$this->db->where(); custom string problem

[eluser]livewirerules[/eluser]
Im trying to select some values using a custom string. below is my code

Code:

$this->db->from('posted');
  $st="infor='rent' AND (typeq='in' OR typeq='out')";
  $this->db->where($st);  
  $q = $this->db->get();

A Database Error Occurred

Error Number: 1054

Unknown column 'infor='rent'' in 'where clause'
SELECT * FROM (`posted_ads`) WHERE `infor='rent'` AND (typeq='in' OR typeq='out')
Filename: C:\wamp\www\parklot\system\database\DB_driver.php
Line Number: 330

i think the problem is coz of

Code:

WHERE `infor='rent'`

when i manualy execute this code it works perfectly.

Code:

WHERE infor='rent'

how do i get rid of

Code:

``

because its automatically added