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Entry  Thu Dec 27 00:12:12 2012, Jinhong Wang, variation of sampling capacitors 
    Reply  Thu Dec 27 09:49:17 2012, Stefan Ritt, variation of sampling capacitors 
       Reply  Thu Dec 27 18:15:14 2012, Jinhong Wang, variation of sampling capacitors 
          Reply  Fri Feb 1 17:43:48 2013, Jinhong Wang, variation of sampling capacitors 
             Reply  Tue Feb 5 14:38:35 2013, Stefan Ritt, variation of sampling capacitors 
Message ID: 215     Entry time: Fri Feb 1 17:43:48 2013     In reply to: 214     Reply to this: 216
Author: Jinhong Wang 
Subject: variation of sampling capacitors 

Jinhong Wang wrote:

Stefan Ritt wrote:

Jinhong Wang wrote:

Hi Stefan,

A quick question, what is the typical variation of the sampling capacitors in DRS4?  Will this variation be significant to affect your sampling result?

 Best,

Jinhong 

The capacitors sample the input voltage, not the charge, so the actual size of the capacitors does not matter on first order (the variations might be in the order of 5%). A bigger effect is the variation of the analog switches in the front of the capacitors, which is about 15%. So the actual bandwidth each cell sees varies by maybe 20% (given by the R and the C), but this comes only into play when sampling steep edges.

Stefan

 Great to know this! Thanks~

Jinhong

 Hi Dr. Stefan,

So the sampling capacitors store the input voltage instead of the charge. What about the readout circuits? I saw there is a buffer followed each sampling capacitor. Do you buffer the charge (like a charge sensitive amplifier)  or the voltage? From Fig.12, 14 in datasheet, it seems most probably the readout is a charging or discharging of a capacitor. Could you please add some comments on this? 

Cheers,

Jinhong

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