User's Manual

Intel
®
820 Chipset Design Guide 3-25
Advanced System Bus Design
should extrapolate back to the appropriate V
REF
Guardband boundary, and not V
REF
. So, for
maximum rising edge correction, extrapolate back to V
REF
+ ∆V
REF
. For maximum falling edge
corrections, extrapolate back to V
REF
- ∆V
REF
.
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 V
REF
Guardband region. This region is bounded by
V
REF
-∆V
REF
and V
REF
+∆V
REF.
The minimum flight time for a rising edge is measured from the
time the driver crosses V
REF
when terminated to a test load, to the time when the signal first
crosses V
REF
-∆V
REF
at the receiver (see Figure 3-12). Maximum flight time is measured to the
point where the signal first crosses V
REF
+∆V
REF
, assuming that ringback, edge rate, and
monotonicity criteria are met. Similarly, minimum flight time measurements for a falling edge are
taken at the V
REF
+∆V
REF
crossing and maximum flight time is taken at the V
REF
-∆V
REF
crossing.
Figure 3-11. Overdrive Region and V
REF
Guardband
V
REF
+ 200 mV
∆
∆∆
∆
∆
∆∆
∆
V
REF
+ 100 mV
V
REF
V
REF
- 100 mV
V
REF
- 200 mV
V
REF
V
REF
V
REF
Guardband
Overdrive Region (200 mV)
Overdrive Region (200 mV)
Figure 3-12. Rising Edge Flight Time Measurement
Overdrive Regio
V
REF
Guardband
Driver Pin into
Test Load
Receiver Pin
Tflight-min
Tflight-max
V
REF
+ 200 mV
V
REF
+ 100 mV
V
REF
V
REF
- 100 mV
∆
V
REF
∆
V
REF