|Publication number||USRE38703 E1|
|Application number||US 10/167,083|
|Publication date||Feb 15, 2005|
|Filing date||Jun 12, 2002|
|Priority date||Apr 28, 1995|
|Also published as||CN1095167C, CN1155937A, DE69623411D1, DE69623411T2, DE69634707D1, DE69634707T2, EP0775359A2, EP0775359B1, EP1213719A1, EP1213719B1, US6075670, WO1996034387A2, WO1996034387A3|
|Publication number||10167083, 167083, US RE38703 E1, US RE38703E1, US-E1-RE38703, USRE38703 E1, USRE38703E1|
|Inventors||Gheorghe S. Stan, Johannus L. Bakx|
|Original Assignee||Koninklijke Philips Electronics N.V.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Referenced by (1), Classifications (38), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates to a device for reading and/or recording information from/in an information track on a disc-shaped information carrier, comprising scanning means for scanning the information track with a linear velocity at a variable distance (r) from a point of rotation of the information carrier, and comprising drive means for causing the information carrier to rotate at an angular velocity, and control means for controlling the drive means.
Such a device is known from U.S. Pat. No. 5,161,142. In the known device a so-termed CLV (Constant Linear Velocity) disc, which is a disc-shaped information carrier on which the information track is filled with information having a constant linear density, is scanned with a Constant Angular Velocity (CAV). If information is to be read from another part of the information track, the scanning means are moved as rapidly as possible to this part of the track by a skip across the tracks to a new radial position. In the known device the angular velocity remains unchanged, so that a short access time to information elsewhere on the disc is realised.
A problem of such a device is that the information scanning velocity close to the centre of the disc is considerably lower than near the outer edge. As a result, the average information scanning velocity is much lower than the maximum information scanning velocity. Also the information processing circuit in the device is required to have a large operational range; that is, to process data having widely varying data rates.
It is an object of the invention to provide, for example, a device that has a high average information scanning velocity, while the access time after a rapid displacement remains short.
This object is achieved by a device as defined in the opening paragraph, characterized in that the control means are arranged to cause the information carrier to be driven in such a way that the angular velocity of the information carrier substantially decreases with an increasing distance (r), and the linear scanning velocity substantially increases.
The invention is advantageous in that the difference between the minimum and maximum operational angular velocities is smaller than when recording or reading operations are carried out with a constant linear velocity, so that the adaptation of the angular velocity in the case of a rapid radial displacement remains limited. In a device according to the invention, a relatively low-power motor and motor drive may be used. This not only restricts the weight and size, but also the energy consumption, the heat build-up and mechanical vibrations.
A further embodiment for the device is characterized in that the control means are arranged to set the angular or linear velocity in such a way that a first period of time necessary for the pick-up means to reach another part of the information track by a rapid radial displacement is longer than or equal to a second period of time necessary to adapt the linear velocity for a rapid radial displacement to a speed at which the information can be processed. This embodiment is advantageous in that, given a specific maximum information processing rate and the physical parameters of the device, the optimum average information rate is obtained with a minimum access time.
A further embodiment for the device is characterized in that the control means are arranged for constant linear velocity scanning during information recording. This embodiment is advantageous in that the recording parameters, such as, for example, the laser power and the shape of the write pulse, need to be determined for only one fixed linear velocity. These parameters continue to be constant during the recording operation.
A further embodiment for the device is characterized in that the control means are arranged for deriving the distance (r) from information in the information track. This embodiment is advantageous in that the distance (r) can be derived from the available signals, for example, addresses, without the necessity of adding another pick-up to the device.
These and other aspect of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings:
In the drawing figures, elements corresponding to elements already described carry like reference characters.
During recording, information is fed via encoder 6 to modulator 5, which encoder encodes the information into an information stream with redundancy for error correction. The encoded and modulated information is recorded at a constant information rate determined by a clock signal. The tracking as well as the linear velocity are controlled via the tracking system and the control loop. For example, when a master disc is manufactured, which is subsequently to be used for manufacturing CD-ROMs, the angular velocity can be controlled by deriving a measuring signal 14 from the drive means 3 and allowing the desired angular velocity to decrease inversely proportionally to r. The recordable information carrier may beforehand be provided with patterns, such as in the sampled servosystem, or a wobbled pregroove, so that a control signal 15 is generated in the read/write head 2. For an extensive description of the manner in which the control signal is generated, reference be made to EP 03262006, or U.S. Pat. No. 4,901,300, which document is deemed incorporated in the description by reference. During recording, the control signal 15 is led to control unit 4 via switch 10, which unit maintains, in dependence on the control signal, a constant value for the linear velocity at which the information carrier 1 is scanned by the read/write head 2. In this manner an information carrier 1 is obtained, whose information density seen in the scanning direction is constant.
During reading, a reading signal produced by the read/write head 2 is decoded by a demodulator 7 and decoder 8 into an information signal while the clock signal 13 is being recovered. The frequency of this clock signal is indicative of the linear velocity at which the information pattern is scanned by the read/write head 2. Switch 10 leads the clock signal 13 to control unit 4 during the reading operation.
In the case of a reading operation according to the so-called CLV system, the rotation is controlled in such a way that a constant linear scanning velocity is obtained, as occurs in the known audio CD player for a CD-DA. For this purpose, the control means 4 are supplied via switch 10 with a linear scanning velocity signal 16, such as said control signal from the servotracking system during the recording operation, or with the recovered clock signal 13 from demodulator 7 during the reading operation. The information is recorded with a constant density in the information track. As a result, a maximum amount of information can be recorded on the disc. In the CLV system the angular velocity depends on the distance r. Since the angular velocity is to be adapted after a rapid displacement of the read/write head 2 to another part of the information track, the motor control will need some time to reach this velocity. For part of this time, that is, as long as the information rate lies outside the operational area of the information processing circuit (i.e. demodulator 7 and decoder 8, modulator 5 and encoder 6, respectively), no information can be processed. A strong motor and a strong motor drive are to be used to obtain a short access time.
During a scanning operation according to the so-called CAV system, the rotation is adjusted in such a way that a constant angular velocity of the information carrier 1 is obtained. For this purpose, the drive means 3 may comprise a sensor which produces a sensing signal 14 which is indicative of the angular velocity. The sensing angle 14 is then applied to the control means 4. When a recording operation is performed according to the CAV system, the information can be recorded at a constant clock rate, so that the density on the information carrier then decreases with an increasing distance r.
When a recording operation is performed according to the CAV system, a constant information density may be obtained by allowing the information rate of the information to be recorded to increase proportionally to the distance r. However, this poses strict requirements on the operational area of the information processing circuit. In addition, the information transfer rate in the case of a small distance r is much smaller than along the outer edge. As a result, the average information transfer rate is much lower than the maximum information transfer rate. The access time after a rapid displacement only depends on the time necessary for reaching the desired part of the information track. A scanning operation according to the CAV system for reading information carriers which have a constant information density in the scanning direction is known from U.S. Pat. No. 5,161,142.
In a third embodiment for the device according to the invention, the linear velocity is set in dependence on the distance r. Control unit 4 is supplied with a signal that is indicative of the real angular velocity i.e. clock signal 13 or signal 15 from switch 10, as is shown in FIG. 1. The sensor and the sensing signal 14 are not necessary now, but may be supplied, as required, for controlling the velocity if the read signal is unreliable, for example, during a rapid displacement. With an increasing distance r a larger linear velocity is set, while the linear velocity increases less than proportionally to increasing r. In the control loop the control means 4 compare the set linear velocity with the signal 16 that indicates the real angular velocity. The driving signal for drive means 3 is derived in dependent on this comparison. The distance r can be sensed by position sensor 20 and presented by means of signal 21, as is shown in FIG. 2.
A fourth embodiment for a device according to the invention is similar to the third embodiment, with the exception that r is derived now from address information of signal 22 or signal 15, as shown in FIG. 3. Position sensor 20 and signal 21 are lacking here.
A fifth embodiment for a device according to the invention is similar to the previous embodiment, except that the angular velocity in the CLV system is controlled while information is being recorded. The recording parameters such as the recording power and the recording pulse may then have fixed settings.
A sixth embodiment for the device according to the invention is similar to the previous embodiment with the exception that the angular velocity in the CAV system is controlled during the information recording. The clock rate is varied inversely proportionally to r, for example, by coupling a signal 21 or 22 indicative of the distance r to a VCO (Voltage-Controlled Oscillator). Then, r may be determined by a sensor 20 or read from a signal 15 or 22 from the information carrier 1. As a result, there will arise a high, constant information density combined with the constant angular velocity. After a rapid displacement it is then possible to record forthwith, because the angular velocity need not be adapted and there is thus no danger of recording too fast or too slowly, so that information would end up in a wrong area of the information carrier 1.
In a first embodiment for the control means 4, the CLV curve 32 is followed from the outer edge at rmax to a specific distance r1. Consequently, the information track having the larger diameters is read and recorded with optimum velocity. From this distance r1 the angular velocity is maintained constant at ωmax, as is shown by curve 34. Mechanical restrictions or restrictions as to high angular velocity servotracking are thus taken into account.
In a second embodiment for the control means 4, the maximum information processing rate is taken into account and the access time is maintained at a minimum level. In the case of a rapid displacement to the centre, the information carrier 1 will have to be accelerated until the angular velocity corresponds to the new distance r. The information rate will thus be temporarily lower and the (recovered) clock will follow this lower rate. To this end, the system control may temporarily adjust, as required, the modulator 5 or demodulator 7, respectively. In the case of a rapid displacement from the centre outwards, the information carrier 1 will have to be decelerated. Since the maximum rate of the information processing circuit is limited, the angular velocity must not be too high when the read/write head 2 arrives at the desired part of the information track. A minimum access time prescribes that the time required for decelerating the information carrier is always smaller than or equal to the time necessary for displacing the read/write head 2. The minimum access time is obtained by selecting the velocity curve in such a way that for each distance r the rapid displacement time is, substantially, at least equal to the deceleration time for each rapid displacement from all other operational distances r. The variation for a specific device is given in curve 33. Under the conditions of the minimum access time, there will then also arise the maximum average information rate.
The variation of the rapid displacement time for a device will have to be determined to attune the velocity curve thereto. If the rapid displacement time is proportional to the radial displacement, the rapid displacement time can easily be determined. In general, however, the displacement of the read/write head 2 will be effected by first strongly accelerating and then decelerating again. The period of time necessary for adapting the angular velocity will have to be determined from the difference of distance to be covered and the motor parameters. For the CLV curve 32 the difference of angular velocity after a rapid displacement is proportional to the radial displacement added to the distance r. As the rapid displacement takes place over a specific distance closer to the outer edge, so the difference of angular velocity will be smaller and so the necessary deceleration time will be shorter.
For a specific distance rclv it will hold that the rapid displacement time is, substantially, equal to the deceleration time. Without a detrimental effect on the access time, the CLV curve 32 can be followed from distance rmax to rclv. In this part of the curve 33 the angular velocity is thus totally determined by the maximum rate of the information processing circuit, whereas in the part from rmin to rclv, the curve 33 is determined by the properties of the motor. Depending on the physical properties of the system, the calculated rclv may also be smaller than rmin (in that case the curve will decrease to the known CLV curve) or larger than rmax (in that case curve 33 lies completely in the area 30). To be certain that the information can always be processed after a rapid displacement, the point rclv can be selected slightly more towards the outer edge. This creates then a slight margin for physical property tolerance of the device.
In a third embodiment for the control means 4, a higher average information rate is obtained than in the previous embodiment if a minimum access time is not required in all situations, so that, for example, some extra time is allowed for rate adaptation in the case of a rapid displacement over more than ⅔ of the operational area. The maximum velocity upon arrival is then to fall within the clock recovery capture range in the demodulator 7, so that the correct linear velocity is sensed. The decoder 8 starts decoding if the linear velocity has come to within the lock range. The curve then shows a variation partly in the area 30 between the CLV curve 32 and the optimum curve 33.
In a fourth embodiment for the control means 4, the minimum access time is obtained by a velocity variation mainly found in curve 33 and, as required, in curve 34. The desired curve may be approximated, for example, by several fixed setting points. The control means 4 then comprise a simple selection mechanism and the sensor and sensing signal 14 may be omitted. The result is then, it is true, a slightly lower average information rate.
For the above embodiments it holds that a simple balancing between average access time and average information rate may be made by suitably selecting a curve in the area 30 between the CLV curve 32 and the CAV curve 31.
In a further embodiment for a device according to the invention, an information carrier 1 is used on which the information density decreases as r increases. For example, the distance r can be divided into zones of constant angular velocity, for example, in accordance with curve 42 in FIG. 5. With a constant clock rate the density within a zone will then decrease with increasing r; the clock is adjusted per zone, so that, substantially, the density in the inner zone is greater than the density in the outer zone. Also the clock rate may be varied inversely proportionally to r, for example, by coupling a signal 21 or 22 indicative of the distance r to a VCO (Voltage-Controlled Oscillator). This causes a constant density to develop, for example, per zone. During recording, such a coupling can be used over the entire distance r in combination, for example, with a constant angular velocity. r may then be determined by a sensor 20 or from a signal 15 or 22 read from the information carrier 1. After a rapid displacement, recording is possible forthwith, because the angular velocity need not be adapted, whereas still a high, constant, information density is obtained.
Combinations of variable density, angular velocity and linear velocity make an optimum tuning possible of the average information rate, the access time and the total storage capacity of the information carrier 1. There should be observed that combinations essentially copying the CAV or CLV variation, for example, by approximating the CLV curve by zones of constant angular velocity, are already known. In that case, however, the angular velocity or linear velocity shows a variation, however, only within a zone different from that of the known CAV or CLV systems, and the angular velocity or lines velocity continues to be constant, substantially.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8773799 *||Dec 21, 2012||Jul 8, 2014||Lsi Corporation||Signal processing circuitry with frontend and backend circuitry controlled by separate clocks|
|U.S. Classification||360/73.03, 369/47.38, 369/47.36|
|International Classification||G11B19/26, G11B20/10, G11B19/20, G11B27/13, G11B27/30, G11B19/00, G11B19/24, G11B19/28, G11B20/12, G11B15/46|
|Cooperative Classification||G11B2220/218, G11B2220/213, G11B2220/2525, G11B20/10, G11B19/26, G11B20/1258, G11B20/1217, G11B2220/2545, G11B19/28, G11B19/20, G11B2220/20, G11B19/24, G11B27/3027, G11B19/00, G11B27/13|
|European Classification||G11B19/20, G11B20/12D23, G11B19/28, G11B19/26, G11B20/10, G11B27/30C, G11B19/24, G11B27/13, G11B19/00, G11B20/12D|
|Jul 15, 2004||AS||Assignment|
Owner name: KONINKLIJKE PHILIPS ELECTRONICS N.V., NETHERLANDS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:U.S. PHILIPS CORPORATION;REEL/FRAME:015561/0132
Effective date: 20040709
|Nov 30, 2007||FPAY||Fee payment|
Year of fee payment: 8
|Sep 22, 2011||FPAY||Fee payment|
Year of fee payment: 12