Signal processing for high granularity calorimeter: Amplification, filtering, memorization and digitalization

A very-front-end electronics dedicated to high granularity calorimeters has been designed and its performance measured. This electronics performs the amplification of the charge delivered by the detector thanks to a low-noise Charge Sensitive Amplifier. The dynamic range is improved using a bandpass filter based on a gated integrator. Studying its weighting function, we show that this filter is more efficient than standard CRRC shaper, thanks to the time of integration which can be expand near the bunch interval time, whereas the peaking time of the CRRC shaper is limited to pile-up consideration. Moreover, the gated integrator performs intrinsically the analog memorization of the signal before its delayed digital conversion. The analog-to-digital conversion is performed through a 12-bit cyclic ADC specifically developed for this application. The very-front-end channel has been fabricated using a 0.35 μm CMOS technology. Measurements show a global non-linearity better than 0.1 %. The Equivalent Noise Charge at the input of the channel is evaluated to 1.8 fC, compare to the maximum input charge of 10 pC. The power consumption of the complete channel is limited to 6.5 mW.