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Design >> Analog Design >> oscillation amplitude depends on initial condition?
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Message started by vikram1977 on Dec 8^th, 2011, 2:24am

Title: oscillation amplitude depends on initial condition?
Post by vikram1977 on Dec 8^th, 2011, 2:24am

hello everybody
i am simulating a vco , to build up the oscillation i set an initial condition on a given node
my probleme is that according to the initial condition i pick, tha amplitude of oscillations change. it dosn't make any sense for me
can you help me please
is that a problem with my circuit or with the simulator
ps: i use spectreRF

regards

Title: Re: oscillation amplitude depends on initial condition?
Post by raja.cedt on Dec 8^th, 2011, 3:43am

hello,
i am sure some thing is wrong, becaz VCO is a non-linear system hence independent of initial conditions, may be starting dynamics are depends some time. Please provide some more info to resolve.

Thanks,
Raj.

Title: Re: oscillation amplitude depends on initial condition?
Post by buddypoor on Dec 8^th, 2011, 5:08am

Hi Vikram,

the most secure and the most realistic method is not to use an initial condition but to switch on one of the power supplies in Tran simulation.

Title: Re: oscillation amplitude depends on initial condition?
Post by loose-electron on Dec 8^th, 2011, 7:47am

Initial Conditions of a current in the inductor is the best way to get a LC oscillator running.

Try it, you will like it!

However the oscillator needs to settle out to a final amplitude, and that may take many thousnads of cycles of the oscillator to do so.

A trick - use the IC current in L method as described. Then see if amplitude builds or drops in transient simulation.

Adjust the current up-down till you get the right amount so its close to the final oscillation amplitude.

Speeds up the simualtion process a lot, especially with high Q things like crystal oscillators