RequirementRequirements:
An amplifier/attenuator on each diagnostic signal. This was motivated by Jim Welch’s calibration procedure, which would benefit from seeing the loss location for hits on each fiber. The wire scanners need amplification, since only a small charge is kicked out by the wire. Jim needs attenuation, since he splats the entire bunch onto the wall of the beampipe. A fiber PLIC may be best with no gain or attenuation. The chips to use (two AD603s in cascade) give both gain and attenuation, depending on a control voltage. The gain control is exponential—a linear conversion from control voltage to dB of gain.
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The chassis bypasses the amplifier if the DAC voltage is less than -1 V. There should be a bypass on/off switch that sets the DAC to something about -1.2 V (to be far from the transition). When bypassed, the path attenuates by -5.6 dB (almost a factor of 2 in voltage). When the bypass is turned off, the DAC can go to 0 V, since that gives almost the same gain, -5.2 dB. The user won’t see a big jump and can tweak from there.
Block Diagram:
