170 www.xilinx.com Virtex-4 RocketIO MGT User GuideUG076 (v4.1) November 2, 2008Chapter 6: Analog and Board Design Considerations RReference ClockBecause a high degree of accuracy is required from the reference clock, an EPSONEG2121CA 2.5V oscillator should be used. (Visit the Epson Electronics America website fordetailed information about this device.) The circuit in Figure 6-7 must be used to interfacethe LVDS or LVPECL outputs of the oscillator with the inputs of the transceiver referenceclock.The EG2121CA can be used for frequencies up to 400 MHz. For frequencies beyond400 MHz, the EG2121CA must be replaced with the VS500, a Voltage-Controlled SawOscillator (VCSO). Figure 6-8 illustrates the VCSO implementation. In addition to thefiltered 3.3V supply voltage shown, the VCSO also requires a control voltage (not shown).Table 6-1: Case A Filtering RequirementCase A Instance Name AVCCAUXRXB AVCCAUXMGTMGT_inst_2 N/A Filtering REQUIREDnot_used_4 Filtering REQUIRED Filtering REQUIREDnot_used_3 N/A Filtering REQUIREDnot_used_2 Filtering REQUIRED Filtering REQUIREDMGT_inst_1 N/A Filtering REQUIREDMGT_inst_0 Filtering REQUIRED Filtering REQUIREDnot_used_1 N/A Suggested but not requirednot_used_0 Suggested but not required Suggested but not requiredTable 6-2: Case B Filtering RequirementCase B Instance Name AVCCAUXRXB AVCCAUXMGTnot_used_4 N/A Suggested but not requirednot_used_3 Suggested but not required Suggested but not requirednot_used_2 N/A Filtering REQUIREDMGT_inst_2 Filtering REQUIRED Filtering REQUIREDMGT_inst_1 N/A Filtering REQUIREDMGT_inst_0 Filtering REQUIRED Filtering REQUIREDnot_used_1 N/A Suggested but not requirednot_used_0 Suggested but not required Suggested but not requiredFigure 6-7: Reference Clock Oscillator Interface (Up to 400 MHz)Z 0Z 0ug076_ch6_05_060107EG2121CA2.5V-LVDS/LVPECL.1 μF(100 nF).1 μF(100 nF)GT11CLK_MGT
