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Università Degli Studi Di Parma Architectural UNIVERSITÀ DEGLI STUDI DI PARMA DIPARTIMENTO DI INGEGNERIA DELL’INFORMAZIONE PARMA (I) - VIALE DELLE SCIENZE TEL. 0521-905800 • FAX 0521-905758 Dottorato di Ricerca in Tecnologie dell’Informazione XIX Ciclo Giulia Papotti ARCHITECTURAL STUDIES OF A RADIATION-HARD TRANSCEIVER ASIC IN 0.13 um CMOS FOR DIGITAL OPTICAL LINKS IN HIGH ENERGY PHYSICS APPLICATIONS DISSERTAZIONE PRESENTATA PER IL CONSEGUIMENTO DEL TITOLO DI DOTTORE DI RICERCA GENNAIO 2007 CERN-THESIS-2007-111 //2007 εστω δε ο λογος υμων ναι ναι ου ου το δε περισσον τουτων εκ του πονηρου εστιν (Simply let your 'Yes' be 'Yes,' and your 'No,' 'No'; anything beyond this comes from the evil one.) (Matthew, 5:37) Acknowledgements I have always been concise, so all you get is a list. Here it goes… Paulo and Sandro for useful comments, critiques, discussions, explanations, feedback, questions, support… Apart from helping out in the completion of the PhD thesis in particular and PhD program in general, they have been role models who helped me in my personal professional growth. At my University in Parma, Prof. Ciampolini for being there every time I needed him, despite the amount of other engagements. I will not forget that he was the one who suggested CERN to me in the first place. Mike and all the Microelectronics group at CERN, for being such a stimulating working environment. In particular Bert, Ernest, Federico, Francois, Giovanni e Giovanni, Guido, Hugo, Kostas, Matthieu, and Rafael. Winnie needs to be specially thanked among them for reading and patiently correcting most of this thesis. Francois, Jan and Karl cannot be forgotten either, for having initiated me to CERN and the world of experimental measurements. They were not thanked in my previous thesis, so here they are. My family: Mamma and Ermanno, to whom this thesis is dedicated. And Alma, Fabio, Giampietro, Sandro, Silvana e Tina. I owe you the fact that I am what I am. Anna, Marci, Vale, and Zsach, the ones I can always rely on. Michele, Tommaso, Nuno for having been so important in my life. 6 Acknowledgements Ale, Andrea, Dora, Elena, Enzo, Giovanni, Giulio, Michele, and Marcello. And in particular Ale, Gio, Marco e Matteo for their crucial smiles (and dinners) the days of the final rush. It would have been much harder without your friendship. All the flatmates with whom I shared life in Geneva: Sarah and Ines, Margherita and Katrin, Cesar, Daniel, Pedro and Rui, Gianluca, Bernd and Nina. Bubba, Carlo, Donio, Elisa, Ferro, Gianpi, Grego, Leo, Marco, Paolo, Siro, and Tom, for the good old days at university, and the bond that survived to the present. Angela, Annemarie and Peder, the closest in Geneva. And also Agaath, Alice, Catalin, Cristiana, Matteo, Olivia, Osamu, Phu, Sabrina and Tom. Many of the Portuguese, among which Frodo, Helder, Martins, Miguel, Parracho, Ricardo, Tony and Ze (my dealer). Marco for sharing one of my deepest passions and buying the tickets, and for the time spent in Verona and Milano. A special thought for Dimitri, from Minsk. Patrice, for interesting updates on LHC and CMS, but also for often not being there, leaving me a whole office for myself. Klaas for his “self-esteem boost” that came just at the right time. Rick for having invented 64b/66b and for having replied to my email. Google and Wikipedia, for making things so much faster, and Lindt for the sugar supply and endorphin releases in tape out times. Finally, all the ones I met along the way, even though their names might be forgotten in these acknowledgements. To all of you, grazie. Table of Contents 1 Introduction------------------------------------------------------------------- 11 1.1 LHC, the experiments and the upgrade ----------------------------- 12 1.2 Optical links for HEP ------------------------------------------------- 13 1.3 FEC and line coding for HEP data transmission------------------- 14 1.4 Thesis structure and contributions----------------------------------- 15 2 Optical Links for radiation environments -------------------------------- 17 2.1 Considerations about optical links----------------------------------- 17 2.1.1 The choice of optical links for data transmission in HEP -- 17 2.1.2 System components --------------------------------------------- 18 2.1.3 Line encoding ---------------------------------------------------- 21 2.1.3.1 Examples of line encodings: CIMT ------------------------ 24 2.1.3.2 Examples of line encodings: 8b/10b ----------------------- 25 2.1.3.3 Examples of line encodings: 64b/66b ---------------------- 26 2.2 Optical links in radiation environments----------------------------- 28 2.2.1 The experiments at the LHC as radiation environments---- 28 2.2.2 Radiation-matter interaction and effects ---------------------- 28 2.2.3 Radiation effects on optical components --------------------- 30 2.2.3.1 Laser diodes--------------------------------------------------- 30 2.2.3.2 Optical fibers -------------------------------------------------- 30 2.2.3.3 Photodiode----------------------------------------------------- 31 2.2.4 Radiation effects on ASICS and hardening techniques ----- 32 2.2.4.1 Hardening by layout------------------------------------------ 33 2.2.4.2 Hardening by system and circuit architecture------------- 34 2.2.5 Examples of links to be used in radiation environments---- 35 2.2.5.1 The CMS Tracker Readout and Control System---------- 35 8 Table of Contents 2.2.5.2 GOL ------------------------------------------------------------ 36 2.3 Summary---------------------------------------------------------------- 37 3 The VBD Link and the GBT ASIC---------------------------------------- 39 3.1 TTC system and the TTCrx ASIC----------------------------------- 39 3.1.1 Timing------------------------------------------------------------- 40 3.1.2 Trigger ------------------------------------------------------------ 41 3.1.3 Control ------------------------------------------------------------ 42 3.1.4 Line coding in the TTC system -------------------------------- 43 3.1.5 TTC limitations -------------------------------------------------- 44 3.2 The Versatile Bi-Directional Link----------------------------------- 45 3.2.1 The concept------------------------------------------------------- 45 3.2.2 Link configurations---------------------------------------------- 46 3.2.3 Frame structure--------------------------------------------------- 48 3.2.4 The GBT ASIC -------------------------------------------------- 49 3.3 Radiation-induced errors characteristics---------------------------- 50 3.3.1 Estimation of error probability in an optical link ------------ 51 3.3.2 Conditional error probability given a rad-induced current - 53 3.3.3 Link errors-------------------------------------------------------- 57 3.4 Existing line codes and error correction ---------------------------- 59 3.4.1 8b/10b ------------------------------------------------------------- 59 3.4.2 64b/66b------------------------------------------------------------ 61 3.5 Summary---------------------------------------------------------------- 61 4 Introduction on error-correction theory----------------------------------- 63 4.1 Basics of Error Correction Theory ---------------------------------- 63 4.1.1 Forward Error Correction systems----------------------------- 63 4.1.1.1 Examples of simple codes ----------------------------------- 67 4.1.2 Linear block codes----------------------------------------------- 68 4.1.3 Cyclic codes------------------------------------------------------ 70 4.2 Reed-Solomon codes-------------------------------------------------- 73 4.2.1 Galois fields algebra--------------------------------------------- 74 4.2.1.1 Example: GF(24) ---------------------------------------------- 75 4.2.2 Code construction and encoding algorithm ------------------ 76 4.2.3 RS encoding ------------------------------------------------------ 78 4.2.4 RS decoding ------------------------------------------------------ 78 4.2.5 Applications of Reed-Solomon codes------------------------- 82 4.3 Interleaving ------------------------------------------------------------- 83 4.4 Summary---------------------------------------------------------------- 84 5 GBT line code---------------------------------------------------------------- 85 5.1 Line code overview---------------------------------------------------- 85 Table of Contents 9 5.2 DC balance and abundance of transitions -------------------------- 87 5.2.1 Introduction on scrambling techniques ----------------------- 87 5.2.2 Scrambler for the GBT ASIC ---------------------------------- 91 5.3 Error correcting scheme----------------------------------------------- 92 5.3.1 Syndromes calculation ------------------------------------------ 93 5.3.2 Proof that RS encoding maintains the pseudorandom characteristics ---------------------------------------------------------------- 94 5.4 Frame alignment issue: error tolerant header ---------------------- 96 5.4.1 Frame locking and unlocking mechanisms introduction --- 96 5.4.2 Locking mechanism --------------------------------------------- 97 5.4.3 Loss-of-Lock mechanism--------------------------------------100 5.4.4 Header error tolerance------------------------------------------100 5.5 Two interleaving options for the proposed line code ------------101 5.5.1 First interleaving option (L = 2, m = 4)----------------------102 5.5.2 Second interleaving option (L = 4, m = 3)-------------------104 5.5.3 Comparison of the two code interleaving options ----------106 5.6 Summary---------------------------------------------------------------106
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