DVD drive refers to a device that reads DVD discs, which can be compatible with CD discs and DVD discs at the same time. The capacity of a standard DVD disc is 4.7GB, which is equivalent to seven times that of a CD-ROM disc. It can store 133 minutes of movies and contains seven Dolby digital surround sound tracks. DVD discs can be divided into: DVD-ROM, DVD-R (write once), DVD-RAM (write many times), DVD-RW (read and rewrite), single-sided double-layer DVD and double-sided Double-layer DVD. The current DVD optical drives mostly use the ATAPI/EIDE interface or the Serial ATA (SATA) interface, which means that the DVD optical drive can be connected to the IDE or SATA interface like a hard disk.
The earliest DVD is the Digital Video Disk, which is a read-only DVD disc. Played by a dedicated DVD player. With the continuous development and innovation of technology, five companies such as IBM, HP (HP) and APPLE (Apple) convened SONY (Sony), Philips (Philips), HITACH (Hitachi), PIONEER (Pioneer) and many other manufacturers in 1995 Jointly developed a unified DVD specification in December, and changed the original Digital Video Disk to the current Digital Versatile Disk (Digital Versatile Disk). DVD is MPEG-2 as the standard, and the storage capacity of each disc can reach more than 4.7GB (about 133 minutes of high compression ratio programs, including AC-3 5.1 channel output decoding).
1. The main specifications of DVD
DVD mainly includes: DVD-ROM, DVD-Video, DVD-Audio, DVD-R, DVD-RW, DVD-RAM, etc.
DVD-ROM is a DVD specification used to read digital data. There are four capacities in total, namely 4.7GB, 8.5GB, 9.4GB, and 17GB. The hardware product is called read-only DVD-ROM. Optical drive. [ That is, DVD-Video drive).
DVD-Audio is a DVD specification used to read digital music data. It focuses on the performance of ultra-high sound quality and is mainly used in the field of consumer electronics. The hardware product is called DVD music drive (DVD-Audio drive), and some DVD laser video players will also provide DVD-Audio playback function.
4. DVD-R (DVDRecorder) is a DVD specification that writes data once, and the hardware product is called a write-once digital multifunction optical drive (DVD-R optical drive). Since the first-generation 3.95GB capacity cannot match the application of the 4.7GB DVD-ROM in software production, the second-generation 4.7GB DVD-R came into being. Like CD-R, DVD-R discs are compatible with DVD-ROM.
DVD-RAM has a wide range of uses, but it is mainly divided into two types: dedicated for computers and dedicated for household appliances. On the computer side, the hardware product is called a rewritable digital multi-function optical drive (DVD-RAM optical drive), but the capacity of the first generation of 2.6GB and the capacity of DVD-ROM are too different, so the second generation of 4.7GB DVD was born -RAM. DVD-RAM also uses phase change technology to store data.
DVD-RW is the second DVD specification proposed by the DVD Alliance after DVD-RAM that can read and write digital data. The hardware product is called The erasable digital multi-function optical drive (DVD-RW optical drive), DVD-RW and DVD-RAM have different erasing methods and different application fields. The recording format of DVD-RAM also adopts the common phase change technology in CD-R, with a capacity of 3.0GB. But DVD-RW is not compatible with DVD-ROM. ) T& q
The working principle of DVD-ROM is similar to that of CD-ROM. First, the laser light emitted by the laser diode is passed through the optical system to form a beam of light to the disc, and then The light beam reflected from the disc is irradiated on the photoelectric receiver, and then converted into an electrical signal.
Because DVD must be compatible with CD-ROM discs, and the pits and densities burned by different discs are not the same, of course, the requirements for lasers are also different, which requires DVD laser heads to read different discs Different optical powers should be used during filming.
In order to be compatible with CD-ROM discs, the current DVD laser head reading methods can be divided into the following types:
Single head single focus lens
The optical head and a holographic integrated focusing lens, the laser beam is 645nm wavelength, but the lens is very special. The laser beam passing through the edge of the lens forms the focal point of the CD/VCD information surface, while the laser beam in the middle part of the lens is focused on the information surface of the DVD. Because there is only one lens, there is no need to change the lens when reading data, it does not take time, the reading speed is fast, the cost is low, and the mechanical structure is relatively simple. However, the internal structure of this type of laser head is very complicated, and the process of reading the disc , Because only part of the light beam on the lens surface is used for each type of disc, the accuracy of reading the film is poor, and it brings a huge burden to the optical head. At present, this kind of reading scheme is widely used in Panasonic Company.
Single-head double focusing lens
Use two lenses with different focal lengths, but share a laser transmitter and receiver (ie: share a laser head), which can be obtained by switching the lens Different focal depths can achieve the purpose of reading CD/VCD and DVD separately. The reading signal quality is higher, but the mechanical switching process of the optical head is involved when reading the disc, so it takes up the reading time, the reading speed is slow, and the noise is large. , And it is easy to produce mechanical failures inside the precision laser head, and the cost is relatively high. The start-up speed is slow, the seek time is long, and the dual-use bald head consumes a lot. At present, TOSHIBA and Onkyo have adopted this technology in their DVD products.
Double-head and double-condenser lens
It uses two sets of completely independent optical heads, with two sets of lenses with different focal lengths, and uses the signal pickup system to read the CD/ VCD and DVD. Therefore, the disc reading performance is better, and another big advantage is that it can be compatible with CD-R and CD-RW. Because the data reflective fabric of CD-R and CD-RW is made of cyan blue dye, it can reflect the laser beam of 780nm very strongly, and for the short-wavelength laser beam of 645nm, it will almost completely absorb, and only the single laser beam of 645nm The bald DVD is not compatible with recordable CD discs such as CD-R and CD-RW. However, the cost is the highest due to the use of double bald heads, and the servo mechanism has a double bald head switching process when reading the disk, which takes time, reads the disk slowly, and has a complicated mechanical system, which is prone to mechanical switching failures. At present, Sony and Hitachi have adopted this kind of bald technology.
This technology uses a laser head with two different laser transmitters installed inside (equivalent to integrating two optical heads together), with high technical content. Reading CD/VCD and DVD by using a set of laser pick-up signals of 650nm and 780nm wavelengths generated by a set of focusing mirrors, which further improves the reading performance and disc recognition speed on the basis of maintaining the advantages of a single-head single-focusing lens. It also eliminates the time consuming and mechanical failure caused by replacing the laser head or focusing lens. And the compatibility is good, can be well compatible with CD-R and CD-RW. This is a relatively new and comprehensive signal pick-up solution. This reading method is the most stable and advanced. Currently, Pioneer, BenQ and other companies use this technology. Take BenQ as an example, the tenth-generation DVD drive-DVP 1650P, which is launched, adopts this excellent reading technology.