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Entry  Tue Mar 30 22:57:34 2010, Hao Huan, ROFS Configuration 
    Reply  Thu Apr 15 13:48:40 2010, Stefan Ritt, ROFS Configuration 
Message ID: 68     Entry time: Thu Apr 15 13:48:40 2010     In reply to: 59
Author: Stefan Ritt 
Subject: ROFS Configuration 

Hao Huan wrote:

Hi Stefan,

    according to the DRS4 datasheet, if we want an input range centered around U0, the ROFS should be 1.55V-U0. However when I read the codes of the evaluation board application, ROFS seems to be 1.6V-1.25*U0 where the coefficient 1.25 is said to come from sampling cell charge injection correction. Is it the right equation to use? What exactly does that charge injection correction mean?

    Thanks a lot.

 

1.55V-U0 is the theoretical values, but there are certain "dirt" effects like chip-to-chip variation and charge injection. The difference between various chips is easily 20-30mV, so there is not a single "correct" value. The formula 1.6V-1.25*U0 I developed for a special evaluation board, where it kind of worked better than the theoretical value, but I never made systematic studies. One should average over several chips and use some solid average there. Best is if you try both formulas and check what give you the better linearity.

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