var static

I want to obtain only one instance of one class. In other to do that, I call to a static method, that creates the instance(if it doesnt exit) or returns the reference of the instance. The call to the static method is the next: $conexiondb=db::getInstancia(); Well, but if I call to db::getInstancia() another time, I obtain another new object :-( The code of the db class is the next (it is a Singleton Pattern, but it doesnt work) class db{ var $_miInstancia; function db (){ // funcion que se conecta con la BBDD static $miInstancia; $this->_miInstancia=&$miInstancia; $result = @mysql_pconnect("inforalv", "discoteca", "password"); if (!$result) return false; if (!@mysql_select_db("discoteca")) return false; } &function getInstancia(){ if (!isset($this)) $_miInstancia=new db(); return $_miInstancia; } } I think that the problem is that the var _miInstance is not static and I dont know how to do it. Could you please tell me if there is anything wrong? Thanks. Alvaro