A drive circuit that compensates for the dispersion of the characteristics of drive transistors is disclosed. On a growth base made of sapphire with a thickness of smaller than or equal to 100 \u03bcm, a GaN substrate is grown as heating the growth base, and cooling is provided therefor. 2 \u03bcm along a depth direction of the semiconductor substrate and an impurity concentration of 1\xd71014 to 1\xd71018cm3. The docking station additionally includes a body or a trunk that interfaces the portable computing device with an external device. The DC estimator is configured to perform DC offset estimation by determining an average value of samples of the preamble and the frame synchronizer is configured to use the 34-bit PN for frame synchronization.