Active Tuning of the Resonance Frequencies of LC Bandpass Filters for Frequency Domain Multiplexed Readout of TES Detector Arrays

Efficient use of the available frequency space for frequency domain multiplexing is essential for space- based TES detector applications such as the X- IFU instrument on the Athena X- ray telescope. For cross talk reasons, there exists a lower limit on the distance between neighbouring pixels in frequency space, so that accurate control of the resonance frequency helps to use the available frequency space. Independently, from the point of view of efficient sinusoidal bias voltage generation, placing the frequencies on a grid with a fixed spacing helps to avoid the effects of nonlinearity on the detector performance. Inevitable tolerances in the lithographic production of LC bandpass filters and margins in the design of stray inductances limit the relative accuracy of the resonance frequencies to a few times 10 - 3. In this paper we will propose a new method which uses the active SQUID readout electronics at room temperature to further fine- tune the resonance frequencies of the LC filters beyond the manufacturing limitations.