Speaker
Description
Summary
The ATLAS pixel detector consists of two barrel layers and two forward and backward
disks which provide at least two space point measurements.
The low voltage differential signal (LVDS) from the pixel detector is converted by
the VCSEL Driver Chip (VDC) into a single-ended signal appropriate to drive a
Vertical Cavity Surface Emitting Laser (VCSEL).
The resulting optical signal is transmitted to the Readout Device (ROD)via a fibre.
The 40 MHz beam crossing clock from the ROD, bi-phase mark encoded with command
signals to control the pixel detector, is transmitted via a fibre to a PIN diode.
This signal is decoded using a Digital Opto-Receiver Integrated Circuit (DORIC).
The PIN and VCSEL are packaged in the so-called opto-packs for connecting to the
chips and fibers.
We implement the VDC and DORIC circuits in standard deep submicron (0.25 micron)
CMOS technology. Employing enclosed layout transistors and guard rings, this
technology promises to be very radiation hard.
After five prototype runs, the chips meet the ATLAS specifications,including the
radiation hardness requirements.
The chips together with the optical devices are mounted on a hybrid circuit board,
opto-board. The board uses BeO as the substrate for heat management. We are
currently producing the 300 opto-boards needed for the pixel detector. The micro-
soldering of the leads of the opto-packs is a particular challenge and we will
present this along with other production experience.
In June 2004, we irradiated the production opto-boards with 24 GeV protons at CERN
up to a dosage of 32 Mrad. We observed no significant degradation of chips and the
VCSEL still produces quite adequate power after the irradiation. The results
indicate that the optical link meets the radiation hardness requirements for the
ATLAS pixel detector.
We are also in the process of converting the VDC and DORIC to operate at Gbit/s
with 0.13 micron technology for the Super-LHC. Some preliminary results from the
conversions will be presented.
In summary, we have developed an opto-link that meets all the requirements for
operation in the ATLAS pixel optical link. The link is expected to be sufficiently
radiation hard for ten years of operation at the LHC. We are also in the process of
converting the chips to operate at much higher speed for the Super-LHC.
