Hi Visjnoe,
as I understand it, the issue is simply one of modulation of the vco's steady state carrier, with the exception that the "control" port is the supply, rather than the VCO's voltage control input.
Therefore any of the "standard" techniques for simulation and analysing the results of those simulations as applied to VCOs should hold true.
Assuming you wish to use a circuit netlist description of the VCO (rather than a mathematical behavioural model) then probably the most direct method is to modulate the supply line with a small squarewave (remember to include an realistic supply impedance) then monitor the output waveform as an "eye diagram". You might like to look at a note I have placed here:
http://www.silicondevices.com/Resources/AppsNotes/ModellingVCOs.htmlto see how this might be done. There are also details of how you may look at the frequency deviation of the output without having to resort to a full-blown FFT of the output (and the time-penalty associated with the FFT).
The deviation meter part of the testbench is interesting as not only is it useful for assessing supply pushing, ity also allows you to simulate load-pull.
Load pull is done with multiple simulations where a half wave transmission line is progressively terminated with a near zero through Zo to a near open circuit load resistance, whilst monitoring the frequency deviation (using the above circuit). This will probably tell you much more about the supply related behaviour of the VCO (provided you have modelled the supply accurately to greater that 10x the VCO output frequency) than simply modulating the supply itself.
Email me directly if you want to know more details: Simon.Harpham@ieee.org
Cheers,
SimonH.
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VCO PSRR simulation set-up Spectre (Read 8239 times)