Deutsche Thomson-brandt Gmbh

Christian Buchler

Friedhelm Zucker

Yasuaki Morimoto

Heinz-Jorg Schroder

Friedheim Zucker

Dietmar Uhde

Yoshiharu Chikazawa

Lieu Kim Dang

Akira Kawamura

Gerhard Weissmann

Tracking error signal in an optical read/write device, such as a CD ROM, are fine tuned for deviations in the positions of the lens structure normal to the recorded medium to provide more precise tracking control. Track error signal is developed by means of DPD-TE circuitry, using for example, signals from a four quadrant photodetector. Selected pairs of the signals from the photodetector are summed and the sums are differenced to develop an intermediate signal. The intermediate signal is amplified with a gain proportional the reciprocal of the intensity of light received by the photodetector, and thereafter combined with the track error signal to provide a corrected track error signal.

Device for scanning optical discs using phase detection in a system with

G factor alignment

A magneto optical disc system includes a disc having permanently recorded tracks overlain with magneto optical recording material. Data is recorded in the magneto optical material in tracks superimposed over the permanently recorded tracks, using the read-only data to define magneto optical tracks. The magneto optically recorded data is correlated with the prerecorded data for defining the location of data stored in the magneto-optic tracks.

Recording and reproduction of items of information using ROM-RAM storage

An optical scanning device includes an object lens for focusing a light beam onto a recorded medium having a helical data track. A tracking regulation circuit guides the object lens along the data track. The tracking regulation circuit includes a coarse drive circuit for driving the optical scanning device and a fine drive circuit for adjusting the object lens. The optical scanning device and the object lens have optical axes which normally are aligned. Deviations of the optical axes from alignment are measured and regulation signals are generated for the coarse drive circuit in accordance with the deviations.

Optical scanning device with coarse and fine scanning control

A digital recorder which includes an A/D converter for converting analog signal to digital form for recording and a D/A converter for converting recovered recorded digital information to analog form, includes switch circuitry for interconnecting the D/A converter and the A/D converter in a manner to perform sample rate conversion of input digital signals to condition the recorder to record digital signals having different sample rates.

Digital recording and reproduction device

A scanning device for recording/reading data in data tracks of a recording medium includes a light source supported by a tracking head for guiding a light beam along the data tracks. The data tracks are rotated and the beam is focussed onto the data tracks. The light source is moved at an angle .alpha. with respect to the radial direction of motion of the data tracks. An optical element directs the light beam to the recording medium and directs light reflected from the recording medium to a detector. An astimatic element is arranged between the optical element and the detector. The scanning device is improved in that the astimatic element has one axis arranged at the angle .alpha. with respect to the radial direction of motion.

Optical scanning device for a disc player including improved focusing

The beam of light reflected from an optico-magnetic recorded medium is reflected by an optical pick-up onto one optical or another in accordance with the direction that the beam's plane of polarization is rotated in. A data signal is obtained from the difference in the photovoltages of the two photodetectors.

Pick-up for selectively reading and writing an optical recording medium

Magneto-optical recording circuitry for reversing a magnetic field

An optical pick-up for selectively reading and writing an optical and magneto-optical recorded medium, in which light projected on the recorded medium is reflected therefrom and directed onto one of two photodetectors, depending on the polarization of the light. The recorded medium has magnetic domains for storing data and a magneto-optical signal is generated from the difference between the two photo voltages from the two photodetectors. The magneto-optical signal represents the data stored in the magnetic domains. The recorded medium also stores data in pit forms, and an optical signal is generated from the sum of the photovoltages of the two photodetectors, to represent the data stored in the pit forms. The arrangement is suitable for reading out simultaneously the optical signal and the magneto-optical signal.

Optical pick-up selectively reading and writing an optical and

An optical scanning system for a compact disc having a sinusoidal data track radially meandering, at a selected frequency, about the axis of rotation of the disc includes a first laser beam for reading data from the data track. A +1 level laser beam and a -1 level laser beam respectively track the opposite edges of the data track and generate a tracking error signal. The +1 level laser beam and the -1 level laser beam are separated, with respect to the disc, by a distance equal to an odd integer multiple of one half the wavelength corresponding to the selected frequency. The +1 and -1 laser beams are not modulated by the sinusoidal data track and standard tracking circuitry can be used to track the data track.

Optical scanning system for a sinusoidal data track

A circuit for reversing a magnetic field in which a bifilar coil is provided with a series of two oppositely-wound windings that are connected together at one end to form a junction. A source of current is connected in series with an inductive resistor, and this series circuit is connected at one end to the junction. At the other end of this series circuit, there is a voltage supply source. Each of the two oppositely-wound windings has its other end connected to a variable switch. The two variable switches have control inputs that are connected to two outputs from a control unit which applies a reference potential to each winding through the variable switch, so that all current from the source of current flows through each winding upon closure of the respective variable switch.

Circuitry for reversing a magnetic field

Circuit arrangement for identifying the type of an optical record carrier

An optically-recorded medium in which a reflecting optomagnetic layer is applied to a transparent substrate layer. The recorded medium stores data magnetically and by pits. The magnetically stored data and the pit stored data are superimposed on each other, so that every spot and region on the recorded medium stores both magnetically stored data and pit stored data. The recorded medium is not divided into separate regions for magnetically stored data and pit stored data, and the magnetically stored data and pit stored data may be read out simultaneously by a single light beam.

Magneto-optical recorded medium with a transparent substrate layer

An optical pick-up for selective playback and recording on a magneto-optically recording medium, in which light is projected from a source onto the medium. The light is provided with a direction of a polarization, and is either reflected from the recording medium or is transmitted through the medium. The reflected or transmitted light becomes deflected onto a predetermined one of several photodetectors, depending on the direction of polarization of the light. The intensity of the reflected light or the transmitted light is held constant to minimize noise components that result from the optical properties of different recorded media as well as from the light. By holding the light intensity constant, moreover, precise readjustment to each of the different recording media that may be used, is not necessary.

Growing community of inventors

Marbach, Germany

Christian Buchler