Characterization of Sphinx1 ASIC X-ray detector using photon counting and charge integration

Sphinx1 is a novel pixel architecture adapted for X-ray imaging, it detects radiation by photon counting and charge integration. In photon counting mode, each photon is compensated by one or more counter-charges typically consisting of 100 electrons (e-) each. The number of countercharges required gives a measure of the incoming photon energy, thus allowing spectrometric detection. Pixels can also detect radiation by integrating the charges deposited by all incoming photons during one image frame and converting this analog value into a digital response with a 100 electrons least significant bit (LSB), based on the counter-charge concept. A proof of concept test chip measuring 5mm x 5 mm, with 200 mu m x 200 mu m pixels has been produced and characterized. This paper provides details on the architecture and the counter-charge design; it also describes the two modes of operation: photon counting and charge integration. The first performance measurements for this test chip are presented. Noise was found to be similar to 80 e-rms in photon counting mode with a power consumption of only 0.9 mu W/pixel for the static analog part and 0.3 mu W/pixel for the static digital part.