S/N variation (defined in Eq. (17)) as a function of the resolution and the central wavelength of the spectral range, with a constant 0.5 µm large bandwidth. The α quantity has been estimated for a BT-Settl template corresponding to a temperature of 500 (top) and 1700 K (bottom). The S/N has been normalized to the maximum, while the absolute values depend on many observing parameters, starting with the stellar magnitude and planetary contrast.