Stats

  • Locked Locked
  • Replies 6
  • Subscribers 126
  • Views 20481
  • 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

Stop Time in Transient Analysis

Hadi Hayati

Hi

I have designed an oscillator which its center frequency is 2GHz and there seems to be a problem with its stop time I guess...

When I choose stop time for example 50ns, the oscillator works well and I can see the output waveforms. And if stop time is greater than 50ns (0.5us for example), then all I have at outputs is a straight line... There is no signal.

Anybody can help me out with this?

 

Regards,

Hadi

 

Parents

  • Hi Hadi,

    > Why should we enable conservative in errpreste?  

    To quote one of my favorite engineers...I've never met a designer who favored a quick result over an accurate one in their final oscillator design...   :-)

    Unless you really understand the simulator options, what each one does, and how they affect each other, you shouldn't modify them.  We have a class "Using Spectre Effectively" that goes into great detail on most of the simulator options.  It's a very good class.

    We do not want users having to tweak with options.  (I know...because we are engineers...if there are "knobs to tweak", we must fiddle with every single one.  <grin>)   Seriously, R&D has spent a lot of time optimizing the simulator and options so that the only "knob" you should need to "tweak" is errpreset=liberal, moderate, or conservative.  Like everything in life, there are exceptions.  Sometimes with oscillators (particularly high Q), you may need to tighten reltol and vabstol even tighter than errpreset=conservative.  How can you tell if you need to further tighten tolerances?  One way is to plot in ViVA your transient output signal.  Really zoom in to an area of curvature.  If you see "piecewise linear behavior" as opposed to a smooth cure, you need to tighten tolerances. 

    And really, for oscillators I would use SpectreRF for accuracy - and the fact that you can plot things like phase noise, print noise contributors, use the oscillator tuning mode, etc.

    best regards,

    Tawna

    Cadence

Reply

  • Hi Hadi,

    > Why should we enable conservative in errpreste?  

    To quote one of my favorite engineers...I've never met a designer who favored a quick result over an accurate one in their final oscillator design...   :-)

    Unless you really understand the simulator options, what each one does, and how they affect each other, you shouldn't modify them.  We have a class "Using Spectre Effectively" that goes into great detail on most of the simulator options.  It's a very good class.

    We do not want users having to tweak with options.  (I know...because we are engineers...if there are "knobs to tweak", we must fiddle with every single one.  <grin>)   Seriously, R&D has spent a lot of time optimizing the simulator and options so that the only "knob" you should need to "tweak" is errpreset=liberal, moderate, or conservative.  Like everything in life, there are exceptions.  Sometimes with oscillators (particularly high Q), you may need to tighten reltol and vabstol even tighter than errpreset=conservative.  How can you tell if you need to further tighten tolerances?  One way is to plot in ViVA your transient output signal.  Really zoom in to an area of curvature.  If you see "piecewise linear behavior" as opposed to a smooth cure, you need to tighten tolerances. 

    And really, for oscillators I would use SpectreRF for accuracy - and the fact that you can plot things like phase noise, print noise contributors, use the oscillator tuning mode, etc.

    best regards,

    Tawna

    Cadence

Children
No Data

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.