32.768k crystal oscillator de-Q freq shift

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tommydidi

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Hi Guys,

I de-Q'd the crystal oscillator by adjusting the values of Cx and Lx to give the right w0, my transient simulation is dramatically faster but why the f0 is shifted a bit to ~33.5KHz? Thanks.


tommydidi
 

What do you mean by de-Q'd? How much is the Q in the Xtal model. Low Q are always faster but will give slightly different Center frequencies. Generally in my simulation I assume Q of abt 50K. But this frequency shift doesnt matter unless u are trying to do some jitter sims.
 

Thanks yuvan.

What I meant was divide Lx by 100 while times Cx by 100, so the center freq is still kept the same but the new Q (de-Q) will be smaller due to the bigger Cx.

Also, how do I calculate the steady state current for the Gm stage? Thanks.
 

I assume you're -ve resistance is done by some common source stage...So, you can refer Vittoz (I forgot ) for optimial sizing of the gm stage..and thus the current required.
 

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