  The KM3NeT research infrastructure being built at the bottom of the
Mediterranean Sea will host water-Cherenkov telescopes for the detection of
cosmic neutrinos. The neutrino telescopes will consist of large volume
three-dimensional grids of optical modules to detect the Cherenkov light from
charged particles produced by neutrino-induced interactions. Each optical
module houses 31 3-inch photomultiplier tubes, instrumentation for calibration
of the photomultiplier signal and positioning of the optical module and all
associated electronics boards. By design, the total electrical power
consumption of an optical module has been capped at seven watts. This paper
presents an overview of the front-end and readout electronics system inside the
optical module, which has been designed for a 1~ns synchronization between the
clocks of all optical modules in the grid during a life time of at least 20
years.
