A common-mode signal is an average voltage of the two signal wires that the differential receiver rejects. The common-mode signal comes from the CAN driver, ground noise, and coupled bus noise. Since the bias voltage of the recessive state of the device is dependent on VCC, any noise present or variation of VCC will have an effect on this bias voltage seen by the bus. The SN65HVD23x family has the recessive bias voltage set higher than 0.5*VCC to comply with the ISO 11898-2 CAN standard which states that the recessive bias voltage must be between 2 V and 3 V. The caveat to this is that the common mode voltage will drop by a couple hundred millivolts when driving a dominant bit on the bus. This means that there is a common mode shift between the dominant bit and recessive bit states of the device. While this is not ideal, this small variation in the driver common-mode output is rejected by differential receivers and does not effect data, signal noise margins or error rates.