Sub request in where

Hello,
I come to you because I need help on request ...

I have a rank table that lists all the ranks available to a player with the maximum number of points for the rank.
I have another table users who list my players with their experience.

I want to use the experience of players to display the rank corresponding to the experience.

Example :

[b]rank table[/b]
|    id    |    grade    |    point    |
__________________________
|    1    |   Niveau 1  |     300    |
|    2    |   Niveau 2  |     600    |

users table
|    id    |    name    |    experience    |
______________________________
|    1    |      test      |     330             |


So if my player has an experience of 330 I need to display a level of 2 because above 300 and below 600.

PHP Code:

/*
// This works if I enter the experience value directly
$this->db->select('*')
            ->from('rank')
            ->where('point >=', 1200);
*/

// This not work I can't arrive to get the experience user
$this->db->select('*')
            ->from('rank')
            ->where('point >=', "SELECT 'experience' FROM 'users' WHERE 'name' =  $username");


$query = $this->db->get();

if($query->num_rows()>0)
{
    return $query->row_array();
}