Because of there advantages is the application of Depletion-Transistors in demand. In the commonly used circuit-simulators are usually only enhancement-transistors as a build-in-model present. That’s way we apply macro-models for the depletion-transistor with use of the build in enhancement-models in a Subcircuit (Picture 1):
Picture 1: Macromodel of the Depletion-Transistor 
The proposed model consists of two MOS-Transistors and a current-source.
Every part of the macro-model models a different range of the Transfer
characteristic. Additionally is a ar-rangement for the soft transition of
the different ranges present. The developed approach avoids discontinuous
or other mathematical problems. In the picture 2 and 3 are the achieved
modelling-results presented.
Picture 2: Transfer characteristic |
Picture 3: Transfer characteristic subthreshold |
It is possible to apply the macromodel, used in the pictures above, in a
wide range of commonly used circuit-simulators.