Implementation of frequency domain multiplexing in imaging arrays of microcalorimeters

Frequency domain multiplexing (FDM) is an attractive approach to reading out imaging arrays of transition edge sensor (TES) based microcalorimeters. We are developing a FDM readout system compatible with the specifications as defined for ESA's XEUS mission. FDM is implemented by using the TES as amplitude modulator of its alternating voltage bias source. A single superconducting quantum interference device current amplifier is used to amplify multiple TES signals, which are separated in frequency space by superconducting LC bandpass filters. The scalability of this concept is bounded by parasitic effects. In this paper, the origin and implications of the parasitic effects will be treated. Among the effects are common inductances and magnetic coupling between noise blocking bandpass LC filters. Both effects lead to cross talk and limit the available bandwidth for multiplexing. Quantitative estimates of these effects are given. Furthermore, the required accuracies of the noise blocking bandpass filters are discussed, as well as bias source topologies