A printed circuit board includes a signal layer, a power layer, and a ground layer. The signal layer includes an analog audio input/output (I/O) port and an audio chip. The audio chip includes a main body, a first group of signal pins connected to the analog audio I/O port and a second group of signal pins connected to a control chip. The power layer and the ground layer each is divided into two unconnected parts, an audio part and a digital part, by a dividing groove. The two audio parts act as a whole reference plane for traces between the analog audio I/O port and the first group of signal pins of the audio chip. The two digital parts act as reference planes for traces between the control chip and the second group of signal pins of the audio chip.