readout of dc coupled double sided sensors with cbmxyter: some first thoughts peter fischer,...
TRANSCRIPT
Readout of DC coupled double sided sensors with CBMXYTER:
Some first thoughts
Peter Fischer, Heidelberg University
P. Fischer, ziti, HD: dc coupled sensor readout 2
Goal of this talk
Think about consequences of dc coupling for readout chip Start a discussion on system issues
(control, readout, supplies)
This is a first collection of thoughts – to be improved!
This talk:• Sensor model• Connecting CBMXYTERs in dc mode• Fault tolerance approach• Chip connections: Power, Slow/ Fast Control, Data Out• Readout options: Some thoughts (also see Walter’s talk!)
P. Fischer, ziti, HD: dc coupled sensor readout 3
Sensor Model: Segmentation
implants bottom side
implantstop side
optionalpunch
through bias
Double sided strip sensor
subdivideinto diodes
one diode(vertical)
P. Fischer, ziti, HD: dc coupled sensor readout 4
N3
Sensor Model: Equivalent Circuit (I)
P1
P2
P3
N1 N2 N3
N2
N1
P3
P2
P1
P. Fischer, ziti, HD: dc coupled sensor readout 5
Sensor Model: Equivalent Circuit (I)
Observation: Input on one side has no ‘partner’ on other side, it’s a mix of all other inputs (across FE-chips!)
Thinking of a differential input, the ‘partner’ is ill defined Detector Signal is a current pulse in one of the diodes
To be more realistic, must:• Add series resistances of implants / aluminum traces• Add inter strip capacitors
N3
N2
N1
P3
P2
P1
N3
N2
N1
P3
P2
P1
(not all caps on n-side shown)
P. Fischer, ziti, HD: dc coupled sensor readout 6
Connecting DC coupled chips. (1/N possibilities)
moreanalog
digital
digitalDAQmore
analogdigital
levelshift
HV decouplingHV
powersupply
digitalsupply
analogsupply
Hybrid on detector Cavern Outside
refer single ended signal
to which ground here?
feedback & leakage compensation analog
supply
P. Fischer, ziti, HD: dc coupled sensor readout 7
Many questions:
Decouple what w.r. to what? Connect which grounds? Where? and how (R, L)? How to connect power supplies?
• Is it allowed to connect grounds in cavern to save cables?
These issues are not related to dc coupling Can be tested with NXYTER. Find out how other
experiments have done. (This stuff is rarely in papers..) Be prepared for several iterations
How to do the level shifting?• optical fibers – elegant!• optical couplers – slow!• inductive couplers – slow!• ac coupling• cascodes – can also be used for analog signals (currents)
P. Fischer, ziti, HD: dc coupled sensor readout 8
Discussion: Fault tolerance
Question: Is a daisy chain architecture excluded ?• Depends on fault tolerance approach
Should we be prepared to operate a module with single non functioning chips?
• How ‘easy’ is a repair of a bad module (access in fixed target exp. is simple)
• When a chip dies, does this kill the module anyway ?(for instance by shorts in supplies, noise on sensor)
• How often does a chip die during operation?
Is fault tolerance ‘nice to have’ or ‘required’?• This needs a discussion & decision
Note: a good burn-in may catch most ‘early failures’
P. Fischer, ziti, HD: dc coupled sensor readout 9
IO Signals required
Supply voltages• Connect chip grounds where?• Connect power supply ground in counting room (‘loop’) or on hybrid
(more cables)?
Slow control• best have this independent of readout (→ read back via slow control)• avoid bi-directional signal (simplify level shifting). This rules out I2C• avoid daisy chains for fault tolerance (?) (this rules out JTAG)• Compromise: Unidirectional bus with geographical address: clk, din,
dout, load, (reset). Very simple interface.
Fast control (‘TTC’)• clock, epoch marker (DLM), timestamp fast reset (can we use DLM?)
Data outputs Monitoring of analog signals
• level shifting difficult. Could use cascodes for currents.• Best use on-chip ADC and digital readout
P. Fischer, ziti, HD: dc coupled sensor readout 10
Readout. Preliminaries.
Use as few cables as possible → fill max. bandwidth Must provide a concept to cope with different occupancies
on different chips
cable data rate distance Connectors driver
optical fiber >2.5Gbps infinite clumsy
or special
Laser (clumsy),
serializer
coax >2Gbps >10m small on chip,
serializer
CAT7 LVDS
250Mbps 10m clumsy on chip,
clk & data
Custom LVDS
100Mbps few m (?) small on chip,
clk & data
P. Fischer, ziti, HD: dc coupled sensor readout 11
Optical Serial Data Transmission
Assume we have it somewhere in the path for level shift Components required:
Protocol FSM
8B/10B
Serializer
LVDS/CML output
Laser Driver
Laser Diode
Connector
fiber
Laser Package
Chip1
Chip2
Mechanics
digital
analog
difficult
Provided bySFP package!
available
available (?)
P. Fischer, ziti, HD: dc coupled sensor readout 12
Readout 1: Event Builder on Module
GBT will be developed by CERN. May be suitable. Probably a bit overkill. Still needs many extra radhard components
FE
FE
GBT
Hybrid on detector Cavern Outside
LaserLaserDriver
PiNTIA
clock, epoch
optionalFPGA
80 Mbps
4.8 Gbps
P. Fischer, ziti, HD: dc coupled sensor readout 13
Readout 2: Event Builder in Cavern
Many ‘LVDS’ cables Number of cables = number of chips
FE
FE
Hybrid on detector Cavern Outside
clock, epoch
FPGA
???
80-250 Mbps
10 m (Walter)
P. Fischer, ziti, HD: dc coupled sensor readout 14
Readout 3: Share cables
Equalize hit rates between chips with short parallel links Number of cables limited by data rate. May be adapted to Module Multiplicity
FE
FE
Hybrid on detector Cavern Outside
clock, epoch
FPGA
???
250 Mbps
P. Fischer, ziti, HD: dc coupled sensor readout 15
Readout 4: Integrated serializer, optical
Pass all hits to one (or more) ‘master’ chips Serializers on other chips are disabed Still Laser Driver, rad hard Laser, Package required
FE
FE
Hybrid on detector Cavern Outside
clock, epoch
optionalFPGA
???
serser
serser
ser
LaserLaserDriver
P. Fischer, ziti, HD: dc coupled sensor readout 16
Readout 5: Integrated serializer, coax
No extra components needed on Hybrid Receiver needed (?) Cost of cables?
FE
FE
Hybrid on detector Cavern Outside
clock, epoch???
serser
serser
ser
FPGA
drv.drv.
drv.drv.
drv.
coax cable rec.
P. Fischer, ziti, HD: dc coupled sensor readout 17
Some conclusions
Sensor model is complicated. See what we really need. I2C is bad for level shifting Analog monitoring is difficult Ground & Power connections will be big issue
• as usual• Should try some basic configurations with NXYTER, if possible
Best readout concept depends on• data rates• radiation levels• distance to shielded cavern (=10m)
Look at Walter’s numbers & suggestions!
P. Fischer, ziti, HD: dc coupled sensor readout 18
To do
Evaluate speed of custom LVDS driver (HD) Look for rad hard Laser driver / package / connector
(→ CERN) Try readout chain: Chip → Coax → FPGA Elaborate on chip → chip protocol Study minimum implementation of a FPGA compatible
serial link (in progress @ HD)