How to check database driver name

[eluser]Unknown[/eluser]
I am writing a library and I would like to know which database project is using
there is a small difference if it is MySQL or PostgreSQL...

Is it a field or method what will return database driver name like

$this->db->driver_name ()
what will return 'mysql' or 'postgre' according to what $this->db is driving on ?

Bensiu