Abstract: An optically readable record carrier for storing digitally coded information having a power spectrum with a substantially zero level at a predetermined frequency. The information is recorded on and/or reproduced from substantially parallel elongated tracks on the record carrier which have a periodic undulation at the aforesaid predetermined frequency. Such undulation generates a clock signal for synchronizing the recording and/or reproduction of the digitally encoded information on the tracks, and does not interfere with the recording or reproduction of such information. Apparatus is disclosed for forming such tracks on the record carrier.

Abstract: The disclosed method for writing information in a magneto-optical record carrier employs two light beams each positioned on one of two tracks on the record carrier. In one track information is recorded by one light beam, while simultaneously the other track is erased by the other light beam. This enables real time information recording.

Abstract: A system for transmitting digital information including a coding arrangement, a transfer medium, for example a record carrier, and a decoding arrangement.In the coding arrangement the digital information is received as groups of input words which are encoded to form code words, each code word corresponding to an input word. Each code word has a time duration equal to s.tau..sub.O and each is assembled from M subgroups G.sub.m of I signal positions t.sub.mi spaced by equal time intervals .tau., where m is a number from 1 to M, inclusive, corresponding to a subgroup G.sub.m and i is a number within each subgroup G.sub.m from 1 to I inclusive. In each subgroup G.sub.m, k of these signal positions t.sub.mi are always occupied by a signal which is distinguishable from the signal in unoccupied positions, where k is an integer smaller than I (1.ltoreq.k.ltoreq.I-1). The first positions of the subgroups G.sub.m are located at mutually different time intervals .epsilon..sub.

Abstract: An absolute differentiator receives a self-clocking digital input signal, and its output is applied to a series of delay elements. The outputs of the differentiator and the delay elements are coupled to an OR-gate. The output of the OR-gate is applied to a phase-locked loop to produce a recovered clock signal. The delay elements can be variable with a delay controlled by an output signal from the phase-locked loop, to thereby track a varying center frequency of the digital input signal.

Abstract: "Method of coding data bits on a recording medium, arrangement for putting the method into effect and recording medium having an information structure."The so-called Miller modulation has the disadvantage that a direct current is generated in the information channel. When this modulation method is used for magnetical or optical recording, the result is that the amplitude values and the zero crossings are deformed as these channels cannot transmit direct current.According to the invention, in order to obtain, a d.c. free modulation, the Miller modulation concept is modified such that sequences of data bits which, after coding, result in the introduction of a d.c. component are coded differently. It appears that, the frequency zero excepted, a good suppression of the response is obtained also in a fairly wide low-frequency portion of the spectrum.

Abstract: MOS switch is provided, in particular for a camera, with which within the line flyback time the whole optically generated signal can be transferred by periodically transferring back a fixed quantity of charge from the drain to the source.

Abstract: An apparatus for recording optically detectable information in a record carrier provided with information areas arranged in accordance with a spiral or concentric track pattern, which areas alternate with synchronization areas each containing the address of the associated information area. Recording is effected with a first modulated laser beam, while a second beam is projected after the first beam for reading the recorded information. The track pattern has previously been provided with a periodic track modulation of a frequency at which the power spectrum of the information to be recorded has a substantially zero value. The apparatus comprises a first and a second filter for filtering a signal corresponding to the track modulation out of the signal derived by detecting the first or second laser beam reflected or transmitted by the record carrier. In series with the second filter there is included a delay network from which a synchronization signal is available.

Abstract: The optical cross talk in a camera tube is reduced by the provision of a filter element which overlaps the entire target. The filter may is be arranged behind the target and is constructed so that it has low reflectance for incoming light. In order to prevent excessive transverse conduction, such a filter has a mosaic structure consisting of mutually insulated areas.

Abstract: A data stream is received from a medium. This stream consists of synchronization words and data words. The synchronization words are either identical or one the inverse of the other when they are correctly received. Between two synchronization words a fixed number of n data words is present. The information received is always consecutively stored in a buffer memory. The buffer memory has connected to it a detection device for generating an instantaneous synchronization signal by way of a majority decision on at least three correctly received synchronization words. Preferably, the buffer memory is a shift register comprising a data output which is situated approximately 1/2n data words +1/2 synchronization word beyond the center of the shift register when n has an even value.

Abstract: Disclosed is an apparatus for reproducing digitally coded information recorded on a disc-shaped record carrier in the form of optically detectable, unit information areas arranged in accordance with a concentric or spiral track pattern. The apparatus comprises a filter which is tuned to a frequency f=V/L, V being the nominal tangential speed of the record carrier and L the nominal center-to-center distance of said unit areas. This frequency component has a frequency equal to twice the bit frequency of the coded information and is situated at a zero point of the power spectrum of said information, so that the extracted signal may be employed for the generation of a clock signal.

Abstract: A system having a medium which presents signal sequences which at least partly consist of binary signal sequences and a device for generating a synchronization signal for synchronizing at least parts of said signal sequence (blocks, words). A binary signal sequence contains a synchronization pattern which consists of (2N+1) groups of codes of m+n bits. A number of (N+1) groups have a code content which exhibits a given, at least minimum Hamming distance with respect to the code (codes) of the other group (groups). The device includes a majority decision device which produces the synchronization signal by means of the n bit codes of said (2N+1) groups on the basis of a majority decision (N+1 out of 2N+1).

Abstract: The invention relates to a method of demodulating a quadphase coded data signal and a receiver for carrying out the method. The quadphase code comprises four elementary wave forms, each wave form representing two bits of the original non-coded binary signal. An elementary wave form consists of four half bit intervals, the signal corresponding to the first and the second bit, respectively, being transmitted in the first and the second half bit interval and the signal corresponding to the inverted value of the first and the second bit, respectively, being transmitted in the third and the fourth half bit interval. In a receiver according to the invention such a signal is sampled in each of the four half bit intervals. In principle all information is already available after the sampling operations in the first and the second half bit interval, but by utilizing all four samples a proper protection from noise, interference and zero level shifts is obtained.

Abstract: The invention relates to a method for the clock synchronization of a receiver for demodulating a quadphase coded data signal and to a clock synchronization device for carrying out the method.In the method according to the invention the first bit is compared (correlated) with the third bit and the second bit with the fourth bit: a high degree of correlation indicates that synchronization has been obtained and a low degree indicates absence of synchronization.

Abstract: The optical cross-talk in a camera tube is reduced by the provision of a filter element which overlaps the entire target. The filter may be arranged in front of the photosensitive target and have a spectral transmission which is adapted to the spectral sensitivity of the target. The filter may also be arranged behind the target and preferably constructed so that it is also low-reflective for incoming light. In order to prevent excessive transverse conduction, such a filter may have a mosaic structure consisting of mutually insulated areas. Optical cross-talk may also be reduced by mounting the target on a support which is separately arranged in the camera tube and which has a small thickness.

Abstract: A disc-shaped record carrier having an information track which is divided into a plurality of sectors per track circumference. Each sector is divided into a data section, in which the data can be recorded, and a synchronizing section. This synchronizing section consists of an optically detectable relief structure and comprises an indicator portion and an address portion. The address portion contains the information about the track number and the sector number. The indicator portion serves to define the beginning of the address portion unambiguously and for this purpose has such a relief structure that the indicator signal produced after cooperation with the radiation beam has a frequency which is clearly distinguishable from signal components resulting from the address portion.

Abstract: A photoconductive layer which is vapor-deposited on a carrier in a television camera tube is provided with a structure of regions having at least one dimension which corresponds in the order of magnitude, measured transversely of the layer, to the transverse dimension of an image point in the layer. These regions are separated by partitions which consist of the same material as the further conductive layer, but for which the structure is such that they exhibit a comparatively low transverse conduction.