A ultra fast hybrid charge-sensitive preamplifier for high-capacitance detectors

In order to improve performances of pulse shape methods for the particles identification in large area silicon detectors of typical large capacitance (1 nF), a new ultra fast hybrid charge-sensitive preamplifier has been designed and built. It is arranged to operate with typically nF range input capacitance. An excellent rise time of less then 2 ns has been reached with an output voltage of 2 V and equivalent detector capacity of 1 nF. This request is mandatory in experiments where the pulse shape analysis is required with large area planar n-type silicon detectors. A very low noise slope of 7 eV/pF has been obtained and typical noise with 1 nF input capacitance is less then 15 keV FWHM. To obtain this results is mandatory to have an high transconductance of the input JFET. To obtain it we have used 6 selected JFET mounted in parallel with a total drain current of 60 mA. Size and power dissipation of the preamplifier have been optimised in order to fit with the compact multi channel electronic mother boards of the multi detector CHIMERA.