CMS FED Testing

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CMS FED Testing

• Update 28-06-2002
• M. Noy J. Leaver
• Imperial College
• Silicon Group

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CMS FED Testing

• Currently

Line driver (optional) level shift
LVDS?LVTTL
I2C slave
Network
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CMS FED Testing
Picture of the DAC evaluation board
DAC
Line driver
LVTTL data in, from level converter
UTP out
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CMS FED Testing
Picture of the key link components
UTP from DAC/line driver
Optical fibre
Opto-Tx
Opto-Rx
Single ended output to scope
I2C cable
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CMS FED Testing
Opto-Tx
DAC Evaluation Board
Line driver
DAC
UTP
UTP
Opto-Rx
Vout
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CMS FED Testing
Signal before the link
?200mV (V-V- 400mV ) differential signal with
no offset. higher bandwidth ? ringing and faster
rise/fall time. Time scale is relative to the
scope trigger point on all plots.

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CMS FED Testing
Signal after the link
Single ended, with offset. No ringing but slower
rise/fall times
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CMS FED Testing
Signal noise/jitter after the link
Noteno scale on the width of the line. This is
an impression of the infinite persistence scope
trace gt spread unknown. (Measurements are real).
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CMS FED Testing
Rise time, 10 to 90 of full scale.
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CMS FED Testing
Fall time 90 to 10 of full scale
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CMS FED Testing
Linearity link is being operated in the linear
region of the Tx/Rx Settings x0, x1, x2, x3,
x4, x50,0,0,0,1 (recommended by CERN)
000 01
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CMS FED Testing
Sample APV25 pair of multiplexed frames with
simulated 1 MIP signal
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CMS FED Testing
Multiplexed APV25 header with zero pipeline
address
2 error bits
pipeline address (16 bits)
6 start bits
2x12x25ns bits
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Zoom in of the 1 MIP signal upon its pedestal

• Approx
• Pedestal value here is 509 lsbs, 4096 levels in
  405mV?0.099mV/lsb
• 1 MIP ? 4096/8512 lsbs
• Total signal
• 570(405/4096)(509512)5700.0991021671mV

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Temperature Control

• We attached a heating element and a thermocouple
  to the laser package and used the following PID
  equation to stabilise the temperature through a
  feedback loop.
• W P (Ts - T0) D d (Ts- T0) /dt I ? (Ts -
  T0)dt
• The temperature was varied between 30ºC and 40ºC
  in 1ºC steps. The output of the Rx was recorded
  after a stabilisation time, for some measurement
  time.

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Temperature Measurements

• Laser threshold bias current behaves like
• IthI0exp(T/T0)
• Which implies
• ?Ith?Ith ?T/T0
• And (after a few lines and other things!)
• ?Vout ? -Reff G ?Rx ?l Ith ?T/T0
• Typical parameter values yield an expected (_at_
  34.1C)
• ?Vout/?T ? -90.8 mV/C

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Temperature Measurement Results
Approximated with a linear fit VmTC Where m
-(89.8 ? 1.8) mV/C and C (4137 ? 62) mV Good
agreement with expected value (of 90.8mV/C), but
some of the parameters are loosely defined
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Temperature Measurement Errors

• Temperature stabilisation is good, with random
  fluctuations of the order ?0.02C. There is some
  unknown systematic error, that does not exceed
  ?0.44C.
• Have statistics of 150x500 voltage points and 150
  temperature points per temperature setting.
• Statistical errors are too small to account for
  the largest random deviation, probably spurious.
• We could repeat the whole measurement again using
  smaller T steps, but probably wont due to time
  constraints.

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CMS FED Testing
Summary
Have a complete working single fibre, possible to
drive 4 with identical signals using the current
Opto-Tx. Possible to obtain a further 2 of the 4
channel prototypes from CERN ? complete 12
channels could in principle be driven with
identical signals. Dependence of laser operation
on temperature is now better understood, and fine
temperature control is possible. We feel
confident that a system such as the one we have
will allow sufficient temperature stability for
the fed testing needs. Work is in progress to
produce an application specific version of the
SEQSI simpler operation longer RAM
pipeline clean/synchronous stop from
VME possible stepping through
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CMS FED Testing

• Future Work
• Have 1 (untested) Opto-Rx emulator to drive the
  analogue stage of the FED directly over copper
  (I.e. eliminating the optical link)
• Verify DAC Linearity Summer student(?)
• More thought into a test vectors and their
  comparison with the FED output