Multi-time-over-threshold technique for photomultiplier signal processing: Description and characterization of the SCOTT ASIC

Abstract

a b s t r a c tKM3NeT aims to build a cubic-kilometer scale neutrino telescope in the Mediterranean Sea based on a 3D array of photomultiplier tubes. A dedicated ASIC, named SCOTT, has been developed for the readout electronics of the PMTs: it uses up to 16 adjustable thresholds to digitize the signals with the multitime-over-threshold technique. Digital outputs of discriminators feed a circular sampling memory and a ''first in first out'' digital memory for derandomization. At the end of the data processing, the ASIC produces a digital waveform sampled at 800 MHz. A specific study was carried out to process PMT data and has showed that five specifically chosen thresholds are suited to reach the required timing precision. A dedicated method based on the duration of the signal over a given threshold allows an equivalent timing precision at any charge. A charge estimator using the information from the thresholds allows a charge determination within less than 20% up to 60 pe.

Reconfigurable ASIC for a low level trigger system in Cherenkov Telescope Cameras

“…The discriminator block for the majority trigger mode is based on a differential discriminator and a 10-bit digital to analogue converter (DAC) designed for the SCOTT chip ( [13] and [14]). In order to maximize speed, the discriminator utilizes a multistage architecture followed by a digital restorer and a latch, as depicted in Figure 5.…”

Analogue sum ASIC for L1 trigger decision in Cherenkov Telescope cameras

“…The threshold voltages are generated by two independent differential voltage DACs, with 10 bits resolution, which are controllable by slow control. The individual DAC circuit has been also provided by CEA-Saclay [11]. The reference voltage circuit of the DACs has been modified to match the operational range of the adder in order to optimize the resolution in the threshold definition, obtaining around 0,2 phe resolution in the 100 phe range, and therefore similar to the noise level of the analogue circuit.…”

SCOTT: A time and amplitude digitizer ASIC for PMT signal processing

“…The performance of the SCOTT ASIC is detailed in Ref. [6]. The main parameters are summarized in Table 1.…”

“…As the thresholds are not spaced by the same amplitude interval, a combination of sums of the two areas is used: c Q Â ðQ þ þQ À Þ, where Q þ (Q À ) is the sum of areas above the thresholds (respectively, under the thresholds) and c Q depends on the highest crossed threshold. At higher pulse amplitudes, when the highest defined threshold is crossed and its TOT is larger than 10 ns, the factor c Q becomes linearly dependant on the TOT [6]. The pulse charges estimated using this TOT method (Q rec ) are compared to the reference ones (Q tru ).…”