[time-nuts] Phase noise & Jitter

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Apr 28 17:48:17 EDT 2008

Henk ten Pierick wrote:
> Hi Don,
> Any comparator or slicer has a noise density and a noise bandwidth.  
> The noise value of this slicer is the integral of the noise density  
> over the noise bandwidth. The noise bandwidth is the slicer  
> bandwidth, not the slicer frequency. Due to the slope, thus the slew  
> rate, of the input signal the input noise is converted to jitter.
Which is why when the input slope (slew rate) is low (< 1E6 V/s or so. 
The exact limit depends on the noise and noise bandwidth of the 
comparator), it is advantageous to amplify the slope using a chain of 
amplifiers of where the gain and bandwidth increases for each successive 
stage. The output of the slope amplifier then drives the 
comparator/slicer/zerocrossing detector.
The optimum sequence of gains and bandwidths depends on the noise on the 
input signal and the noise characteristics of each amplifier stage. The 
disadvantage of such circuits is the accompanying phase shift and 
associated tempco due to the low pass filter components used in each stage.
> Henk

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