[time-nuts] Phase noise & Jitter
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
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.
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