224 www.xilinx.com 7 Series FPGAs GTP Transceivers User GuideUG482 (v1.9) December 19, 2016Chapter 5: Board Design GuidelinesReference ClockOverviewThis section focuses on the selection of the reference clock source or oscillator. An oscillator ischaracterized by:• Frequency range• Output voltage swing• Jitter (deterministic, random, peak-to-peak)• Rise and fall times• Supply voltage and current• Noise specification• Duty cycle and duty-cycle tolerance• Frequency stabilityThese characteristics are selection criteria when choosing an oscillator for a GTP transceiver design.Figure 5-4 illustrates the convention for a single-ended clock input voltage swing, peak-to-peak.This figure is provided to show the contrast to the differential clock input voltage swing calculationshown in Figure 5-5.MGTREFCLKP/MGTREFCLKN Float (if not used)MGTRXP/MGTRXN GNDMGTTXP/MGTTXN FloatMGTRREF MGTAVTT through a 100Ω resistorTable 5-6: Unused GTP Quad Column Connections (Cont’d)Pin or Pin Pair of the Unused GTP Quad ConnectionX-Ref Target - Figure 5-4Figure 5-4: Single-Ended Clock Input Voltage Swing, Peak-to-PeakMGTREFCLKPUG482_c5_04_080612Single-endedVoltageMGTREFCLKN+V0Send Feedback
