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9.2.
GTL+ SIGNAL QUALITY SPECIFICATIONS
Table 9-2 and Figures 8-3 and 8-4 describe the GTL+ signal quality specifications for the
Pentium II processor.
Table 9-2. GTL+ Signal Groups Ringback Tolerance
T#
Parameter
α:
Overshoot
τ:
Minimum Time at High
ρ:
Amplitude of Ringback
φ:
Final Settling Voltage
δ:
Duration of Sequential Ringback
NOTES:
1.
Specified for the edge rate of 0.3 – 0.8 V/ns. See Figure 9-2 for the generic waveform.
2.
All values specified by design characterization.
3.
Ringback below V
REF
9.3.
NON-GTL+ SIGNAL QUALITY SPECIFICATIONS
Many scenarios have been simulated to generate a set of GTL+ layout guidelines which are
available in the Pentium
three signal quality parameters defined: Overshoot/Undershoot, Ringback and Settling Limit.
All three signal quality parameters are shown in Figure 9-2 for non-GTL+ signal groups.
9.3.1.
Overshoot/Undershoot Guidelines
Overshoot (or undershoot) is the absolute value of the maximum voltage above the nominal
high voltage or below V
V
or V
due to the fast signal edge rates. (See Figure 9-2 for non-GTL+ signals.) The
CC
SS
processor can be damaged by repeated overshoot events on 2.5V tolerant buffers if the charge
is large enough (i.e., if the overshoot is great enough). However, excessive ringback is the
dominant detrimental system timing effect resulting from overshoot/undershoot (i.e.,
violating the overshoot/undershoot guideline will make satisfying the ringback specification
difficult). The overshoot/undershoot guideline is 0.8V and assumes the absence of diodes on
the input. These guidelines should be verified in simulations without the on-chip ESD
protection diodes present because the diodes will begin clamping the 2.5V tolerant signals
beginning at approximately 1.25V above Vcc
reaching the clamping voltage, this will not be an issue. A system should not rely on the
diodes for overshoot/undershoot protection as this will negatively affect the life of the
components and make meeting the ringback specification very difficult.
Min
100
–250
250
+250 mV is not supported.
II Processor GTL+ Guidelines (Order Number 243330). There are
®
. The overshoot/undershoot guideline limits transitions beyond
SS
SIGNAL QUALITY SPECIFICATIONS
Unit
mV
1.5
ns
mV
mV
N/A
ns
and 0.5V below V
CORE
Figure
Notes
8-3, 8-4
1, 2
8-3, 8-4
1, 2
8-3, 8-4
1, 2, 3
8-3, 8-4
1, 2
8-3, 8-4
1, 2
. If signals are not
SS
9-3
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