements from a prototype chip incorporating the discussed techniques confirm the prediction of the analytical model. In environments where the reference clock is noisy or where multiple timing circuits are cascaded, this jitter amplification effect should be carefully evaluated.Index Terms-Delay-locked loop (DLL), injection locking, jitter peaking, jitter transfer, multiplying delay-locked loop (MDLL), phase-locked loop (PLL).

The stability of specialty choices of 519 graduates of the University of Washington School of Medicine were studied by means of a mail survey in 1986. The graduates' actual practice specialties were compared with the one or more specialties each had indicated as possible career specialty choices when they entered medical school. Nearly 70% of the graduates' early choices remained stable, double the percentage found by other studies that based stability on an entering medical student's single choice of a career specialty. The findings suggest that students entering medical school have in mind a variety of acceptable specialties and later are likely to choose one of these as a career.

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