Readout options.Some ideasR. Turchetta, STFC-RAL, UK
F.Anghinolfi, CERN
ATLAS CMOS WG1 f2f meeting20th February 2014 - CERN
Tony’s slides on 27/1/14
Tony’s slides on 27/1/14
4
Pixel: 74.5umx50um
Segment: 74.5umx800umNumber of pixel/segments: 16
Number of segments: 32Number of contiguous segments in X: 256
Size of sensing area: 19.1mmx25.6mm
Number of bits per segmentM (X pos.) = 8N (Z pos.) = 5Total = 13
Z-encoding
Z
X
Only what I would call the basic unit is considered below. It is close to reticle size, so good for both stitched and non-stitched sensors. All coordinates below list first X dimension then Z.
5
Z-encoding
The next slides will try to answer the following main questions:
1) How do we get the digital information out of the pixels?
2) What should go in the periphery of the sensor?
3) How do we interface with the ABCxxx and what are the
implications for the ASIC?
6How do we get the digital
information out of the pixels? Option 1.
16 input OR
Distributed priority encoderUse asynchronous “toggle” per segment: No clock propagation less power consumption and substrate noise; Asynchronous hit encodingUse priority encoding, for example 4:2 building blocks to build the 32:5 encoding.
(see Alice-ITS)
7How do we get the digital
information out of the pixels? Option 2.
16 input OR
Straight wiring32-bit wide bus from pixels, then priority encoder in the periphery.The bus could be driven by a digital buffer or a current method could be adopted.
The trade-off is between power and noise. Need some accurate design to be studied.
It would then need an encoder in the periphery
8
Options review
Option 1 Option 2
Pros Cons Pros Cons
Data in periphery decoded
More complicated design in the pixel area
Minimal in pixel electronics
Pixel area not used for encoding electronics
Complicated electronics only in
periphery gives more options for trade-off
9What should go in the
periphery of the sensor?
Option 1.Each strip generates 5-bit per hit.It needs an additional 256:8 encoder to generate the X position.After this, one hit would be coded over 5+8=13 bits.
Option 2.Each strip needs a 32:5 encoder. Then, as for option 1, it needs an additional 256:8 encoder to generate the X position.After this, one hit would be coded over 5+8=13 bits.
10How do we interface with the ABCxxx and what are the implications for the
ASIC?
Both options are going to generate 13 bits per hit.The information is already encoded, so no need for decoding within the ABCxx DCL not needed.
Pipeline size: at the moment 256 bits per BCO. They would become 13*max. number of hits per BCO
Data transmission.
Q: Would the ABCxxx need to process clusters?
Tony’s slides on 27/1/14
12Standard stereo
As in Z-encoding, pixel outputs are ORed to generate a single output. Then they connect straight into ABCxxx = ABC130 – front-end
Tony’s slides on 27/1/14
14Binary stereo
As in Z-encoding, pixel outputs are ORed to generate a single output.256:8 encoder is integrated in the peripheryThe ABCxxx receives 8 bits per hit
Pipeline size: at the moment 256 bits per BCO. They would become 8*max. number of hits per BCO
Data transmission.
Q: Would the ABCxxx need to process clusters?
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