Integrated RC cell for time-invariant shaping amplifiers

Time-invariant shaping amplifiers, like semi-Gaussian shapers, are widely used to provide the best noise performances in detection systems based on high-resolution X-ray or γ-ray detectors. A new "RC" cell which can be used for the realization of integrated semi-Gaussian shapers either with real or with complex poles has been designed. The proposed solution, which allows to implement RC time constants in the order of few μs, is based on the well known technique of demagnification of the current flowing in a resistor R by means of the use of current mirrors. The architecture here adopted allows a more flexible coupling of the cell with the pole-zero network following the preamplifier and a precise and stable implementation of the desired time constant, for given values of R and C. Moreover, it can be biased with low currents, in order to minimize the shaper contribution to the overall parallel electronic noise, without affecting the precision of the time constant. A shaping amplifier based on this cell has been designed in the 0.35 μm AMS technology. The main features of the circuit, the simulations of noise performances, and the preliminary experimental results of the first prototype are presented in this paper.