Development of a Laser Driver Chip Test Setup for SLHC Experiments

Development of a Laser Driver chip test setup for SLHC experiments

A. Cazzorla(a,c), B. Checcucci(a), G. Mazza(b), S. Meroli(a), A. Moschitta(a,c), L. Servoli(a)

(a) INFN sez. di Perugia, Perugia, Italy

(b) INFN sez. di Torino, Torino, Italy

Modern High Energy Physics (HEP) experiments, such as the ones currently undergoing commissioning at the Large Hadron Collider (LHC), require tens of thousands of optical links each, needed to extract raw data from the detector and to distribute clock and control data to the front-end electronics.An upgrade of the current LHC (Super LHC or SLHC), planned for 2016-18, is expected to increase the luminosity to 1035/cm2/s, which implies more data to be transmitted (assuming more complex detector systems) and higher radiation doses to be sustained. To reduce the mass inside the detector, one possible solution is to increase the bandwidth in order to have less links as possible. Optical links for SLHC are being developed in collaboration between CERN and other institutes, including INFN Perugia and INFN Torino.A chip named GigaBit Laser Driver (GBLD) for data transmission at high bit-rate has been developed as part of the GigaBit Transceiver (GBT) project. The GBT project aims to design a radiation tolerant optical transceiver providing a bidirectional connection between the frontend electronics and the DAQ, trigger and DCS systems. The GBLD, following named Laser Driver, has been developed in this framework. The Laser Driver is designed for a maximum output data rate of 5 Gb/s and due to the wide range of selectable modulation and laser bias current is targeted at driving both VCSELs and some types of edge emitting lasers. To minimize the total dose effects due to the high levels of radiation, the chip will be fabricated in a commercial CMOS 130 nm technology, with Single Event Upset protection on the control logic.To evaluate the Laser Driver properties, the INFN Perugia Group has developed an electronic test card with fully dedicated setup equipment, embedding the Laser Driver chip made out by the INFN Torino Group. The operating high-speed of the board has required a specialized design and delicate engineering job. In particular, as impedance-controlled transmission lines are mandatory to ensure signal integrity, microstrip lines geometry and size have been determined by means of accurate simulation analysis and design, in order to avoid impedance mismatch and thus reflections. It is also important to notice that an accurate characterization of the GBLD prototypes may require a large number of measurements, performed by repeatedly changing the data rate and the modulation current. Similarly, the prototype can be finely tuned, by properly configuring a set of related parameters throughout a digital serial port. Consequently, an automated test set-up has been designed and implemented (Fig. 1).

Fig. 1 Automatic Test SetUp

Such a setup includes a proprietary LABVIEW application, providing the real-time instrumentation control required to carry out the desired measurements, which include eye diagram, bathtub curve, SNR, BER, rise/fall time and jitter. Using this test set-up, environmental features, reliability, and performances of the GBLD have been extensively tested and qualified according to a rigorous protocol test (Fig. 2).

Fig. 2 GBLD Data Output Transition Time

In this paper we will describe some aspects of test card implementation and test setup used, giving particular emphasis to the protocol test employed for the GBLD evaluation and qualification.

[1] P. Moreira et al., "The GBT : A proposed architecture
for multi-Gb/s data transmission in high energy physics",
Proc. of the 13th Workshop on Electronics for LHC and
Future Experiments, CERN-2007-007 pp. 332-336
[2] P. Moreira and J. Troska, "Radiation-Hard Optical
Link for Experiments", CERN PH Faculty Meeting Apr. 2008