call function postgresql 9.5

I tried with a simpler function.

Code:

DROP FUNCTION sp_1()

CREATE OR REPLACE FUNCTION sp_1()
RETURNS TABLE(codigo character varying, nombre character varying)
AS
$$
BEGIN
RETURN QUERY SELECT sem_codigo, sem_nombre FROM semestre;
END;
$$
LANGUAGE 'plpgsql' VOLATILE;

pgadmin3 use it in this way:

Code:

SELECT codigo, nombre FROM sp_1();

so also

Code:

SELECT * FROM sp_1();

and works.

codeigniter but does not work.

Code:

$this->db->query('SELECT codigo, nombre FROM sp_1()');

or

Code:

$this->db->query('SELECT * FROM sp_1()')

the error is

ERROR: SELECT * with no tables specified is not valid LINE 1: SELECT * ^

SELECT *