difference between subcircuit and model

[whitchurch85]

hi,

i would like to know what is the difference between a subcitcuit .X and a .Model definition in hspice.

thanks

 

[keith1200rs]

A .model is for one of the pre-defined devices such as NMOS, NPN etc. A subcircuit is usually a combination of devices which may include dozens or even hundreds odds devices.

Keith

 

[whitchurch85]

Thanks Keith,

So a subcircuit can be made up of lots of .model elements. whereas a .model is the basic fundamental element.

A .model is for one of the pre-defined devices such as NMOS, NPN etc. A subcircuit is usually a combination of devices which may include dozens or even hundreds odds devices.

Keith

 

[keith1200rs]

Correct. It can be confusing sometimes because some foundries create subcircuits with just a model in them. I think this is just to do with parameter passing.

Subcircuits are useful for breaking down large circuits. A large circuit might have a few opamps, comparators, a DAC etc. Each of the building blocks can be designed and tested as a subcircuit and then included in the larger design.

Keith