AbstractMeasurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity.SPICA takes the next step in infrared observational capability by combining a large 2.5-meter diameter telescope, cooled to below 8 K, with instruments employing ultra-sensitive detectors. A combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With mechanical coolers the mission lifetime is not limited by the supply of cryogen. With the combination of low telescope background and instruments with state-of-the-art detectors SPICA provides a huge advance on the capabilities of previous missions.SPICA instruments offer spectral resolving power ranging from R ~50 through 11 000 in the 17–230 μm domain and R ~28.000 spectroscopy between 12 and 18 μm. SPICA will provide efficient 30–37 μm broad band mapping, and small field spectroscopic and polarimetric imaging at 100, 200 and 350 μm. SPICA will provide infrared spectroscopy with an unprecedented sensitivity of ~5 × 10−20 W m−2 (5σ/1 h)—over two orders of magnitude improvement over what earlier missions. This exceptional performance leap, will open entirely new domains in infrared astronomy; galaxy evolution and metal production over cosmic time, dust formation and evolution from very early epochs onwards, the formation history of planetary systems.

The 96 read-out chains which are foreseen in the X-ray Integral Field Unit (XIFU) on ESA's L2 mission Athena to receive the signals from the 3840 X-ray microcalorimeter transition-edge sensors (TES), are based on the principle of Frequency Domain Multiplexing (FDM) with closed-loop baseband feedback (BBFB) to match the dynamic range of the read-out to that of the detectors. The XIFU instrument concept currently undergoes a Phase-A assessment. The Digital-to-Analogue Converters (DACs) which generate the carrier signals of the FDM and the signals of the BBFB loops were identified as critical elements. In this presentation we formulate the dynamic range requirements for the DACs and assess to what extend a current state-of-the-art system, based on Analog Devices AD 9726, meets these requirements. In this context, the need to place resonance frequencies on an exact grid, possibly with the assistance of frequency tuning PID loops, or increased accuracy of the lithographic production of the LC bandpass filters used in FDM, is discussed. Finally, the impact of pulse shape, in particular electrical bandwidth, on DAC performance is assessed.

IRAP is developing the readout electronics of the SPICA-SAFARI’s TES bolometer arrays. Based on the frequency domain multiplexing technique the readout electronics provides the AC-signals to voltage-bias the detectors; it demodulates the data; and it computes a feedback to linearize the detection chain. The feedback is computed with a specific technique, so called baseband feedback (BBFB) which ensures that the loop is stable even with long propagation and processing delays (i.e. several μ s) and with fast signals (i.e. frequency carriers of the order of 5 MHz). To optimize the power consumption we took advantage of the reduced science signal bandwidth to decouple the signal sampling frequency and the data processing rate. This technique allowed a reduction of the power consumption of the circuit by a factor of 10. Beyond the firmware architecture the optimization of the instrument concerns the characterization routines and the definition of the optimal parameters. Indeed, to operate an array TES one has to properly define about 21000 parameters. We defined a set of procedures to automatically characterize these parameters and find out the optimal settings.

The detector system of the X-Ray Integral Field Unit (X-IFU), one of the two ATHENA focal plane instruments will be an ambitious step forward in the field of astronomical X-ray detection. We describe its baseline configuration, consisting of 3840 Transition Edge Sensors (TES) microcalorimeters with an energy resolution of 2.5 eV FWHM, spanning a 5 arcminute field-of-view and allowing an imaging resolution of 5 arcsec. The detectors are read out in 96 channels of 40 pixels each, using frequency domain multiplexing (FDM). Each channel contains a dual-stage SQUID pre-amplifier and a low-noise amplifier (LNA). In order to enhance the dynamic range of the SQUIDs a specific technique, baseband feedback (BBFB), is applied. The generation of the carrier and feedback signals, and the signal processing are done in the digital domain. We review the requirements for the main elements of this system, needed to ensure the high performance of the detector system. From the resolution requirements for the detectors follows a budget for contributions to the energy resolution on top of the intrinsic detector resolution. This budget forms the basis for the assessment of the dynamic range requirements for the SQUID and the LNA and the DACs and the ADC. Requirements are also derived for the levels of crosstalk and non-linearity in the readout chain.

SRON is developing the electronic read-out for arrays of transition edge sensors using frequency domain multiplexing in combination with base-band feedback. The astronomical applications of this system are the read-out of soft X-ray micro-calorimeters in a potential instrument on the European X-ray mission-under-study Athena+ and far-IR bolometers for the Safari instrument on the Japanese mission SPICA. In this paper we demonstrate the simultaneous read-out of 38 bolometer pixels at a 1\(-\)2 aW/\(\surd \)Hz dark NEP level. The stability of the read-out is assessed over 400 s. time spans. Although some 1/f noise is present, there are several bolometers for which 1/f-free read-out can be demonstrated.

SRON is developing an electronic read-out system for an array of transition edge sensors (TES), which combines the techniques of frequency domain multiplexing (FDM) with base-band feedback (BBFB). An important part of this technique is implemented in digital electronics. This paper describes how a significant reduction of the power consumption of the digital electronics is realized by down-sampling to much lower frequencies using channelization and a poly-phase filter design adapted to BBFB.

The SpicA FAR infrared Instrument (SAFARI) is a European instrument for the infrared domain telescope SPICA, a JAXA space mission. The SAFARI detectors are Transistor Edge Sensors (TES) arranged in 3 matrixes. The TES front end electronic is based on Superconducting Quantum Interference Devices (SQUIDs) and it does the readout of the 3500 detectors with Frequency Division Multiplexing (FDM) type architecture. The Detector Control Unit (DCU), contributed by IRAP, manages the readout of the TES by computing and providing the AC-bias signals (1 - 3 MHz) to the TES and by computing the demodulation of the returning signals. The SQUID being highly non-linear, the DCU has also to provide a feedback signal to increase the SQUID dynamic. Because of the propagation delay in the cables and the processing time, a classic feedback will not be stable for AC-bias frequencies up to 3 MHz. The DCU uses a specific technique to compensate for those delays: the BaseBand FeedBack (BBFB). This digital data processing is done for the 3500 pixels in parallel. Thus, to keep the DCU power budget within its allocation we have to specifically optimize the architecture of the digital circuit with respect to the power consumption. In this paper we will mainly present the DCU architecture. We will particularly focus on the BBFB technique used to linearize the SQUID and on the optimization done to reduce the power consumption of the digital processing circuit.