Xilinx RocketIO User Manual

Also see for RocketIO: User guide User guide User guide

Contents

Xilinx RocketIO User Manual Manual pdf 84 page image

84 www.xilinx.com UG024 (v1.5) October 16, 20021-800-255-7778 RocketIO™ Transceiver User GuideChapter 4: Analog Design ConsiderationsRPre-emphasis TechniquesIn pre-emphasis, the initial differential voltage swing is boosted to create a stronger risingor falling waveform. This method compensates for high frequency loss in the transmissionmedia that would otherwise limit the magnitude of this waveform. The effects ofpre-emphasis are shown in four scope screen captures, Figure 4-2 through Figure 4-5 onthe pages following. The STRONG notation in Figure 4-3 is used to show that thewaveform is greater in voltage magnitude, at this point, than the LOGIC or normal level(i.e., no pre-emphasis).A second characteristic of RocketIO transceiver pre-emphasis is that the STRONG level isreduced after some time to the LOGIC level, thereby minimizing the voltage swingnecessary to switch the differential pair into the opposite state.Lossy transmission lines cause the dissipation of electrical energy. This pre-emphasistechnique extends the distance that signals can be driven down lossy line media andincreases the signal-to-noise ratio at the receiver.The four levels of pre-emphasis are shown in Table 4-2.Table 4-1: Differential Transmitter ParametersParameter Min Typ Max Units ConditionsV OUT Serial output differentialpeak to peak (TXP/TXN)800 1600 mV Output differentialvoltage is program-mableV TTX Output terminationvoltage supply1.8 2.8 VV TCM Common mode outputvoltage range1.5 2.5 VV ISKEW Differential output skew 15 psTable 4-2: Pre-emphasis ValuesAttribute Values Emphasis (%)0 101 202 253 33