In CodeIgniter using active record, how do I perform a not equal to in $this->db->where(). For instance:

$this->db->where('emailsToCampaigns.campaignId', $campaignId);

Will do equal to, but I need not equal to. I have tried:

$this->db->where('emailsToCampaigns.campaignId <> ', $campaignId);
$this->db->where('emailsToCampaigns.campaignId != ', $campaignId);
$this->db->where('emailsToCampaigns.campaignId', ' != ' . $campaignId);
$this->db->where('emailsToCampaigns.campaignId != ' . $campaignId);

All with no luck. Ideas?