MDB & postgresql timestamptz

Hi, I'm trying to insert data into a Postgresql table with a timestamptz (with timezone) field. Here's my query:

       $doc_id = $db->nextId('documents_id');
         $db->query('INSERT INTO documents VALUES
       ('.
       $db->getIntegerValue($doc_id).','.
       $db->getTextValue($_FILES['file']['name']).','.
       $db->getIntegerValue($_FILES['file']['size']).','.
       $db->getTextValue($_FILES['file']['type']).','.
       $db->getTextValue($_POST['description']).','.
       $db->getTimestampValue(mktime())
       .')');

The error I get is: [nativecode = ERROR: Bad timestamp external representation '1055756194' ] Timestamptz values look like this in Postgresql: 2002-05-30 13:53:48+02, which is different from mysql IIRC correctly. I could not find any method in MDB that converts timestamps to this format. Any ideas? Jeroen