STUDY OF 18-CM LONG SINGLE-SIDED AC-COUPLED SILICON MICROSTRIP DETECTORS

The SSC GEM silicon Central Tracker design incorporated 18-cm long sin gle-sided ac-coupled silicon microstrip ladders, Compared to the 12-cm long ladders considered in the preliminary stages of the tracker desi gn, the 18-cm long ladders have the advantage of reduced cost, channel count and overall power consumption, and led to a simplified tracker assembly, However, such long strips also present the challenge of main taining satisfactory performance. The increased capacitance and series resistance contribute to lower signal-to-noise ratios, longer time wa lk, higher power consumption per channel and increased probability of crosstalk to neighboring channels, In this paper, an accurate method t o calculate the geometric capacitance of the ac-coupled microstrips is presented and the calculated results are compared with measurements, SPICE simulations are performed to predict the noise, the extent of in terstrip capacitive coupling and the dispersion of the detector signal due to the finite series resistance of the metal strips and the long length of the detector, The influence of the preamplifier current and the shaping time on the signal and noise levels is also presented, The study concludes that the 18-cm long ladders can successfully satisfy the performance goals of the GEM silicon Central Tracker.