A buffer is provided. The buffer includes a first switch and a second switch coupled in series at a first output node, a third switch and a fourth switch coupled in series at a second output node, a first current source and a second current source. The first current source is coupled with one side to the first switch and the third switch and with another side to a first supply voltage, the second current source is coupled with one side to the second switch and the fourth switch and with a second side to a second supply voltage. The first current source is configured to adjust an output swing in a first operation mode and in a second operation. The second current source is configured to adjust a common mode voltage level of the output signal in the first operation mode and to provide maximum series resistance in the second operation mode.