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LC Oscillator - Cadence

rsrk

 Hi

This is could be quite obvious to many of you. Still ...

When I tried to simulate ideal LC oscillator with initial conditions(voltage across the capacitor) using cadence tools ... I realised that output voltage is decaying as time progresses. I mean ... without any series resistance across either capacitor and/or inductor how could I expect output voltage to decay ??

Secondly ... though output voltage is oscillating, I expect voltage across the capacitor, at t=0, to be the one I imposed ... rather in transient analysis I am observing it to be zero. I wanted to be clear as I need to work phase differences.

Could someone throw light on it.

Regards
SRK

Parents

  • A good place to start would be the Virtuoso® Spectre® Circuit Simulator and Accelerated Parallel Simulator User Guide  in the documentation. You can access this from cdnshelp command (if picked up from the IC hierarchy, you may need to add the path to the documentation as a library - the docs are in <MMSIMinstDir>/doc - you can do this in Edit->Settings in the Library tab).

    Or go to <MMSIMinstDir>/doc/spectreuser/spectreuser.pdf .

    There's a chapter on Analyses, within which there's a section on Transient analysis, with sections covering errpreset (which is a quick and easy way of trading off accuracy versus speed), and the integration method (the method parameter).

    Techniques on best practice for simulating oscillators are potentially quite lengthy. General principles would be that often it's a good idea to use method=traponly, and you may want to set maxstep to (say) 1/20th of the expected oscillation period to force sufficient timesteps - but the usual challenge is figuring out how to start the oscillator. This is not a unique problem to spectre, but a consequence of the numerical methods used in circuit simulators.

    To find out more, I'd suggest looking at a copy of The Designer's Guide to SPICE and Spectre by Kenneth S. Kundert, 1995. Also, Cadence offers a course "Using Spectre Effectively" which is a good way to understand the simulator in depth (look at the training catalogs under Support & Training at the top of this web site).

    Regards,

    Andrew.

Reply

  • A good place to start would be the Virtuoso® Spectre® Circuit Simulator and Accelerated Parallel Simulator User Guide  in the documentation. You can access this from cdnshelp command (if picked up from the IC hierarchy, you may need to add the path to the documentation as a library - the docs are in <MMSIMinstDir>/doc - you can do this in Edit->Settings in the Library tab).

    Or go to <MMSIMinstDir>/doc/spectreuser/spectreuser.pdf .

    There's a chapter on Analyses, within which there's a section on Transient analysis, with sections covering errpreset (which is a quick and easy way of trading off accuracy versus speed), and the integration method (the method parameter).

    Techniques on best practice for simulating oscillators are potentially quite lengthy. General principles would be that often it's a good idea to use method=traponly, and you may want to set maxstep to (say) 1/20th of the expected oscillation period to force sufficient timesteps - but the usual challenge is figuring out how to start the oscillator. This is not a unique problem to spectre, but a consequence of the numerical methods used in circuit simulators.

    To find out more, I'd suggest looking at a copy of The Designer's Guide to SPICE and Spectre by Kenneth S. Kundert, 1995. Also, Cadence offers a course "Using Spectre Effectively" which is a good way to understand the simulator in depth (look at the training catalogs under Support & Training at the top of this web site).

    Regards,

    Andrew.

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