Status of the Beetle Readout for the Multianode Photomultipliers

1
Status of the Beetle Readoutfor the Multianode
Photomultipliers

• Achievements since last LHCb week
• Update on the MaPMT needs for the comparator
• Present status
• Things to do
• Conclusion

Stephan Eisenhardt University of Edinburgh
Photodetector review, 14.05.2003
2
Achievements since last LHCb week

• Specified board Beetle (signal tracing, readout
  I/O) and
• interface board (proper timing of LCDS signals,
  trigger for ADC from DataValid, )
• New LED driver limiting the electronic pulse
  length to few ns and
• providing jitter-free timing between
  SEQSI-LED-Beetle
• Checked MaPMT needs against Beetle1.3 comparator
  design
• ? see below
• Study on digital switching noise visible on
  analog output signals
• ? see below, discussed at VELO Beetle meeting
  30.04.2003
• Infrastructure upgrades done
• (LVDS drivers for SEQSI, cabling, feed-throughs,
  proper timing)
• Scan/Optimisation of relative timing between
  Clock, Trigger, TestPulse
• Setup of corresponding Beetle and SEQSI
  configurations (DAQ, TP, modes)
• Upgrade of FED based readout for Beetle signals
  using the 1-port option
• (16 header 128 data)
• Readout of Beetle with TestPulse signals through
  full data chain
• ? see next slide

3
3-bit comparator in Beetle1.2

• from discussions with Hans Verkoojien

• 1 MIP 22000e- 1538mV
• comparator DC offsets ? 26mV (3?)
• trade off
• range covered at a time vs. resolution,
• e.g. 140mV, 220.0mV, 410.0mV or 85.0mV
• Comparator buffer gain 0.7
• Beetle1.2MA0 12-dyn 300000e- ? 30mV
• Signal 300000e- ? 0.730mV 21mV
• Noise 7500e- ? 0.70.75mV 0.525mV
• Beetle1.2 8-dyn 50000e- ? 85mV
• Signal 50000e- ? 0.785mV 60mV
• Noise 1000e- ? 0.71.7mV 1.2mV

Idelta Vdelta Vdelta range Vdelta step
size 0.125?A ? 2.5mV 04.375mV ? 0.625mV
? 0.250?A ? 5.0mV 08.75mV ? 1.25mV
? 0.625?A ? 12.5mV 021.875mV ? 3.125mV
? 1.250?A ? 25.0mV 043.75mV ? 6.25mV ?
No access to negative DC offsets!!
4
5-bit comparator in Beetle1.3 (08/2003)

• from discussions with Hans Verkoojien

• 1 MIP 22000e- 1538mV
• comparator DC offsets ? 15mV (3?)
• wrt. Beetle1.2
• comparator input buffer gain 0.7 ? 1.0
• DC offsets reduced due to removal of one buffer
• Beetle1.3MA0 12-dyn 300000e- ? 30mV
• Signal 300000e- ? 1.030mV 30mV
• Noise 7500e- ? 1.00.75mV 0.75mV
• Beetle1.3 8-dyn 50000e- ? 85mV
• Signal 50000e- ? 1.085mV 85mV
• Noise 1000e- ? 1.01.7mV 1.7mV

Idelta
Imain
Idelta- Imain
Idelta Vdelta Vdelta range Vdelta step
size 0.125?A ? 2.5mV 04.84375mV 0.15625mV 0.625
?A ? 12.5mV 024.21875mV ? 0.78125mV ? 1.000?A ?
20.0mV 038.75mV ? 1.25mV ?
Access to negative DC offsets possible!
5
Digital switching noise

• As discussed at VELO Beetle meeting 30.04.2003
• 80 MHz noise on analogue outputs and DataValid
• Stems from digital circuit and multiplexer
• (tested by cut in power line internal to the
  Beetle)
• Different claims whether pos. or neg. parts of
  LVDS signals have larger contribution
• No understanding at that time
• Meanwhile understood, fix for Beetle1.3 proposed
  ? Nigel

data frame (128 ?4)
data frame (128 ?1)
DataValid
1-port data out
4-port data out
6
Status I

• Beetle1.2 data frames pedestal
• MaPMT test pulses

• Edinburgh setup

Beetle1.2
128 ? 1 data frame
12-channel read-out
128 TP signal channels
single base
LED in housing
8 dynode MaPMT
7
Status II

• Match dynamic range of FED (0.01.5V) done
• Solve linearity problem in region 1.01.5V done
• Increased serial resistor to opamp (50 ? 130?)
• Reduced Ipre 1200 ? 600?A
• Signal ready for DAQ
• DAQ runs smoothly
• with these signals

with linearity problem
good match of dynamic ranges - linearity fine
8
Status III

• Attaching the front-end increased strongly the
  common mode!!
• Main increases due to
• tracks on HD board
• cable connection to base
• MaPMT
• No common mode visible for capacitive decoupled
  channels
• No trigger phase or other parameter dependence
  found
• Looks like a ringing or RF problem

HD board without front-end
with front-end and MaPMT
9
Status IV

• Started shielding of front-end and cables
• Saw effect of significant reduction of common
  mode (by 50)
• By accident short-circuit between 2.5V and GND
  on HD mother board
• This killed the Beetle chip!!! (probably the
  pipeline),
• very surprisingly as the chip behaved very
  robust before
• A new chip bonded on a HD daughter board is in
  the mail

10
Things to do

• Solve common mode problem (otherwise serious
  problem for binary readout)
• Take data with analog readout for 8-dynode stage
  MaPMT
• Adapt data analysis from APVm readout
• Switch to binary readout, test/tune comparator
  and compare to analog data
• Switch to 12-dynode stage MaPMT Beetle1.2MA0
  and repeat tests
• Prepare testbeam in August/September

11
Conclusions

• The Board Beetle is expected to be available in
  June
• The comparator implementation for the Beetle1.3
  is comfortable wrt. the needs of the MaPMT
• The DAQ is working
• The common mode problem may pose a serious
  problem for the binary readout
• Work with Beetle will resume this week with new
  hardware
• The schedule becomes very tight

12
Spare slides
13
Beetle1.2 Heidelberg board I
board at Oxford

• at Edinburgh
• Heidelberg mother- and daughter board
• Beetle1.2 mounted on daughter board
• Beetle1.2MA0 as soon as available
• connect 8/12-stage MaPMT to this read-out

daughterboard with Beetle1.1
motherboard

• What can be done with it
• readout up to 12 MaPMT channels of 8 dynode stage
  MaPMT
• analog and binary readout
• 128 ? 1 and 128 ? 4 multiplexing (in 3600/900ns
  per event)
• existing FED/MIDAS/VME DAQ can read this out
• proof of principle for Beetle1.2 / 8-dynode MaPMT
  combination
• proof of principle for Beetle1.2MA0 / 12-dynode
  MaPMT combination

14
MaPMT Comparator Needs I

• the 8-dynode stage MaPMT gives per signal pulse
  in average 50000 e- at 800V
• we are aiming for a signal-to-noise ratio of 401
• the noise values for the Beetle1.2 are of the
  order 1000 e- provided the capacitive load in
  front of the Beetle is of the order of 10pF
• (so S/N should be OK provided we meet the 10pF
  load...)
• the best usable resolution for a comparator
  threshold would be 1_sigma of the electronic
  noise, i.e. 1000 e-
• (a worse resolution means a larger signal loss
  due to higher threshold values in the signal
  spectra of individual channels)

15
MaPMT Comparator Needs II

• in the Beetle1.2 design 1 MIP corresponds to
  22000 e- and translates to a 25mV signal
• the channel to channel variations of the pedestal
  position of the channels (offset) span a range
  from -0.8 to 0.8 MIP, corresponding to -20mV to
  20mV, i.e. a 40mV full range
• we need to cover this full range with one setting
  of the global threshold and a resolution of the
  individual settings, if possible, similar to the
  1_sigma requirement stated above (e.g. if it
  rather would be like 5_sigma we would suffer
  strongly as we probably would loose 10-15 of our
  signal)

16
MaPMT Comparator Needs III

• the comparator in the Beetle1.3 uses a common
  IDAC(8-bit) with a LSB of 8uA
• this them gets divided by 64, so the effective
  LSB becomes 0.125uA
• (opposed to the Beetle1.2 implementation where
  it was only divided by 8 and the effective LSB
  became 1.0uA)
• then the 5-bit individual setting gets applied
  which can have positive and negative values of
  the factors -1, -1/2, -1/4, -1/8, -1/16
• so with the finest resolution chosen (global
  setting 0.125uA) one gets an effective comparator
  resolution of 0.125uA/16 8nA but one only can
  span a range of 5mV in total
• as we want to cover a full range of 40 mV we
  rather would go for a global resolution of 1.0uA,
  giving an effective comparator resolution of
  1.0uA/16 0.0625uA which translates to steps of
  1.25mV at the 20kOhms resistor

17
MaPMT Comparator Needs IV

• the comparator design in the Beetle1.3 has an
  additional factor of 2 gain in front of the
  comparator as the gain of the buffer amplifier
  has changed wrt. the Beetle1.2 implementation
  (0.7 -gt 1.4)
• thus the effective MaPMT signal at the Beetle1.3
  comparator has the average size of 255mV 110mV
• (2 from the change of the buffer amplifier,
  55mV 50000 / 22000 25mV)
• the noise level at the comparator then will be 2
  1000 / 22000 25mV 2.3mV, i.e. the S/N still
  50
• these 110mV signals at the comparator then get
  compared to thresholds set with a 1.25mV
  resolution (spanning the needed -20mV...20mV
  range), i.e. the threshold resolution then is
  better than the 1_sigma requirement set above

18
How to readout a full MaPMT?
design PCB board Beetle

• allows readout for 1 Beetle1.2(MA0) and 2(1)
  MaPMTs per board
• no Kapton cables, flexible for 3x3 and 4x4
  geometry in the test beam
• not yet settled symmetric GND lines? (PGA 10x8
  instead of 9x8)
• time scale for production 1 engineer x 2 months
• main tasks lay out signal traces pitch adaptor

19
MaPMT signal shape measurement

• 12-dynode MaPMT _at_ HV -1000V
• (nominal gain 3.3M e-)
• direct to scope (50?) ? density plot
• 5000 single photon events (stray light)
• 5000 pedestal events
• signal shape
• signal walk
• input to simulations by Nigel Smale

pedestal
av. single photon signal
signal walk

• 12-dynode MaPMT _at_ HV -1000V
• (nominal gain 3.3M e-)
• direct to scope (50?)
• average of time measurements
• 5000 single photon events (stray light)
• av. fall time 1.1ns
• av. rise time 2.7ns
• av. pulse width 2.6ns

20
3 x 3 MaPMT Cluster Set-up

• 3x3 array of MaPMTs
• RICH 1 Prototype
• CF4 _at_ 700 mbar
• 120 GeV pion beam

3x3 MaPMTs
40 MHz Read-out APVm chip
Quartz lenses