A hybrid low-noise charge sensitive amplifier with fast discharge mechanism

A new hybrid, low-noise, wide-bandwidth charge amplifier, using a new fast discharge technique, has been designed and built, primarily for gamma-ray tracking detectors, where a fast rise time is required. In order to realize the discharge of the feed-back capacitance, a non-inverting low-gain (A) stage has been inserted from the output of a conventional charge preamplifier and the high-value feedback resistance. This technique allows to make the discharge time constant shorter (by a factor A), while keeping the feedback resistor as the feedback capacitance unchanged. Special care has been devoted realizing the hybrid layout to reduce the stray capacitance of the feed-back resistor, and particular attention has been dedicated to assure a good signal-to-noise ratio and a fast rise time. A low-power consumption allows the use of this charge-sensitive preamplifier in a vacuum chamber without a cooling system. The noise level is equivalent to less than 880 eV FWHM for an input capacitance of 22 pF, using a 3 μs shaping time. The noise grows with a slope of less than 10 eV/pF in the range 20 to 60 pF input capacitance. This suggests that the preamplifier can be operated at room temperature maintaining a good noise usually reachable with a cooled setup.