WO1997028530A1 - Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or pre-formatted discs - Google Patents
Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or pre-formatted discs Download PDFInfo
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- WO1997028530A1 WO1997028530A1 PCT/CA1997/000069 CA9700069W WO9728530A1 WO 1997028530 A1 WO1997028530 A1 WO 1997028530A1 CA 9700069 W CA9700069 W CA 9700069W WO 9728530 A1 WO9728530 A1 WO 9728530A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
- G11B19/20—Driving; Starting; Stopping; Control thereof
- G11B19/24—Arrangements for providing constant relative speed between record carrier and head
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/14—Digital recording or reproducing using self-clocking codes
- G11B20/1403—Digital recording or reproducing using self-clocking codes characterised by the use of two levels
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/02—Editing, e.g. varying the order of information signals recorded on, or reproduced from, record carriers
- G11B27/031—Electronic editing of digitised analogue information signals, e.g. audio or video signals
- G11B27/034—Electronic editing of digitised analogue information signals, e.g. audio or video signals on discs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
- G11B27/102—Programmed access in sequence to addressed parts of tracks of operating record carriers
- G11B27/105—Programmed access in sequence to addressed parts of tracks of operating record carriers of operating discs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
- G11B27/11—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information not detectable on the record carrier
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
- G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
- G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
- G11B27/28—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording
- G11B27/30—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on the same track as the main recording
- G11B27/3027—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on the same track as the main recording used signal is digitally coded
- G11B27/3063—Subcodes
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
- G11B27/36—Monitoring, i.e. supervising the progress of recording or reproducing
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/14—Heads, e.g. forming of the optical beam spot or modulation of the optical beam specially adapted to record on, or to reproduce from, more than one track simultaneously
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B2220/00—Record carriers by type
- G11B2220/20—Disc-shaped record carriers
- G11B2220/21—Disc-shaped record carriers characterised in that the disc is of read-only, rewritable, or recordable type
- G11B2220/215—Recordable discs
- G11B2220/218—Write-once discs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B2220/00—Record carriers by type
- G11B2220/20—Disc-shaped record carriers
- G11B2220/25—Disc-shaped record carriers characterised in that the disc is based on a specific recording technology
- G11B2220/2537—Optical discs
- G11B2220/2545—CDs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B2220/00—Record carriers by type
- G11B2220/60—Solid state media
- G11B2220/65—Solid state media wherein solid state memory is used for storing indexing information or metadata
Definitions
- This application relates to optical recording and/or reading apparatus, collectively referred to as an optical drive.
- Constant Linear Velocity (CLV) optical record carrier bodies such as Compact Discs (CDs)
- CDs Compact Discs
- a spiral track pattem which is typically read by scanning with a focused laser spot of approximately 800 to 1000 nm in diameter measured at the so- called "50% power radius".
- the spot is scanned along the path of a spiral track composed of data marks at a constant linear velocity, (e.g. either 1.4 or 1.20 m/sec in the CD system).
- CLV systems exploit this uniform scanning rate to increase data density by using a marking strategy known as Uniform Spatial Density (USD) by which data is recorded using marks of standardized lengths or channel bits which are typically organized in frames or data blocks of uniform length.
- USD Uniform Spatial Density
- This strategy typically requires that CLV systems vary the spindle rotation rate in order to scan tracks formed at different radii.
- the spindle of a Compact Disc (CD) player rotates at approximately 8 revolutions per second (rps) while scanning the innermost part of a CD's data area and slows in a measured way, maintaining a constant linear velocity, to approximately 3.3 rps when scanning the outermost turns of the spiral track.
- the constant linear velocity maintains a uniform frame rate and a constant channel bit rate of 4.3218 MegaHertz (MHz) throughout the entire 5.7 km length of the track.
- Such control of rotation and scanning rate is typically accomplished by recovering a clock frequency from the data recorded in the track and synchronizing the scanning rate with a clock crystal by means of a phase-locked loop. It is well known that as a result of this arrangement, conventional CLV players and recorders can only operate one head at a time for recording or reading because only one point on the disc will have the rotation rate required to produce the requisite linear velocity.
- Optical data track patterns are most often formed on truly featureless blank discs by so-called "mastering" machines which resort to various rotary encoders and linear translation systems which are precisely coordinated by one or more microcomputers.
- mastering machines which resort to various rotary encoders and linear translation systems which are precisely coordinated by one or more microcomputers.
- CD-R or CD-RECORDABLE
- CD-R or CD-RECORDABLE
- CD-R employs a pre-grooved track across the entire data area of the disc which is used to control its servosystems.
- the "track" of this recordable record carrier body takes the form of a spiral groove pattern which can be readily followed by the optical head of a CD-R recorder, guiding it to form an appropriate data spiral.
- This preformed spiral track is typically a groove formed to a depth of one-eighth the wavelength of the scanning laser spot (typically 1/8 of 780 nm). Also, this groove is formed typically so that it incorporates a radial wobble on die order of +/- 100 nm or less, which, when scanned at the specified linear velocity can be detected as a clocking pattern typically on the order of 22 kiloHertz (kHz).
- Detection of this wobble serves as an indication of linear velocity and the wobble frequency can be synchronized with a much faster data clock during record operations.
- the groove may also be characterized to facilitate detection by a side beam formed by passing the spot through a diffraction grating but otherwise focused and positioned normally which is commonly employed in the method known as "3-beam tracking".
- STOL Self Timing Optical Lathe
- One form of STOL utilizes a separate timing track or encoder disc having reference marks corresponding to a clock cycle at a correlated location on the data carrier. In this manner, the disc may be operated at constant angular velocity (CAV) but a timing signal may be derived for each position of a head.
- CAV constant angular velocity
- the speed of operation of a single optical head is limited by two key factors - namely, the opto-mechanical limit, i.e. the capacity of known tracking and focus actuators to execute the requisite repositioning and refocusing of the spot as track velocities increase, which limits both reading and recording apparatus, and the modulation limit, i.e. the speed at which laser diodes may be pulsed under sufficient control to form satisfactory marks, which limits recording operation.
- the opto-mechanical limit i.e. the capacity of known tracking and focus actuators to execute the requisite repositioning and refocusing of the spot as track velocities increase, which limits both reading and recording apparatus
- the modulation limit i.e. the speed at which laser diodes may be pulsed under sufficient control to form satisfactory marks, which limits recording operation.
- the disc is uniquely inserted each time it is read or written to. Inevitably, this means that the track pattern on the disc will be more or less eccentric, and, typically, this eccentricity will produce the largest component of tracking error encountered by
- the present invention provides an optical drive to record to and/or read from a data carrier optical data recorded as an optically detectable pattem of marks modulated in at a uniform spatial density.
- the data carrier is rotatable about an axis and a plurality of optical heads are circumferentially spaced about said carrier.
- Each optical head is radially adjustable relative to the carrier to scan said data carrier and has a clock recovery circuit associated with it to recover a clock signal from data processed by the optical head.
- a plurality of parallel data streams may be processed to enhance the cumulative data transfer rates.
- one of said clock signals is used to control rotation of said carrier and maintain said clock signal at a predetermined frequency.
- said clock signal is derived from a timing track conjointly rotatable with said carrier and providing a clock signal correlated to the radial position of each of said heads.
- a pattem is utilized that provides a course clock signal with intermediate clock signals inte ⁇ osed between said course clock signals.
- the intermediate clock signals are preferably structured to accommodate the interrogating beam between the pattem.
- each head assembly By providing each head assembly with a clock recovery circuit, individual data streams may be recorded and/or recovered and subsequently utilized. Where a separate timing track is utilized, the clock recovery may be enhanced by utilizing a specific timing pattem that matches the characteristics of the interrogating beam.
- FIG. 1 is a plan view of an optical disc drive and data carrier
- Figure 2 is a side elevation of the drive shown in Figure 1 ;
- Figure 3 is a plan view showing the configuration of a data carrier and data encoding pattem
- Figure 4 is a plan view similar to Figure 1 showing the relationship of the optical disc to a single recording/reading head;
- Figure 5 is schematic representation of a data structure used on the disc and data encoding pattem
- Figure 6 is a schematic circuit diagram showing the extraction of the clock cycle from the data encoding pattem.
- Figure 7 is a schematic diagram of a control for the motor shown in Figure l;
- Figure 8 is a further embodiment of the control for the motor shown in
- Figure 9 is an alternative embodiment of the control for the motor shown in Figure 1;
- Figure 10 is a schematic illustration of a data recording arrangement
- Figure 11 is a schematic side elevation of an alternative arrangement of encoding disc.
- Figure 12 is a side view showing a further form of encoding disc.
- an optical data carrier 10 has a data carrying area 12 located between radially inner and outer extremities 16.
- Carrier 10 includes a central hole 11 and an outer periphery 13 to conform to standard physical dimensions for an optical data carrier and data is stored on a spiral track 14 as a series of pits and lands that represent sets of data channel bits and which are combined as frames of predefined format as is well known.
- An encoding disc 20 is located radially outwardly of and concentrically with the carrier 10 and is formed as a permanent part of an optical drive 17 that may both record and read data on the track 14.
- the drive 17 includes a motor 19, support platen 18 and spindle 21 as will be described more fully below.
- Disc 20 is inco ⁇ orated into the platen 18 so that data carrier 12 and disc 20 are generally concentric to the spindle 19.
- the encoding disc 20 has an encoding area 22 located between inner and outer extremities 25 that has the same radial extent as the data carrying area 12.
- the encoding area 22 is formed with an optically addressable spiral track 29 having a pitch corresponding to the pitch of the track 14 and carries timing marks having a direct relationship to the length of track 14 occupied by sets of channel bits.
- the length of track 14 occupied by one frame or data block remains constant along the track.
- the track 29 is offset radially relative to the data carrier 10 the length of each mark on the track 29 will be factored relative that on the data carrier by the ratio of the radiuses.
- the angular rotation of the data carrier 10 necessary to scan one channel bit of track 14 will correspond to the angular rotation necessary to read a timing mark corresponding to one channel bit on track 29.
- the timing mark may b scanned to derive a waveform of sufficient precision to derive a timing signal related to the fundamental channel bit length of the data signal.
- the signal derived from track 29 is called a "pseudoclock" and, as it is a physical measurement of rotation that is encoded in a manner which corresponds to each track rotation to be recorded on the target disc, it serves as an alternative means of measuring channel bit length which is independent of the track scanning velocity.
- a data carrier 10 bounded by an outer radius R 4 and an inner radius R 7 in Figure 3 is recorded with a spiral track 14 in the data area 12 lying between radius 22.5 mm and radius 57.5 mm.
- a pseudoclock pattem in the form of spiral track 29 on the encoding area 22 is offset radially 47 mm from the position to define an annulus between the extremities 25 having approximate radii of 64 mm and 114 mm respectively.
- the track 29 has the same spiral pitch (1.6 ⁇ m) as that of track 14 of the data carrier to be recorded and is marked off in circumferential sections which correspond to the rotation necessary to scan each relatively offset CD data frame. In this manner, every CD frame on track 14 has its own correlated radially offset frame on the track 29.
- Each offset frame may be further divided into a plurality of offset marks which can be used to measure an appropriate circumferential location for any combination of the potential pit land transition points which may be encoded on data on the track 14.
- arc 7 on the spiral track 29 can be seen to be a radial offset of arc 8 representing a frame on track 14 and it can be understood that each channel bit in the entire data pattem to be recorded in the CD data area 12 has a corresponding location on the track 29.
- the form of data pattem employed on the track 14 and track 29 is shown in
- each frame as represented by arc 8 includes a pair of synchronizing blocks 27 each formed from 11 channel bits having track length Tc.
- the synchronizing blocks 27 are followed by a subcode block 28 formed from 14 channel bits and 3 merging bits and a data block 30 configured as a series of data words formed from channel bits.
- Each frame therefore includes 588 channel bits.
- the corresponding frame on the track 29 is shown as Figure 5b where the segment Tec represents the length of track 29 corresponding to the channel bit Tc at the offset radius.
- the track 29 is formed with synchronizing blocks 62 followed by a subcode block 68 and a data block 30a which is formed with a uniformly repeating pattem to provide a repetitive clock-like signal. Rotation of the support platen 18 to scan one channel bit Tc will cause a corresponding rotation of the encoder disc 20 to scan the radially offset channel bit Tec.
- scanning of the pattem on track 29 can yield a measure of all required pit/edge locations on the track 14 regardless of scanning rate.
- a plurality of head assemblies 33 are circumferentially spaced about data carrier 10.
- Each head assembly 33 which is shown in greater detail in Figures 2 and 4, is radially movable in a support 32 and its position is monitored by a position sensor 31.
- Each head assembly 33 includes a pair of optical heads 34,36 which are spaced apart a fixed distance corresponding to the radial spacing of the inner extremity 16 of the data carrying area 12 and the inner extremity 25 of the track 29 area.
- the two heads 34.36 are mounted on a common radial support 32 and their position can be manipulated by a coarse positioning actuator 35.
- Both optical heads 34,36 are equipped with a fine positioning/focusing actuator typically referred to as a two-dimensional actuator (or 2-d actuator) such as is well known in the art.
- the head 36 is a READ/WRITE head which addresses the data carrier 10 and the head 34 is a tracking and timing head which addresses the track 29.
- the READ/WRITE head 36 may be capable of Read-After- Write operation or of simply reading data already recorded on the target disc by reference to the pseudoclock.
- Initial adjustment of the offset between heads 34,36 of the head assembly 33 is obtained by moving the two heads 34,36 to address two offset alignment tracks 50,51 formed on inner and outer peripheries of the encoder disc 20.
- the tracks 50,51 are radially spaced by the offset between a track on the disc 10 and the corresponding track on encoder 20. This provides an initial alignment for the heads 34,36 prior to reading respective patterns.
- the alignment tracks 50,51 are recorded as track pattems radially offset from the other and recorded on the encoder disc 20 as part of the recorder 17. As the encoding disc 20 and the data carrier 10 are co-rotated on the spindle
- the two optical heads 34,36 scan the tracks 29,14 respectively. For each radial position of the head 36 on the data carrying area 12, the head 34 is located at a correlated location on the encoding area 22 and the timing mark recorded at that location on track 29 is used to demodulate the data. Assuming that the carrier 12 has data recorded, as the data carrier 10 is rotated, each head 36 will read the corresponding portion of the data track 14. A timing signal will be obtained from the head 34 scanning the encoder track 29 and the data stream demodulated as described with reference to the circuit shown in Figure 6.
- pseudoclock reference is a measure of spatial positioning along the spiral rather than a time-based clock signal, it permits a number of heads to be operated at the same time at different radii with different and varying linear scanning velocities and provides an appropriate demodulating clock signal for each location.
- the pit pattem formed by a single offset data frame on the track 29 as shown in Figure 5b is an idealized representation of the electrical signal produced by the photodiodes associated with the optical head 34 while scanning the pit pattem on track 29 on the encoding disc 20 with a focused laser spot.
- the signal read from track 29 on the encoder disc 20 is fed to a clock pit extraction circuit 48 which can identify the synchronization blocks 62 directly or by means of run length violations.
- Such a clock pit extraction produces a signal such as that shown in Figure 5c.
- the extracted clock pit signals are then fed to a clock synchronization circuit such as that shown schematically in Figure 6.
- the output of extraction circuit 48 is fed to a phase detector 50 before passing through a low pass filter 54 to a voltage controlled oscillator 55.
- the VCO 55 is coupled to a divide-by-n counter 56 which is in turn linked to the phase detector 50. In this manner, the frequency of the VCO 55 can be controlled so as to produce a pseudoclock output which is equal to, or a multiple of the local channel bit rate associated with any given frame.
- the output of VCO 55 is applied to the demodulation circuit 57 that also receives data from the track 14.
- a clocking signal is provided that is representative of the channel bit length at that location and the linear velocity at which the record is being scanned by that specific head.
- the clocking signal is applied to the data stream recovered from the track 14 by the associated head 36 to recover the channel bit stream.
- Each head is therefore able to recover from or record to data recorded on the track 14 of carrier 10 and provide multiple data strings that can be combined serially or processed in parallel.
- the VCO circuit may also inco ⁇ orate a secondary phase comparison circuit indicated at 58 which can detect the pattem produced by scanning the pseudoclock pattem between the synchronization marks and such a circuit may further refine the frequency- control of the VCO 55 so as to keep it more closely aligned with the linear track velocity and hence improve pit location and measurement on the target disc.
- Such systems may be further refined by resort to circuits employing various digital filtering techniques including application specific digital signal processors in procedures which are genetically referred to as PRML, (partial -response maximum-likelihood), channels, and, by variations on such approaches which are referred to as Adaptive PRML.
- Such techniques are particularly useful for resolving Inter Symbol Interference, (ISI) by inco ⁇ oration of a sample detection scheme which typically filters analog read-out data once per clock cycle as opposed to traditional continuous-time zero- crossing detection.
- ISI Inter Symbol Interference
- Such a system typically detects so-called "Channel Samples” and employs them in a digital filtering scheme whereby each analog sample from the read-out signal is compared once per bit time with each adjacent sample.
- a number of existing schemes for discriminating analog data pattems from ISI and other forms of interference have been demonstrated and may be employed here.
- Such systems have been employed in both conventional magnetic hard drives and in magneto optical drives in configurations which call for enhanced data recovery due to ISI and essentially enhance retrieval of data.
- such means may be employed to enhance recovery of the linear track reference whether it is encoded on the target disc or on a displaced encoder disc.
- non-linear pseudoperiodic circuits such as those disclosed in various papers, notably by T.L. Carroll and L.M. Pecora of the Naval research Lab in Washington D.C. disclose techniques by which to cascade synchronized chaotic systems in what they have termed the "chaotic analog to a phase locked loop", may be adapted for use in synchronizing the linear track position by locking the recovered frequency pattem detected by the scanning optical head from the encoder disc 20 to a VCO frequency.
- an offset timing track 29 with the conventional CLV characteristics to support multiple head operation.
- the pit pattem is enhanced in order to improve the clock recovery for multi-head operation.
- Analysis of the requirements of the multi-head machines indicates that while conventional CD pit pattems are sufficient to derive the timing signal during CLV operation they do not provide optimal pseudoclock data for timing multi-head operations.
- the frame synchronization marks can be phase-locked to a crystal clock and the product of a divide by 588 counter can thus be stabilized to produce a working clock signal.
- a crystal clock cannot be employed.
- the problem is tied to geometry. If the outermost head is scanning or writing between radius 49 mm and radius 58 mm the change in linear scanning velocity for the innermost head scanning between radius 22.5 mm and radius 31.5 mm during the same operation will change dramatically. As a direct consequence, the clock rate of the data varies dramatically as well because in a CLV system the clock rate is a constant relative to track velocity. In the case described above, the linear velocity and the spatially demarcated clock signal change on the order of 20% during the period that the 9 mm of tracks are scanned. Similarly, if the clocking signal is tracked by a Voltage Controlled Oscillator (VCO), the VCO must be able to recover a pseudoclock signal over a range of about +/- 9% around its center frequency.
- VCO Voltage Controlled Oscillator
- VCO loop must be made unacceptably “loose” if it is to follow the variations in scanning rate using a reference pattem as diverse as a normal EFM pit pattem. It would appear that there is simply not enough clocking or, more precisely, enough detailed linear positional data in a conventional EFM pattem with which to operate conventional circuits.
- This limitation is a direct function of the limited degree to which the clock content expressed in an EFM pattem can be used as a linear track encoder.
- EFM code like any optical data recording pattem employs a data slicing technique which requires a long integrator in the circuit in order to determine the so-called "zero-crossing" point or "slicing level" which marks a transition from a pit to land.
- This operational parameter is a function of the DC balancing of the pit/land pattem which uses a comparatively crude measure known as the "Zero Sum Factor".
- the track 29 has the following characteristics.
- the accuracy with which the pits can be scanned is a function of the size of the pits relative to the size of the laser spot, or, more precisely, the size of the 50% power radius of a focused spot.
- the smallest pit or land is approximately 890 nm in length and the 50% radius of the focused spot (which has a wavelength of 780 nm) is on the order of 1000 nm.
- analog scanning techniques eg. continuous-time zero-crossing
- This maximum contrast occurs with pits or lands which are on the order of 1800 nm or larger because the light within the 50% power radius of the focused spot no longer spills over from one feature to another but, rather, is fully on or off such a feature.
- the transition point can be more reliably detected despite normal operational limitations caused by momentary defocusing of the spot, comat error, etc.
- the pit pattem on track 29 is predominantly composed of pits of 1800 nm or more in length. This dramatically enhances the capacity of the optoelectronic circuits to detect transitions.
- the track for the most part, avoids the use of Offset 1-3 marks because for the most practical offset pattem formations such marks are shorter than 1800 nm. More generally, the pits have a length when measured in the direction of the track 29 greater than the 50% power radius of the focused spot.
- each radially offset frame indicated at 60 is a radial offset of a 588 Channel Bit CD frame.
- the head of each frame is composed of a radially offset pattem of one synchronization block 62 (composed of one 11 -clock cycle pit 64 and one 11 -clock cycle land 66) followed by a sub-coding block 68 made up of a combination of pits and lands such that the block 68 will not be longer than 14 clock cycles.
- the subcoding block 68 typically contains serial data which encodes address information.
- the balance of the frame 60 is composed of 138 pit/land pattems 70, each a radial offset of 4 channel bits. In sum, each frame will contain 588 offset channel bits (OCB) in the following pattem:
- the recovery of the clock signal is further enhanced by using a specialized subcode pattem in the subcode block 14.
- the DC content of the photodetectors used in optical scanning never goes through zero because some light is always reflected from the lands between adjacent passes of the track and the portions of the spot which, though below the 50% power level, nevertheless spill over into the lands between pits.
- This is ameliorated in the in-track direction, (what is referred to as "inter symbol interference” or ISI), by the comparatively large scale of the features of track 29 but only to a limited degree transverse to the track because the track pitch of 1.6 ⁇ m is identical to that employed on standard CLV devices which produces comparable cross talk and reflection from the lands between tracks.
- An active "data sheer” is used to determine the zero crossing level between a pit and a land in a manner comparable to that employed in a conventional player.
- each track stmcture will be self balanced, that is, there are an equal number of offset channel bits forming the pits and lands in each pattem as follows:
- the subcode block contains address information and requires a total of 12 pit land pattems to produce 2 Subcoding sequence pattems (SI and SO) which denote the start of blocks of sequential data, and 10 self-balancing data words each of which represents a number.
- SI and SO Subcoding sequence pattems
- the following is only one possible version of such a self-balancing code.
- the important features are that whatever pattem is employed should be self-balancing with respect to pit/land lengths, and, should be reasonably efficient so as not to unduly reduce the total length of data block 30a available as offset pseudoclock reference within each channel bit frame.
- the self-balancing code is expressed as two characters: the first a numeral; the second either a "P” or an "L".
- the numeral indicates the number of clock cycles required to scan the feature at normal CLV and the P and L represent whether the feature is either a Pit or a Land respectively.
- S 1 for example, is described as "7P/7L” meaning it is the radial offset of a pattem of a pit 7 standard CLV Channel Bits in length and a land 7 standard CLV Channel Bits in length which, when scanned would have a "Zero Sum" as such a conditional DC balance is usually described:
- the conventional compact disc system groups the 588 bit frames into blocks formed from 98 frames or 57,624 channel bits. This not only provides 98 subcode blocks 68 in each block but the recovered address used in conjunction with a frame counter and, if desired a channel bit counter, can be used to resolve the address of every channel bit edge over the entire 5.5 km of track to a resolution of +/- 50 nm.
- the preferred embodiment only requires six pattems in the subcode to identify an address, there is ample room within the serial data structure of 98 frames to build redundancy which will protect against error.
- the preferred embodiment includes provision for such redundancy in the following manner: 1.
- the first subcoding mark, S 1 followed in the next frame (i.e., 588 channel bits later) by the second subcoding mark, SO. indicates the start of a subcoding sequence.
- ⁇ e subcode sequence will reverse such that SO precedes S 1 to signal the beginning of a redundant series.
- the Compact Disc system utilizes one of two linear scanning rates, the first being 1.4 meters per second and the second being 1.25 meters per second, (m/sec). Both systems are designed to be demodulated by conventional devices using a phase-locked loop and crystal clock running at 4.3218 MHz or some multiple thereof conventionally referred to as 2x, 4x. etc.
- the difference between the standards is strictly linear:
- the 1.25 m/sec tracks employ 588 Channel Bits per Channel Bit frame but use proportionately smaller patterns. This means that 1.4 m/sec marks are proportionally longer as 1.25 m/sec marks.
- a pattem formed on track 29 to a 1.4 m/sec standard as a linear encoder in order to stabilize the generation of a frequency suitable for a m/sec recording operation.
- a frequency converter 70 is included to convert the scanned pseudoclock signal/derived VCO frequency such that 112 clock cycles are generated for each 100 recovered cycles of pseudoclock data formed at an offset at 1.4 m/sec.
- the data recovered from track 14 may therefore be demodulated at the required frequency.
- the frequency conversion may be accomplished in one of a number of known manners and is, of course, switchable upon the standard being detected.
- a 1.25 m/sec subcoding channel can employ such a sequence start mark at the same point in the 1.4 m/sec sequence once every 28 frames, after which sequence initiation the serial data may be encoded in that sequential position relative to subsequent 1.4 m/sec sequential data.
- a circuit which compares the relative frame counts can provide a further redundancy check and/or 1.25 m/sec positional address as desired.
- the self-balancing code discussed above with respect to Figure 7 also makes it possible to refine the control of the data sheer circuitry and hence to more accurately measure pit/edge locations.
- This in rum facilitates the recovery of a more precise pseudoclock signal by means of a primary phase-locked loop which acquires coarse synchronization of a VCO frequency with that of the recovered pseudoclock signal from the disc.
- This is implemented as a circuit which recognizes the I- 11 synchronization blocks 62 and pulls the VCO frequency into approximate phase using a divide-by-588 counter. Once this has been accomplished an edge triggered phase-detector corrects for phase by comparison of the VCO frequency and that derived from the 1-4 clock pattem which comprises the bulk of each frame.
- the edge comparison continuously adjusts the frequency produced by divide-by-588 counter, keeping it fine tuned relative to the pseudoclock recovery signal.
- the divide-by-588 signal produced by the divider is maintained continuously so it functions, in effect, as a "flywheel" during the periods when synchronizing and address bits are being recovered.
- the pseudoclock recovery circuit may also incorporate a programmable resistor which can be employed to adjust the phase-locked loop parameters in such a way that the VCO center frequency can be adjusted electronically to maintain "tighter" loop operations.
- the subcode addresses are recovered using the circuit of Figure 6. As the pseudoclock VCO frequency becomes finely locked, it is applied to the subcode demodulation component 84 of the circuit. A subcoding sequence is detected by pattem recognition circuit 86 enable by the frame pulse 82. When subcoding blocks SI and SO appear in the 14 Channel Bit space reserved for subcoding data in two successive frames, the circuit begins to assemble in register 88 the serial data which comprise the address. Each successive subcoding block is measured by comparison to the pseudoclock VCO frequency.
- Pattem recognition 88 Recognition of a specific subcoding pattem by pattem recognition 88 results in the storage of an 8-bit digital word in register 88.
- the register signals the system controller, preferentially a microprocessor, that a frame address has been received.
- the controller is then enabled to poll the register 88 in order to retrieve the address.
- the circuit is driven asynchronously by the recovered pseudoclock signal from VCO during its READ operations and is configured so as to deliver address data out to a system microprocessor as required. Provision may be made so that data being retrieved will be reclocked to conform with a standard crystal clock frequency suitable for communication with the system controller.
- Each of the heads 34 recovers an address from the subcode in the portion of the track 14 being read by that head so that the system controller can identify the relative positions of the head assemblies at any given time.
- each head obtains an accurate clock signal from the track 29 that may be used to demodulate data recovered from the track 14 during reading or modulate data to be recorded on the track during WRITE operations.
- a clock signal with enhanced accuracy is obtained and the address is readily retrieved for each block.
- the limits imposed by the opto-mechanical system are essentially independent of the rate at which data is read and depend more upon the angular velocity.
- the demands placed upon the opto-mechanical system tend to be greatest at d e radially innermost track and accordingly where the opto-mechanical system is the limiting factor, control should be accorded to the radially innermost track.
- control of the motor may be affected in a number of ways, as described below with reference to Figures 7-10.
- the clock signal recovered from each of the heads 33 are fed to restrictive comparators 90.
- Each of the comparators also receives the reference clock which corresponds to the designed CLV rate.
- the comparators 90 provide respective error signals indicating whether me recovered clock signal is less than or greater than the reference clock.
- the output signals 92 are supplied to an arbitrator 94 which determines which of the signals will be used for control pu ⁇ oses.
- the arbitrator provides a control signal 96 to the control of the motor to adjust the rotational speed.
- the arbitration performed by the arbitrator 94 will depend upon the limiting factors of the system. Assuming that the electro-optic factors, i.e. the data rate, is the limiting factor, the arbitrator will provide a signal at the output 96 causing the motor to increase speed so long as each of the recovered track clocks is less than the reference clock. As the outermost head attains a data rate corresponding to the CLV data rate, its control signal 92 changes from a speed-up to a slow-down signal. The arbitrator detects the change of state, which may be simply a voltage threshold level, and utilizes the control signal 92 as the output to control 96.
- the error signal will again call for an increase in motor speed and the arbitrator will adjust the motor speed until a slow-down signal is received from one of the other heads.
- the arbitrator will cause the motor to increase speed until each of the comparators 90 provides a slow-down signal. In this case, the arbitrator accords control to the last head to issue the slow-down instruction.
- the address recovered from the track 29 is utilized as a control function.
- the address read by each of the heads 33 is supplied from an address register 100 to a comparator 102.
- the comparator 102 compares each of the addresses and determines which address represents the greater radial position.
- the head having the greatest address is selected through a channel selector 104 so that the data clock associate with that head is fed to a comparator 106.
- the comparator compares the data clock with the reference clock indicating the designed CLV rate and issues an error signal at 108 to the control to adjust the motor speed accordingly.
- each of the addresses is recovered from a register 110 and provided to a look-up table 112.
- the look-up table 112 stores a spin rate for the motor to achieve CLV for each address.
- Each of the addresses from the address registers 110 retrieves the requisite spin rate and a comparator 114 determines which of those spin rates is appropriate.
- the spin rate selected will be a minimum spin rate; where the opto-mechanical factors limit the operation, the spin rate selected will be the maximum.
- the comparator 1 14 outputs the selected spin rate to the motor for control.
- the position of the multiple heads 33 provides a number of different operating parameters.
- Each of the heads 33 may be used to supply a data stream retrieved from the carrier 12 to independent sources.
- each communication channel operates independently at the data rate recovered from the carrier. If the data rate is to be provided at a fixed predetermined rate, then the communication channel may include buffering that permits the temporary storage of data that could be clocked out at the required rate.
- the heads supply a common communication bus.
- the data stream may be buffered and directed onto the communication bus under the control of the buffer either at a constant clock rate or as an asynchronous transfer at the clock speed recovered from the track 29.
- control of the contents of the buffer can be achieved by causing a head to rescan or delaying scanning of the tracks so that the buffer is not caused to overflow.
- Control and co-ordination of the various subsystems require the development of a dedicated microprocessor for the multiple head system as a whole.
- the preferred embodiment inco ⁇ orates separate microprocessors for each stage which are soft programmed at start-up by the microprocessor and which control positioning, data timing and fine control of the write pulse. It will be understood that such operational controls can be configured in a number of ways known to prior art.
- 4 HEAD PARALLEL WRITE machines configured for point-of-sale manufacturing will operate at cumulative rates from 12-60 times that of a normal CD-R recorder by utilizing four to twelve heads, each of which will write a portion of the track data area 12 between radius 22 mm and radius 58 mm in the following manner. Only the four-head (12 times normal rates) machine is considered here.
- Each of the WRITE heads to be deployed for parallel operation must address a portion of the data area 12.
- the track pitch is a uniform 1.6 microns per rotation, and all of the heads are addressing the same rotating surface, each goes through the same radial translation. Therefore, the approximate area recorded by 4 heads operated in parallel is as follows:
- HEAD # 1 Radius 22 mm to radius 31 mm
- HEAD # 2 Radius 31 mm to radius 40 mm
- HEAD # 3 Radius 40 mm to radius 49 mm
- HEAD # 4 Radius 49 mm to radius 58 mm
- the use of multiple heads to write simultaneously to respective bands on the data carrier requires matching of the recorded data for continuity.
- HEAD # 1 (the outermost head) is directed to a radius of approximately 49 mm.
- This position can be acquired in the preferred embodiment by executing a series of single track kick pulses in co-ordination with the encoder disc 20 in order to compensate for contrary radial translation during repositioning.
- the location from which to begin the kick pulse repositioning can be readily determined by reference to end marks in the preformatted track or by the end position of track 29.
- HEAD # 2 the next outermost head is also addressed to this address and reads the data which HEAD #1 begins to WRITE. In effect, d is written pattem and the address on encoder disc 20 can now be closely correlated. As HEAD #2 reads the start of HEAD #l's track, it can correlate the position it finds the track with the position it would have placed it if it had been the first to write. In this way, radial and offset misalignments may be compensated for electronically.
- the read-out from lens position sensors in each head it is possible to determine whether the radial offset between the encoder head and the write head are maintained at a constant offset in order to provide a check on the accuracy of the kick track positioning count.
- the encoder and address structure can be employed to address two or more heads to write any portion of a preformatted spiral track represented by any radial section of the preformatted spiral track.
- a similar technique may be used on a single head to obtain continuous data recordal if even when the recording process is interrupted, such as for an archival process.
- the ability to reposition a head assembly from the address of a previous track may also be used to interrupt scanning, such as when a buffer is full, and recommence scanning when the buffer permits.
- the degree of precision with which the track matching is accomplished may be varied according to the requirements of the recording standard being recorded. For example, for recordings such as CD-digital audio recordings, the track matching requirements may be accomplished with little more than a deliberate gap left at the point where the tracks formed by two adjacent heads meet. In effect that approach mimics a scratch on the medium. In cases where greater precision is required, it is possible to interrupt the write operation of HEAD 2 for example as it approaches its end point (which is also the point where HEAD 1 began to write). At that point, the coarse positioning actuator can be disabled in order to minimize interference from that source and the final gap measured relative to the encoder disc 20. This gap can be measured more precisely by using a circuit which produces multiples of the basic pseudoclock signal sufficient to meet the measurement requirements of the recording standard being employed.
- HEAD 3 can then be redirected to where it left off and can continue writing.
- a circuit which employs the higher frequency pseudoclock as a reference selects a strategy whereby the difference between the two points are measured by these triggering edges and the circuit adjusts the one to the other in small, non-disruptive increments.
- Such a configuration presents a subtly different range of requirements than does a READ-ONLY system.
- the outermost WRITE HEAD encounters the highest linear track velocity for a given angular velocity and hence the outermost head must deliver the highest rate of write pulses. Since the write pulse/marking characteristics impose significant increases in costs for each increase in laser power, control electronics speed, etc., it is most practical to specify that the outermost head should operate at the design limits of the system. That is, the outermost head should have the fastest operating rate and, optimally the spindle control should maintain a constant linear velocity consistent with that maximum so that the system operates at its specified maximum data rate at all times.
- each of the other heads will record its assigned data area at a rate which is slower than the outermost head depending on its relative radial position (eg., the innermost head will operate at less than half the data rate of the outermost head).
- Parallel operation of multiple heads also requires either an interleaved single data stream or appropriately proportioned parallel data streams. In sum, data destined to each of the different heads will be interleaved so that data frames can be fed to each head at appropriate rates which more or less match the local data rate at each head.
- interleaving rates are functions of the relative radial position of each head the interleave ratios can be readily determined by, for example, monitoring the addresses recovered from the track 29. In some circumstances it is desirable that the data to be recorded should be stored on a system which can in fact deliver appropriately interleaved data.
- the write data buffer associated with each head must be capable of reclocking data from input lines recovered from a network or satellite operating at a single clock rate. It must then be clocked out of the buffer at the pseudoclock rates determined by the track 29 at a location corresponding to that head. Each head will require its ovm data strobe/buffer interface.
- the most satisfactory WRITE-PULSE control configurations make provision for specific shaping of the WRITE-PULSE pattem such as an increased power output from the laser at the beginning of any individual pit formation operation in order to overcome (largely lateral) transmission losses and deliver sufficient energy to produce appropriate leading edges while the following portions of each mark are generally formed by lower power pulses because pulses delivered immediately prior will contribute a "pre-warming" component through transmission.
- This is typically referred to as a "WRITE-PULSE shaping circuit".
- Such a circuit must make provision to compensate for any differential cooling rate which occurs as a result of the lower linear velocity encountered by the inner, (i.e. slower), heads and in some configurations such compensation may include modulating die secondary WRITE-PULSE form.
- the multiple heads provided on the drive also permits simultaneous operation of writing of data and reading of data for verification.
- the head 33a may be utilized to write data to the data carrier 12 and the diametrically opposed head 33c may be used to read the data recorded by the head 33a and verify the accuracy of the recorded data.
- the data will be readable by the head 33c as it derives the appropriate clock circuit from the track 29.
- Such an arrangement is particularly beneficial for archival backup.
- the provision of the encoding disc 20 permits the archival recordal to be interrupted and for the data position to be recovered with the appropriate timing when archival recording is reinstated.
- the ability to radially position the heads independently may also be used to enhance the maximum data transfer rate as shown in Figure 10.
- a wide divergence of the heads - that is, place of the heads at radially disparate locations - will restrict the data rate retrieved from one of those heads.
- One head will be operating at a maximum rate while the other is operating at below optimum.
- each of the heads 33 is located in one of a number of sectors on the disc surface.
- the heads are grouped together in a relatively narrow band and data is provided to the heads as described above to record respective areas of the data carrier. Because the heads are grouped closely together, the disparity between the maximum and minimum rates of the head is reduced and the overall data rate of recordal is enhanced.
- the heads are repositioned and realigned as described above, and the next sector written. This is repeated sector by sector until the recording is complete.
- the heads may be switched from a WRITE to a READ mode and continue to read the data previously recorded by the adjacent head.
- the radially outer head is repositioned at the radially inner track of the sector just recorded so that each portion of the sector is verified.
- this arrangement permits writing and verification at the maximum data rate of each of the heads and may proceed on a sector-by-sector basis until the recording is complete.
- the control and coordination of the various subsystems described above is accomplished with the use of a dedicated microprocessor.
- Each of the head assemblies 33 is controlled by a separate microprocessor which may be self-programmed at startup by the controlling microprocessor.
- each of the heads control positioning, data timing and fine control of the WRITE pulse. It will be understood that such operational controls could be configured in a number of ways known in the prior art. Although the nature of the control software will depend upon the particular application and strategies to be employed, an example of the control effected by the microprocessor is set out below as a sequence of control steps upon initiation. It is assumed for the pu ⁇ ose of description that a pair of head assemblies are used, although it will be appreciated that similar sequences are implemented where more than two heads are utilized with appropriate modification to the command structure.
- circuits which closely control the relative power of the WARMING and WRITE pulses and it is possible that such a circuit may be required to differentiate between the writing of short and long marks due to the impact of the outer portions of die laser spot extending into the area of the next mark to be written.
- Automatic circuitry to maintain such control is implemented in a microprocesser utilizing known control sequences is discussed below.
- CONTROLLER CIRCUIT SETS A DC OFFSET FOR THE FINE TRACKING CIRCUIT OF THE ENCODER DISC 20 HEAD
- CONTROLLER CIRCUIT SETS WRITE ENABLED STATUS FOR BOTH HEADS
- CONTROLLER CIRCUIT READS ADDRESSES FROM ENCODER DISC 20 ADDRESS RECOVERY CIRCUIT FOR THE OUTERMOST (CLV) HEAD PAIR.
- CONTROLLER CIRCUIT READS ADDRESSES FROM ENCODER DISC 20 ADDRESS RECOVERY CIRCUIT FOR THE OUTERMOST (CLV) HEAD PAIR.
- CONTROLLER CIRCUIT READS ADDRESSES FROM ENCODER DISC 20 ADDRESS RECOVERY CIRCUIT FOR THE INNERMOST (CLV) HEAD PAIR.
- CONTROLLER CIRCUIT SETS PSEUDOCLOCK PLL/VCO CENTER FREQUENCY TO APPROPRIATE RANGE
- CONTROLLER CIRCUIT TAKES DIRECT CONTROL OF COARSE POSITIONING MOTORS AND MOVES BOTH STAGES OUTWARD ALONG
- the timing signal has been retrieved from the encoded disc that is concentrically located about the carrier 12.
- An alternative arrangement is shown in Figure 1 1, in which the encoder disc 20 is located below the carrier 12.
- the radial extent of the encoding disc 20 and the data carrier is d e same so that a CLV-like pattem may be used on the encoding disc.
- Each of the heads 34,36 is radially aligned and directed in opposite direction so that head 34 derives the timing signal from the encoding disc 20.
- the data format for the encoding disc described above may of course be utilized to provide the requisite accuracy. It should be noted that other zero-sum code pattems may be desirable for use with encoder discs which do not employ a radial offset and so require different scales to assure scanning at I-top.
- the encoding disc 20b is formed with two layers 120,122.
- the layer 120 carries the encoding pattem for one of the standards and the layer 122 carries the encoding pattem for the other of the standards.
- the head 34 is provided with a differential focus so that it can be switched between the two layers 120,122 and thereby read the timing pattem associated with the appropriate standard.
- a further enhancement of the synchronization of the timing pattem provided by the track 29 may be obtained by utilizing the relationship between adjacent passes of the track. Each of the passes contains marks which are approximately ten clock cycles longer than the preceding rotation. Accordingly, the timing pattem may be adjusted by redirecting the scanning spot on the track 29 in or out in single track increments to effect a fine-tuning of the recovered frequency to that at which the disc was recorded. This method of measuring data pit lengths on the carrier 12 appears to be superior to the conventional approach about these two orders of magnitude.
- a separate encoder disc is utilized to generate the timing pattem. While the use of a separate track is considered most desirable and offers optimum accuracy, it will be recognized that a clock signal may be derived from the data recorded directly on the carrier 12.
- a clock signal may be derived from the data recorded directly on the carrier 12.
- the frequency can be maintained with sufficient stability by comparing the frequency recovered from the data track of a recorded disc to the frequency of a fast system clock numerically while making provision for a count of each and allowing for the increase in frequency which will occur as the head transits outward.
- a circuit derives a numerical measure of ⁇ e rotation rate and the frequency recovered can be compared numerically to a frequency reference value stored in a look-up table with reference to the absolute track address recorded in subcode. This requires that the primary modulation rate - either 1.2 or 1.4 m/s - is factored into the equation.
- the relative clock rate may be calculated as a function of the number of the spiral, i.e. radial location, employing the incremental change in track length between mutually adjacent tracks, again allowing for the primary modulation rate.
- some combination of the synchronizing marks (which are separated by 588 clock cycles corresponding to 588 channel bits) may be compared to a frequency produced in d e manner of a sampled servo using the intervals between subcode addresses and either or both frequencies may be phase locked to the pit/edge transitions which record the data.
- a further technique for retrieving a clock signal is to rely upon the tolerances found in typical discs in the CD system which can be formed with a basic clock rate that varies +/- I % from the precise standard specified. The variation produces a deviation from a fixed clock rate which is referred to as the "jitter margin" and which is normally solved by a buffer structure.
- the track 29 provides a superior solution.
- each track contains marks which are approximately 10 clock cycles longer than the preceding track.
- Inco ⁇ oration of a track-offset circuit capable of redirecting the scanning spot on the track 29 in or out in single track increments will, in effect, fine-tune the pseudoclock frequency to that at which the disc was recorded.
- This method of measuring data pit lengths on the target disc is superior to the conventional approach by at least two orders of magnitude.
- the recovery of die clock signal may employ elements of the sampled servo approach discussed above, the detection of ATIP mark from a CDR disc, for example, or by simple use of the synchronization pulses embedded in the data of a conventional CD or odier such disc.
- Logic circuits can be employed to determine whether the relative clock rates are changing in an incremental fashion which exceeds the specified tolerance. Such a determination will then be used to control a pseudoclock compensation circuit in both WRITE and READ-ONLY applications. Where an encoding disc is utilized, then the detected variations can be made to compensate for differences between the spatial pattem encoded on the disc and the patent formed on the carrier 12.
- the clock timing may be recovered by a combination of the above techniques such as in one embodiment the provision of an ATIP sampled servo pattem and address extraction circuitry that can recover the ATIP addresses.
- the ATIP addresses can be included with a sample servo circuit that may provide additional reference to control for eccentricity, etc.
- a pre-formatted disc may be utilized for recording which inco ⁇ orates a wobble track pattem as well as the sample servo mark such as the A ⁇ P marks which provide the requisite clock accuracy.
- the provision of the encoder disc 20 permits control of the clocking as the radial position of the heads is adjusted by monitoring the track previously written by means of a side spot formed by placing a detraction grating in d e optical path of the head. In this way, the spacing from the previously recorded track can be maintained constant using detection circuits similar to a three-beam optical tracking system.
- optical heads should make provision for inco ⁇ oration of a lens position sensor and read-out circuit which signal can be used for coordination of fine lens positioning between the READ and WRITE heads and as a control parameter for a course positioner and as a secondary positional reference for offset track location.
- lens position sensors may be developed to be retrofitted to conventional READ heads or circuits can be employed which measure lens position by reference to the fine tracking error drive signal.
- the same system is employed witi die exception that the pre-formatted recordable disc employs a sampled servo pattem, such as A ⁇ P, and me drive contains circuitry capable of recovering the A ⁇ P addresses.
- a ⁇ P sampled servo pattem
- me drive contains circuitry capable of recovering the A ⁇ P addresses.
- This embodiment permits the recovered A ⁇ P addresses to be employed for die verification of track positioning by the kick track circuit.
- the preformatted disc inco ⁇ orates a wobble track pattem (or comparable contrasting timing pattem) as well as sufficient sampled servo marks such as ATIP marks which are sufficient to effectively replace the offset or otherwise displaced encoder.
- the present invention may inco ⁇ orate a radial tracking system which enables it to record on featureless flat target discs making more extensive use of the STOL reference in combination with the detection of the adjacent track just written by a side spot formed by placing a diffraction grating in the optical path of the head which operation is possible using a device similar to a 3 -beam optical tracking means widi provision for electronic circuitry to compare signals retrieved from position sensors inco ⁇ orated into the offset heads with the tracking signal received from a single side of the
- optical heads should make provision for inco ⁇ oration of a lens position sensor and read out circuit which signal can be used for co-ordination of fine lens positioning between the READ and WRITE heads and as a control parameter for ⁇ e coarse positioner and as a secondary positional reference for offset track location.
- lens position sensors may be developed to be retrofitted to conventional read heads or circuits can be employed which measure lens position by reference to the fine tracking error drive signal.
- each head in a pair may be mounted on a separate stage and aligned electronic offset by reference to minimal address data on either a preformatted CD-R disc or to the data subcode on a recorded disc such that an approach may be preferable in that it reduces physical alignment requirements for the radial translation stages which position d e heads and thus simplifies fabrication of the drive.
- head assemblies may operate independently so that one may record while another verifies and the balance read data.
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Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP97900921A EP0878005A1 (en) | 1996-02-03 | 1997-02-03 | Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or pre-formatted discs |
AU14352/97A AU1435297A (en) | 1996-02-03 | 1997-02-03 | Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or pre-formatted discs |
CA002281687A CA2281687A1 (en) | 1996-02-03 | 1997-02-03 | Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or pre-formatted discs |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9602213.2 | 1996-02-03 | ||
GBGB9602213.2A GB9602213D0 (en) | 1996-02-03 | 1996-02-03 | Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or preformatted discs |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1997028530A1 true WO1997028530A1 (en) | 1997-08-07 |
Family
ID=10788081
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/CA1997/000069 WO1997028530A1 (en) | 1996-02-03 | 1997-02-03 | Multihead recording and retrieval apparatus and procedure for use with self-timing optical lathe or pre-formatted discs |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0878005A1 (en) |
AU (1) | AU1435297A (en) |
CA (1) | CA2281687A1 (en) |
GB (1) | GB9602213D0 (en) |
WO (1) | WO1997028530A1 (en) |
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EP0994469A2 (en) * | 1998-10-13 | 2000-04-19 | Matsushita Electric Industrial Co., Ltd. | Recording/reproducing apparatus for optical information recording medium and optical head |
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WO2006102856A1 (en) * | 2005-03-30 | 2006-10-05 | Zdenek Varga | Protection of disk data carriers against making illegal copies |
EP1788565A1 (en) * | 2005-11-16 | 2007-05-23 | Thomson Licensing S.A. | Method for fast optical reading and recording |
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- 1996-02-03 GB GBGB9602213.2A patent/GB9602213D0/en active Pending
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- 1997-02-03 CA CA002281687A patent/CA2281687A1/en not_active Abandoned
- 1997-02-03 AU AU14352/97A patent/AU1435297A/en not_active Abandoned
- 1997-02-03 EP EP97900921A patent/EP0878005A1/en not_active Withdrawn
- 1997-02-03 WO PCT/CA1997/000069 patent/WO1997028530A1/en not_active Application Discontinuation
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US7460442B2 (en) | 2004-02-24 | 2008-12-02 | Sony Corporation | Optical disk apparatus |
WO2006102856A1 (en) * | 2005-03-30 | 2006-10-05 | Zdenek Varga | Protection of disk data carriers against making illegal copies |
EP1788565A1 (en) * | 2005-11-16 | 2007-05-23 | Thomson Licensing S.A. | Method for fast optical reading and recording |
Also Published As
Publication number | Publication date |
---|---|
AU1435297A (en) | 1997-08-22 |
GB9602213D0 (en) | 1996-04-03 |
EP0878005A1 (en) | 1998-11-18 |
CA2281687A1 (en) | 1997-08-07 |
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