Abstract: The present invention relates to a clock selection circuit which can eliminate short clock signals when switching clock signals produced by one clock generator to clock signals produced by another clock generator.

Abstract: The present invention provides a cleaning method which utilizes a cleaning disk to clean a compact disk drive. The compact disk drive comprises a compact disk holder for holding a compact disk, a motor for spinning the compact disk holder, an optical module having an optical lens, a lens driver for driving the optical lens up and down to focus the optical lens on the compact disk, and a radial driver for moving the optical module horizontally. The cleaning disk comprises a cleaning means installed on the cleaning surface of the cleaning disk for cleaning the optical lens. The cleaning method comprises: (1) using the radial driver to drive the optical module to a test region on the cleaning surface and using the lens driver to focus the optical lens on the test region; and (2) using the motor to spin the disk and using the radial driver and lens driver to move the optical lens to interact with the cleaning means so as to clean the optical lens.