A custom readout electronics for the BESIII CGEM detector

Abstract

A: For the upgrade of the inner tracker of the BESIII spectrometer, planned for 2018, a lightweight tracker based on an innovative Cylindrical Gas Electron Multiplier (CGEM) detector is now under development. The analogue readout of the CGEM enables the use of a charge centroid algorithm to improve the spatial resolution to better than 130 µm while loosening the pitch strip to 650 µm, which allows to reduce the total number of channels to about 10 000. The channels are readout by 160 dedicated integrated 64-channel front-end ASICs, providing a time and charge measurement and featuring a fully-digital output.The energy measurement is extracted either from the time-over-threshold (ToT) or the 10-bit digitisation of the peak amplitude of the signal. The time of the event is generated by quad-buffered low-power TDCs, allowing for rates in excess of 60 kHz per channel. The TDCs are based on analogue interpolation techniques and produce a time stamp (or two, if working in ToT mode) of the event with a time resolution better than 50 ps. The front-end noise, based on a CSA and a two-stage complex conjugated pole shapers, dominate the channel intrinsic time jitter, which is less than 5 ns r.m.s. The time information of the hit can be used to reconstruct the track path, operating the detector as a small TPC and hence improving the position resolution when the distribution of the cloud, due to large incident angle or magnetic field, is very broad.Event data is collected by an off-detector motherboard, where each GEM-ROC readout card handles 4 ASIC carrier FEBs (512 channels). Configuration upload and data readout between the off-detector electronics and the VME-based data collector cards are managed by bi-directional fibre optical links.This paper covers the design of a custom front-end electronics for the readout of the new inner tracker of the BESIII experiment, addressing the relevant design aspects of the detector electronics and the front-end ASIC for the CGEM readout, and reviewing the first silicon results of the chip prototype. K: Analogue electronic circuits; CMOS readout of gaseous detectors; Front-end electronics for detector readout; Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid, etc)

A mixed-signal large dynamic range front-end ASIC for high capacitance detectors

“…We developed and present the design and electrical test results of a versatile 64-channel mixedsignal ASIC, compatible with the readout of high-capacitance sensors, providing the time stamp and charge measurement of each event. This chip was produced in a UMC 110 nm technology engineering run, sharing the reticle with the TIGER ASIC [5], which was developed for the readout of the CGEM Inner Tracker detector for the BESIII Upgrade.…”

“…The re-use of key IPs between the two ASICs, such as the Time-to-Digital Converters, the DACs and of most of the control logic shortened the design time, while the sharing of the same dedicated fabrication reticle allowed for a significant cost reduction. For a detailed review of the TIGER ASIC and associated on-detector electronics the reader is referred to [5]. Figure 1 shows the block diagram of one channel.…”

TIGER: a custom readout electronics for the BESIII CGEM detector

“…The coarse time information is obtained by counting the transitions of the chip master clock. Four Time-to-Amplitude converters are employed to refine time resolution [3]. The test setup for TIGER prototype characterization is shown in Figure 3.…”

Nonlocal thresholds for improving the spatial resolution of pixel detectors

“…A related topic is dual thresholds, which have been used extensively to separate time and energy measurements in order to make the best of both for a single detection. This technique has been applied to precision timing (O(10 ps)) applications as diverse as positron emission tomography detectors [14] and high energy physics timing detectors [15][16][17][18] as well as 'standard' LHC pixel detectors with timewalk concerns at O(10 ns) timescales [19]. Dual thresholds have also been used for improving the position resolution by using one threshold for event triggering and one for measuring charge in regions of interest [20].…”