32.768k crystal oscillator de-Q freq shift

[tommydidi]

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

 

[yuvan]

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.

 

[tommydidi]

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.

 

[yuvan]

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.

 

[FvM]

Is it asking too much if we want see a circuit schematic?