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harmonic balance oscillator

kpti

I'm trying to simulate a simple passive LRC resonator circuit (https://www.dropbox.com/s/nlzpv9b9gvtceca/Untitled.png), i get results as expected from AC and transient sim (resonance at 10 MHz) but can't get HB to work. it seems that no matter what settings I choose, i have the error: 

 V(resonator) is too small to reliably detect the period of the oscillator.Perhaps  nodes with insignificant signal levels were chosen, or perhaps the oscillator was never properly started.

any thoughts? i'm using spectre with icfb 5.1.0. i found tutorials on HB simulation options, but none that showed the circuit, so I'm wondering if my circuit is set up incorrectly for HB. 

resonator

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  • Dear kpti,

    I believe the issue is that in your your pss simulation result, there is no oscillation in the steady-state. The resonator you are illustrating shows a resistance of 50 ohms I believe provides the possible solution of damping out any steady-state oscillation. Hence with time, a steady-state solution consists of a DC voltage across capacitor c0 of 1 V and no current through the resonant arm. Hence, there is no steady-state oscillation for this solution. A second solution is to have oscillatory behavior with the resistive losses of your resonator provided by the DC 1 V source. Perhaps to force a steady-state oscillatory solution, you might insert a piecewise linear voltage source as a short pulse in the resonant arm (or a parallel piecewise linear current source) at the beginning of your simulation to create a source of transient noise that will initiate oscillation. By setting pss time "tstab" after this pulse, I think the likellihood of achieving a steady-state oscillatory solution is much greater. Please also make sure to set maxstep to a value much less than (< 1/50 or 1/100) of the period of the resonance frequency and use an "errpreset" of at least "moderate".

     

    Shawn  

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  • Dear kpti,

    I believe the issue is that in your your pss simulation result, there is no oscillation in the steady-state. The resonator you are illustrating shows a resistance of 50 ohms I believe provides the possible solution of damping out any steady-state oscillation. Hence with time, a steady-state solution consists of a DC voltage across capacitor c0 of 1 V and no current through the resonant arm. Hence, there is no steady-state oscillation for this solution. A second solution is to have oscillatory behavior with the resistive losses of your resonator provided by the DC 1 V source. Perhaps to force a steady-state oscillatory solution, you might insert a piecewise linear voltage source as a short pulse in the resonant arm (or a parallel piecewise linear current source) at the beginning of your simulation to create a source of transient noise that will initiate oscillation. By setting pss time "tstab" after this pulse, I think the likellihood of achieving a steady-state oscillatory solution is much greater. Please also make sure to set maxstep to a value much less than (< 1/50 or 1/100) of the period of the resonance frequency and use an "errpreset" of at least "moderate".

     

    Shawn  

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