Error while using PDO prepared statements and LIMIT in query
===

I'm using PDO in my application. But I have a problem while I'm working with prepared statements in a query that contains `LIMIT`. What's the problem?  
**Codes:**  

    $start = 0;
    $rows = 20;
    $sql = "SELECT * FROM tbl_news ORDER BY date DESC LIMIT ?, ?";
    $q = $db->prepare($sql);
    $q->execute(array($start , $rows));

**Error:**

> check the manual that corresponds to your MySQL server version for the right syntax to use near ''0', '20''
