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Entry  Fri Aug 3 15:53:25 2018, gautam, Update, SUS, Low noise bias path idea LT1055_precOpAmp.pdf
    Reply  Fri Aug 3 16:27:40 2018, rana, Update, SUS, Low noise bias path idea 
       Reply  Sun Aug 5 15:43:50 2018, gautam, Update, SUS, Another low noise bias path idea HV_Bias_schematic.pdfTF.pdfbias.pdfHVbias_currentNoise.pdf
          Reply  Wed Aug 8 23:06:59 2018, gautam, Update, SUS, Another low noise bias path idea 
             Reply  Wed Aug 15 19:18:07 2018, gautam, Update, SUS, Another low noise bias path idea HV_Bias.pdfHVamp_TF.pdfHVamp_noises.pdfcurrentNoises.pdfHVamp.fil.zip
                Reply  Thu Aug 16 23:06:50 2018, gautam, Update, SUS, Another low noise bias path idea HVamp_schem.PDFHvamp.zip
                   Reply  Mon Oct 1 22:20:42 2018, gautam, Update, SUS, Prototyping HV Bias Circuit CoilDriverBias.pdfcurrentNoise.pdfPSRR.pdf
Message ID: 14147     Entry time: Wed Aug 8 23:06:59 2018     In reply to: 14135     Reply to this: 14165
Author: gautam 
Type: Update 
Category: SUS 
Subject: Another low noise bias path idea 

Today while Rich Abbott was here, Koji and I had a brief discussion with him about the HV amplifier idea for the coil driver bias path. He gave us some useful tips, perhaps most useful being a topology that he used and tested for an aLIGO ITM ESD driver which we can adapt to our application. It uses a PA95 high voltage amplifier which differs from the PA91 mainly in the output voltage range (up to 900V for the former, "only" 400V for the former. He agrees with the overall design idea of 

  • Having a LN opamp with the HV amp inside the feedback loop for better voltage noise at low frequencies.
  • Having a passive RC network at the output of the HV amp to filter out noise at high frequencies.

He also gave some useful suggestions like 

  • Using the front panel of the box that as a heatsink for the HV amps.
  • Testing the stability of the nested opamp loop by "pinging" the output of the opamp with some pulses from a function generator and monitoring the response to this perturbation on a scope.

I am going to work on making a prototype version of this box for 5 channels that we can test with ETMX. I have been told that the coupling from side coil to longitudinal motion is of the order of 1/30, in which case maybe we only need 4 channels.

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