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Push Push VCO Simulation Guidance

Yasir Shafi

Hi, 

Anyone who has simulated the push push VCO design in cadence can guide me how to find the convergence state of the even harmonics incase of push push VCO since cadence will only look at the convergence state of the fundamental harmonic and continue the simulation but how can we let cadence know that this time we are looking for the convergence state of the second harmonic. 

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  • ShawnLogan

    Dear Yasir,

    Yasir Shafi said:
    Anyone who has simulated the push push VCO design in cadence can guide me how to find the convergence state of the even harmonics incase of push push VCO since cadence will only look at the convergence state of the fundamental harmonic and continue the simulation but how can we let cadence know that this time we are looking for the convergence state of the second harmonic. 

    I don't believe your comment is accurate as the spectre simulator performing a transient analysis will simulate the netlist you provide it. It has no knowledge of the fundamental frequency of any VCO within the netlist. If you find that the analysis results indicate that oscillation is occurring on the fundamental, it suggests that there is nothing from a circuit perspective that will prevent it from operating on the fundamental. Typically, as is the case in harmonic based VCO (i.e., those designed to operate on the 3rd or 5th fundamental), some means of reducing  the magnitude of the sustaining amplifier's negative resistance at the fundamental frequency is introduced to make oscillation on the fundamental frequency far less likely (or impossible) than operation on the desired harmonic.

    Did I understand your question correctly? I hope so anyway.

    Shawn

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  • ShawnLogan

    Dear Yasir,

    Yasir Shafi said:
    Anyone who has simulated the push push VCO design in cadence can guide me how to find the convergence state of the even harmonics incase of push push VCO since cadence will only look at the convergence state of the fundamental harmonic and continue the simulation but how can we let cadence know that this time we are looking for the convergence state of the second harmonic. 

    I don't believe your comment is accurate as the spectre simulator performing a transient analysis will simulate the netlist you provide it. It has no knowledge of the fundamental frequency of any VCO within the netlist. If you find that the analysis results indicate that oscillation is occurring on the fundamental, it suggests that there is nothing from a circuit perspective that will prevent it from operating on the fundamental. Typically, as is the case in harmonic based VCO (i.e., those designed to operate on the 3rd or 5th fundamental), some means of reducing  the magnitude of the sustaining amplifier's negative resistance at the fundamental frequency is introduced to make oscillation on the fundamental frequency far less likely (or impossible) than operation on the desired harmonic.

    Did I understand your question correctly? I hope so anyway.

    Shawn

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