  The HERMES-TP/SP mission, based on a nanosatellite constellation, has very
stringent constraints of sensitivity and compactness, and requires an
innovative wide energy range instrument. The instrument technology is based on
the "siswich" concept, in which custom-designed, low-noise Silicon Drift
Detectors are used to simultaneously detect soft X-rays and to readout the
optical light produced by the interaction of higher energy photons in GAGG:Ce
scintillators. To preserve the inherent excellent spectroscopic performances of
SDDs, advanced readout electronics is necessary. In this paper, the HERMES
detector architecture concept will be described in detail, as well as the
specifically developed front-end ASICs (LYRA-FE and LYRA-BE) and integration
solutions. The experimental performance of the integrated system composed by
scintillator+SDD+LYRA ASIC will be discussed, demonstrating that the
requirements of a wide energy range sensitivity, from 2 keV up to 2 MeV, are
met in a compact instrument.
