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Entry  Mon Dec 7 02:59:38 2009, Zach, Misc, SUS, LED Driver noise (with AD743) noise_comp_low.pngnoise_comp_high.pngS-K_respons_vs_R.png
    Reply  Mon Dec 7 12:01:14 2009, rana, Misc, SUS, AOSEM LED Driver noise (with AD743) 
Message ID: 136     Entry time: Mon Dec 7 02:59:38 2009     Reply to this: 137
Author: Zach 
Type: Misc 
Category: SUS 
Subject: LED Driver noise (with AD743) 

 I retook the measurement from my last post, this time using an AD743 in place of the OP27 (per Rana's comment). The results are below.

Low-frequency:

noise_comp_low.png

RA: Although it says m/rHz, this is not measured displacement noise, but rather estimated displacement noise due to the LED noise. The previously measured conversion from the LED RIN to apparent displacement is used to convert from the voltage noise of the LED driver to the contribution to the OSEM's displacement readout.

High-frequency:

noise_comp_high.png

Seems better than before, but not quite what expected. I observed that the transfer function of the S-K filter was what it should be up until a decade or two above the corner frequency, after which it appeared to spring zeroes out of nowhere and level off at high frequency. I tried to see what would happen if I changed the resistor values, and the following plot is what I got.

S-K_respons_vs_R.png

This plot seems familiar from my electronics courses, but I haven't put a finger on what is causing this behavior yet. I'm sure that the answer is somewhere in H&H (or in the brain of a kind soul who happens to be reading this--wink wink).

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