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switched cap and PSS/PAC analysis

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Hello all!!

I'm designing a bandpass filter using switched-cap (100Hz center frequency and Q=5 with two low-Q and one high Q biquad).
At typical case, the pss simulation converges well and the AC results are similar to what is expected.
However at corners, especially at lowest temperature, the pss simulation do not converge or converge with difficulty.
If pss finally converges, the AC results given are wrong and the transient results (of one period) that can be seen with pss, shows big oscillations (some signals go down to zero with a fixed period). This issue is solved if opamps are replaced by ideal ones. Also, this oscillation cannot be seen with traditional transient simulation.

Does anyone have some ideas on that issue?
Any idea is welcome.

Thks in advance

AXP


Originally posted in cdnusers.org by axp
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  • Bear in mind that PSS finds the steadystate - it accelerates settling, and so if the oscillation takes a long time to build up, you wouldn't see it in the initial transient unless that initial transient is very long.

    Try running a very long transient to see what happens.

    Regards,

    Andrew.


    Originally posted in cdnusers.org by adbeckett
Reply

  • Bear in mind that PSS finds the steadystate - it accelerates settling, and so if the oscillation takes a long time to build up, you wouldn't see it in the initial transient unless that initial transient is very long.

    Try running a very long transient to see what happens.

    Regards,

    Andrew.


    Originally posted in cdnusers.org by adbeckett
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