Readout Electronics for the ALICE Time Projection Chamber

In this paper we present the architecture of the Readout Electronics for the Time Projection Chamber (TPC) of the ALICE experiment at CERN LHC. The ALICE TPC electronics consists of 557568 channels. A single readout channel is made of two basic units: (a) an analogue ASIC (PASA) that incorporates the shaping/amplifier circuits for 16 channels; (b) a mixed-signal ASIC (ALTRO) that integrates 16 channels, each consisting of a 10-bit 25-MSPS ADC, the baseline subtraction, tail cancellation filter, zero suppression and multi-event buffer. The complete readout chain is contained in Front End Cards (FECs), with 128 channels each, connected to the detector by means of kapton cables. From the control and readout point of view the FECs are organized in 216 partitions, each being an independent system steered by one Readout Control Unit (RCU). The RCU, which is physically part of the on-detector electronics, implements the interface to the Data Acquisition (DAQ), the Trigger and Timing Circuit (TTC) and the Detector Control System (DCS). It broadcasts the trigger and clock information to the FECs, performs the initialization and readout via a high bandwidth bus, and implements monitoring and safety control functions via a dedicated link. The radiation load on the TPC is low (1 krad ⊕ 10 neutrons/cm over 10 years). Thus standard radiation-soft technologies are employed for the implementation of this electronics. However, some special care has been required to protect the system against potential damages caused by Single Event Effects. A fraction of the final electronics has been benchmarked by realistic measurements with a prototype of the ALICE TPC. Test show that the system fulfils all design requirements. At present, the mass production of all components is being completed. After the installation of the electronics, the whole detector will undergo a six month commissioning phase before being lowered into the experimental hall in fall 2006.