I need to simulate digital circuits which have custom gates.

For now I am not concerned about the specific CMOS technology, the transistor Length and Width, etc. I only need to glue NMOS and PMOS transistors together and build some primitive digital components, like inverters, AND and OR gates, etc. and simulate circuits built with those basic components. The reason that I can not use the standard library provided in simulator software such as LTSpice and MultiSim is that I need some special latches and gates (like Muller gate) which is not available in standard CMOS 4000 series so I have to build everything from scratch in transistor level.

Can I just randomly pick a technology like: 0.35u CMOS components

Does the technology really matter?

If not, then what CMOS library models do you suggest for general purpose simulation of digital circuits built with MOSFETs? Is the link to colorado.edu 0.35u CMOS models which I mentioned above good enough?


2 Answers 2


The technology will determine the following things

  • Speed (smaller is faster)
  • Power consumption (smaller transistors consume less power)
  • Supply voltage (smaller transistors require a lower supply voltage)
  • And of course the required chip area

A 0.35um technology should be OK and you can work with 3.3V. If it is good enough depends on your requirements. In order to determine the speed you can achieve you can wire up a few simple gate structures and make a simulation.

A big advantage of 0.35um CMOS is that this technology is very cheap and protoyping is quite affordable.


If you want to know what the gate delays will be, how much drive current they'll be able to provide to downstream stages, what your circuit setup and hold times will be, or anything quantitative about your design, then you'll want to use models that represent the process with which you'll implement your circuit.

If you just want to work out what topology to connect the FETs in to construct a given gate, then generic models will likely be adequate. You'll still have to adjust W and L parameter if, for example, you want to make an inverter with its switching threshold at Vdd/2. Then you'll have to re-optimize new W and L parameters when you get your process-specific models to design for the real process you'll be using.


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