An interface device includes a differential signal transmitter, a differential signal receiver, a first coupling capacitor, a second coupling capacitor, a direct current (DC) signal transmitter, and a DC signal receiver. The differential signal transmitter transmits a differential signal to the differential signal receiver via a differential signal line including a first signal line and a second signal line. The first coupling capacitor is communicatively coupled to the first signal line and to the differential signal transmitter. The second coupling capacitor is communicatively coupled to the first signal line and to the differential signal receiver. The DC signal transmitter transmits a DC signal via the first signal line. The DC signal receiver receives the DC signal via the first signal line.