Intel VC820 Design Guide - Page 125
Flight Time Definition and Measurement, Overdrive Region and V, Guardband
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Advanced System Bus Design should extrapolate back to the appropriate VREF Guardband boundary, and not VREF. So, for maximum rising edge correction, extrapolate back to VREF + ∆VREF. For maximum falling edge corrections, extrapolate back to VREF - ∆VREF. Figure 3-11. Overdrive Region and VREF Guardband VREF+ 200 mV VREF + VREF - 100 mV VREF ∆ 100 mV VREF∆VREF VREFGuardband Overdrive Region (200 mV) Overdrive Region (200 mV) VREF- 200 mV 3.5.4 Flight Time Definition and Measurement Timing measurements consist of minimum and maximum flight times to take into account that devices can turn on or off anywhere in a VREF Guardband region. This region is bounded by VREF-∆VREF and VREF+∆VREF. The minimum flight time for a rising edge is measured from the time the driver crosses VREF when terminated to a test load, to the time when the signal first crosses VREF-∆VREF at the receiver (see Figure 3-12). Maximum flight time is measured to the point where the signal first crosses VREF+∆VREF, assuming that ringback, edge rate, and monotonicity criteria are met. Similarly, minimum flight time measurements for a falling edge are taken at the VREF+∆VREF crossing and maximum flight time is taken at the VREF-∆VREF crossing. Figure 3-12. Rising Edge Flight Time Measurement Receiver Pin Driver Pin into Test Load VREF+ 200 mV VVRREEFF-+1100V0R0EmmF VV∆VREF ∆VREF Overdrive Regio VREF Guardband Tflight-max Tflight-min Intel®820 Chipset Design Guide 3-25