Stop Time in Transient Analysis

Hi Hadi,

This may be more information than you want to know...but here it goes.  :-)

• When simulating an oscillator in transient analysis, you need to make sure you've started the oscillator (otherwise, you will see a straight line when you simulate).
• When simulating oscillators, you should set errpreset=conservative.
• Starting in MMSIM 12.1, transient analysis has been enhanced to calculate the intial conditions for rapid oscillator startup. 
  • linearic enables the linear IC method to calculate the initial conditions automatically from a type of stability analysis in the range [0.5*oscfreq,11.5*oscfreq].  The linearic parameter overrides the user-defined initial conditions, if instability is detected.
  • oscfreq: provides an estimation of the oscillator frequency when the linear IC method is enabled.

For more information, see the Virtuoso Spectre Circuit Simulator Reference Guide.

Now, having said all of that....

If you are simulating an oscillator at 2GHz, I strongly recommend using SpectreRF. 

• Use hb analysis if a sinusoidal/LC/high Q oscillator or pss if a ring oscillator (rather than transient analysis). 
• There are step by step design examples in the MMSIM 12.1.1 and 13.1 Virtuoso Spectre Circuit Simulator and Accelerated Parallel Simulator RF User Guide. 
  • See Appendix A:  Ring oscillator and LC oscillator examples
  • Chapter 3 - Frequency domain analysis - Harmonic balance
  • Chapter 4 - Single Input Large and Small Signal analysis (pss)
• In MMSIM 13.1.1, we have a new Oscillator Tuning Mode analysis.  Here's a snippet from the SpectreRF manual:  Oscillator tuning mode 

  Tuning mode adjusts a parameter in the circuit to produce the set frequency target. This is done automatically when tuning mode is enabled without setting any sweep parameters or interpolation of the resulting curves. When the tuning frequency is reached, any small-signal analyses like noise are run. This allows the simulator to tune the oscillator to a specified frequency and then make a noise measurement. This is useful in Monte Carlo analysis to see how the oscillator performs with process variations. The parameter to be tuned can be a variable, temperature, or a specified device parameter. Oscillator tuning mode is also supported in the pss analysis using the shooting or harmonic balance engines. See Chapter 4, "Single Input Large and Small-signal Analyses," for details.

  In this mode, the target frequency to tune to is the frequency that is specified in the harmonic balance form as the fundamental frequency. You specify a parameter that is to be varied to achieve the desired frequency. This can be a variable, a device parameter, or temperature. When the analysis runs, the oscillator will be tuned to the desired frequency, and then all the small-signal analyses will be run.

• There are also Articles on Cadence Online Support for simulating oscillators.  http://support.cadence.com .

best regards,

Tawna

Hi Hadi,

This may be more information than you want to know...but here it goes.  :-)

• When simulating an oscillator in transient analysis, you need to make sure you've started the oscillator (otherwise, you will see a straight line when you simulate).
• When simulating oscillators, you should set errpreset=conservative.
• Starting in MMSIM 12.1, transient analysis has been enhanced to calculate the intial conditions for rapid oscillator startup. 
  • linearic enables the linear IC method to calculate the initial conditions automatically from a type of stability analysis in the range [0.5*oscfreq,11.5*oscfreq].  The linearic parameter overrides the user-defined initial conditions, if instability is detected.
  • oscfreq: provides an estimation of the oscillator frequency when the linear IC method is enabled.

For more information, see the Virtuoso Spectre Circuit Simulator Reference Guide.

Now, having said all of that....

If you are simulating an oscillator at 2GHz, I strongly recommend using SpectreRF. 

• Use hb analysis if a sinusoidal/LC/high Q oscillator or pss if a ring oscillator (rather than transient analysis). 
• There are step by step design examples in the MMSIM 12.1.1 and 13.1 Virtuoso Spectre Circuit Simulator and Accelerated Parallel Simulator RF User Guide. 
  • See Appendix A:  Ring oscillator and LC oscillator examples
  • Chapter 3 - Frequency domain analysis - Harmonic balance
  • Chapter 4 - Single Input Large and Small Signal analysis (pss)
• In MMSIM 13.1.1, we have a new Oscillator Tuning Mode analysis.  Here's a snippet from the SpectreRF manual:  Oscillator tuning mode 

  Tuning mode adjusts a parameter in the circuit to produce the set frequency target. This is done automatically when tuning mode is enabled without setting any sweep parameters or interpolation of the resulting curves. When the tuning frequency is reached, any small-signal analyses like noise are run. This allows the simulator to tune the oscillator to a specified frequency and then make a noise measurement. This is useful in Monte Carlo analysis to see how the oscillator performs with process variations. The parameter to be tuned can be a variable, temperature, or a specified device parameter. Oscillator tuning mode is also supported in the pss analysis using the shooting or harmonic balance engines. See Chapter 4, "Single Input Large and Small-signal Analyses," for details.

  In this mode, the target frequency to tune to is the frequency that is specified in the harmonic balance form as the fundamental frequency. You specify a parameter that is to be varied to achieve the desired frequency. This can be a variable, a device parameter, or temperature. When the analysis runs, the oscillator will be tuned to the desired frequency, and then all the small-signal analyses will be run.

• There are also Articles on Cadence Online Support for simulating oscillators.  http://support.cadence.com .

best regards,

Tawna