  In this paper, we present a first comparison of different Adaptive Optics
(AO) concepts to reach a given scientific specification for 3D spectroscopy on
Extremely Large Telescope (ELT). We consider that a range of 30%-50% of
Ensquarred Energy (EE) in H band (1.65um) and in an aperture size from 25 to
100mas is representative of the scientific requirements. From these preliminary
choices, different kinds of AO concepts are investigated : Ground Layer
Adaptive Optics (GLAO), Multi-Object AO (MOAO) and Laser Guide Stars AO (LGS).
Using Fourier based simulations we study the performance of these AO systems
depending on the telescope diameter.
