advance use hspice problem on Mos cutOff or saturation..

[andy2000a]

Hi
If I want to know whick Tx is Saturation regio or linear regio or Cut_off
region and by hspice (not by my eye ) , how to use hspice command ?

and how to calculate node impedance or node capacitance by hspice command ? use LX21 on transient simulation ??

 

[shiowjyh]

As I know,
no command to check MOS's sat.,linear, and cut-off... But my friend wrote a perl to grep and analyze MOSs working on which region. Basically, it uses Vds(>,<,=)Vgs-Vt

node cap
--> .options captab
node impedence
--> 1. think of voltage drop divided by id(for large signal)
2. ro=dVds/dId ~ 1/[(channel-length modulation coefficient)*Id]
3. read reference to define which stage your circuit is, then plug into a simplified formula to get output impendence.
What do you need node impendence for??

comments?

 

[rfsystem]

I use Composer/Spectre and ECS/Smash. Both have an attribute display for "region". In Composer the region is a number. In ECS it is a string with additional highligting.

 

[bastos4321]

The .OP gives you the transistor working region.

In transient use ".op time" to get the operational point at the time you want.

Bastos

 

[yschuang]

Biaschk statement in HSPICE probably helps to identify what region it is.