Trigger-less readout electronics for the PANDA Electromagnetic Calorimeter

The PANDA experiment at the future FAIR facility at Darmstadt, Germany, will employ a novel electronics-readout concept: the trigger-less readout. This concept implies an event selection based on the physics properties of detected particles, such as reconstructed invariant mass or a detected secondary vertex. Such an approach requires a completely new design of the readout chain from the front-end to the data acquisition. This paper describes a fully-functional prototype of the readout chain for one of the PANDA subdetectors - the Electromagnetic Calorimeter. The prototype consists of digitizer and data-multiplexer modules. The crucial component of the prototype is the synchronous optical-link connection, which allows to transfer clock signal and time-synchronisation commands in an unambiguous way. The implementation and performance tests of the synchronous optical-link connection are described in the paper.