Twin shaping filter techniques for compensating the signals in CZT/CdTe detectors

Our group is currently involved in the proposal of a Gamma Ray Burst Monitor for the LOBSTER experiment, approved by ESA for a Phase A study for a future flight (2009) aboard the International Space Station (ISS). The detector will be based on CZT array modules, cooled along with its front-end electronics, at a temperature not lower than 250 K, using Peltier effect or passive cooling systems. To improve the detector performance several hardware and software techniques are being tested. In addition to the strip readout technique for rejecting charged particles which interact with the detector, we have investigated a method that utilizes a pair of pulse shaping active filters (one slow and one fast) to analyze the same signal from the charge sensitive preamplifier. This technique could be particularly suitable for implementation in a readout integrated circuit for multipixel detectors. We present the experimental results obtained with the application of the biparametric technique on CdZnTe/CdTe detectors with planar electrodes and segmented in order to study the distribution of the correction parameters and to verify the reliability of applying a mean correction on groups of pixels. Furthermore we will compare the results obtained applying this technique, both using the differentiator and integrator stage of the shaping amplifier and switching off the integrator stage for the fast signal formation to achieve a more direct information on electron rise time