DVD Technical Notes(2) - Physical

DVD Technical Notes

Updated: July 21, 1996

Physical

Physical parameters of DVD
Disc
Data sectors
Channel codes
Disc manufacturing
Decoder stages
The trackbuffer
Disc labels

Physical parameters

Capacity
Parameter	Units	DVD	CD
max payload	GBytes	4.7 (12 cm SL) 8.54 (12 cm DL) 1.46 (8 cm SL) 2.66 (8 cm DL)	0.742 ( mode 2) 0.650 (mode 1)

Data rates
channel rate	mbit/sec	26.16	4.3218
FEC rate	mbit/sec	3.00	0.4704
user rate	mbit/sec	11.08	1.47
actual data rate	mbit/sec	10.08	1.4112

Pits and tracks
pit width	micron	0.5???	0.5
track pitch	micron	0.74	1.6
Min pit length	micron	0.40 (SL) 0.44 (DL)	0.833 to 0.972
Max pit length	micron	1.87 (SL) 2.13 (DL)	3.054 to 3.560
min pit length	-	2T	2T
max pit length	-	10T	10T

(Note: the minimum pit length for each layer of the Double layer disc is 10% greater than single layer disc. Hence the 10% less dense figure for Dual layer discs.)

Data format
sector size	bytes	2048	2352 (mode 2) 2048(mode 1)

Movement
Spiral direction		clockwise	clockwise
max revolutions/sec	Hz	25.5 (12 cm disc)	8 (12 cm disc)
min revolutions/sec	Hz	10.5	3.5
Reference scanning velocity	m/s	3.49 (SL) 3.84 (DL)	1.2 to 1.4

Optics
wavelength	nm	650 or 635	790
Numerical Aperture of Objective Lens	-	0.60	0.45
refractive index	-	1.55	1.55
Spot Size (lambda/NA)	-	0.63	1
Focus Depth (Focus Margin, lambda/NA^2)	-	0.47	1
Chromatic Aberration (Title margin, lambda/NA^3)	-	0.35	1
Spherical Aberration (Thickness Tolerance, lambda/NA^4)	-	0.26	1
Reflectivity	%	70 minimum (SL) 25 to 40 (DL)	70 minimum

Mass
Thickness of substrate	mm	0.6	1.2
disc thickness	mm	1.2	1.2
disc mass	grams	13 to 20 (12 cm) 6 to 9 ( 8 cm)	14
Thickness of spacing layer in Dual Layer	micron	40 to 70	N/A

FEC
Error correction	method	RS product code	CIRC
FEC consumption	%	13	25
FEC format	bytes	(208,192,17)x(182,172,11)	(28/32)x(24/28)
Sector constraint length	-	16 (=32 Kbytes)	1
correctable burst length	mm	6.0 (SL) 6.5 (DL)	2.5

Channel code
Channel modulation	method	8/16 (EFM+)	8/14 + 3 merge bits
Run length	bits	(2,10)	(3,11)

Diameters
outer	mm	120 (12 cm) 80 (8 cm)	120
outer lead in	mm	117 (12 cm) 78 (8 cm)	117
outer data	mm	116 (12 cm) 76 (8 cm)	116
inner data	mm	48 (12 cm) 48 (8 cm)	50
inner lead in	mm	45 (12 cm) 45 (8 cm)	46
center hole	mm	15 (12 cm) 15 (8 cm)	15

---

Disc Areas

Recording order on the disc (Track Structure)

===============================================



Legend:

  I     Lead-in area (leader space near edge of disc)


  D     Data area     (contains actual data)


  O     Lead-out area (leader space near edge of disc)


  X     un-usable area (edge or donut hole)


  M     Middle area (interlayer lead-in/out)


  B     Dummy bonded layer (to make disc 1.2 mm thick instead of 0.6mm)



Single layer disc:

  direction: continuous spiral from inside to outside of disc.



       |   ----------------------->


       |BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB     outer edge 


       |XXIIIDDDDDDDDDDDDDDDDDDDDDOOOXX     of disc


       |



      reference

      axis



Dual layer disc:



  (A) Parallel track path (for computer CD-ROM use)

    Direction: same for both layers.                     

    

          ----------------------->


        XXIIIDDDDDDDDDDDDDDDDDDDDDOOOXX    Layer 1


        XXIIIDDDDDDDDDDDDDDDDDDDDDOOOXX    Layer 0


          ----------------------->


                         



  (B) Opposite track path (for movies)

    Direction: opposite directions 

     Since the reference beam and angular velocities are the same

     at the layer transition point, the delay comes from refocusing.  

     This permits seamless transition for movie playback.

    

          <----------------------


      XXOOOODDDDDDDDDDDDDDDDDDDDDMMMXX    Layer 1


      XXIIDDDDDDDDDDDDDDDDDDDDDDDMMMXX    Layer 0


          ----------------------->

Sectors

Data Sector Configuration

The 2064 byte sector is, for purposes of error correction, organized into 12 separate rows, each with 172 bytes. The first row starts with the 12 Byte sector header (ID, IEC, Reserved bytes), followed by the remaining data bytes. The following 10 rows contain only data. The final row is punctuated with a 4 Byte field (EDC).

Row                           Fields within row


--- ----------------------------------------------------------------------


 0  ID (4B) IEC (2B)  RESERVED (6B)  Main data  (160 Bytes: D[0] - D[159])


 1               Main Data (172 Bytes: D[ 160] - D[ 331])


 2               Main Data (172 Bytes: D[ 332] - D[ 503])


 3               Main Data (172 Bytes: D[ 504] - D[ 675])


 4               Main Data (172 Bytes: D[ 676] - D[ 847])


 5               Main Data (172 Bytes: D[ 848] - D[1019])


 6               Main Data (172 Bytes: D[1020] - D[1191])


 7               Main Data (172 Bytes: D[1192] - D[1363])


 8               Main Data (172 Bytes: D[1364] - D[1535])


 9               Main Data (172 Bytes: D[1536] - D[1707])


10               Main Data (172 Bytes: D[1708] - D[1879])


11        Main Data (172 Bytes: D[1880] - D[2047])           EDC (4B)



 ID:  Identification Data (32-bit sector number)

 IEC: ID Error Correction

 EDC: Error Detection Code

From the original Toshiba DVD proposal (circa Spring 1995), the following three items changed:

sector information in ID

EDC Generation Method

Initial Value of Main Data Scrambling

EEC Block Configuration

To combat bursty errors characteristic of CD-ROM, 16 sectors are further interleaved together, forming a block of 192 rows (16 sectors * 12 rows/sector = 192 rows). Error correction bytes are concatenated to the data block in a 2-dimensional fashion (hence the term "product" in the phrase "Reed-Soloman product codes").

Specifically: at the end of each row, 10 bytes of RS data are added, hence the RS(182,172,11) vector. At the end of the block, 16 rows of RS data are added (hence the RS(208,192,17) vector). Therefore out of 37,856 total bytes (182*208) for the interleaved block of data, only 33,024 bytes (192*172) or roughly 87% is payload.

   <-----  data block -----------> <---------- P1 -------------->




D  B[  0][  0] ...   B[  0][171]  |  B[  0][172] .... B[  0][181]


a  B[  1][  0] ...   B[  1][171]  |  B[  1][172] .... B[  1][181]


t  .                              |


a  .                              |


   .                              |


   B[190][  0] ...   B[190][171]  |  B[190][172] .... B[190][181]


   B[191][  0] ...   B[191][171]  |  B[191][172] .... B[191][181]


   --------------------------------------------------------------


   B[192][  0] ...   B[192][171]  |  B[192][172] .... B[192][181]


   .


P  .


0  .


   B[207][  0] ...   B[207][171]  |  B[207][172] .... B[207][181]





  P0: RS(182, 172, 11)

  P1: RS(208, 192, 17)

EFM

8/16 Modulation

The lowest layer of the communications channel is the 8/16 channel code, which helps reduce DC energy (illegal run-lengths of '1' or '0' bits), effectively lowering the SNR threshold for the pickup signal. Although half the channel rate is doubled thanks to the 8/16 code, the overall user throughput for the desired uncorrected rate of 1x10^-3 is greater because of it. The advantage of the 8/16 code is:

Small DC component

No merge bits (Red Book)

Applicable RAM

Simple decoding circuits

From 16 channel bits, 8 user data bits are produced.

Disc Manufacturing Technology and Equipment

Source: Nimbus

DVD Laser Beam Recorder

with respect to CD, DVD only requires changes to recorder mask.

Ultra violet laser, argon ion

Wavelength of 351 nanometres

c.5000 hours lifetime

final objective lens, n.a. 0.9

secondary focusing

aperture for CD mastering

spot beam focus checker is mot critical part.

yield rate for DVD (SS/SL): 90%

Operation in DVD or CD mode

Identical glass preparation and chemicals

universal lenses

switchable aperture

secondary focusing

elliptical spot for CD mastering

Elliptical spot:

reduces resolution across track

maintains DVD resolution along track to improve control of pit ends.

Production:

200 - 300 master titles per month

1.2 - 1.5 million stamped discs per month

Decoder

Flow of Data in player:

[Notes from Hitachi presentation]

Stage 1: SYNC detection, 8/16 Demodulation, ID Detection.

A total of 8 sync codes are inserted into the 8/16 modulated channel bitstream representing the current physical sector. Sync code words are unique in the 8/16 code table (so they cannot be generated by the 8-to-16 mapping).

The Detection stage looks for sync codes in order to determine where sectors begin and end. Here the channel bit rate input to this block is 26.16 Mbits/sec, and output is 13 Mbit/sec.

Stage 2: Error detection and correction

If the check bits (EDC) don't match the fingerprint of the unscrambled data, the Reed Soloman bytes (IEC) are used to attempt error correction of the corrupted data. Here the channel rate output by this block is 11.08 Mbit/sec (~2 Mbit/sec of error correction parity data, IEC, has been stripped).

Stage 3: Descramble/Decrypt

Data on the disc is descrambled for purposes of further DC energy reduction. Decryption is performed for purposes of copy protection.

Stage 4: EDC Check

The fingerprint of the unscrambled data is checked against the EDC code to verify whether the data was correctly descrambled.

Stage 5: Track buffer

This FIFO (First In First Out buffer) maps the constant user data bit rate of 11.08 Mbit/sec to the variable bit rate of the program streams. DSI and PCI packets (used to control the behavior of the player) are stripped yielding a 10.08 mbit/sec rate into the MPEG systems decoder. The mux_rate of all program streams is 10.08 mbit/sec regardless of actual elementary stream rates.

Stage 6: Transfer to MPEG system decoder.

Packets are demultiplexed in the system decoder, and distributed to the respective elementary stream decoders (video, audio, subpicture, VBI).

Track Buffer

The size of the track buffer is left to the implementation, although the minimum recommended size is 2 Mbit. This is computed as: B > Tmax * VBRmax = 0.104 sec * 10.08 Mbit/sec

Tmax is the maximum latency of one disc revolution, and VBRmax is the maximum mux rate for any Program.

In some systems, the Track Buffer and the MPEG STD/VBV (System Target Decoder/Video Buffer Verifier) may be combined.

Seamless playback illustration

Input stream to Track Buffer:

  Time


  ---->           n: sector number   




                      |<------- T --------->|


  [n-3][n-2][n-1][  n]   ... track jump ...  [m  ][m+1][m+2][m+3][etc.]




                     (no data transfer during


                           discontinuity)









Corresponding output from Track Buffer:



    Initial buffer


    delay introduced by track buffer


  |<--------->|


               [n-3][n-2][n-1][  n][m  ][m+1][m+2][m+3][etc.]


                                  ^^


                                   no apparent discontinuity


                                   from perspective of MPEG Systems


                                   decoder.

The memory size needed for seamless playback control can be computed as:

T * VBR = 0.25 seconds * 8 Mbit/sec = 2 Mbits

This is of course implementation-dependent. T here is them maximum jump distance (10,000 sectors).

Disc Labeling

[from Warner Advanced Media Operations]

Labeling can be similar to standard CD labels or one of three new types:

Reverse Printing: underside of blank 0.6mm clear substrate provides unique wet look and additional protection

Mastered in Graphics: by transferring images directly to the glass master ensuring 100% yield.

Laser Scribed Titles: on stampers, Image added right at press.

DVD Doubled Sided Disc Label solution:

The inner radius of DVD is smaller than regular CD's (to improve areal utilization of disc, hence capacity). This favors the outer edge.

labels are printed along outer 5mm edge of disc.

  Label                         Angular arc size

  --------------------------    --------------------

  Movie Title Information:      217 degrees

  Disc ID Code:                  57 degrees

  Side:                          25 degrees

  Company:                       29 degrees

  Gaps between above labels:      8 degrees x 4 gaps