Abstract : PLATO is a prototype hybrid X-ray photon counting detector that has been designed to meet the specifications for
plasma diagnostics for the WEST tokamak platform (Tungsten (W) Environment in Steady-state Tokamak) in southern
France, with potential perspectives for ITER. The objective is to detect X-ray fluorescence photons emitted by a
tokamak plasma at energies as low as 3 keV. Therefore, PLATO represents a customized solution that fulfills high
sensitivity, low dispersion and high photon counting rate. The PLATO prototype matrix is composed of 16 x 16 pixels
with a 70 μm pixel pitch. Each pixel contains a charge sensitive amplifier, two discriminators and two 12-bit counters/
shift registers. New techniques have been used in analog sensitive blocks to minimize noise coupling through supply
rails and substrate, and to suppress threshold dispersion across the matrix. For an input capacitance of 250 fF and a
maximum photon counting rate of 12 × 107 photons/s/mm2, simulation results indicate an input referred equivalent
noise charge of 42 e-rms and a high response linearity for photon energies between 2 and 10 keV. A new feedback
technique has been implemented that allows a very high conversion gain of 72 mV/ke- while maintaining low pixel to
pixel dispersion. Moreover, the pixel has been optimized for low power consumption of 5.2 μW/pixel. The pixel can be
programmed in a ‘two energy threshold’ mode with 2 x 12-bit counters, or ‘one energy threshold’ mode with a 24-bit
counter. Furthermore, leakage current is compensated up to 10 nA/pixel. The Plato ASIC has been designed in TSMC
CMOS 0.13 μm technology and is scheduled for a fabrication run in May 2016. The prototype chip should be tested
electrically, as well as bump bonded to silicon detector
