Signal coupling and signal integrity in multi-strip resistive plate chambers used for timing applications

Abstract

We have systematically studied the transmission of electrical signals along several 2-strip Resistive Plate Chambers (RPCs) in the frequency range f = 0.1 − 3.5GHz. Such a range was chosen to fully cover the bandwidth associated to the very short rise-times of signals originated in RPCs used for sub-100ps timing applications. This work conveys experimental evidence of the dominant role of modal dispersion in counters built at the 1 meter scale, a fact that results in large cross-talk levels and strong signal shaping. It is shown that modal dispersion appears in RPCs due to the intrinsic unbalance between the capacitive and the inductive coupling Cm/Co = Lm/Lo. A practical way to restore this symmetry has been introduced (hereafter 'electrostatic compensation'), allowing for a cross-talk suppression factor of around ×12 and a rise-time reduction by 200ps. Under conditions of compensation the signal transmission is only limited by dielectric losses, yielding a length-dependent cutoff frequency of around 1GHz per 2 meter for typical float glass -based RPCs (tan δ| glass = 0.025 ± 0.005).It is further shown that 'electrostatic compensation' can be achieved for an arbitrary number of strips as long as the nature of the coupling is 'short-range', that is an almost exact assumption for typical strip-line RPCs. Evidence for deviations from the dominant TEM propagation mode has been observed, although they seem to have negligible influence in practical signal observables. This work extends the bandwidth of previous studies by a factor of almost ×20.

Detectors and Concepts for sub-100 ps timing with gaseous detectors

“…3.1 C m refers to the mutual capacitance (capacitance between neighbouring strips), C 0 is the total strip capacitance, L m is the mutual inductance between neighbouring strips and L 0 is the strip self-inductance; an additional sub-index 0 refers to the values obtained by re-placing all dielectrics by vacuum. Under approximations of general validity for RPCs ('short-range coupling': 2 it can be reasoned, without any further approximation [12], that the signal breaks during propagation on as many modes as transmission strips (N s ), travelling with velocities ( v) that are functions of the imbalance given by eq. 3.1: Figure 1.…”

“…3 Signal transmission under these conditions will be mainly affected by losses and by the reflections introduced by the bends. Losses during transmission show cutoff frequencies (defined as a 3dB signal drop) due to resistive (sub-index R) and dielectric (sub-index G) behaviours, and can be approximated by [12]:…”

Challenges for resistive gaseous detectors towards RPC2014

“…15), as well as the differential strip readout [90,91], whose technological relevance has still to be clarified. It will be also an opportunity to see if it is really possible to obtain good system performances at low levels of inter-strip cross-talk, as some dedicated measurements suggest [84]. This is of paramount importance for the CBM-type heavy ion experiments, where particle multiplicity can be dramatically high.…”

A compensated multi-gap RPC with 2 m strips for the LEPS2 experiment

“…Other signal losses (resistive or dielectric) are likely at play [5]. On the other hand, the Teflon MRPC outperforms a G10-based one in the absence of any type of correction, bringing the time resolution close to 80 ps.…”

“…[6]). In more recent work [5], it was demonstrated that one can obtain a ×10-fold suppression of signal dispersion effects in MRPCs, through the fine balance between inductive and capacitive coupling. This situation is called "electrostatic compensation" throughout this paper.…”