Frequency domain multiplexing technology of transition-edge sensors for x-ray astronomy

We are developing Frequency Domain Multiplexing (FDM) read-out of Transition-Edge Sensors (TESs) for the X-ray Integral Field Unit (X-IFU) on board of the future European X-Ray observatory Athena. The X-IFU Focal-Plane Assembly consists of a $sim$ 3000-pixel array, read out by SQUID-based FDM. The multiplexing readout scheme is a critical technology for the X-IFU instrument because of the cooling and electronic power limits for the satellite. In this contribution, we report on the development of FDM readout technology and on the performance of TESs array under an AC bias at MHz frequencies.