Re: SI5351 quadrature VFO

Jerry Gaffke
 

As I recall, Hans reported that the samples he tested did work up to 290mhz,
above which they definitely failed.

If you want to be sure, then should follow the datasheet spec.    
    https://www.silabs.com/documents/public/data-sheets/Si5351-B.pdf

Or go to a different part
    https://www.silabs.com/documents/public/data-sheets/Si5338.pdf

Datasheet says the si5351 has a vco max of 900 mhz and output msynth min of 4,
so that suggests it could do 900/4 = 225mhz. 
Datasheet also says a max output clock of 200 mhz, I'd guess beyond that
they can't guarantee proper CMOS logic levels from the driver.

To hit 290 mhz, the vco must be operating at 290*4 = 1160 mhz.
Jitter might be getting bad, as the vco loop filter is not designed for this.
Heat could also cause trouble. 

Jerry, KE7ER 


On Fri, Jun 15, 2018 at 08:31 am, Ashhar Farhan wrote:
Are you sure these work upto 290 mhz? 

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