This paper studies the frequency synthesis for precision time protocol clock generation circuit, and more particularly focused on a multi-rate phase locked loop structure for generating an output signal at a desired frequency with reduced jitter towards the magnitude of femtosecond. We proposed a unique structured model that makes use of a multiple rate digital filter to match the noise spectrum characteristics of both input digital controlled oscillator reference and output voltage controlled oscillator respectively. The simulation for two rate case is carried out. This concept can be extended to more than two rates to match with additional noise sources' spectrum from the other devices such as fractional divider, etc.

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The development of B-lymphoid cells from hematopoetic stem cells in the bone marrow involves an orchestrated interplay between transcription factor networks and external signals. In order to better understand B-lymphocyte lineage restriction, we have investigated molecular and functional properties in early B-lineage cells from Pax-5 and Notch-1 deficient animals carrying a B-lineage restricted reporter gene, allowing us to identify B-lineage specified progenitors independently of conventional surface markers. Pax-5 deficiency resulted in a dramatic increase in the frequency of B-cell progenitors marked by expression of a λ5 (Igll1) promoter controlled reporter gene. Gene expression analysis of ex vivo isolated cells revealed that Pax-5 deficient cells expressed several B-cell restricted genes, however, they displayed a high degree of plasticity for development into other lymphoid lineages at a single cell level. Even though the Pax-5 deficient progenitors expressed higher levels of Notch-1 and respond to delta-signaling in vitro, these cells expressed lower levels of the Notch-1 target gene Deltex-1, arguing for a minor role of Notch signaling in B-cell commitment in the BM. By comparison of gene expression patterns in ex vivo isolated Pax-5 and Ebf-1 deficient progenitors, it was possible to identify a set of B-cell restricted genes dependent of Ebf-1 but not Pax-5, revealing that B-cell specification and commitment is controlled by distinct regulatory networks.