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Entry  Mon Nov 14 17:03:06 2016, yinzi, DailyProgress, TempCtrl, frequency response and noise measurements 8x
    Reply  Wed Nov 16 12:13:42 2016, awade, DailyProgress, TempCtrl, frequency response and noise measurements 
Message ID: 1768     Entry time: Mon Nov 14 17:03:06 2016     Reply to this: 1769
Author: yinzi 
Type: DailyProgress 
Category: TempCtrl 
Subject: frequency response and noise measurements 

Here is the data that was taken last week on the driver circuit.

At first there was a LF356 chip instead of the AD743, and it gave the following response:

Which looked reasonable, but it made sense to take noise measurements using 2 AD743s so I swapped it out, but then the response was this:

For some reason, the cutoff frequency moved to close to 100Hz. The noise measurement was:

I also tried replacing the 10uF capacitors with 22uF capacitors to try to move the cutoff frequency back down, and got the following response:

So that worked, but then the noise measurement went up by a lot:

I'm not sure what the noise requirements are, but it looks like using 10uF caps gives a pretty high cutoff frequency, but using 22uF caps increases the noise.

I also put in the BUF634 chip but when I powered it, I smelled something burning, so I'm going to test out that chip in isolation before trying to integrate it with the rest of the circuit.

 

Edit (11/17/2016): Attached Matlab workspace with relevant data, plotting script, and Andrew's freqStich script (used to combine noise measurements).

Attachment 6: workspace.mat  215 kB  Uploaded Thu Nov 17 10:57:05 2016
Attachment 7: plot_tf.m  1 kB  Uploaded Thu Nov 17 10:58:54 2016  | Hide | Hide all
%s2-3 old chip tf
%s12-s17 10uF noise
%s18-19 10uF tf
%s20-21 22uF tf
%s23-27 22uF noise
close all

freq_array_1 = [s12_f s13_f s14_f s15_f s16_f s17_f];
data_array_1 = [s12_m s13_m s14_m s15_m s16_m s17_m];

... 48 more lines ...
Attachment 8: freqStitch.m  3 kB  Uploaded Thu Nov 17 10:59:06 2016  | Hide | Hide all
%%  This is a module for stiching spans of overlapping PSDs of different frequency bin size from SR785
%
%   Assuming a logerithmic scale of frequency, it is desirable to 
%   stich the smaller frequecy ranges to the bottom of the larger ones
%   wilst truncating out bins in the larger span.
%
%Feed in frequency matrix f(n,m) with correesponding floating point
%data(n,m).  
%%  Synopsis:
%     [freqStitch,dataStitch] = freqStitch(freqPoints,dataPoints)
... 62 more lines ...
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