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Introduction
1.5 Timings
Samsung ASIC
1-19
STD150
1.5.3 BEST AND WORST CASE CONDITIONS
The timing value of best-case (worst-case) can be calculated by using the
derating factor derived from the following equations:
T
BC
(T
WC
) = K
P
×
K
T
×
K
V
×
T
NOM
where,
T
BC
(T
WC
)
is a best-case (worst-case) timing.
K
P
is the local process derating factor which has different value according to
each cell,
K
T
is the local temperature derating factor which has different value
according to each cell,
K
V
is the local voltage derating factor which has different value according to
each cell,
T
NOM
is the nominal timing characterized under typical-process, 25
°
C and
1.2V power supply.
The best-case (worst-case) timing values may be determined by picking the
proper derating values from Table 1-3, Table 1-4 and Table 1-5. Derating factors
for conditions between those shown in the tables may be determined by a linear
interpolation.
1.5.4 DERATING FACTORS OF STD150
Cell timing is primarily determined by cell drive capability and loading determined
by cell input capacitance and wiring. The following critical variables also affect the
timing in a system environment of design:
-
-
-
Process variation (P)
Supply voltage (V)
Junction Temperature (T)
Process variation occurs due to the manufacturing environments and the
variation may change the physical characteristics. Its variation affects the
electrical characteristics of devices, increasing or decreasing performance and
power. On the other hand, to design chips which operate in a wide range of
voltage and temperature environments, you have to consider typical-case, worst-
case and best-case conditions to compensate for all variations. To yield much
more timing accuracy, the cell-specific local derating factor is used in STD150
standard cells.
For an example, the process, temperature and voltage derating factors for IV cell
are as follows in Table 1-3, Table 1-4 and Table 1-5 respectively.
Table 1-3.
STD150 Cell Process Derating Factor (K
P
)
Table 1-4.
Temp. (
o
C)
K
T
STD150 Cell Temperature Derating Factor (K
T
)
125
85
1.083
1.052
1.039
Table 1-5.
Voltage (V)
K
V
STD150 Cell Voltage Derating Factor (K
V
)
1.10
1.114
Notice that K
P
, K
T
and K
V
shown as Table 1-3, Table 1-4 and Table 1-5 are only
available in standard cells.
Process Factor (K
P
)
Slow
1.233
Typ
1.000
Fast
0.864
70
25
0
–40
0.963
1.000
0.989
1.20
1.000
1.30
0.920