how to design a 20M clock generator /oscillator

[wuxy]

20m oscillator

Hi all,

I need YOUR advice.now i am designing a 20M clock generator for digtal circuit,and the frequency must be within 5% of the target value. what is a effective and proper means? Now i have a scheme: use a SMIT trigger ,two invertor and R C to compose a RC oscillator,and then trim the frequecy to the desired range by trimming R.But this circuit is susceptive to supply votage and hard to trim because the R C cannot choose too large in order to get a 20M Hz frequecy and the trimming switch's Ron and parasitical C will have bad effect or prevail.

 

[gharuda]

how to design a generator

you could use a ring oscillator

 

[wuxy]

smittrigger

you could use a ring oscillator

But i wonder if it is ease to control a ring oscilator to adjust it to 20M?And if that means i need a accurate voltage reference and buffer? Sorry, i have little experence in this. Thanks!

 

[eecs4ever]

oscillator clock ckt

try this
**broken link removed**

use a variable/controllable R to get the exact frequency

 

[wuxy]

oscillator and clock circuit design

try this
**broken link removed**

use a variable/controllable R to get the exact frequency

Thanks very much!But the circuit need a minus supply voltage,and it is seem still sensitive to supply voltage,i am afaid it won't meet my requirement.