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APS: Matrix is singular

Cesare Buffa

Dear Colleagues and Experts,

I have been facing many times "singular matrix" issue using APS simulator.

It happened with different types and size of circuits and I have not been able to find a stable and permanent solution to solve this problem.

It can happen that changing the circuit (and so the matrix to be solved) with some stupid tricks may help to avoid this issue. But it is a luck and unstable solution.

I have been playing for a long time with all possible settings of APS and simulator without any positive outcome.

Same circuit simulated with standard spectre works but takes 4/5x longer.

Same circuit simulated with proprietary simulators is also an alternative and works.

I would like to address the following general question please:

when I face a "Matrix is singular" with APS, how should I behave? Are there some guidelines how to solve it?

Thank you

Best regards

  • Andrew Beckett

    Generally if you have a singular matrix, you have a problem with your circuit. It means that your circuit has non isolated solutions, which means that you have parts of the circuit which are floating somehow. Because of this, there's an infinite number of solutions - and so this presents a problem for the matrix solvers.

    There are various things that spectre (and APS) does to help (such as insertion of gmin resistors, and matrix reordering), but usually looking in more detail at some of the warnings you are getting is the best bet.

    If you're unsure, contact customer support so that a Cadence AE can take a look.

    Regards,

    Andrew.

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