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VSC8116QP2 Datasheet(PDF) 6 Page - Vitesse Semiconductor Corporation |
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VSC8116QP2 Datasheet(HTML) 6 Page - Vitesse Semiconductor Corporation |
6 / 20 page VITESSE SEMICONDUCTOR CORPORATION Data Sheet VSC8116 ATM/SONET/SDH 622/155Mb/s Transceiver Mux/Demux with Integrated Clock Generation Page 6 © VITESSE SEMICONDUCTOR CORPORATION G52220-0, Rev 4.1 741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896 1/8/00 Clock Multiplier Unit The VSC8116 uses an integrated phase-locked loop (PLL) for clock synthesis of the 622MHz high speed clock used for serialization in the transmitter section. The PLL is comprised of a phase-frequency detector (PFD), an integrating operation amplifier and a voltage controlled oscillator (VCO) configured in classic feed- back system. The PFD compares the selected divided down version of the 622MHz VCO (CMUFREQSEL selects divide-by ratios of 8 or 32, see Table 2) and the reference clock. The integrator provides a transfer func- tion between input phase error and output voltage control. The VCO portion of the PLL is a voltage controlled ring-oscillator with a center frequency of 622MHz. The reactive elements of the integrator are located off-chip and are connected to the feedback loop of the amplifier through the CP1, CP2, CN1 and CN2 pins. The configuration of these external surface mounted capacitors is shown in Figure 6. Table 1 shows the recommended external capacitor values for the configurable reference frequencies. Good analog design practices should be applied to the board design for these external components. Tightly controlled analog ground and power planes should be provided for the PLL portion of the circuitry. The dedi- cated PLL power (VDDA) and ground (VSSA) pins should have quiet supply planes to minimize jitter genera- tion within the clock synthesis unit. This is accomplished by either using a ferrite bead or a C-L-C choke ( π filter) on the (VDDA) power pins. Note: Vitesse recommends a ( π filter) C-L-C choke over using a ferrite bead. All ground planes should be tied together using multiple vias. Table 1: Recommended External Capacitor Values Reference Frequency [MHz] Divide Ratio CP CN Type Size Tol. 19.44 32 0.1 0.1 X7R 0603/0805 +/-10% 77.76 8 0.1 0.1 X7R 0603/0805 +/-10% |
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