CountingDaq 220318

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Meeting information

 Meeting time:  12:00pm Eastern
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  • Presentation by J. Musson about JLab beam monitor instrumentation status/plans: John's slides in DocDB 877
  • Activity updates
  • General discussion


Recording on Zoom: [1]

Participants: J. Musson, M. Pitt, A. Camsonne, B. Moffit, Y. Mei, J. Fast, R. Michaels, R. Carlini, K. Evans, N. Rider, D. Armstrong, K. Cole, D. Flay, D. McNulty, C. Ghosh, D. Mack, C. Zorn, Y. Kolomensky

  • John Musson's presentation
    • The digital receiver was initially designed for BPMs in Hall D, so low current sensitivity was a priority
    • The "calibration cell" is where the wire multiplexing is done. The switching is a 1 MHz cycle, ~0.5us for one wire then ~0.5 us for the other.
      • The cavity BPMs also have a calibration cell, that multiplexes the current cavity alternately with the two position cavities
      • Charge monitors or Unsers don't have a calibration cell and are not multiplexed; their signal goes into a single receiver channel
    • The raw 1497MHz signals are downconverted to 45MHz and this is sampled at 60 MHz (with 16-bit ADC) to get a sequence of "I" and "Q" values. About 15 of each of I and Q are summed for each wire to get values for I & Q values for the two wires at 1 Msps.
      • Presumably for the charge monitor or Unser, all thirty of the I and Q samples in the 1 us are used to get the I & Q values at 1 Msps.
    • The receiver box has one set of 18 bit DACs that can output the 1 Msps wire values. I am not clear on what actually gets output; it looks like there are four outputs on the front panel, but we'd have an I and Q for each of the four wires, so that would be 8 signals.... The latency is a few microseconds, but can be measured precisely.
      • The DACs are AD5781 chips
    • The receiver has more filtered output streams that can be output: 250kHz BW of magnitude and phase, or down to 10 Hz. These might be useful for counting mode.