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Entry  Thu Jul 26 10:58:02 2012, Sarah, DailyProgress, ISS, ISS Box Transfer Function 8x
    Reply  Mon Jul 30 20:26:39 2012, Sarah, DailyProgress, ISS, ISS Box Transfer Function 13x
       Reply  Mon Aug 6 18:28:08 2012, Sarah, DailyProgress, ISS, ISS Box Transfer Function 7x
          Reply  Tue Aug 7 03:00:31 2012, rana, DailyProgress, ISS, ISS Box Transfer Function 
          Reply  Wed Aug 8 20:57:15 2012, Sarah, DailyProgress, ISS, ISS Box Transfer Function 
          Reply  Wed Aug 8 23:03:52 2012, Sarah, DailyProgress, ISS, ISS Box Transfer Function 7x
Message ID: 1030     Entry time: Thu Jul 26 10:58:02 2012     Reply to this: 1031
Author: Sarah 
Type: DailyProgress 
Category: ISS 
Subject: ISS Box Transfer Function 

 Tara and I measured the transfer function for the TCS ISS Box we got from Livingston.

Schematic:

We had to make a cable for the three pronged power input for the box before we could test anything. After making the cable, we found differences between the pdf schematic and the values of the components in the box. Specifically, the capacitors in op amp stages defining the transfer function, C38, C44, C59, and C63 are all a factor of ten higher than reported in the schematic. I updated the schematic with the correct values and attached it to this elog. The following picture shows the circuitry which defines the shape of the transfer function:

TF_stages.png

There are currently only two op amp stages being used, and then a flip sign stage at the end. 

Measurements and Calculations:

We measured the transfer function for the two filter stages individually, as well as the overall transfer function for both stages. I also modeled the three circuits in LISO and compared the generated transfer function with what we measured. The following three plots show the results:

TF_compare_1.png

TF_compare_2.png

TF_compare_1_2.png

The results for the transfer function generated with LISO agree with the measured TF in all three cases. The overall transfer function for both stages does not include the flip sign stage, which when turned on just flips the phase.

Modifications:

Since the transfer function for both stages is not quite the shape we want for our ISS, we will need to make a few modifications:

1. We want a gain of  ~60dB for a factor of 1000 of intensity noise suppression

2. We want the transfer function to block DC components, and thus fall off at low frequencies

In order to get a gain of ~60dB at the peak, we can use variable gain stage preceding the filters. The data sheet for the vga is: AD8336 VGA Data Sheet. We tested this and confirmed that a gain of 60dB is easily achievable. 

A high pass filter will have to be added in one of the unused op amp stages, in order to get a transfer function that blocks the DC component and falls off at low frequencies. I should be able to design a high pass filter and model the whole TF in LISO to optimize the shape, and then filling one or two of the unused stages with the design should be pretty easy.

Attachment 5: TF_compare_1_2.fig  177 kB
Attachment 6: TF_compare_1.fig  164 kB
Attachment 7: TF_compare_2.fig  169 kB
Attachment 8: D080351_REV_A3.pdf  1.434 MB  | Hide | Hide all
D080351_REV_A3.pdf D080351_REV_A3.pdf D080351_REV_A3.pdf
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