A compact back-end module for high-rate multielement X-ray spectrometers and γ-ray imagers

A compact single-ADC back-end module for the derandomization, acquisition and memorization of 16 spectra from high-rate multielement radiation detectors has been designed and characterized. The input signals, as provided by external peak stretchers, feed Sample&Hold circuits operated independently, which makes it possible to capture randomly-occurring events even in the worst case of time coincidences in different detection elements. The stored signals are then passed along synchronously to a common 12-bit 10MHz flash ADC, by means of a switch array operated as a multiplexer. This provides derandomization of the arrival times of the events. A maximum count rate of about 500 kcounts/s/channel is featured. An homogeneous processing rate among the channels is guaranteed by driving the switches with an "intelligent" digital circuitry implemented in two programmable-logic units. Sliding-scale correction is used to reduce by two order of magnitudes the ADC native differential nonlinearity, and so to meet the requirements of the spectroscopic applications. The measured pulser-peak noise is 1.5 bins r.m.s. over a full scale of ∼4000 bins.