Stats

  • Locked Locked
  • Replies 2
  • Subscribers 125
  • Views 13909
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

How operating points are calculated in DC analysis?

BaaB

I have a simple circuit below. I am wondering how Spectre determine the operating region and calculate operating point VDS of each transistor in DC analysis.

Does it first determine the operating region of each transistor and then solve differential equations that relates element in circuit?

That does not seem to be right because to know the region, first we need to know VDS of each transistor. 

So how does it calculate VDS here?

Thank you.

  • Andrew Beckett

    I'm not going to explain in detail the internals of how the simulator solves the equations (I have better things to do on a Sunday morning), but essentially it solves the simultaneous non-linear differential equations for the entire circuit iteratively - and as it comes up with each estimate of the voltages and currents, it updates the equations and iterates again until the errors are small (as I outlined before).

    So it is not a matter of determining the operating region first and then solving the equations. That wouldn't work.

    More detail on this can be found in the literature (such as Ken's book that I referred to before - in fact you can see enough in this excerpt). We cover it in our (Cadence's) Using Spectre Effectively training course too. There is also Steady-State Methods for Simulating Analog and Microwave Circuits (The Springer International Series in Engineering and Computer Science) by Ken Kundert, Jacob White, and Alberto Sangiovanni-Vincentelli. This is a book that isn't aimed at designers - it's more for those interested in how simulators work and might be developing simulators. I don't have my copy to hand (I've left it in the office), but if you really want to understand more detail on how circuit simulators work, you could look for it in your university library.

    Andrew.

  • BaaB
    Thank you for the answer. I am just interested in how the simulator work in general.

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.