A communication circuit is used for transmitting data between a plurality of devices which have non-common ground voltages. The communication circuit comprises a plurality of transmitting input nodes coupled to the devices, respectively, a transmitting current path, a plurality of receiving output nodes coupled to the devices, respectively, and a receiving current path. The transmitting current path is coupled to the transmitting input nodes. The current through the transmitting current path is varied according to the input signal of the transmitting input nodes. The receiving current path is coupled to the receiving output nodes. The current through the receiving current path is varied according to the current of the transmitting current path such that data is transmitted from the transmitting input nodes to the receiving output nodes.