Intel® Celeron® Processor for PGA370 up to 1.40 GHz on 0.13 µ Process
Figure 19. Low to High AGTL Receiver Ringback Tolerance
τ
α
VREF + 0.2
VREF
φ
ρ
δ
VREF - 0.2
0.7V Clk Ref
Vstart
Clock
Time
Note: High to low case is analogous
3.2.1
Overshoot/Undershoot Guidelines
Overshoot (or undershoot) is the absolute value of the maximum voltage above the nominal high
voltage or below VSS. The overshoot guideline limits transitions beyond VCC or VSS due to the fast
signal edge rates. The processor can be damaged by repeated overshoot events on 1.25 V or 2.5 V
tolerant buffers if the charge is large enough (i.e., if the overshoot is great enough). Determining
the impact of an overshoot/undershoot condition requires knowledge of the magnitude, the pulse
direction and the activity factor (AF). Permanent damage to the processor is the likely result of
excessive overshoot/undershoot. Violating the overshoot/undershoot guideline will also make
satisfying the ringback specification difficult.
When performing simulations to determine impact of overshoot and undershoot, ESD diodes must
be properly characterized. ESD protection diodes do not act as voltage clamps and will not provide
overshoot or undershoot protection. ESD diodes modeled within Intel I/O Buffer models do not
clamp undershoot or overshoot and will yield correct simulation results. If other I/O buffer models
are being used to characterize the processor performance, care must be taken to ensure that ESD
models do not clamp extreme voltage levels. Intel I/O Buffer models also contain I/O capacitance
characterization. Therefore, removing the ESD diodes from an I/O Buffer model will impact results
and may yield excessive overshoot/undershoot.
Datasheet
43
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