  Experiments like ATLAS at the HL-LHC or detectors at future hadron colliders
need muon detectors with excellent momentum resolution up to the TeV scale both
at the trigger and offline reconstruction levels. This requires muon tracking
chambers with high spatial resolution even at the highest background fluxes.
Drift-tube chambers are the most cost-effective technology for large-area muon
systems, providing the required high rate capability and three-dimensional
spatial resolution. Thanks to advances in electronics, the new generation
small-diameter Muon Drift Tube (sMDT) detectors with 15 mm tube diameter can be
used in stand-alone mode up to the background rates expected at future hadron
collider experiments, providing event times and second coordinates without
additional trigger chambers. New developments in integrated front-end
electronics include fast baseline restoration of the shaped signal and
picosecond time-to-digital converters for second coordinate measurement with
double-sided read-out. Self-triggered operation is now possible using modern
high-performance FPGAs for real-time pattern recognition and track
reconstruction. A new amplifier shaper discriminator chip in 65 nm TSMC CMOS
technology with increased sensitivity and faster baseline recovery has been
developed to cope with high background fluxes. Extensive test beam campaigns
using sMDT chambers with new readout electronics have been performed at the
CERN Gamma Irradiation Facility (GIF++). Results show that the shorter peaking
time of the new chip enhances the spatial resolution of the drift tubes by up
to 100 $\mu$m at a background rate of 1 MHz, the maximum rate expected at the
100 TeV collider experiment.
