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ACS8515LC Datasheet(PDF) 13 Page - Semtech Corporation |
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ACS8515LC Datasheet(HTML) 13 Page - Semtech Corporation |
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13 / 47 page  Revision 2.05/Jan 2001 ã2001 Semtech Corp www.semtech.com 13 ACS8515 LC/P ADVANCED COMMUNCIATIONS FINAL Figure 3: Wander and Jitter Transfer Characteristsics 3HDNWRSHDN MLWWHU DQG ZDQGHUDPSOLWXGH ORJ VFDOH -LWWHU DQG ZDQGHUIUHTXHQF\ ORJ VFDOH G% 8, # I G% -LWWHU FXWRII ORZ IUHTXHQF\ +] -LWWHU FXWRII KLJK IUHTXHQF\ +] Phase Variation There will be a phase shift across the ACS8515 between the selected input reference source and the output clock. This phase shift may vary over time but will be constrained to lie within specified limits. The phase shift is characterised using two parameters, MTIE (Maximum Time Interval Error), and TDEV (Time Deviation), which, although being specified in all relevent specifications, differ in acceptable limits in each one. Typical measurements for the ACS8515 are shown in Figures 4 and 5, for locked mode operation. Figure 6 shows a typical measurement of Phase Error accumulation in Holdover mode operation. The required performance for phase variation during Holdover is specified in several ways depending upon the particular circumstances pertaining: 1. ETSI 300 462-5, Section 9.1, requires that the short- term phase error during switchover (i.e., Locked to Holdover to Locked) be limited to an accumulation rate no greater than 0.05 ppm during a 15 second interval. 2. ETSI 300 462-5, Section 9.2, requires that the long- term phase error in the Holdover mode should not exceed {(a1+a2)S+0.5bS2+c}, where a1 = 50 ns/s (allowance for initial frequency offset) a2 = 2000 ns/s (allowance for temperature variation) b = 1.16x10-4 ns/s2 (allowance for ageing) c = 120 ns (allowance for entry into Holdover mode). 3. ANSI Tin1.101-1994, Section 8.2.2, requires that the phase variation be limited so that no more than 255 slips (of 125 µs each) occur during the first day of Holdover. This requires a frequency accuracy better than: ((24x60x60)+(255x125µs))/(24x60x60) = 0.37 ppm. Temperature variation is not restricted, except to within the normal bounds of 0 to 50 Celsius. 4. Bellcore GR.1244.CORE, Section 5.2. Table 4. shows that an initial frequency offset of 50 ppb is permitted on entering Holdover, whilst a drift over temperature of 280 ppb is allowed; an allowance of 40 ppb is permitted for all other effects. 5. ITU G.822, Section 2.6, requires that the slip rate |
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