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Message ID: 1294     Entry time: Wed Feb 9 01:35:06 2011
Author: Zach 
Type: Laser 
Category: GYRO 
Subject: gyro RFPD transfer function (sort of) 

With Koji's help, I was able to get the PD working today. Yesterday, I was having trouble getting the DC readout to work. We traced it back to the conical inductor to ground from the PD anode, which was open for some reason (I later broke it when removing it from the board, but it wasn't obviously broken before that --- I am trying to fix it). I replaced it with a normal coil for the moment.

After this, things worked fine. There was a strange ~75 kHz oscillation in the DC signal, but Rana postulated that this could be from the less-than-stellar lab supplies. I decided to move on to the RF output. I hooked it up to the Jenne Laser rig and swept it. Below is a log-scale plot and a linear close-up. I am still working on the calibration and making it match up with the model, but I have to have another look at the measurement setup and measure some component values tomorrow.

Essentially, though, it looks like what we expect:

  • AC coupled
  • "Resonant" spike at 33 MHz for the REFL readout (the actual peak is at a higher frequency, but the transimpedance at 33 MHz is at a point where it is very weakly sensitive to diode capacitance fluctuations
  • Notch at 66 MHz, for 2f rejection
  • Roll-off at higher frequency

More details and comparison with the model to follow.

plotlog.pngplotlin.png

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