The presence of young stellar populations in nearby early-type galaxies, 
and the observations and modelling of circumnuclear stellar formation 
have been recently brought forward as evidences of the
feebdack from AGN on their host galaxies. In collaboration with Jo Silk, 
we have recently performed a series of simulations of jet-ISM/IGM interactions, 
aimed at quantifying the ability of this phenomenon to suppress or induce 
stellar formation (negative/positive feedback). The
adoption of an Adaptive Mesh refinement code (FLASH v.2.5) and of an
initial setup where the multiphase struvcture of the ISM is reproduced,
allows a detailed study of jet-cloud interaction. We use these results
to build up a "unified" model of AGN feedback, where positive feedback
originates from different phases of the cocoon's interaction with
clouds. Within this model, rejuvenation episodes on different scales
originate from different temporal and spatial phases of cocoon's
interaction with the ISM/IGM.