by Panos Charitos. Published: 01 March 2014

Last month a team of physicists and electronic engineers who are currently working on the development of the SAMPA chip visited CERN. The SAMPA chip is the common front-end read-out chip for the TPC and muon chambers (MCH) for the ALICE upgrade after LS2. The SAMPA chip is a collaborative project between Electrical Engineering, Polytechnic School of University (EPUSP) and Institute of Physics (IFUSP) at the University of São Paolo in Brazil, University of Bergen and University of Oslo. The team also works closely with CERN colleagues and with collaborators from institutes IPNO in the University of Paris-Sud, IN2P3/CNRS, the Service de Physique Nuclaire (SPhN), the CEA-IRFU Saclay. The main funds are provided by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, São Paulo State Research founding agency) (read also The Sampa Chip ).

Arild Velure, a PhD student from the University of Bergen in Norway, Hugo Daniel Hernandez Herrera, Bruno Sanchez and Heitor Neves from the Department of Electrical Engineering of the University of Sao Paolo (USP) and Marco Bregant from the Nuclear Physics Department of the University of Sao Paolo travelled to CERN where they met representatives from the TPC and muon chamber teams as well as Alexander Kluge, our electronics coordinator, in order to present the work status, discuss the final specifications and plan for the chip and detector chain tests.

In January, members of the SAMPA team travelled to CERN to discuss the work status and final plans for the new chip. During their stay they got the chance to try their skiing abilities: From left to right: Hugo Daniel Hernandez Herrera, Bruno Sanchez, Arild Velure and Sohail Musa Mahmood.

In the last few months a lot of effort has been invested in finalizing the design and performing simulations of the new chip that will allow for a first time the continuous read-out of a TPC.

SAMPA comprises an analog part, which amplifies the tiny electrical signals generated in the detector when hit by particles and a digital part that converts the analog signals to digital values, performs the data compression, and sends the data stream out to a read-out board. The charge delivered by the ALICE TPC and muon chamber detectors is very small and is delivered during a short time period (think of a current of 7 μΑ during 1 ns). That makes it hard to process the signal immediately from the detector.

The SAMPA chip is an advancement of the present TPC electronics. Currently, the ALICE TPC uses the 16 channel-PASA and ALTRO chips for the analog and the digital part, respectively, that were designed in order to record data from the first runs of the LHC. The new chip will have 32 read-out channels, integrates both the analog and digital functionality and allows for a continuous trigger-less read-out as required by the beam conditions after LS2.

One of the most challenging aspects is that the interaction rate during the third LHC run will get much higher by a factor of more than 5 for Pb-Pb collisions. Marco Bregant explains: “Due to the characteristics of the TPC signals (it is a time projection chamber with a drift time of 90 µs), the high interaction rate implies the need of a continuous read-out of our detector and to cope with larger amount of data.” The new chip will allow the continuous operation with no need of a trigger in order to meet the specifications of the ALICE detector upgrade that foresees a collision rate of 50 kHz for Pb-Pb and 200 kHz for pp and p-Pb collisions.

Finally, the SAMPA chip will provide the option to handle both positive and negative signals, three different gain settings and three different shaping time setting to allow operation in the TPC and MCH environment. SAMPA will be used with the new GEM detectors of the TPC as well as with the muon chambers. Also other experiments outside CERN show interest in using the chip.

The first prototype (a few channels, limited signal processing capabilities) of the chip will be produced in late spring. Its aim is to validate both the general layout and the different sub-circuits of the SAMPA chip. Validation of the chip includes several tests, and, eventually, the chip will be connected for the first time to a real detector.

The author would like to thank Alex Kluge and Marco Bregant for their valuable contributions to this articles and for the enlightening discussions in the field of microelectronics.