Abstract: An optical method for recording, reproducing, and erasing a digital signal of a mark length recording system onto/from an optical recording medium such as an optical disc or the like eliminates a fluctuation of the edge position of the reproduction signal due to heat interference between pits, thereby reducing a fluctuation of the edge position due to a fluctuation of external environmental conditions. For this purpose, there are proposed the following methods: 1) the shape of the recording pulse waveform is controlled, 2) the density at which data is recorded to the disc is variably set in accordance with the disc position, 3) a test recording is executed prior to recording user data, and the like. With these methods, a superhigh density optical recording can be realized.

Abstract: In a write control method on an optical recording, at least one shift amount selected from the defocus amount of a laser beam on a recording medium, the shift amount of a recording position on a recording track and the shift amount of laser power during recording is controlled such that the selected amount falls within a predetermined range. Subsequently, a trial signal is trially recorded at a plurality of trial zones on the recording medium by using a laser power value as a parameter. The recorded trial signal is read and a difference .DELTA.V between center levels of a highest density waveform and a lowest density waveform is detected. In connection with each trial zone, the laser power value when a reading trial signal which makes the difference .DELTA.V minimum is recorded is defined as an optimum recording power value.

Abstract: An optical recording control method determines an optimum recording laser power by effecting a test recording before information to be recorded is recorded on a disk. The recording laser power is formed of a plurality of powers. A relationship among the plurality of laser powers is regulated by power level ratios between respective powers, whereby a power used when a laser light is radiated on the disk can be controlled to be constant independent of an ambient temperature and a structure of a disk. Therefore, accurate recording marks can be formed on the disk.

Abstract: An information reproducing apparatus is capable of stably and correctly binarizing a signal reproduced from a recording medium, such as an optical disk, even if the reproduced signal contains a fluctuation of its low frequency component. The reproduced signal is replaced by an AC signal in a period other than a period during which the reproduced signal is to be demodulated so that DC fluctuation of the reproduced signal is reduced to thereby stably and correctly binarize the reproduced signal.

Abstract: A magneto-optical disk recording control method using the mark length recording method wherein the marks and gap regions between marks are recorded on the surface of the disk by maintaining a constant temperature distribution during the recording. The laser is driven to a non-recording level in gap regions between marks that exceed a base recording level used for reproduction of the marks. When a mark is recorded, the laser power is increased to a recording power level and after the mark has been recorded, the laser power level is reduced to the base power level, followed by being raised to the gap recording level. Control of the laser is performed by superposing a plurality of pulse trains that are synchronized with respect to a clock having a cycle T. The pulse trains are derived from the code train to be recorded and have pulses with a duration that is an integral multiple of (1/2)T.

Abstract: A signal reproducing system discriminates signals stably in the case of reproducing a signal from an optical recording medium which has coexistent recording areas with the signals recorded in different recording forms therein. Parts that constitute a reproduced signal are respectively derived by corresponding signal detectors from the optical recording medium in which a preformat area and a data area are included as the coexistent recording areas. The average potentials of VFO parts, which are respectively contained in the reproduced signal parts, are detected on the basis of the envelopes of the signal parts by a peak detecting circuit and a bottom detecting circuit. The detected average potentials are compared with a reference voltage, and the resulting difference potentials are added to the reproduced signal by an adder to bring the average potentials of the VFO parts into agreement.

Abstract: In a receiver of quadraphase modulation signals, a receiver of quadraphase modulation signals which is provided with two kinds of equalizers being different in each sine and cosine phases, together with an equalizer extracting a clock signal.

Abstract: A separation type optical head according to the present invention includes at least a light source portion for emitting collimated beams, a focusing device (a focusing lens) for focusing the collimated beams onto an information recording surface of an optical disc medium, a focal point control mechanism for the position of the spot on the information recording surface, and a photo-detection portion for receiving beams reflected by the information recording surface. The structure is divided into a fixed portion including the light source portion and the photo-detection portion and a movable portion including the focusing device (focusing lens) and the focal point control mechanism. At least the movable portion of the separation type optical head is movably accommodated n a frame (sealing case) for the optical head so as to prevent irregular vibrations of the movable portion due to high speed air flows or turbulence.

Abstract: An automatic equalization apparatus useful for supplying an output signal of a transversal filter simultaneously to two juxtaposed comparators, one of the two comparators performing signal identification, the other of the two comparators detecting an equalization error with the reference level changed, and extracting data from resultant two kinds of data trains by taking at least (N-1)/2+1 bits as the unit, N being the number of taps of the transversal filter, performing correlation computation, and setting tap coefficients of the transversal filter on the basis of the resultant accumulated value.

Abstract: Non-linear intersymbol interference and noise in a received data signal are corrected through use of a Viterbi detector which estimates the most likely sequence of transmitted data symbols by keeping track of candidate data sequence that are recursively updated, based on likelihood measures which are determined by a signal processor which includes circuits for estimating hypothesized channel outputs in the absence of noise. Non-linear input-output relations are stored in one or more look-up tables which, in a preferred embodiment, are registers that store hypothesized channel output symbols in the absence of noise. The contents of the look-up tables may be modified in response to an error signal representative of the difference of the channel output signal and the look-up table output signal.

Abstract: A tape recorder of the present invention comprises a pair of feed and take-up spools for winding a tape as recording media, a rotatable drum rotated to wind and run the tape between the pair of spools over the drum surface helically, a head for recording, reproducing or erasing signals on the tape wound over said drum surface, and control means for controlling the relative positional relationship between the head and the tape wound over the drum surface based on an error signal such that said signals are stably recorded, reproduced or erased along a desired track, the control means having means for holding the error signal during the period in which the tape is discontinued over a drum surface.

Abstract: An adaptive transform encoder can keep a recording rate of a digital signal at a constant level.

Abstract: In a system for transmitting a binary source signal from a data transmitter to a data receiver through a noisy dispersive channel, the data transmitter includes a sliding block encoder which converts the binary source signal at a given symbol rate 1/T into an encoded binary data signal at a symbol rate P/(NT), where P and N are positive integers such that N/P.ltoreq..sup.2 log(3)/2= 0.79248. Since the channel introduces intersymbol interference and noise into the encoded data signal, the data receiver is formed from the cascade of an equalizer, a sampler and a reconstruction circuit which serves to reconstruct the binary source signal at the symbol rate 1/T. The reconstruction circuit includes a detector in a cascade with a decoder having memory the equalizer, sampler and detector are arranged for the detection of a ternary data signal at the symbol rate P/(2NT).

Abstract: A waveform equalization method whereby a transversal filter having 5 or more tapes is included, and a difference signal output, which is obtained when an isolated impulse response waveform of a digital modulated signal is inputted to the above described filter and the output of the filter is inputted to an adder, is allowed to have intersymbol interference at .+-.T/2 with respect to the central axis time and has zero outputs at .+-.nT/2 (where n.gtoreq.2 and n is an integer).

Abstract: An original digital signal is converted into either a Miller-squared code signal or a Miller code signal, and undergoes serial-to-parallel conversion to produce n-phase signals (where n is desired to be a positive even number). N-phase virtual demodulated signals are simultaneously generated at clock timing having a period equivalent to 1/n times the period of the transmission clock. Out of the n-phase virtual demodulated signals, n/2 phases are selected to undergo parallel-to-serial conversion, the original digital signal being thus obtained.

Abstract: An optical tape apparatus having improved focus and tracking control. An optical head records, reproduces, or rewrites data on an optical tape by helically scanning the tape with a laser beam. A guide plate is disposed between the optical head and the tape to prevent the beam from becoming unfocused due to fluctuation of the tape cuased by an air film between the optical head and the tape. The optical head contains a semiconductor laser and an optical system exhibiting chromatic aberration for directing the laser beam onto the tape. The optical system includes a condenser lens for focusing the beam onto the tape. Fine focus control is achieved by changing the wavelength of the laser beam by directing part of the beam reflected from the tape back to the laser, thereby changing the focal point of the beam by virtue of the chromatic aberration of the optical system.

Abstract: An apparatus for recording an reproducing a digital video signal is disclosed which includes n sampling circuits each for performing a sub-Nyquist sampling operation for the digital video signal in such a manner that the amount of data is reduced to one-n-th of an original amount (where n is a positive integer) and a pixel sampled by the sub-Nyquist sampling operation is not sampled by the remaining sampling circuits, recording/reproducing means for recording and reproducing information at all or part of pixels which are sampled by the n sampling circuits and a device for reconstructing the digital video signal from reproduced information at pixels with the aid of a synthesizing technique or interpolation technique.

Abstract: A demodulation circuit for demodulating a modulated digital including a unit for detecting a specific pattern contained in a series of data before modulation, a unit for judging the phase relation between the specific pattern and a clock pulse used for demodulation, a unit for performing a counting operation on the basis of the result of said judgment, and a unit for controlling the phase of said clock pulse for demodulation on the basis of the count.

Abstract: A device for decoding coded digital signals for every symbol consisting of a plurality of binary signals comprises first circuit for generating a first reliability for every binary signal; hard decided from the received or reproduced signal, in the symbol and second circuit for generating a second reliability for every symbol consisting of n binary signals on the basis of the first reliability, whereby decoding processing e.g. soft decision decoding is effected for every signal, depending on the second reliability.

Abstract: An error detection and/or correction is achieved in the horizontal direction in a block and then an error state is determined by use of an error correction in the vertical direction; furthermore, the correcting system is changed over according to the result of the determination.