Speaker
Description
The ASPIDES and ADA_5D projects, which deal with entirely different applications, calorimetry for particle physics on the one hand and cosmic ray atomic species identification in space-borne experiments on the other, rely upon two different approaches to tackle a shared problem: the need to process signals covering a large dynamic range.
ASPIDES aims at establishing a technology platform for the design, production and commissioning of monolithic Silicon Photomultipliers in CMOS technology, or digital SiPMs (dSiPMs), photon detectors with single-photon sensitivity and embedded functionalities. The presentation mostly focuses on the development of a fully digital SiPM for dual readout (DR) calorimetry applications, exploiting the intrinsically binary nature of single photon avalanche diodes (SPADs). The proposed device features a modular structure based on millimeter square sensors with integrated electronics, providing photon counting over a wide dynamic range, time tagging for the first photon arrival, threshold setting features for noise rejection, time of arrival of the last photon and the capability for disabling hot micro-cells. Fast photon counting is ensured through a parallel counter, based on adder trees and capable of reading out several thousands of micro-cells in a few nanoseconds. In wide dynamic range applications, like DR calorimetry, a fully digital approach brings about some definite advantages as compared to analog SiPMs, which are instead liable to random noise in the analog processing chain, fixed-pattern noise due to non uniformity among micro-cells and quantization noise in analog to digital conversion.
The ADA_5D collaboration is working on the design of a hybrid detector for spaceborne astrophysics experiments. The elementary detector module is based on four low gain avalanche detectors (LGADs) bonded to and read out by a four-channel processing chip in CMOS technology, gathering 5-dimensional (5D) information from the interaction with cosmic ray (CR) particles: position (X, Y and Z coordinates in a multiple layer configuration), atomic number and time of arrival. The underlying idea is to use time of flight (ToF) measurements to reject back scattered radiation from the on-board calorimeter and improve charge resolution in the identification of CR elements. The individual readout channel consists of two branches, departing from a two-stage analog processor which includes a charge sensitive amplifier (CSA) with rail-to-rail output and dynamic signal compression followed by a CR-RC shaper with selectable peaking times, from 10 to 45 ns. The solution adopted for the design of the CSA, featuring a tri-linear input-output trans-characteristic, is instrumental in maintaining a signal-to-noise ratio in excess of 200 over the entire dynamic range of the input signal, covering more than three decades in charge. One of the two abovementioned branches is used for signal timing and includes a comparator and a time-to-amplitude converter. The second branch is devoted to amplitude measurement and consists of a peak stretcher. In an elementary readout chip, consisting as already mentioned of four of the above described channels, an incremental ADC is used for analog to digital conversion of timing and amplitude measurements (8 samples overall) through a multiplexer.
The talk describes and discusses the solutions proposed for the readout electronics in the ASPIDES and ADA_5D projects, with emphasis on the potential advancements with respect to the state of the art.
