Data acquisition board with optical gigabit interface

The precision vertex tracker, based on the technology of active CMOS pixel sensors, is a proposed addition to the tracking system of the STAR experiment . The proposed tracker consists of two cylindrical layers formed by 24 ladders. Each ladder contains a row of 10 monolithic CMOS detector chips and each chip has a 640 × 640 array of 30 micron square pixels. The total number of pixels is 0.98×10⁸. The mission critical tasks for this detector are data reduction and data transfer. Different approaches to implementation of the data acquisition system (DAQ) are under consideration. The approach discussed in this paper is to use commercially available components, like FPGAs, on the detector side and commercial Ethernet modules on the host computer side. A prototype DAQ board has been designed, manufactured and is in use for system development and testing. In this paper, the data transfer is discussed in details, including the concept, the protocol and data transfer rates.