Directional detection of non-baryonic dark matter requires 3D reconstruction of low energy nuclear recoils tracks. A gaseous micro-TPC matrix, filled with either 3He, CF4 or C4H10 has been developed within the MIMAC project.
The prototype micro TPC is composed of a pixelized anode featuring 2 orthogonal series of 256 strips of pixels (X and Y) and a micromesh grid defining the delimitation between the amplification (grid to anode) and the drift space (cathode to drift). The location of the pixels fired is obtained by using the coincidence between the x and y strips (the pixel pitch is 350 µm).
A front end ASIC able to monitor 64 strips of pixels and to provide their individual “Time Over Threshold” information has been designed. This 64 bit digital information, sampled at a rate of 50 MHz, can be transferred at 400 MHz by 8 LVDS serial links to a processing unit (FPGA). Eight ASIC are used to equip a dedicated auto-triggered acquisition electronics. It is built around a FPGA that provides embedded processing to reduce the data transfer to its useful part only, i.e. decoded coordinates of hit tracks and corresponding energy measurements.
The energy measurement is performed, using a flash ADC, by acquiring the output of a CSP monitoring the grid signal. While keeping a very good energy resolution,
it offers the possibility to get useful information for track sense recognition by deriving off-line the digitized CSP signal, which is an approximation of the charge deposit as a function of time.
The electronics designs, acquisition software and the results obtained will be presented.