Hi sck326,
Please see my comments/opinions, i hope they help:
sck236 wrote on Aug 29th, 2006, 3:28am:In power down(shutdown) mode,
I want to see if the circuit has no floating nodes which might cause leakage current.
How can I do this simulation in spectre?
Just apply power down signal and watch the current out of the power supply?
Yes, just applying the power down signals in a simulation should be fine. What is a tell tale sign of floating nodes, is the time it takes for the current to discharge to zero (or the DC value in power down) when one does a transient rather than DC simulation.
sck236 wrote on Aug 29th, 2006, 3:28am:If the current goes down near to zero, is it safe for leakage current?
Yes, assuming you have captured any non-schematic effects such as layout only devices like antenna diodes and alike.
sck236 wrote on Aug 29th, 2006, 3:28am:In my opinion, even if there is no leakage current, there could be a floating node of which potential is zero.
Agreed
sck236 wrote on Aug 29th, 2006, 3:28am:I think this node may have leakage problem in a real circuit. Am I correct?
Again if you capture all the layout devices, and have good models, you should NOT have a leakage problem.
cheers
aw