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M393B1G70BH0 Datasheet, PDF (24/55 Pages) Samsung semiconductor – 240pin Registered DIMM based on 4Gb B-die
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Registered DIMM
datasheet
Rev. 1.5
DDR3 SDRAM
13.2 VREF Tolerances.
The dc-tolerance limits and ac-noise limits for the reference voltages VREFCA and VREFDQ are illustrate in Figure 1. It shows a valid reference voltage
VREF(t) as a function of time. (VREF stands for VREFCA and VREFDQ likewise).
VREF(DC) is the linear average of VREF(t) over a very long period of time (e.g. 1 sec). This average has to meet the min/max requirements of VREF. Fur-
thermore VREF(t) may temporarily deviate from VREF(DC) by no more than ± 1% VDD.
voltage
VDD
VSS
time
Figure 1. Illustration of VREF(DC) tolerance and VREF ac-noise limits
The voltage levels for setup and hold time measurements VIH(AC), VIH(DC), VIL(AC) and VIL(DC) are dependent on VREF.
"VREF" shall be understood as VREF(DC), as defined in Figure 1.
This clarifies, that dc-variations of VREF affect the absolute voltage a signal has to reach to achieve a valid high or low level and therefore the time to
which setup and hold is measured. System timing and voltage budgets need to account for VREF(DC) deviations from the optimum position within the
data-eye of the input signals.
This also clarifies that the DRAM setup/hold specification and derating values need to include time and voltage associated with VREF ac-noise.
Timing and voltage effects due to ac-noise on VREF up to the specified limit (+/-1% of VDD) are included in DRAM timings and their associated deratings.
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