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Accuracy of different simulators: APS, spectre, spectre X

anwx

Hello, I am wondering is there any difference in accuracy between APS, spectre and SpectreX? I am currently simulating a Verilog-A model of a 18 bit ADC, where I encountered a wierd problem: using Spectre X with preset = CX and all other settings default, I get a SNDR of 83dB and a strong 3rd order tone (which is wierd because all components are ideal and linear, and there's no saturation); however, as I switch to APS and Spectre with errorpreset = conservative and all other settings default, I get a SNDR > 100dB with low distortion. The schematic is exactly the same and there's no parasitic since it's a Verilog-A model. As I referred to SpectreX manual, I noticed that SpectreX should have the same accuracy with Spectre. Why there's a such a difference? Which result should I trust?

I'm using virtuoso ic618 with spectre 211.

PS: some other information which might help: I found that as I set a smaller reltol (i.e., 1e-4 (default) -> 1e-5) and vabstol (i.e., 1e-6 (default) -> 5e-7) in APS and Spectre, I see a growth in SNDR.

  • Having the same accuracy does not necessarily mean that you get the same answer. That's because in the APS case you're almost certainly getting better accuracy than the tolerances you've requested - whereas Spectre X may be closer to the tolerances you've requested (I'd expect both to be giving results within the tolerances requested though).

    This is really best handled by talking to customer support - it's a bit complex to describe what might be going on without more info - so I'd advise you to speak to an application engineer.

    Andrew

  • in reply to Andrew Beckett

    thanks, Andrew. I will contact customer support.

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