Multi-Channel Electronics
SCUBA2 MCE
• 4 readout cards (RC)
– each reads 8 output columns through 14-bit 50MHz ADCs
• 1 address card (AC)= SQ1_bias
– addresses the [41] rows at add ≤ 850kHz, set by L/R
– frame ≤ add /41≈ 20kHz
• 1 clock card (CC)
– master card: interprets commands and synchronizes all the
cards. Drives fibre to PC.
• 3 bias cards (BC)
– BC 1: Squid Series Array Feedback (x32) + TES bias(x1)
– BC 2: Squid 2 feedback (x32)
– BC 3: SQ2 bias(x32) + TES heaters(x1)
SPIDER MCE
• SPIDER (as well as SPUD and BICEPII) have
up to 33 rows and 16 columns for each array
• Repackaged MCE:
– 2 RC’s
– Reorganized BC’s duties
• Additional features:
– More DET_BIAS (already in place)
– SQ2_fb fast switching (to achieve a better lock and to
remove summing coil pickup switching off all SQ1_bias and
adjusting SQ2_fb. However with fixed values. Or we could
effectively connect the dark SQ sq1_fb with the sq2_fb)
Cards in SPIDER MCE
• 3 BC’s
• BC1 0/16 SSA_fb, 0/16 SQ2_BIAS, DET_BIAS_ORG
• BC2 0/16 (possibly fast switching) SQ2_FB
• BC3 0/16 DET_BIAS
• In the current configuration slow SQ2_FB and 16 DET_BIAS
slightly different from DET_BIAS_ORG
• 2 RC’s
• RC1 0/7 SQ1_FB, 0/7 SSA_BIAS
• RC2 8/15 SQ1_FB, 8/15 SSA_BIAS
• 1 AC, 1 CC
Subrack in SPIDER MCE
T Felton design
Backplane in SPIDER MCE
SQ1_fb: it was 450A, now 150 A because of the
increase in the mutual inductance of MUX06. Is it
fine?
DET_BIAS: the maximum we can achieve now is
4mA. It can be increased. Should it?
PSU in SPIDER MCE
• Power supply:
– We currently use an ACDCU with a switching
power supply
– For SPIDER:
• we may use batteries
– 119W for SCUBA2. For SPIDER: 16 columns
73W (23W each RC)
Cooling SPIDER MCE
to the
• Cooling: gondola
frame,
used as
– We currently heatsink
use fans and
filtered air with
positive pressure
– SPIDER MCE will
be radiatively
cooled using
circulating
fluid with a pump
T Felton design
SEU in SPIDER MCE
• Cosmic rays on FPGA and SEU tolerance: 1 per month at
JCMT ~1 SEU / board / LDB flight. We are already in
contact with the TRIUMF particle accelerator for realistic
neutron fluency test (in fact, test flight would not reveal the
real effect).
• Altera Stratix III FPGA’s offer additional on chip monitoring
and testing features wrt Stratix I. We would not use it for the
test flight. Maybe for SPIDER.
• PC’s in pressure vessel (HD). Two with crosscomunication.
• The syncbox could be there as well.
Schedule for SPIDER MCE
• For the new repackaged MCE with no cards redesign:
– Finalize the design 1-2 weeks
– Backplane 6-8 weeks
– Chassis our machine shop, 6 weeks
– New FPGA? Probably not for the test flight. Maybe for
SPIDER
– Cooling system 4-5 weeks
– New filter box and flex (rigid-flex, 1 connector less, and no
ground plane) 6-8 weeks
– Test 6-8 weeks
– SEU test ?
– New boards new year
Modulation schemes
– TES bias
– SQ1 bias
– SQ1 fb (switching)
– SQ1 fb (ramping)
TES bias
– The TES bias could be square (or sine) wave
modulated at ~1kHz. We have the firmware for s.w.
that can run as fast as half the framerate
– However, if the bias crosses zero for more than few
hundreds s, than the TES’ may not recover
Superconducting branch
Normal branch
Superconducting
transition
Acquired on the ACT CCam camera
TES bias
– In any TES bias modulation scheme we need a
firmware that has to run two separate servo loops.
Synchronization is needed. Major firmware change
for the read-out and the demodulation.
– It can be tested in software since we can already
acquire fast data at 2.2kHz (33 rows, 32GB/h), 26kHz
(1row). We’d need bolometers to do tests.
Acquired on the ACT MBAC
TES bias
– In any TES bias modulation scheme we need a
firmware that has to run two separate servo loops.
Synchronization is needed. Major firmware change
for the read-out and the demodulation.
– It can be tested in software since we can already
acquire fast data at 2.2kHz (33 rows, 32GB/h), 26kHz
(1row). We’d need bolometers to do tests.
SQ1 bias modulation
– We visit the SQ1 at up to 20kHz with RS on bias.
We could select 2 different on bias’ and switch at
sub-harmonics of 20kHz.
– The firmware demodulation (i.e. remove off from
on) would be straightforward since it would be a
modification of the coadding we already implement.
Acquired on the ACT CCam camera
SQ1 bias modulation
– We visit the SQ1 at up to 20kHz with RS on bias.
We could select 2 different on bias’ and switch at
sub-harmonics of 20kHz.
– We could invert the polarity of the SQ1_bias
(although now it is not bipolar) and keep the same
inverted polarity lock point.
Acquired on the ACT CCam camera
SQ1 fb modulation (switch)
– The SQ1_fb could be switched so that the PID
feedback loop works in opposite SQ1 slope
– A firmware should be created that enables opposite
locking. That could be done with I-term=I·(-1)#frames
except that it would take time
– However it should require a fine tuning and
…
Acquired on the ACT CCam camera
SQ1 fb modulation (switch)
– The SQ1_fb could be switched so that the PID
feedback loop works in opposite SQ1 slope
– A firmware should be created that enables opposite
locking. That could be done with I-term=I·(-1)#frames
except that it would take time to relock
– However it should require a fine tuning and
any asymmetry of the SQ1 V-phi doesn’t help
Acquired on the ACT MBAC
camera
SQ1 fb modulation (switch)
– The SQ1_fb could be switched so that the PID
feedback loop works in opposite SQ1 slope
– A firmware should be created that enables opposite
locking. That could be done with I-term=I·(-1)#frames
except that it would take time to relock
– However it should require a fine tuning and
any asymmetry of the SQ1 V-phi doesn’t help
a combination of
SQ1_bias and SQ1_fb
modulation so that there
are 4 different locking
points and/or we keep
the same lock point as
K.Irwing suggested.
SQ1 fb modulation (ramp)
– We throw away the PID feedback loop and we
continuously ramp the SQ1_fb. This creates an effective
modulation of the signal coming form the SQ1 V-phi
curves
– We already have a data mode that ramps the SQ1 fb. In
the 14bits DAC each step can be as high as 10kHz
– We look forward to test in software on a system with TES
Acquired on the ACT CCam camera