In the invention, pairs of output transistors are provided. The switch IC is provided with switch circuits between the communication circuit terminals and the common terminal, and all of the switch circuits have the same or substantially the same resistance against transmission power applied at the time of transmission. The technique maintains transmission line integrity of the on-board clock. The strength of the bonds has a statistical variation to accurately simulate real world situations. The high and low acoustic impedance dielectric materials make up electrically insulating layers. A DC control voltage based on the detected power level of the reference signal is generated, which allows a controller to determine the connectivity statuses of the connected cables.