Summary of ATLAS optical link meeting, CERN, 14 May 1996. Conclusions and actions from OPTICAL LINK meeting of 14 May 1996. ----------------------------------------------------------------- 1. Electronics architecture. - presentations by Tony W, Philippe F, Francois V. - options of C&C architecture must be carefully evaluated, but after assessment of position of optical hybrid (see below). Both of the current options (clock modulated by amplitude or frequency) have advantages and disadvantages. - it was emphasised and agreed that redundancy of the C&C against point failures was important. - (see below) there was significant discussion on optimal choices for respectively VCSELS and LED's. 2. LED and PIN DIODE performance and radiation hardness. - presentations by Tony, Kurt B., and Ian D. - LED radiation hardness currently uncertain; tests continue and superficially inconsistent data neeed to be understood. Studies with and without in-situu powering and monitoring continue. - Driver module being considered. LT pair preferred wrt current mirror by RAL/Oxford. KB noted possible advantages of the (modified) current mirror architecture. These suggestions will be studied. Power consumption was considered important (see the VCSEL and twisted pair options below). Kurt emphasised also the larger signals from VCSELS => implying different receiver design, and possibly an optimal choice of C&C. He noted that twisted pairs do not require a receiver. - John D. emphasised the need for CERN-based effort on the receiver circuit. This was agreed to be studied, but also wrt other help required for the project. - VCSELS remain a viable option. Full twisted pair readout must remain an option. The VCSEL option to be studied after receipt of units later this year. - Tony noted the new GEC diodes, and first results (before radiation testing). It was noted that these are the only units so far packaged to be suitable for single hybrids for each module (2 LED's, 1 pin diode). Given that these devices passed the specs, they could be considered a final package for the SCT. - There was an initial discussion on the location of the optical hybrid (see below). GEC offer possibility of a single LED package- allowing a package with one pin diode and 2 LED's per optical hybrid. The package is 10*5.6mm. ABB, and the VCSEL option, require 8-fold packages. - Tony noted status of the pin diodes. Nominal radiation studies are encouraging, but full radiation testing is necessary. This includes full electronics specs as a function of time following irradiation. 3. Optical fibres - Presentation by John D. - Summary of the meeting of April 4th. Various items noted: * radiation - not yet proton radiations, silicon core required => cost increase. * connectors MT look promising but spring clip unsatisfactory * cost needs review: his estimate, without labour and without fibre assembly, is a factor 2 higher than CORE. 4. Action and summary discussion. ----------------------------- * It was agreed that all aspects, would be reviewed as best as possible, with full consultation to other activities, to reach the best possible solution. * It was agreed that redundancy against point failures should be maintained. * It was agreed to concentrate first on agreeing on aspects of the design and architecture having implications on the front-end chip, readout, module design, and mechanics. In this context it was decided to meet at or near the next ATLAS week (end June) and to have reports on the following: A) A further understanding of costing for the fibres (John Dowell and Ian Dawson) B) Investigation of options for the receiver low-noise amplifier (Allan Clark) C) A report from a working group (Robert Kowalewski and Tony Weidberg) detailing key issues concerned with the placement and packaging of the optical hybrid. In particular it was requested to understand the options of a seperate optical hybrid per module, as compared with grouped LED/PIN's at the end of each local support, and connected to individual modules via twisted pair. This study was requested to include mechanical, electronic and cost issues. Allan C. was requested to ask implications on the FE drivers, from the electronics group; that is driving a (say) 80cm twisted pair rather than a 10cm hybrid line and/or twisted pair. * It was agreed that the question of C&C architecture, and the study of LED's cf. VCSELS or twisted pairs, should follow the above study. A majority considered it premature to make a base line too early. * I was agreed that radiation studies of the LED's and the PIN's was still a key issue, and that ongoing work was crucial (LED's) and that similar studies were necessary for PIN's (Ian Dawson noted possibility of this study, to be confirmed ). NEXT MEETING. ------------ CERN, Bat 304-A 9:00 - 13:00 ------------- (Minutes prepared by Allan Clark)