QPSS simulation

Hi ThaoCao,

I recommend filing a support ticket at https://support.cadence.com .   We have a team of AEs dedicated to helping customers and this is how you contact them. 

There could be many causes of non-convergence.   And there really isn't enough information to assist.  Again, a Support AE is your best bet.  Andrew and I answer questions when we get a chance, but we have our "day job" to do, too.  :-) 

Here are two articles that discuss convergence:

• Spectre RF Convergence Tips for Shooting PSS Analysis 
• FAQ: Convergence tips for driven and autonomous circuits in Harmonic Balance 

If you have a single tone input:

• For mostly sinusoidal signals, I recommend using the "hb" interface.   
• For sharp transitions, I recommend "pss Shooting".   (setting harmonics > 10 can increase memory and runtime in pss shooting

If there are 2 or more input frequencies, usually hb is preferred.  (You can use shooting if the pss beat frequency is larger than the highest input frequency/10)

• When setting up harmonics in hb multi-tone:
  • The tone that causes the most distortion is always tone 1.
  • Set "auto" for number of harmonics in tone 1. This is the "automatic" way to set harmonics.  (See *** for the manual way to set harmonics)
  • If the rest of the tones are small in amplitude, use ~3 harmonics for the rest of the tones.
  • If the 2nd tone produces a large amount of distortion,
    • start w/11 harmonics for tone 2.  Run simulation, plot desired output
    • raise harmonics to 17, run and plot again
    • if the results change, keep raising harmonics until the result stabilizes.  Use smallest amount of harmonics that produce a stable result.
  • *** As an alternative, the manual way set the number of harmonics in hb (square wave, pulse):
    • Take the ratio of the period divided by the rise time.   Example:  1n period, 20p rise/fall times.  Ratio=50.
      • If the timing of the edge is important, set number of harmonics to the ratio, i.e. 50
      • If the square/pulse wave drives other circuitry, set oversample=4 and start w/Number of harmonics=25
    • Run simulation, plot desired signal
    • reduce harmonics by 30%, run again, and replot
    • If the measurement changed, you need more harmonics.
    • If it didn't, reduce the harmonics until the result changes.
    • Use the smallest number of harmonics that produce a stable result.

I also recommend these Articles:

1. Getting the Most Out of Spectre® X-RF 21.1: Maximizing Performance (the above is discussed in this AppNote)

2. SpectreRF Application Notes and Tutorials - One of our best kept secrets!  (We have a workshop showing how to simulate mixers)

• If you don't have access to https://support.cadence.com, look at the mixer example in the SpectreRF Analysis in ADE Explorer workshop. The workshop documentation is in the Virtuoso hierarchy here:

  <IC618 or ICADVM20.1>/lnx86/64/doc/spectreRFexplorerWorkshop/spectreRFexplorerWorkshop.pdf

• ​Workshop database is located here: <SPECTRE21.1>/tools.lnx86/spectre/examples/Legacy/RF_Doc_Database.tar.gz

Hi ThaoCao,

I recommend filing a support ticket at https://support.cadence.com .   We have a team of AEs dedicated to helping customers and this is how you contact them. 

There could be many causes of non-convergence.   And there really isn't enough information to assist.  Again, a Support AE is your best bet.  Andrew and I answer questions when we get a chance, but we have our "day job" to do, too.  :-) 

Here are two articles that discuss convergence:

• Spectre RF Convergence Tips for Shooting PSS Analysis 
• FAQ: Convergence tips for driven and autonomous circuits in Harmonic Balance 

If you have a single tone input:

• For mostly sinusoidal signals, I recommend using the "hb" interface.   
• For sharp transitions, I recommend "pss Shooting".   (setting harmonics > 10 can increase memory and runtime in pss shooting

If there are 2 or more input frequencies, usually hb is preferred.  (You can use shooting if the pss beat frequency is larger than the highest input frequency/10)

• When setting up harmonics in hb multi-tone:
  • The tone that causes the most distortion is always tone 1.
  • Set "auto" for number of harmonics in tone 1. This is the "automatic" way to set harmonics.  (See *** for the manual way to set harmonics)
  • If the rest of the tones are small in amplitude, use ~3 harmonics for the rest of the tones.
  • If the 2nd tone produces a large amount of distortion,
    • start w/11 harmonics for tone 2.  Run simulation, plot desired output
    • raise harmonics to 17, run and plot again
    • if the results change, keep raising harmonics until the result stabilizes.  Use smallest amount of harmonics that produce a stable result.
  • *** As an alternative, the manual way set the number of harmonics in hb (square wave, pulse):
    • Take the ratio of the period divided by the rise time.   Example:  1n period, 20p rise/fall times.  Ratio=50.
      • If the timing of the edge is important, set number of harmonics to the ratio, i.e. 50
      • If the square/pulse wave drives other circuitry, set oversample=4 and start w/Number of harmonics=25
    • Run simulation, plot desired signal
    • reduce harmonics by 30%, run again, and replot
    • If the measurement changed, you need more harmonics.
    • If it didn't, reduce the harmonics until the result changes.
    • Use the smallest number of harmonics that produce a stable result.

I also recommend these Articles:

1. Getting the Most Out of Spectre® X-RF 21.1: Maximizing Performance (the above is discussed in this AppNote)

2. SpectreRF Application Notes and Tutorials - One of our best kept secrets!  (We have a workshop showing how to simulate mixers)

• If you don't have access to https://support.cadence.com, look at the mixer example in the SpectreRF Analysis in ADE Explorer workshop. The workshop documentation is in the Virtuoso hierarchy here:

  <IC618 or ICADVM20.1>/lnx86/64/doc/spectreRFexplorerWorkshop/spectreRFexplorerWorkshop.pdf

• ​Workshop database is located here: <SPECTRE21.1>/tools.lnx86/spectre/examples/Legacy/RF_Doc_Database.tar.gz