CD player

CD-Spieler Frontansicht
CD player frontal view

a CD player (English. CD more player) is playing equipment for CDs. CD players serve exclusively playing audio CDs and can no other medium formats such as z. B. DVD or data CD-ROM process.

There are it in different versions:

To table of contents

fundamental function

the information on that CD are on spiral a data track in form, running from the inside outwardstored of pit and country (small recesses/increases). The changes between pit and country correspond thereby to a binary 1, pit or a country without changes correspond to binary 0 (see to structure CD). The data track becomes contactless in the CD player by an infrared laser diode with a wavelengthscanned by 780 Nm 10 Nm of the back that CD. The light reflected by that CD is taken up from an array from several photodiodes and converted into an electrical signal. Lasers and photodiodes are summarized in the scanning unit, the so-called Pickup.

structure

a CD player divides itself into two ranges:

drive assembly

drive assembly with vane drive of the Pickups, without CD load mechanics

the drive assembly covers all mechanical and electronic portions for loading and scanning that CD. The loading procedure is usually made with stationary devices by onemotor driven drawer. After complete bringing of the drawer in the CD on the drive plate one lowers and/or. the drive plate with scanning unit is lifted under the CD. With portable devices the CD usually directly on the drive plate one puts and by latches of the cover secured.
The drive that CD effected via a direct current motor, with high-quality devices also via a wear resistant electronically kommutierten engine. The driving speed is regulated by associated servo electronics.
The scanning unit (Pickup) scans the data track that CD from the lower surface and becomes radial ofinside outward moves. This Tracking movement can take place as lagging as with a record player clay/tone arm or linear. In the first case (see picture) the drive is done via a coil, which is installed at the swivel arm directly and is moved in a kreisringsegmentförmigen magnetic field. In the second case that becomesPickup shifted on two guide rods linear, the rough positioning is usually made by a rack gear with a direct current motor. This is called carriage (Sled) engine. The fine positioning is made by a moving coil drive similarly the diaphragm drive of a loudspeaker. With current CD players unfortunately that has itself due to the smaller manufacturing expenditurewear-more susceptible linear drive interspersed with direct current motor.
For the focusing of the laser beam on the information layer that CD a moving coil drive is likewise used. It moves the objective lens in the scanning unit up and downward and changes so their distance to CD.

electronics

electronics oneCD player is divided into several subranges:

current supply

the current supply makes all available to the enterprise of the equipment necessary operating voltages. A goal is about among other things to keep the mutual influence of the individual electronics ranges minimal.

all

functions are summarized control block in the control block,have with the operation and controlling of the CD player to do. In addition count the inquiry of the keyboard at the equipment and the receipt of remote maintenance signals, the controlling of the display and the drive assembly functions. One or more micro CONTROLLERs are used.

servo electronics

in a CD playerexist three automatic control loops, those independently the driving speed to that CD, the focusing of the laser (focus) and the Spurhaltung (Tracking) regulate.
The CD player plays the CD from the inside outward. The further the laser unit induces itself to the outside edge that CD, the more slowly those turnsCD, so that the peripheral speed, with which the data track is scanned, and thus the data set per time unit remain constant. The driving speed is regulated in such a way with the fact that the data stream is just as large as necessarily by following signal processing. Depending upon position those is appropriate for the scanning unitNumber of revolutions between 200 min -1 and 500 min -1.
The focus automatic control loop refers its input signals of the photodiodes accommodated in the scanning unit. By the astigmatische optics in the scanning unit focusing error shows itself and lead to an appropriate correction signal to the focusing also coil drive.
The Tracking automatic control loop receivesits input signals likewise of the photodiodes accommodated in the scanning unit. Small trace attitude errors are corrected first with the radial moving coil drive. The scanning of the spiral data track on that CD leads to constant increasing of the Tracking error; if a certain threshold is crossed, takes place radial movements of the scanning unit by means ofthe rack gear and the carriage (Sled) engine. This procedure is necessary in the distance of some seconds and by the Tracking automatic control loop is likewise controlled. In case of the vane drive for the Trackingbewegung the partitioning is void in rough and fine movement, here the complete procedure by the direct drive radial motor is taken over.

signal processing

the electrical signals of the scanning unit are first strengthened and in a FIFO buffer buffered, whose level serves as input signal for the speed regulation of the CD driving motor. Follow the error correction after the CROSS Interleaved Reed Solomon code and the extraction of the audio and the Subcodedaten.
Closethe over scanning filter, the digital analog transformation and low-pass filters on. In case of of CDs, which were produced with Höhenanhebung (Emphasis), a mirror-image sinking of the high clay/tone portion (Deemphasis) takes place, in order to repair a altogether linear frequency response. The elevator sinking becomes from a Subcodebit on thatCD automatically switched on, is however used only rarely. Afterwards the signal in similar form at the exit of the CD player is available.
Additionally the digital audio signal in the S/P-DIF format in electrical or optical form can be made available by the CD player, around a loss-free transmission to other digital audio devicesto make possible. The Serial CoPy management system (SCMS) is used in order to guarantee that only one copy generation of copyright-protected Cds can be made.

characteristics

usually the rendition that is crystal-controlled and effected CD with firm speed. There are however also CD players for DJs, with which the speed of the music can be regulated (pitchen).

Newer CDs contains CD text. These additional information, e.g. over the artist and the titles, can be indicated by an accordingly equipped CD player.

Most CD players know data and music CDs also mixedplay.

Some CD players have problems to play copy-protected CDs correctly because this CDs not the CD talk Book - correspond to standard. This applies in particular to newer CD players, who are based on PC drive assemblies.

Newer developments permit a playing of MP3 - and to similar formats. For playing DVDs are DVD players necessarily, who are similarly built in principle, however in the data density, recording techniques and formats of that CD differ.

see also

 

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