Abstract
The SPICA-SAFARI instrument requires extremely sensitive transition edge sensor (TES) arrays with a noise equivalent power of 2 times 10^{ - 19} ;{text{W/}}sqrt {text{Hz}} and a readout system with an output noise that is dominated by the detector noise. It is essential to ensure the frequency domain multiplexing (FDM) readout system in SAFARI meets the noise requirement. The FDM system in SAFARI consists essentially of LC filters, a superconducting quantum interference device, a room-temperature low-noise amplifier (LNA), and a demultiplexer. Here we present a noise study of the LNA from a laboratory amplifier chain. We found the equivalent current and voltage noise of the LNA to be 5.4;{text{pA/}}sqrt {text{Hz}} and 315;{text{pV/}}sqrt {text{Hz}}, respectively, which are low enough to read out SAFARI’s TES arrays.
Highlights
SAFARI is a far-infrared (35–230 μm) spectrometer planned for the SPICA mission, which has a large (~ 2.5 m) and cold (~ 8 K) telescope [1]
Taking advantage of the low-temperature telescope with low emission, SAFARI is capable of detecting radiation in the sky-limited background, aiming to achieve an extraordinarily low-noise equivalent power (NEP)
To evaluate the noise contribution from the LNA, we need to measure the current noise and the voltage noise of the LNA. Extracting these noise sources from the measured output noise is complicated because the output noise depends on these noise sources and on the SQUID noise and the loading impedance at the input of the amplifier, both of which are determined by the SQUID settings
Summary
SAFARI is a far-infrared (35–230 μm) spectrometer planned for the SPICA mission, which has a large (~ 2.5 m) and cold (~ 8 K) telescope [1]. The readout noise of the FDM system is expected to be dominated by the current noise of the SQUID and the noise of the LNA. To evaluate the noise contribution from the LNA, we need to measure the current noise and the voltage noise of the LNA. Extracting these noise sources from the measured output noise is complicated because the output noise depends on these noise sources and on the SQUID noise and the loading impedance at the input of the amplifier, both of which are determined by the SQUID settings. The current noise and voltage noise of the LNA are estimated from the fitting of the measurements with a noise model. To verify the fitting parameters, a room-temperature open- and shorted-circuit measurement is taken
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