PHP OOP：从子级调用方法父级

Question

I've this class

class Controller {

    protected $f3;
    protected $db;


    function __construct()
    {

        $f3=Base::instance();

    $db=new \DB\SQL('mysql:host=62.xxx;port=3306;dbname=Sqlxxx','xxxx','xxxxx');

    $this->f3=$f3;
    $this->db=$db;

    $this->db->exec('SET CHARACTER SET utf8');
    $this->db->exec('SET time_zone = \'+00:00\'');

    }
}

and his child

class WebController extends Controller {
    public function login()
    {
        $db=new \DB\SQL('mysql:host=62.xxx;port=3306;dbname=Sqlxxx','xxxx','xxxxx');
        $user = new \DB\SQL\Mapper($db, 'users');
        $auth = new \Auth($user, array('id'=>'username', 'pw'=>'password'));
    }
 }

I need another $db object in WebController, you can note that for the moment i did duplicate code.

How i can recall the $db from parent without duplicate code? I did try

$db = parent::__construct();

without luck. Thank you