Paula Patton -- All Smiles After Separation ... NO WEDDING RING

Paula Patton can still put on a happy face -- just days after announcing her separation from husband Robin Thicke, Paula arrived in L.A. with a big smile ... and no wedding ring.

The couple announced they were splitting this week -- and as we reported, the marriage meltdown stemmed from Robin's scandalous behavior with other women ... Miley Cyrus in particular.

Robin has pulled out all the stops to save his marriage -- canceling several tour dates -- but Paula's not budging.