U.S. Philips Corporation

Edmond De Niet

Albert M Rijckaert

Adrianus Wilhelmus Van Den Enden

Willem Frederik Druyvesteyn

Martijn H Hofelt

Franciscus Antonius Kuipers

Roelof Vreeken

Marinus Adriaan Deurwaarder

Jacobus P Beun

In an arrangement comprising a phase control circuit the phase comparator, when receiving input pulses with which the clock pulses are in phase, will produce an output signal having a pulse frequency which is twice the pulse frequency of the input pulses. The ripple on the control-voltage for the oscillator to be controlled resulting therefrom is compensated for by adding to the output signal of the phase detector a signal which is opposite in phase to the output signal. The result is that only frequency- and phase errors produce a ripple (change) on the output signal.

Circuit for synchronizing an oscillator to a pulse train

The invention relates to apparatus for reading a record carrier on which digital information and tracking signals of comparatively low frequency have been recorded. The apparatus comprises a correction circuit to which the regenerated digital signal is applied, which correction circuit has a transfer characteristic which at least within the frequency band of the tracking signals corresponds to the transfer characteristic of the chain comprising the recording element, the record carrier and the read element. The correction signal supplied by the correction circuit is subtracted from the signal that is read and the tracking signals are derived from the signal thus obtained. In this way cross-talk components produced in the tracking signals by the digital signal are compensated for.

Apparatus for reading a record carrier

An apparatus for reproducing information from a track of a magnetic record carrier by means of a reproducing head divided into two reproducing portions. The apparatus comprises an amplifier circuit having a pair of input terminals, connected to the outputs of the two reproducing portions, a first signal combination unit, at least one variable gain amplifier and an output terminal. The controllable amplifier is connected between the output of the signal combination unit and the output terminal of the amplifier circuit. The gain of the amplifier is controlled in such a way that upon application of the two signals to the input terminals of the amplifier circuit, a signal is obtained on the output terminal having an amplitude u which is in a fixed ratio to the amplitude of the larger of the two signals applied to the two input terminals.

Reproducing apparatus with controlled gain output independent of

For a controlled positioning of a read element relative to a track to be read during the read-out of such a record carrier, low-frequency tracking signals may be recorded in the tracks. Instead of adding separate tracking signals to the information signal, these tracking signals are represented by the d.c. content of the information signal. During conversion of the information words of the information signal into channel words steps are therefore taken to provide two channel words whose d.c. content is equal but opposite for each information word. The choice between these two channel words is made depending on a control signal which depends on the desired tracking signal.

Method and apparatus for recording a digital information signal

A device for introducing digital data into a medium having bivalent or multivalent states and having a coding device and a commutation device. The coding device receives under the control of a first clock pulse series, data signals and forms therefrom a number of code bits which are combined as an input to the commutation device. The coding efficiency is smaller than 1. Under the control of a second clock pulse series, the commutation device switches each input to apply the code bits to a number of channels of the medium, so that for each channel certain code restrictions are satisfied.

Device for coding signals which are distributed between a number of

A magnetic tape recorder or playback apparatus, especially suitable for tape having a large number of parallel longitudinal tracks, has a positioning device for independently correcting tracking and skew errors. A first positioning system uses two piezo-electric elements parallel to each other and equally spaced on opposite sides of the pivot axis, and a second positioning system arranged between the first two piezo-electric elements, having at least three piezo-electric elements regularly spaced around and extending longitudinally about the pivot axis.

Magnetic tape recording and/or reproducing apparatus with automatic head

A method of and a device for automatically compensating the error in the angular position of a reproducing head, the upper half and the lower half of a track being scanned simultaneously, while the time difference between the zero passages of the signals is determined and a signal for the compensation of the angular error is derived therefrom.

Azimuth correction of head gaps

A device for receiving analog and discrete input signals and for converting the spectrum thereof without loss of information. The resultant signal has a frequency response curve which exhibits zero points at the frequency zero and at half the sample frequency. The second zero point is then suitable for addition of a pilot tone, without the required bandwidth being increased and without interference with the data signal. The device comprises two integrating feedback loops (32, 24/40), the output signals of which are alternately activated. The sign of the active output signal determines the sign of the input signal of the feedback loops and of the output signal of the device. One feedback loop directly receives said output signal, while the other feedback loop receives this output signal via a multiplier which alternately receives a positive and a negative multiplicand.

Spectrum converter for analog signals

A magnetic reading head having a magnetoresistive element which is connected to a reading amplifier. In order to reduce the modulation noise (Barkhausen effect) when making the relationship between the resistance variation and the strength of the signal field linear in a negative feedback loop of the reading amplifier an electric turn is present which turn is positioned relative to the magnetoresistive element in such manner that a negative feedback field (Ht) can be generated with it which causes a magnetic flux in the element which is directed oppositely to the magnetic flux caused in the element by a magnetic field (H.sub.y) to be detected.

Magnetoresistive reading head

In a coding device, a pseudo-ternary signal is derived from a binary data flow. Two of the three values of the latter signal represent the same data status. The three values of the pseudo-ternary signal determine the transition instant between the two values of the status quantity of the medium used. The transition instants are advanced and delayed, respectively, by said two values. The other signal value each time produces a nominal transition instant. A status transition then exists between every two successive bit cells. As a result of said mutual time shifts, a bipolar, phase-modulated signal with inserted pilot tone is generated. This signal, furthermore, does not contain a d.c. component and is suitable for saturation storage in a magnetic medium. The extraction of the data is realized by the formation of an exclusive-OR-function between the signal received and the output signal of a phase-locked loop which is cosynchronized by the signal received.

Device for coding/decoding data for a medium

A recording and/or reproducing apparatus for a record carrier in the form of a tape, with a plurality of parallel longitudinal tracks. The apparatus comprises positioning means for controlling the position of the write/read head transverse to the direction of movement of the record carrier. The control signal for these positioning means is obtained with the aid of two optical systems, which each comprise a light-emitting element for emitting a radiation beam which is aimed at one edge of the record carrier and a light-receiving element for picking up the amount of light which shines past said record carrier, at least one of the elements of each optical system being rigidly connected to the write/read head. A detection device is coupled to the two light-receiving elements, which device derives the desired control signal from the amounts of light received by these two light-receiving elements.

Recording and/or reproducing apparatus for a magnetic record carrier in

The invention relates to a device for generating a time-dependent current in a coil, for example, a magnetic coil. Such a magnetic coil can be used, in combination with a second coil of this kind, for generating rotary magnetic fields in a device for transporting magnetic bubbles along a bubble guide structure consisting of discrete elements on a plate of magnetic material. The device comprises two or more current connection terminals, an LC oscillator circuit, a switching element connected in series with the coil, and a control unit.

Current pulse generator

The invention relates to a plate of magnetic material wherein magnetic domains can be formed and driven along guide structures consisting of discrete elements of magnetizable material, for example, vapor-deposited permalloy. The plate is used as a memory, a number of mainly parallel extending input structures forming paths for the domains between relevant outputs of the memory and relevant inputs of a decoding device. The decoding device comprises delay elements which can each be activated by a specific rotary field sequence. The output of the decoder device has connected thereto a detection element which can thus selectively detect a domain from a predetermined input structure, because exactly for the relevant domain a synchronization exists between a part of the rotary field sequence and the arrival of the relevant domain at a delay element. Therefore, neither further current wires are required for activating the decoding device, nor separate detection lines for detectors which are selective per input structure. A number of simple delay elements which have a compact construction and which can be readily activated are described.

Memory device

The invention relates to a device for generating time-dependent currents in a coil, for example, a magnetic coil. A magnetic coil of this kind can be used, in combination with a second similar coil, for generating rotary magnetic fields in a device for transporting magnetic bubbles along a guide structure, consisting of discrete elements, on a plate of magnetic material. The device comprises two or more current connection terminals, an LC series oscillator circuit and a switching element which is connected in series with the coil. If the switching element is opened for a period of time amounting to one half to one whole oscillator period, the oscillator performs a whole period. A short-circuit element, connected parallel to the capacitor, can fully discharge the capacitor. When two switching elements are connected between a connection of the coil and a positive and a negative current connection terminal, respectively, whilst the other connection of the coil is connected to an earth terminal, oscillations at a phase difference of 180.degree. can occur. In that case two short-circuit elements are required. A second magnetic field coil can be energized by a device which continues to energize the coil in the rest state, so that the direction of rotation of the rotary magnetic field can be reversed.

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Eindhoven, Netherlands

Edmond De Niet