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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: 2164     Entry time: Thu Apr 5 02:04:49 2018     In reply to: 2162     Reply to this: 2165
Author: Koji 
Type: Summary 
Category: BEAT 
Subject: Compensation for MAX4107 at G=4.5 

MAX4107 is stable only when G>+10. Because of this fact, the 25MHz PD has a too-high transimpedance for our purpose. To lower the gain without losing the stability of the amp, I have implemented a compensation network.

Attachment 1 shows the compensation network. This 10Ohm+100pF pair effectively makes the high freq noise gain higher (~10) while the low freq gain is G=4.5.

The actual implementation is found in Attachments 2 and 3. The overall schematic can be found in Attachment 5.
I also chose the resistor values so that their noise contributions are reduced.

The resulting output spectrum is compared with the one before the modification (Attachment 4).
Even with the lower gain, the gain peaking of the amplifier output is reduced.

LISO model (not shown here) indicates the input referred noise is ~1nV/rtHz. Considering the voltage division by the 50Ohm termination, the output voltage is as low as 2.25nV/rtHz. This is not a high number. Thus, we practically need a mid power / low noise amplifier attached to the output of the unit.

The total performance of the PD unit will be tested again shortly.

Attachment 1: max_circuit.pdf  13 kB  Uploaded Thu Apr 5 03:06:21 2018  | Hide | Hide all
max_circuit.pdf
Attachment 2: IMG_3667.JPG  3.838 MB  Uploaded Thu Apr 5 03:06:52 2018  | Hide | Hide all
IMG_3667.JPG
Attachment 3: IMG_3668.JPG  1.704 MB  Uploaded Thu Apr 5 03:07:04 2018  | Hide | Hide all
IMG_3668.JPG
Attachment 4: IMG_3665.JPG  732 kB  Uploaded Thu Apr 5 03:09:15 2018  | Hide | Hide all
IMG_3665.JPG
Attachment 5: CTN25_schematic_180404_KA.pdf  135 kB  Uploaded Thu Apr 5 03:09:25 2018  | Hide | Hide all
CTN25_schematic_180404_KA.pdf
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