W632GU6NB
Publication Release Date: Aug. 20, 2018
Revision: A01
- 102 -
The DC-tolerance limits and AC-noise limits for the reference voltages V
REFCA
and V
REFDQ
are
illustrated in Figure 89. It shows a valid reference voltage V
REF
(t) as a function of time. (V
REF
stands
for V
REFCA
and V
REFDQ
likewise).
V
REF(DC)
is the linear average of V
REF
(t) over a very long period of time (e.g., 1 sec). This average
has to meet the min/max requirements in
Table 17. Furthermore V
REF
(t) may temporarily deviate from
V
REF(DC)
by no more than ± 1% V
DD
.
V
REF(DC)
max
V
REF(DC)
min
V
DD
/2
V
DD
V
SS
voltage
time
V
REF(DC)
V
REF
(t)
V
REF
AC
-noise
Figure 89
– Illustration of V
REF(DC)
tolerance and V
REF
AC-noise limits
The voltage levels for setup and hold time measurements V
IH(AC)
, V
IH(DC)
, V
IL(AC)
, and V
IL(DC)
are
dependent on V
REF
.
“V
REF
” shall be understood as V
REF(DC)
, as defined in Figure 89.
This clarifies that DC-variations of V
REF
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 V
REF(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 V
REF
AC-noise. Timing and voltage effects due to AC-noise on V
REF
up
to the specified limit (± 1% of V
DD
) are included in DRAM timings and their associated deratings.