Difference: ClicSigDigi (4 vs. 5)

Revision 522 Aug 2012 - FrancisCullinan

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Digitiser Effects

In order to investigate the effect of the digitiser specifications, the noise and non-linearities of the electronics were removed. This allowed the limits imposed on the resolution by the digitiser noise to be determined. A simulation was run with the same parameters as in ClicSigProc but with a position sweep in x with a single train at each point so that the minimum resolution of the digitiser is visible. The minimum offset visible above the digitiser noise was also determined. This came to 170 nm and is the same for both deconvolution and DDC processing algorithms. The bandwidth of the digital filter used for the DDC was 45 MHz in both cases.

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  digires2.png
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Processing Parameters

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New Resolution Measure

 
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The processing parameters (bandwidth of the DDC filter and shaping of the inverse-response for the deconvolution) do not have a significant effect on the resolution because noise has been omitted.
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A measure of resolution that may be useful in simulation is calculated from the difference between the measurement at a particular sample number and the interpolated bunch position at that time. A simple illustration of the measured and interpolated positions with a DDC filter bandwidth of 80 MHz is shown below.

newres.png

This measure is constant when normalised by the level of bunch to bunch jitter. It doesn't vary a low but shows noticeable changes with the DDC filter bandwidth.

jitternorm.png ddcfilter.png

This measure of resolution (dubbed 'averaging resolution') goes above 1.0 (the value it would take if simply averaging over the whole bunch) when the bunch to bunch jitter dips below the BPM resolution.

smalljit.png
 
 
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