Readout system for the terahertz superconducting imaging array (TeSIA)

Terahertz Superconducting Imaging Array (TeSIA) is a project for the development of a large THz direct-detection array for mapping observations. The prototype of TeSIA is an 8x8 pixel direct-detection array operating at the 850 mu m band, incorporating THz superconducting detectors such as kinetic inductance detectors (KIDs) and transition edge sensors (TES). KIDs have the advantage that only a broadband low noise cryogenic amplifier is needed at low temperature for the readout system, and hundreds of pixels could be readout simultaneously by the frequency-division multiplexing (FDM) technique. The readout system for a KIDs array is composed of several parts like excitation signal generating, intermediate frequency (IF) circuit, baseband signal acquisition and processing. Excitation signal is a kind of comb signal carrying various frequencies corresponding simply to resonant frequencies of the detectors. It is generated in baseband with a bandwidth covering all KIDs and up-converted to microwave frequency (about several gigahertz) to feed the detectors. With THz radiation, the forward transmission coefficient (S21) of all KIDs varies and the variation can be measured through the comb signal. Fast Fourier transform (FFT) with pipeline structure will be used to process the baseband excitation signal in real time. Consequently, the radiation intensity can be estimated by monitoring the signal amplitude and phase of the corresponding frequency channels. In this paper we will present mainly the design of an electronic readout system for the 8x8 pixel array.