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Entry  Thu Mar 29 02:51:35 2018, Koji, Summary, BEAT, The design for a new beat PD  6x
    Reply  Mon Apr 2 00:15:34 2018, rana, Summary, BEAT, The design for a new beat PD  
       Reply  Wed Apr 4 02:06:45 2018, Koji, Summary, BEAT, First article of the CTN beat PD 7x
          Reply  Thu Apr 5 02:04:49 2018, Koji, Summary, BEAT, Compensation for MAX4107 at G=4.5 max_circuit.pdfIMG_3667.JPGIMG_3668.JPGIMG_3665.JPGCTN25_schematic_180404_KA.pdf
             Reply  Fri Apr 6 04:48:02 2018, Koji, Summary, BEAT, Compensation for MAX4107 at G=4.5 CTN25_transimpedance.pdfcurrent_noise_CTN25.pdfidet_CTN25.pdf
                Reply  Sun Apr 22 17:46:55 2018, awade, Summary, BEAT, Compensation for MAX4107 at G=4.5 D980454-01.pdf
Message ID: 2175     Entry time: Sun Apr 22 17:46:55 2018     In reply to: 2165
Author: awade 
Type: Summary 
Category: BEAT 
Subject: Compensation for MAX4107 at G=4.5 

For reference I have attached original schematic to this post.  Koji sent me the link to the original document that can be found here: https://labcit.ligo.caltech.edu/~rana/dale/Length_Sensing_and_Control/LSC_Photodiode/Version_B/D980454-01.pdf

This version of the document includes page 1 with the pinouts for the power connector.


Performance of the modified photodetector unit:


- Resonant frequency f_res = 26.0MHz
- Transimpedance gain at 26MHz is 1.27kOhm (560Ohm resistance of the resonant circuit x G=4.5 x 1/2 by 50Ohm termination)
- Input referred curent noise = 9pA/rtHz
- Shotnoise intercept current is 0.24mA


- There is a gain peaking at 280MHz as explained in the prev elog. If one does not like this, remove 700Ohm resistor from the max4107 stage. It will increase the amplifier gain from 4.5 to 5, and the gain peaking is reduced.

- The transimpedance gain might be still too high. Then, a shunt resistor at the location of R24 can be added to the resonant circuit. This way, the shunt resistance is seen only from the RF path. Of course, lowering the signal level has to be paid by the increase of the input referred current noise level.


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