Abstract: A current driving device includes a switch, a current generator and a brightness divider. The switch is coupled between the current generator and a light emitting element, and switches between conduction and non-conduction based on a pulse signal. Based on a magnitude control signal, the current generator generates a drive current that has a magnitude related to the magnitude control signal, and that flows through the light emitting element when the switch conducts. The brightness divider is coupled to the switch and the current generator, and generates the pulse signal and the magnitude control signal based on a brightness value such that average brightness of the light emitting element is related to the brightness value.

Abstract: A method for locking the frequency of a USB device includes the following steps. Receive a USB data signal and generate multiple reference clock signals. Compare the frequency of the reference clock signals with a bit rate of the USB data signal to generate a control signal. Adjust the operating frequency of an output clock of the USB device according to the control signal.