The Digital Readout Electronics (DRE) of the X-ray Integral Field Unit (X-IFU) instrument onboard Athena is made of two main parts: the DRE demultiplexor (DRE-DEMUX) and the DRE event processor (DRE-EP). The DRE-DEMUX drives the frequency domain multiplexed readout of the X-IFU Focal Plane Assembly (FPA) and it linearises the readout chains to increase their dynamic range. The DRE-EP processes the pixels’s data in order to detect the events and to measure the X-ray photon energy and arrival time. We have developed a prototype of the DRE-DEMUX module. We used a modular architecture with several boards in order to validate the different key functionalities one by one with a short design-test-rework cycle. To test the functionalities and performances of the DRE-DEMUX breadboards in a representative environment we developed several test equipments. Although the prototype is not flight representative in many aspects (EMC, power supplies, components grade, . . . ) it is intended to demonstrate the DRE-DEMUX functionalities and to validate the numerous operating procedures of our electronics. The preliminary tests conducted on the DRE-DEMUX prototype coupled to the dedicated test equipments validated its functionalities but also demonstrated that it is compliant with the its energy resolution requirement, which is the most constraining for the DRE.
The X-IFU (X-rays Integral Field Unit), one of the two instruments of the Athena mission, is a cryogenic Xray spectrometer for high-spectral resolution imaging. The large array of 3840 detectors each composed of an absorber coupled to a Transition Edge Sensor (TES) will be operated with a bath temperature of 50 mK. This instrument is designed to provide a challenging energy resolution of 2.5 eV in the 0.2 to 7 keV range. The DRE (Digital Readout Electronics) drives the frequency multiplexed readout of the sensors and implements the feedback required to optimise the detection chain dynamic range. To comply with the instrument energy resolution requirement, the constraints on the detection chain sub-systems are very stringent (thermal stability, signal to noise ratio, linearity,...). This implies a strong optimisation effort during the design of the sub-system in order to both satisfy the performance requirements and to fit in the mass, volume and power allocations. We have developed a numerical simulator of the X-IFU detection chain in order to validate the architecture of the DRE. The simulator implements the contributions of the different detection chain elements in the overall instrument performance. The details of the DRE architecture are included in the simulator and we use it to validate the different design options.