pwidth 54
nwidth 40
unitcap 1.0
min_capacitance 2
max_capacitance 260
max_fanout 6
fanout_load 1
a1 lower_lh_pct 7
a1 upper_lh_pct 93
a2 lower_lh_pct 7
a2 upper_lh_pct 93
b lower_lh_pct 8
b upper_lh_pct 92
a1 lower_hl_pct 7
a1 upper_hl_pct 93
a2 lower_hl_pct 8
a2 upper_hl_pct 92
b lower_hl_pct 8
b upper_hl_pct 92 |
|
pwidth and nwidth are used for the leakage current
calculation.
unitcap sets the load capacitances in the Lookup
Table (LUT). These are the product of unitcap, the
drive strength and the values of total_output_net_capacitance
from the technology.pmd file.
$ more magic/spice_vsclib013/technology.pmd
total_output_net_capacitance 1 4 12 30 62 130 |
For the aoi21v0x2 this means 1×2×130 for the
maximum load, or 260fF.
The maximum load should be set such that when both the input and
output rise transitions are 1500ps, the load capacitance lies between
the maximum and second largest values … between 124fF and 260fF
in this case.
If for the aoi21v0x2 the unitcap is set
to 1.0, then when we check the LUT we see:
timing() {
related_pin : "a1" ;
...
rise_transition(x2_260_6x10) { /* 7%-93%, scaled to 0%-100% */
values( " 89.0, 125.4, 223.5, 445.7, 841.6, 1683.1", \
...
" 367.2, 404.6, 500.2, 702.8, 1046.4, 1821.1" ); }
|
This shows that the max load is 260fF (1.0×130×2),
and that the transition time at this load and an input
transition time of 1500ps is 1821.1ps, which is larger
than 1500ps. At the previous load of 124fF
(1.0×62×2), the transition time is 1046.4ps,
which is less than 1500ps. 1500ps is defined as the max
allowed transition time, and we want delays at this load
to be interpolated between 2 values in the LUT rather than
extrapolated beyond the LUT.
The values min_capacitance, max_capacitance
and fanout_load
are written straight to the .LIB file, except that the
max_capacitance will be reduced to the load that gives
an output transition of 1500ps when the input also has a
transition time of 1500ps.
The upper and lower threshold values have to be determined
for each technology by test simulations. For this technology
the values are listed on the
threshold page. |
