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Analogue Optical Link Setup
Based upon the output of Laurent Mirabito and Benjamin Trocme's OptoScan procedures, one obtains a plot of tick max and tick base vs. I2C setting of the laser driver:

By taking the difference you find the amplitude of the tick:

Assuming an amplitude of 800mV for the tick at the input to the AOH one can calculate the optimal settings for both Gain and thus Bias settings. The FED has a gain of ~3.5mV/count (based on the measurement of a single FED at CERN - you should check the gain of your own FED). The nominal gain of the optical link is 0.8V/V, so you should set your link so that the ticks amplitude at the FED is in the range 150-210 ADC counts. Having set your laser driver gain to achieve this, you can find the optimum bias setting using the procedure defined by Benjamin:
  1. Find the maximum tick amplitude
  2. Find the lowest bias for which the amplitude is (0.98*max)
  3. Find the highest bias for which the amplitude is (0.98*max)
  4. The plateau is defined as lowest to highest
  5. If the plateau contains two or more settings, pick the second setting on the plateau (starting from lowest)
  6. If not choose the first setting
Check here for similar results from the TOB system test
Last modified by JT: Fri, 21-Feb-2003 14:11