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How is the external crystal connected to the PLL?

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casual3_2002

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crystal and PLL

we have a chip with XIN/XOUT (crystal in/out) pins defined which are supposed to be connected to the on-chip PLL, but I'm not sure how is the external crystal connected to the PLL, is it direct connection or through some other components?

Thanks!
 

Re: crystal and PLL

xtal is soldered to the board and connected to pins....

If you want to see some explanation how it works look for example for Pierce oscillator.
On chip is circuit ( for example inverter with feedback) and together with the xtal it oscillates at given frequency. (theory is rather simple)
Then it is connected to PFD (directly or through prescaler) and so to PLL
 

Re: crystal and PLL

We have a PLL hard macro, I'm not sure what to put between the PINs and
the PLL, is it a cell I can get from the foundry or something else, what about
the parameters? Thanks!

Teddy said:
xtal is soldered to the board and connected to pins....

If you want to see some explanation how it works look for example for Pierce oscillator.
On chip is circuit ( for example inverter with feedback) and together with the xtal it oscillates at given frequency. (theory is rather simple)
Then it is connected to PFD (directly or through prescaler) and so to PLL
 

Re: crystal and PLL

depending on foundry - usualy they have xtal oscillator (simple) .

you connect the output from xtal oscillator to your Reference input of PLL
 

crystal and PLL

sometimes you should connect the crystal though a cap.
 

Re: crystal and PLL

I would like to ask if there's anybody there who has some basics of pierce crystal and or the armstrong oscillator.
 

crystal and PLL

crystal can be seen as a circuit including Resister/Cap/inductance ,and the Q value is very hign at the fixed frequency
 

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