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CMOS Crystal Oscillator duty cycle
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schmitt trigger:
Benta;
I like to come to this forums to learn, and to correct any incorrect knowledge which I may have. I won't be offended if I am shown my errors.

In the attached datasheet, page 10, it shows that a maximum VCO frequency of 24 Mhz, whereas the OP only requires in the vicinity of 10 Mhz.... Why wouldn't it work in a straight 1:1 mode?
Benta:

--- Quote from: schmitt trigger on November 06, 2018, 02:13:17 pm ---Benta;
I like to come to this forums to learn, and to correct any incorrect knowledge which I may have. I won't be offended if I am shown my errors.
q
In the attached datasheet, page 10, it shows that a maximum VCO frequency of 24 Mhz, whereas the OP only requires in the vicinity of 10 Mhz.... Why wouldn't it work in a straight 1:1 mode?

--- End quote ---

The VCO is not the issue here, although it's marginal. The maximum frequency of the VCO is not that interesting, but the center frequency is, which in this case would be 12 MHz (fMAX/2).

The limiting factor is the PFD. There is no stated maximum frequency in the data sheet, but if you start adding up the propagation delays, you'll quickly see that maximum input frequency is a couple of MHz. It's not an issue for frequency synthesizers, where the VCO frequency is much higher than the reference frequency, but in a 1:1 configuration it won't work.

Hope this helps.


iMo:
Another idea: you may try with NE602 - Xtal oscillator and a freq doubler on a single chip. Add an LC tank tuned to 21.4MHz (at the Ne602 outputs pins 4-5), a 74AHC04 shaper and the 74AHC74 divider by 2 and you get your 50/50..
http://www.b-kainka.de/Daten/HF/NE602Xtal.pdf
http://www.n4iqt.com/BillRiley/multi/8x.JPG
You may try without the LC, not sure the fundamental 10.7MHz will not mess with the doubled freq..

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