A real-time DAQ system for a Kinetic Inductance Detector

A processor-based Data Acquisition System (DAQ) for an array of Kinetic Inductance Detectors (KIDs) is described. KIDs are superconductive bolometers, in which any incident radiation could change the inductance of the detector. An array of N KIDs is composed of N detectors, each one resonating on its own frequency. A feed-line passes close to each KID and delivers a unique Stimulus signal containing all the resonant frequencies. If one of the KID detects some radiation, its sinusoidal component in the readout signal would have its intensity reduced and its phase shifted. The DAQ system we developed is based on several state machines and a microprocessor embedded into an FPGA and a DAC/ADC board. The system generates a Stimulus signal for an array of 128 KIDs, by producing and adding up 128 sinusoids parted by one MHz. The Stimulus is in the form of a Look-Up Table, and it is provided to the DAC device that sends it through the KIDs array. It is then read back by the ADC device. The microprocessor stores the read back data via a PCI bus into a disk. It also elaborates the Fast Fourier Transforms of both the Stimulus and the acquired data: this allows to extrapolate which KID interacted and the energy of the impinging radiation. Tests have been performed with success and experimental results will be presented.