GRETINA Auxiliary Detector Workshop

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GRETINA Auxiliary Detector Workshop
Electronics

• Sergio Zimmermann
• LBNL

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Outline

• Electronic Interface Options
• Digitizers
• Trigger/Timing System
• Grounding and Shielding
• Summary

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Interface Options

• Three options
• Ethernet readout connects directly to the switch
• Use standard Gretina digitizers the auxiliary
  detectors connect directly to GRETINA digitizers
• Digital data stream example FERA interface
  (Marios talk)
• Presently, the only interface that is funded and
  is part of the requirement document is the
  Ethernet Readout

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System
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Ethernet Readout

• Is part of the requirement document and it will
  be part of GRETINA
• Requirement 2.1.1 Readout
• Data from the auxiliary detectors shall be
  combined with the GRETINA data (Ethernet switch)
• Requirement 2.1.2 Trigger
• The GRETINA trigger system shall provide 8
  digital inputs with any logical combination
  look up table. 8 digital outputs that inform
  when a Level-2 trigger occurred etc.

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Ethernet Readout

• Requirement 2.1.3 Time Stamp
• The auxiliary detectors shall provide their own
  time stamp with the same resolution as the
  GRETINA time stamp.
• Requirement 2.1.4 Clock Synchronization and
  Verification
• GRETINA shall provide clock and reset signals to
  synchronize the auxiliary detectors with GRETINA.
  Verification methods shall be implemented to
  verify that the auxiliary detector is properly
  synchronized with GRETINA.

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Ethernet Readout

• Example
• The auxiliary detectors have a circular buffer
  where data is stored.
• The buffer depth (size of the memory) allows for
  the GRETINA and Auxiliary Detector latency.
• GRETINA (or the auxiliary detector) provides a
  trigger. The data is removed from the circular
  buffer and moved to the readout buffer.
• If no trigger, the data is overwritten on the
  circular buffer.
• After some reasonable amount of data is stored in
  the readout buffer, it is transmitted to the
  GRETINA DAQ (through Ethernet).

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Standard GRETINA Digitizers

• The auxiliary detectors are connected to the
  GRETINA digitizers
• Most likely, the same timing (with time stamp),
  trigger and readout applies.
• The data is readout by the same type of CPU
  readout controller and sent to the switch
• Information we will need
• Number of channels
• Voltage range
• Rise time
• Pulse shape
• Condition for trigger, etc.
• Also, more in Marios talk

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System
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Digitizers
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Digitizers

• When the digitizer received a trigger, it
  transfer the data from a circular buffer (inside
  the FPGA) to the FIFO. If not, the data is
  overwritten.
• When the FIFO has data (say, half full), the
  Crate Controller readouts out the data.

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Digitizers

• Data processing in FPGA
• Leading Edge Discrimination
• yn xn - xn-k (differentiation)
• yn (xn xn-2) xn-1ltlt1 (?4, Gaussian
  filtering)
• Threshold comparison ? LED time
• Constant Fraction Discrimination
• yn xn - xn-k (differentiation)
• yn (xn xn-2) xn-1ltlt1 (?2, Gaussian
  filtering)
• yn xn-k- fxn (constant fraction, f is an
  attenuation factor)
• Zero crossing comparison ? CFD time
• Trapezoidal filter and energy determination (V.T
  Jordanov, G.F. Knoll, NIM A345 (1994) 337-345)
• yn yn-1 ( (xn xn-2m-k) ) (xn-m xn-m-k) )
• Maximum tracking ? energy
• Pole-Zero correction
• yn xn In /t (where t is the pre-amplifier
  time constant)
• In In-1 xn

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Flow of data in the DSP board
Digitizers
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Detector-Digitizer Connection
Digitizers
Connector
Cable

• Centi Line 2D from ITT/Cannon
• Proper pin assignment reduces the crosstalk

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Trigger/Timing System
Transmit data and timing information from
Trigger/Timing units to/from Digitizers
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Trigger/Timing System

• The following trigger algorithms are planned at
  this point (and are part of the requirements)
• Multiplicity
• A programmable number of energy over threshold
  occurs inside some walking time window.
• Energy
• Segment and/or central contact energy at lower
  resolution (which appears earlier in the
  digitizer). It can use the energy of a segment
  or central contact or the sum of energies of
  segments and central contacts. When this energy
  falls within some pre-set window (within some low
  and high energy limit) a Level-2 trigger is
  generated.

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Trigger/Timing System

• Pattern distribution
• GRETINA shall trigger if the Trigger System
  detects coincidence of gamma-rays energy at lower
  resolution above threshold in any two
  pre-programmed central contact of the crystals.
• Auxiliary detector trigger
• GRETINA will receive an external trigger within
  the pipeline depth presently at 20 ?s, goal 100
  ?s.

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Serializers
Trigger/Timing System
VCXO Specifications Freq 100MHzPull
/-70ppmJitter 5ps RMS
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Grounding and Shielding

• Detector modules
• Isolated from support and from other modules
• Reduce capacitance to support structure
• One common safety ground for each module, no
  other connection to ground.
• Detector enclosure (iridite) provides Faraday
  cage
• Detector power supplies and bias
• Each crystal has its own set of floating supplies
• Power twisted pair, shielded cable
• Bias high voltage coaxial
• All electronics for one detector module is
  assembled close together
• Signals optical or twisted shielded pairs
• Clean AC power

20
Grounding and Shielding

• Need to coordinate the grounding and shielding of
  the auxiliary detectors with GRETINAs grounding
  and shielding.
• We have documented GRETINAs grounding and
  shielding.