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Message ID: 1076     Entry time: Wed Sep 22 00:58:47 2010
Author: Zach 
Type: Electronics 
Category: GYRO 
Subject: RFPD LISO model 

Attached are a transfer function and noise estimate for a proposed gyro (TRANS) RFPD circuit, generated by LISO. It is topographically identical to the one that Rana made a while back, with the two following modifications:

  • the components have been adjusted to change the resonant frequency from 80 MHz to 95 MHz to reflect the current setup, and
  • the "resonant readout" and "AC coupling" inductors have been interchanged, in line with how it is done on the aLIGO board.

Here I have included reasonable series resistances for the large and small inductors.

If you compare with the above-linked post, you can see that the noise is at about the same level, with a slight increase because we are right at the MAX4106's bandwidth limit for the prescribed gain of 450/50 = 9.

I am not sure what the other options for photodetector circuitry are, but it seems that this sort of LC design will work (at least for the TRANS PDs, where the signal will be limited by the shot noise of the REFL PDs that gets imprinted on the cavity light, as mentioned in Rana's post), and it can be done on the aLIGO boards.

gyro_PD_TF.pnggyro_PD_noise.png

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