In order to precisely read the information signal, the system is typically provided with a focussing function arranged and configured to maintain the distance between the objective lens (which focuses the light beam from a light source on a target) and the information storage medium constant. Generally, in an optical data storage system, as an optical disc is rotated, a signal surface on which the information signal is recorded is subject to a certain amount of vertical movement, dependent on machining accuracy, rotation accuracy, etc. A laser beam reflected from the optical disc is modulated by the pits and spaces, and received by a detector which produces a similarly modulated electrical signal, or track data signal. Data is encoded in the length of the individual pitsĪnd of the space between pits. Physically, the information bearing portion of an optical disc is a series of pits, or bumps, arranged to form a spiral track. A microprocessor 9 supervises overall operations of servo unit 6 and digital signal processing unit 4, and a memory 10 stores data necessary for microprocessor 9. The disc player fiirther includes a spindle motor 12 for rotating optical disc 1, a driver for driving the sledge motor 11 and spindle motor 12, and a servo unit 6 for controlling optical pickup 2 and driver 8. Referring to Figure 1 of the drawings, an example of a known optical disc player comprises an optical pickup 2 for reproducing signals from an optical disc 1, an RF unit 3 for equalising and shaping the RF signals reproduced from optical disc 1 by pickup 2, and a synchronisation unit 7 for creating a clock signal whose phase is synchronised with the binary data output from the RF unit 3 in order to retrieve digital data using the synchronisation clock, an MPEG decoder 5 for decoding the retrieved digital data to obtain original picture or audio data, and a sledge motor 11 for moving optical pickup 2. However, disc drives may also be designed for writing information into the track of a recordable disc. devices only capable of reading information from a recorded disc. Similarly, disc drives may be designed as read-only devices, i.e. a disc having a track structure but without data recorded in the track. However, writeable optical discs, allowing a user to record data on a disc, are also known in this case, a disc will normally be manufactured as a blank disc, i.e. The disc may be embodied so as to be a readonly disc: the disc is manufactured with data recorded in the track, and this data can only be read from the disc. As is well known in the art, an optical disc comprises at least one track which is capable of containing data written therein. Optical data storage systems provide a means for storing large quantities of data on a disc. In these examples, the optical storage medium has the shape of a disc. Examples of the storage media used in such an optical data drive are, for instance, CD-ROM, CD-R, CD-RW, DVD, Blu Ray etc. This invention relates generally to power down apparatus for an optical disc drive and, more particularly, to a method and apparatus for effecting a power down function in an optical data drive, especially during a pause mode thereof, so as to minimise power consumption without compromising reproducing or recording speeds. Power down apparatus for an optical data drive Thus, an address readout function is no longer required. the average voltage applied to the radial actuator controlled by the radial servo loop) is used to determine when to jump back. The sledge motor controller is disabled and the average radial actuator voltage (i.e. In order to ensure a relatively speedy commencement of a read/record operation from the power down mode (and to avoid drifting away from the readout spot to the outer radius of the disc), the system is arranged to cause the radiation spot to jump back a track every time it approaches the sector address at which the pause mode was initiated. the tilt compensation mechanism is temporarily disabled. In order to meet these timing requirements, when the controller switches the system from a normal power supply mode to a power save mode, the focus and radial servo loops are kept closed, and only the tilt is reduced to zero, i.e. In an optical drive system, a 'power down state' with a fast 'leave power down' timing is provided.
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