[time-nuts] Phase Noise/Jitter/SNR/N to Slope ratio etc

Don Collie jnr merdon at xtra.co.nz
Tue Apr 29 01:27:35 EDT 2008

So to summarise : To make a synthesiser`s phase noise low :

 - Apply the KIS principle [Keep It Simple]
 - Use high speed [non-saturating?] logic rather than low  
 - The logic supplies should be well regulated, distributed
           and decoupled.
 - Make the PRF to the P/F detector as high as possible.
 - The loop filter should have a sharp rolloff 
           .... and maintain loop stability ;-)   
 - The loop BW should be as low as possible.
           [ ie loop filter should rolloff at the lowest frequency
 - The reference frequency should have the highest slope to
            noise ratio possible Since slope is proportional to 
            amplitude if frequency is constant, then this ratio
            equates to a high SNR - and we all might as well 
            go shoot ourselves if the reference frequency
            changes - eh guys ;-).  
 - Use quality, low noise, components in the VCO including
             the active device.
 - Employ great craftiness in the choice of circuit 
            configuration for the VCO.
 - The VCO resonant circuit should be of the highest  
            "Q" possible - Why?
 - Use a YIG in preference to Varicaps, and use back-to-
             back matched varicaps if possible.
 - Use great care with PSU, and earth returns between the
             digital [phase detector] circuits, and analogue
             circuits [ VCO].   
 -The VCO supply Voltage needs to be very clean, and
 - Minimise the tuning range of the VCO where possible
             to minimise the effect of any jitter that *does*
             reach the VCO through the loop filter.
 - Keep the RF Voltage across the varicaps small
             [class "A" oscillator?/crafty design]
 - Maximise the VCO output voltage to maximise SNR
             or output amplitude to phase noise amplitude.

Some of these are at odds with each other, but can anyone 
constructively criticise or refute these points, or add more, or expand on any of them, please?
    Again, thankyou for your thoughts,.......................Don C.


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