What's the meaning of this optimization with Hspice?(help!!)

[hbchens]

The spice description as follows:

.lib “ls35_4_1.l” tt
.option post probe
.param Cload =10p
.param Tpw=opt1(0, 0, 15n)
.model optmod opt method=passfail
.tran 0.1n 20n sweep optimize=opt1
+ result = Tprop
+ model = optmod
.measure Tran Tprop Trig V(in) Val=2.5 Rise = 1
+ Targ v(out) Val=2.5 Fall = 1
vcc 1 0 5
vin in 0 pulse(0 5 1n 1n 1n Tpw 20n)
....
.end

I read this optimization example with hspice in a book,but I cann't understand it.Who can tell me ???
Thanks!!

 

[mdcui]

this is bi-section sweep, a feature embedded in hspice, basically spice will sweep parameter tpw in a bi-section way, which means:
1. min value
2. max value
3. (min + max) /2
4. 1/4 min +3/4max or 3/4min+1/max (depends on measure result)
5. ....

until it find the sweep-spot

 

[hbchens]

To mdcui:
Thanks for your help!Is this optimizaton way for digital circuits?

Added after 22 minutes:

To mdcui:
By the way,I don't know its' optimizational goal.Can you explain the goal of this optimization for me?
Thanks!

 

[xuel]

This bi-section sweep try to find the setup of hold time of a dff. But when I tried this method in another dff, it sometimes failed.