[time-nuts] Ultra low noise Pierce oscillator???

[Bruce Griffiths]

Hans

Hans Rosenberg wrote:
> Hi Bruce,
>
> Thanks a lot for all the input.
>
> Do you have any figures on the noise voltage on a led? A good buried zener reference does 100nV/rt Hz, what does a led do?
>
> You mention that an amplitude control mechanism influences phase noise. Are you suggesting that a good amplitude control is better than turning off the active device for some time each cycle?
>
>   
There is some debate about this in the literature.
> I started having a close look at the driscoll design. It looks really nice. It seems much more elegant than what I was trying to do. I do have one question about the AGC circuit. The tune-voltage must be kept in the middle of the supply, otherwise the amplitude control loop will modulate the overall capacitance of the capacitive attenuator. 
The input  capacitance doesn't vary that much if the attenuator is
correctly proportioned:
http://www.karlquist.com/97bri.pdf
> So this is critical to set correctly in practice. There probably is a good reason why the current in the transistor is not changed to achieve amplitude control. Do the capacitances in the transistors vary so much that they start introducing more phase errors than when tuning a capacitive attenuator correctly? Or is there another reason.
>
>
> Thanks again for the nice input.
>
> Best regards,
>
> Hans Rosenberg 
>
>   

Bruce