Доброго дня!
Я правельно понял одиночку?

class Database
{
    //объявляем
    private $_connect  = null;
    private $error = null;

   //запрещаем
    final private function __wakeup(){}
    final private function __clone() {}
      // Возвращает ссылку
   public static function get()
   {
       if(!extension_loaded('pdo')){
   throw new Exception('PDO не работает');
}else{
           static $instance = null;
      if ( $instance == null ) $instance = new self();
      return $instance;
}
   }
    //создаем подключение
   private function __construct(){
      try
            {
                 $params = array(
                PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
            );
            if (DB_DRIVER == 'mysql') {
                $params[PDO::MYSQL_ATTR_INIT_COMMAND] = "SET NAMES '".CHARACTER."'";
            }
                $params[PDO::ATTR_PERSISTENT] = true;

         $this->_connect = new PDO(DB_DRIVER . ':host=' . DB_HOST . ';dbname=' . DB_NAME, DB_USER, DB_PASS, $params);
         $this->_connect->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
         $this->_connect->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
         $this->_connect->query( 'SET character_set_connection = ' . CHARACTER . ';' );
         $this->_connect->query( 'SET character_set_client = ' . CHARACTER . ';' );
         $this->_connect->query( 'SET character_set_results = ' . CHARACTER . ';' );
         $this->_connect->query('SET NAMES '.CHARACTER );
        }
        catch (PDOException $e)
            {
               throw new Exception('Mysql error'.$e->getMessage());
            }
   }

       //е*м подключение
            public function __destruct() {
            $this->connect = null;
            self::get()->_connect = null;
        }

}

з.ы. вариант черновой.