U.S. Philips Corporation

Peter J Janssen

Gerard E Van Rosmalen

Leonardus A Verhoeven

Pieter D Schuitmaker

Maarten Rutger De Haan

Wilhelmus J Christis

Franciscus T Sleegers

Petrus J Aarts

Jan Zwier

Hans J Apeldoorn

Kees Teer

Willem F Mellink

Laurentius Antonius De Bot

Hendrik Kolk

Harm Lotterman

A transparent substrate has an information layer on an entirely flat side, and a centering member on the other side adapted to cooperate with centering means of an apparatus for inscribing and/or reading the disc. The centering member may be glued in place and have an aperture for engagement by an apparatus spindle.

Optically readable disc with a centering member fixed to a transparent

An inlet opening in an evacuatable vacuum system is substantially enlarged and closed off by a porous plate so that the ingress of dust is avoided and a very uniform inflow of gas is realized. A similar plate can be used for closing off a gas outlet opening of the vacuum chamber.

Vacuum system

A transparent substrate has an information layer on an entirely flat side, and a centering member on the other side adapted to cooperate with a centering device of an apparatus for inscribing and/or reading the disc. The centering member may be glued in place and have an aperture for engagement by an apparatus spindle.

A record carrier is described with an optically readable trackwise-arranged information structure, and an apparatus for reading said carrier. The distances between the tracks of the information structure vary so that by projecting, in addition to a read spot, at least one address spot to the information structure of a size such that is spans a number of tracks approximately equal the quotient of the average track distance and the amplitude of the track distance variation, the read spot can be rapidly addressed to a specific group of tracks. This is done with the aid of two detectors which are disposed in the path of the address-beam radiation which is diffracted in a first order by the information structure in a direction transverse to the track direction.

Record carrier with an optically readable trackwise-arranged information

An opto-electronic apparatus for inscribing and/or reading recording tracks on a record carrier by means of a radiation beam comprises an objective mounted in an objective holder. The objective holder is supported in a frame by bearing arrangement for movement in accordance with a number of desired degrees of freedom and the apparatus includes electromagnetic actuator means for driving the objective holder in accordance with the desired directions of movement. The bearing arrangement of the objective holder on the frame comprises electromagnetic bearing means for counteracting movements in accordance with at least one undesired degree of freedom. An objective-position measuring device supplies a positional error signal which represents the deviation of the objective holder in accordance with the undesired degree of freedom relative to the frame and which is utilized by a levitation control circuit which counteracts movements of the objective holder relative to the frame in accordance with the undesired degree of freedom by means of electromagnetic levitation forces.

Opto-electronic apparatus for inscribing and/or reading recording tracks

An optically readable storage disc comprises a transparent substrate 1 on which a recording layer 2 is deposited which can be modified locally by means of a radiation beam, which recording layer is covered by a cover disc 3 which is secured to the substrate in a gas-tight manner at some distance from the part of the recording layer which is intended for recording, so that a sealed space 4 is enclosed between the substrate 1 and the cover disc 3. The cover disc 3 will be deformed to the greatest extent under the influence of differences between the gas pressure in the sealed space 4 and the barometric pressure because its resistance to deformation is substantially smaller, so that deformation of the substrate 1 is substantially precluded.

Optical disc pressure-collapsible cover

An error correction circuit in a television receiver for receiving, for example, Teletext information, Viewdata information or information of comparable systems. The codes representing symbol information received by the receiver are classified into one out of two or more classes in dependence on the frequency of their occurrence, this classification being an indication of the extent to which it is probable that a received code is correctly received. In FIG. 1, a picture text television receiver has a receiving section, audio and video amplifiers 4 and 9 and a picture tube 10, 11. A text decoder 21 receives symbol information which is stored in a store 25 for display. An error detector circuit 40 including a comparison circuit 43 and two parity circuits 41 and 42, and checks for parity between newly received and already stored symbol information. A reliability circuit 60 is also included.

Error correction circuit using character probability

An effective control of the degree of suppression in a sound suppression filter in a television receiver is obtained when the required control signal is derived from the product of the amplitudes of the sound intercarrier signal and the chrominance sub-carrier signal, this product being in practice a measure of the disturbing difference frequency component between the chrominance sub-carrier signal and the sound intercarrier signal.

Television receiver having a controllable sound suppression filter

Multi-gun color television display apparatus having for each gun an identical beam current reference level control system wherein the relative position of a reference level in the video signal and a setting voltage of the electron guns are periodically shifted for obtaining, for the control system outside the measuring periods, a coincidence of the reference level in the video signal and the cut-off point of each of the electron guns for a proper color rendition at a low brightness.

Color television CRT beam current correction circuit

Television system having first and second FM sound carriers, the receiver comprising a picture intermediate frequency section, a conventional first sound demodulation circuit connected thereto via a video detector for demodulating a first sound signal being frequency modulated on the first sound carrier, and a new second sound demodulation circuit connected directly to the picture intermediate frequency section with which a second sound signal being frequency modulated on the second sound carrier can be demodulated, even at a low amplitude of the second sound carrier.

Television system with two FM sound carriers

In a television receiver having a synchronous video signal detector from which a signal is obtained for controlling a function such as an automatic volume control or a synchronization signal separation, a correction signal, obtained by means of full-wave rectification from a frequency deviation detector, is added to the signal to improve the operation of said function of the receiver in the case of more serious detuning.

Television receiver having a synchronous detection circuit and a

A color television system for transmitting a color television signal, specifically for recording on and subsequently reproducing from a record carrier. The color television signal to be transmitted contains a first carrier which is frequency-modulated with the luminance information and a second carrier which is modulated with the chrominance information, whose frequency lies between zero and the first-order lower side band of the modulated first carrier which corresponds to the highest modulation frequency. Said second carrier does not have a fixed frequency, but is locked to the instantaneous frequency of the modulated first carrier by a constant integral ratio. Depending on the characteristics of the transmission medium and the signal processing equipment said ratio is preferably two or three.

Color television recording system employing frequency modulation and

An apparatus for reading a disc-shaped record carrier on which information is stored in a preferably spiral-shaped track. Said information is read optically with the aid of a radiation beam, which via a directing system transfers the information contained in the scanning point of the record carrier to a read detector. The radial position of the scanning point is controlled with the aid of a control system which via a first pattern of radiation spots which is projected onto the record carrier receives information about said radial position and by means thereof controls the directing system. In order to ensure that the system is stable under all conditions use is made of a second pattern of radiation spots which are projected onto the record carrier, which pattern is radially shifted relative to the first pattern, and from which a control signal is derived with which the transfer function of the control system is varied so as to stabilize the control system.

Apparatus for reading a disc-shaped record carrier with plural scanning

Facsimile transmission can be effected in a conventional television system by means of code words which occur in a television line period in a field blanking interval. Transmission in the UHF band does not give rise to specific problems, but transmission in the VHF band does, in particular in that pulse disturbances occur. The influence of these disturbances can be eliminated by transmitting the same facsimile information during two (or more) successive line periods. The receiver is provided with a circuit which includes three delay devices, one having a delay time equal to a line period and the other two having delay times equal to at least the duration of a facsimile code word. The pulse disturbance is detected by means of a superposition stage and a signal detector, and the undisturbed code word is supplied via a change-over stage to a storage stage.

Television facsimile transmission system

A system comprising a playback unit and an associated long-playing record on which sound information is recorded in a time division multiplex code on several tracks. Upon reproduction the same track is scanned n times with the aid of a beam of light before this beam of light is directed to the next track. With the aid of a sampling gate the pulses comprising the sound information in time division multiplex code and associated with a first sound channel are sampled with the aid of said sampling gate while during a second revolution pulses from a second sound channel etc. are sampled. In order to operate this sampling gate in synchronism with the scanning of said pulses the playback unit comprises first synchronizing means responding to pulses also comprising the sound information. Furthermore, at the commencement of each track, starting pulses are provided to which second synchronizing means respond. The output signals thereof control the first synchronizing means and a pivoting mirror reflecting the beam of light which after the record has made n revolutions with one and the same track being scanned is pivoted so that the beam of light is directed to the next track to be scanned. In another embodiment the pulses comprising the sound information are distributed in m groups of pulses 1 to n over a track and each group is preceded by a group pulse to which third synchronizing means respond. The output signals of these third synchronizing means control the first synchronizing means.

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Eindhoven, Netherlands

Peter J Janssen