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PSS problem in VCO design

whitefan
Hello all,

I am trying to design VCO with feedback topology (common source amplifier + pi-feedback) i.e Hartley oscillator with active inductors. First I designed a circuit with all passive components in feedback and that works fine in all PSS and PNOISE etc. Now I replaced both the inductors of feedback with active inductors and PSS doesn't work at all. I don't know whether it is a problem with my circuit or some special settings are needed, the error in PSS is like:

Error found by spectre at time = 121.667 ns during periodic steady state analysis 'pss'.

V(net0209) is too small to reliably detect the period of the oscillation. This may be because nodes with insignificant signal levels were chosen or it may be because the oscillator was never properly started.

I am using Virtuoso front to back design environment (IC 5.1.41) and simulator is spectre (not spectreRF). Here I am attaching the circuit of my oscillator where L1 and L2 are active inductors.

  • Did you try simulating it in transient to check it actually oscillates? Also, are you using a current version of the simulator (i.e. not spectre from IC5141 which is ancient, as there have been 10 major releases of spectre (in the MMSIM stream) since then. OK for you to be using IC5141 as the schematic and simulation environment (you may be limited by your design kit), but the simulator should be something more recent. But either way, you need to check the simulation in transient to ensure that it's actually working.

    Regards,

    Andrew.

  • Hello sir,
        
    Thank you for your advice, you were right about oscillation, I checked the transient its getting damped after certain time period so at steady state it will show me zero voltage. You mention about MMSIM in spectre, does it really matter in performance of oscillators? I don't have idea about it (forgive me for asking silly questions but I am working in Cadence since last 4-5 months so don't have much idea and don't have any kind of help from my lab) I found that may be I have issues with active inductors because oscillator working fine with passive inductors.

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