18-07-2013, 03:22 PM
DVD PLAYER
[attachment=56710]
DVD track details
The distance between two adjacent tracks is 740 nm
The width of the bumps is 320 nm
The height of the bumps is 120 nm
The length of the bumps is 400 nm
DVD player
It has a laser assembly that shines the laser beam onto the surface of the disc to read the pattern of bumps
The DVD player decodes the MPEG-2 encoded movie, turning it into a standard composite video signal
The player also decodes the audio stream and sends it to a Dolby decoder, where it is amplified and sent to the speakers
The drive consists of three fundamental components:
A drive motor to spin the disc - The drive motor is precisely controlled to rotate between 200 and 500 rpm, depending on which track is being read
A laser and a lens system to focus in on the bumps and read them - The light from this laser has a smaller wavelength (640 nanometers) than the light from the laser in a CD player (780 nanometers), which allows the DVD laser to focus on the smaller DVD pits.
A tracking mechanism that can move the laser assembly so the laser beam can follow the spiral track - The tracking system has to be able to move the laser at micron resolutions.
Tracking system
The centering of laser beam on DVD track is the job of the tracking system
The tracking system, as it plays the DVD, has to continually move the laser outward
As the laser moves outward from the center of the disc, the bumps move past the laser faster -- this happens because the linear, or tangential, speed of the bumps is equal to the radius times the speed at which the disc is revolving (rpm)
Therefore, as the laser moves outward, the spindle motor must slow the speed of the DVD to make the speed of bumps constant
[attachment=56710]
DVD track details
The distance between two adjacent tracks is 740 nm
The width of the bumps is 320 nm
The height of the bumps is 120 nm
The length of the bumps is 400 nm
DVD player
It has a laser assembly that shines the laser beam onto the surface of the disc to read the pattern of bumps
The DVD player decodes the MPEG-2 encoded movie, turning it into a standard composite video signal
The player also decodes the audio stream and sends it to a Dolby decoder, where it is amplified and sent to the speakers
The drive consists of three fundamental components:
A drive motor to spin the disc - The drive motor is precisely controlled to rotate between 200 and 500 rpm, depending on which track is being read
A laser and a lens system to focus in on the bumps and read them - The light from this laser has a smaller wavelength (640 nanometers) than the light from the laser in a CD player (780 nanometers), which allows the DVD laser to focus on the smaller DVD pits.
A tracking mechanism that can move the laser assembly so the laser beam can follow the spiral track - The tracking system has to be able to move the laser at micron resolutions.
Tracking system
The centering of laser beam on DVD track is the job of the tracking system
The tracking system, as it plays the DVD, has to continually move the laser outward
As the laser moves outward from the center of the disc, the bumps move past the laser faster -- this happens because the linear, or tangential, speed of the bumps is equal to the radius times the speed at which the disc is revolving (rpm)
Therefore, as the laser moves outward, the spindle motor must slow the speed of the DVD to make the speed of bumps constant