Abstract: An adaptive equalization circuit for magnetic recording channels which derives an error signal to change the equalizer compensation value from the timing of random signal data and provides continuous feedback compensation.

Abstract: In a serial binary digit stream, when a single bit follows at least two bits of the opposite polarity and is succeeded also by a bit of that opposite polarity, a comparator produces a correction signal which is combined with the first-mentioned bit so as to broaden it in time span. As a result, the amplitude of reception or reproduction of the broadened bit is enhanced so as to compensate for deficiency of amplitude which would result from the imperfection of the transmission channel or recording and reproduction process. The broadening of the critical bit pulse can be performed by a correction pulse that enhances its amplitude, followed by Nyquist filtering and then by amplitude limiting to the normal binary digit amplitude level, or else the broadening can be accomplished by providing a correction pulse shifted in phase by an adjustably shifted clock pulse or train.

Abstract: A method and system provide for the compensation of peak shift of digital data recorded on D.C. premagnetized (erased) magnetic media. D.C. erasure results in the entire magnetic medium being aligned (polarized) in a single direction. The subsequent magnetic recording of data on such premagnetized medium normally results in a peak shift whenever the subsequently recorded signal traverses in the same direction of polarization as the single polarized direction of the D.C. erased medium. Such peak shift is compensated for in the present invention by utilization of a compensation circuit which, upon the receipt of an encoding signal which would cause data to be recorded which would traverse (be polarized) in the same direction as the premagnetized medium, is activated to provide a modified encoding signal to vary the placement of the magnetic boundaries of the recorded signal to compensate for its anticipated peak shift.

Abstract: A method and apparatus for the elimination of any net d.c. component from the transmission of binary sequential data in a run length limited code where the encoding set has less than the number of code values required to provide one-to-one mapping from source data to an encoded set satisfying preselected constraints. The past and current parity and charge of the encoded words are employed as parameters in the method to determine encoding schemes satisfying criteria such as run length limit.

Abstract: In a magnetic recording/reproducing apparatus having a multi-track head for writing a digital signal on a magnetic recording medium, a plurality of head of the multi-track head is electrically divided into a plurality of groups which are respectively driven by writing currents produced in accordance with a plurality of modulated signals indicative of input digital data. The writing currents fed to the heads of the same group are produced in response to a pulse signal such that a plurality of pulse signals having different phases are used for respective groups. The head in the same group are positioned so that they are not adjacent to each other, and therefore, undesirable crosstalk can be reduced because heads corresponding to adjacent tracks are prevented from being driven simultaneously, while the entire writing current power can be reduced.

Abstract: A magnetic recording method for digital signals, and more particularly to a magnetic head driving current waveform wherein digital signals to be recorded on a magnetic tape at a high density have the waveform of the head driving current shaped in order to reduce the degradation of the waveform. That is, in a case where the period of the current reversal of the driving current is long and continues for at least 1.5 times the bit period, the amplitude of the current in the rise part of the wave is made small. The driving current of this waveform has a reduced waveform degradation, and the magnetic recording at the high density becomes possible.

Abstract: A circuit is provided for encoding digital data to be recorded on high-density magnetic storage media. The circuit converts serial data to modified phase modulation encoded serial data with time encoding or write precompensation.

Abstract: An apparatus is disclosed for detecting the peaks of a signal recorded on a magnetic storage medium. An absolute value circuit is used to generate an output that is approximately equivalent to the mathematical absolute value of the raw signal input from the storage medium. The absolute value signal is then coupled to both a differentiator circuit and a noise rejection comparator circuit. A second comparator which detects the zero voltage crossings of the differentiator circuit is enabled and disabled by the output from the noise rejection comparator so that transitions of opposite polarity are produced, corresponding to the peaks and positive going reference level crossings of the raw signal input, while noise on the raw signal input below a qualification level established by the noise rejection comparator circuit is rejected.

Abstract: Encoded digital information signals are magnetically recorded on a magnetic recording medium with the assistance of a magnetic head to which write current is supplied. As a function of the encoded information signals, a head change is carried out wherein the current applied to the magnetic head is changed from a first current value to a second current value and vice versa. After each head change, an amplitude of the write current is varied in stepwise amounts from the first or second current value, respectively, and wherein the number of steps depends on a chronological spacing of the head changes from one another. Distortions of resulting read signals are reduced given the method and apparatus of the invention.

Abstract: A bi-level signal is recorded so as to minimize distortion when that signal is reproduced, comprising pre-distorting the duty ratio of the bi-level signal by increasing the duty ratio when the repetition rate of the bi-level signal increases abruptly, and then recording the distorted bi-level signal.

Abstract: In a data recording system employing an AC bias signal that is superimposed on the data signal, the AC bias signal is phase modulated to compensate for the difference in the phase angle between the alternating bias and the data signals. The frequency of the AC bias signal is no greater than ten times the frequency of the data signal.

Abstract: The invention relates to a method and circuit arrangement for magnetic recording of a digital data signal composed of a set of transitions. A recording signal is formed by superposition on the data signal of a high frequency, constant amplitude, magnetic biasing signal S.sub.p. The biasing signal is phase-modulated relative to the data signal transitions. The invention remedies "peak shift" and can be applied to any rectangular or sinusoidal biasing signal.

Abstract: A digital magnetic recording system in which information is recorded as transitions between regions magnetized in opposite senses. In the read channel the output of the read head is applied to modulate a carrier, passed through a surface acoustic wave transversal filter and then demodulated, and the resulting transformed waveform is sampled. The surface acoustic wave transversal filter is designed to control the manner in which the transformed versions of elementary read pulses interfere at the sampling instants in such a way as to facilitate recovery of the recorded bits.

Abstract: The invention relates to the generation of a digital magnetic recording signal modulated in phase in correspondence with the transitions of the corresponding data signal. According to the invention, the D.C. component of the recording signal is suppressed so that the recording winding can be excited by this signal by means of a transformer. The recording head can include only a single turn.

Abstract: The invention relates to a method and circuit arrangement for magnetic recording of a digital data signal composed of a set of transitions. A recording signal is formed by superposition on the data signal of a high frequency, constant amplitude, magnetic biasing signal S.sub.p. The biasing signal is phase-modulated relative to the data signal transitions. The invention remedies "peak shift" and can be applied to any rectangular or sinusoidal biasing signal.

Abstract: A pulse improvement circuit for a magnetic readback system produces a data representative signal having symmetrical, equal-amplitude pulses of limited time widths. The circuit includes an equalizer made in accordance to a final transfer function produced as a result of a mathematical convolution of first and second transfer functions. The first transfer function is based on the theory of a matched filter for receiving a signal having data representative and non-white noise pulses contained therein to produce a filter signal having maximum signal to noise ratio. The second transfer function is based on the theory of a Papoulis window function for slimming the pulses contained in the filter signal. A specific circuit implementation of the final transfer function is an eight-pole, inductor-capacitor, ladder network for amplitude equalization coupled to an inductor-capacitor, lattice network including first and second order sections for phase equalization.

Abstract: m bit data words are converted into one or two n bit (n>m) record words wherein the absolute value of a recording current is less than a predetermined value so as to eliminate a DC component from the recording current. Reproduction is made according to a partial response method thus enabling high linear bit density.

Abstract: A circuit is provided for encoding digital data to be recorded on high-density magnetic storage media. The circuit converts serial data to modified phase modulation encoded serial data with time encoding or write precompensation.

Abstract: A read circuit for a floppy disk drive is disclosed. The circuit comprises a read head for generating an electrical signal corresponding to recorded data, plus an amplifier, equalizing filter, low pass filter and decoder for processing the electrical signal.

Abstract: A system for compensating misalignment between information represented by transitions in a data bearing medium and a played back signal, the played back signal having consecutive opposite-polarity peaks corresponding to said data transitions, which system comprises a low-pass filter, which receives a signal from a non-linear element, preferably a pulse forming circuit, into which has been introduced the misaligned played back signal, and circuitry for converting the filtered signal to a series of pulses representative of the data transitions, which pulses have reduced misalignment with respect to the data transitions.

Abstract: A tapped delay line (38) terminated with its characteristic impedance at both ends is connected to receive a differential input signal in intermediate taps (27, 29) of a delay line. Delay line taps (25, 27, 29, 31), as well as ends (21, 23) are connected symmetrically to two pair of summing networks (59, 61 and 83, 85) where voltage signal components having different delays from the input signal are linearly combined. One pair of summing networks (59, 61) produces a balanced differential output signal which is an amplitude equalized and differentiated version of the input signal, while the other pair of summing networks (83, 85) produces another balanced differential output signal which is a different amplitude equalized version of the input signal. Each version is needed in one of the channels of a dual channel signal detector for detecting the peaks of the variable amplitude input signal.

Abstract: In the apparatus disclosed herein, data recorded on a floppy disk in double density MFM mode is read back using a digital, adaptive time base system which permits accurate recovery of data despite bit shifting due to a high bit density on the magnetic recording surface. The adaptive time base provides successive data windows of non-uniform duration following detection of a data bit and, further, alters the starting reference time based upon the relation of the just received data bit to its predecessor.

Abstract: A pulse shaping network for the read circuitry of a floppy disc memory system in which encoded digital data is recorded in a double density format. The pulse shaping network processes an uncompensated input read signal in order to substantially eliminate cross talk between the bivalent pulses of the read signal, thereby correcting the peak phase shift and peak amplitude distortion that characterizes intersymbol cross talk. The resulting phase and amplitude corrected read signal can then be accurately decoded in order to retrieve the information contained in the peak phases of the read signal. The pulse shaping network includes a sine pulse-forming filter comprised of a capacitively terminated parallel cascade of series LC sections characterized by respective half-period harmonic transfer functions whose impulse responses are substantially finite time duration sine pulses of a successively odd multiple of half cycles.

Abstract: A tapped delay line (39) terminated with its characteristic impedance at both ends is connected to receive a differential input signal across ends (35, 37) of the delay line. Delay line taps 41, 43), as well as ends, are connected symmetrically to a pair of summing networks (71, 73) where voltage signal components having different delays from the input signal are linearly combined. The output waveforms from both summing networks are combined to provide a balanced differential signal that has been both amplitude equalized and differentiated from the input signal with variable amplitude for use in a signal detector (87, 89) that requires such a shaped signal waveform.

Abstract: A method and apparatus for implementing the same are provided for digitally synchronizing the timing of a sequence of electrical output pulses in accordance with a selectable, permissably non-linear function of the timing of a sequence of electrical input pulses. The method and apparatus are illustrated with reference to application thereof to overcoming the problem of degradation of synchronization caused by so-called "peak shift" due to the adjacent data effect in the reading of binary data stored on magnetic disks or the like. Pulses of a timing reference signal having a uniform interval equal to a sub-multiple of the normal average interval of the desired output pulses are continuously counted to a number base equal to the denominator of said sub-multiple, and output pulses are produced whenever a pre-selected count value occurs. Output pulse timing correction values in accordance with the synchronizing function selected are stored in memory.

Abstract: Information to be written in the form of magnetic flux reversals on the surface of a disk or diskette is applied in serial fashion to a first shift registor. The parallel outputs of the shift register address a PROM. The PROM output is applied to a second shift register in the form of clock and data bits to be written on the disk or diskette magnetic surface. Control signals applied to the PROM address terminals select the mode, FM or MFM, the address mark or if precompensation is required.

Abstract: In magnetic recording devices, such as floppy disk drives, operational difficulties in the faithful reproduction of recorded data include peak shifting. The invention overcomes these difficulties by introducing a read back compensation circuit comprising a frequency equalizer which favorably amplifies a certain harmonic of the original read signal. In a recording device using a modified frequency modulation encoding scheme (MFM), for instance, this harmonic would be the second harmonic. In order to minimize the effect of circuit paramater variations the frequency equalizer may be split between two circuits, specifically between the read filter network and the read differentiating network. First switching means connected to the filter network and second switching means connected to the differentiating network are arranged as to change the damping factor and the frequency of the filter and differentiating network.

Abstract: A method and apparatus provide for the elimination of any net DC component from the transmission of binary data sequentially in successive clocked bit cells of a transmission channel wherein logical first bit states, e.g., 0's, are normally transmitted as signal transitions relatively early in respective bit cells, preferably at cell edge, and logical second bit states, e.g., 1's, are normally transmitted as signal transitions relatively late in respective bit cells, preferably at mid-cell, and any transition relatively early in a bit cell following a transition relatively late in the next preceding bit cell is suppressed.

Abstract: In a device for encoding and recording digital signals on a magnetic recording medium, precompensation in respect of errors which arise with high bit packing densities is effected by selectively advancing and delaying the signals. The delay or advance is obtained by presetting a counter according to the value of following and preceding signals.

Abstract: Magnetic recording apparatus including signal equalization means for recording data so as to obtain read pulses therefrom which are symmetrical about their peak and substantially narrowed at both the base and half amplitude points whereby increased packing density may be achieved without attendant peak shift, the equalization being provided by means for generating an ac bias signal in conjunction with data transitions and associated equalizer transitions referenced to the bias signal for application to magnetic recording means.

Abstract: A logic system is provided for precompensating data and clock bits of a formatted binary information stream during a modified frequency modulation (MFM) encoding for recording on a magnetic medium. The binary information stream is formatted into a gap field, an address preamble field, an address mark field and a data field. Clock bit generation is inhibited during the gap and address preamble fields. Further, a second of three clock bits occurring during the high order half-byte of the address mark field is suppressed to provide a modified MFM (M.sup.2 FM) field. An address mark is provided thereby for indicating the near proximity of a data field. Beginning with the low order half-byte of the address mark field, both MFM clock precompensation and MFM data precompensation is applied as required. The amount of peak shift occurring in the MFM encoded information stream after precompensation is substantially reduced.

Abstract: The disclosure relates to a method and device for reading data in the form of data pulses in a pulse train. The pulse train is obtained by the sensing of a flexible disc and contains, conventionally, a sequence of clock pulses which, in at least a portion of the pulse train, define mutually subsequent bit cells. These contain at most one of the data pulses. A bistable circuit is switched to its one state by the clock pulses and switched to its other state by the data pulses. The time which has elapsed after each switching of the bistable circuit is measured by means of a time circuit and the bistable circuit is switched if the elapsed time exceeds a value which is settable for each switching. A combinational circuit is provided for setting the above-mentioned level in dependence of the contents of at least the preceding bit cell.

Abstract: In a magnetic recording system having a medium for storing information in the form of encoded digital data, an improvement in the recording head control circuit including means and a method for determining the temporal occurrence of a major write transition of the encoded digital data and producing a minor write pre-transition and a minor write post-transition each having a lower amplitude and an opposite direction to that of the major write transition thereby providing a readout pulse corresponding to the combined write transitions having a narrower pulse width and improved symmetry which enhances the accuracy in reading out the recorded digital data and increases the packing density in the storage medium of the recording system.

Abstract: A portable tester for testing tape drive units, which provides means for generating a selective repetitive composite data pattern, which includes a direct pattern and a reverse pattern which is an inverted image of the direct pattern, and writing the composite pattern on tape. Means are provided for reading the composite pattern off the tape and providing a read signal which is the result of amplifying and differentiating the signal from the read head. Means are provided for applying this read signal to an oscilloscope in a conventional manner, and to trigger the sweep of the oscilloscope at a selected time in advance of a critical portion of the read signal, for each of the direct and reverse patterns. Thus, an analog pattern signal will be displayed on the oscilloscope screen for the critical parts of both the direct and reverse portions of the pattern, for tape movement both direct and reverse.

Abstract: A dual channel signal detector circuit comprising an equalizer for responding to a variable peak amplitude input signal, in which the peaks are representative of data, so as to provide a substantially constant peak amplitude output signal having discrete data representative pulses spaced along a base line, which is substantially flat at the zero level in regions intermediate the pulses, for application to separate peak detection and amplitude detection channels. The peak detection channel produces data pulses each indicative of the relative time occurrence of the peak of a respective data representative pulse while the amplitude detection channel is triggered by signal levels of the data representative pulses exceeding a predetermined threshold to produce gating pulses for gating the data pulses to the circuit output substantially exclusive of any noise that may be present at the input of the circuit.

Abstract: An improved method and apparatus for the storage of binary data on a magnetic surface is described. The binary data to be stored is provided in the form of electrical pulses occurring sequentially at intervals of time T. The method and apparatus provide for exciting a recording head and causing a flux transition at a first predetermined time T.sub.1 during the data pulse interval in order to store a first binary character or, alternatively, for exciting the head at a second predetermined time T.sub.2 for storing a second binary character. A minimum transition separation time T.sub.min equal to the interval period T is established by inhibiting excitation of the head at those times which are separated from another transition by a period of time less than T. A limited maximum transition separation time T.sub.max is provided by shifting the excitation of the head in an interval immediately adjacent an interval during which excitation of the head was inhibited.

Abstract: A data decoder is provided which is useful for decoding data magnetically encoded on a magnetic stripe on the back side of a credit card which may be manually moved through a reader at a variable velocity. The data is decoded by comparing the occurrence of voltage pulses after the onset of a bit interval, representing binary data encoded as magnetic flux changes, with a preselected portion of the measured time duration of the preceding bit interval. If a voltage pulse occurs after the onset but before the end of the preselected portion, the data is determined as a binary "one"; if a voltage pulse occurs after the end of the preselected portion, the data state is determined as a binary "zero".

Abstract: Apparatus in a high-density disk storage controller for qualitatively testing circuits recovering self-clocking data, on-line and independently of any storage device. The ability of the data recovery apparatus, which is designed with broad-tolerance circuits and components, to recover a data pattern having predetermined and worst-case phase-shift or jitter is tested dynamically under microprocessor control. The test results are evaluated and apparatus in the data recovery circuits selectively positions a read strobe precisely in the center of the data window to compensate for variations of delay encountered in different combinations of the broad-parameter components.

Abstract: A data writing and recording system and method and circuitry therefor is disclosed in which peak shift due to pulse crowding of data recorded on a magnetic medium is substantially reduced. The recorded data time pattern is preemphasized to compensate for peak shift such that an optimum magnetic pattern is recorded on the magnetic medium. The preemphasis of recorded peak shift errors is accomplished either by delaying or advancing the time when a particular peak shifted data transition caused by a known encoding data pattern will occur. NRZI type encoded data is coupled to a first serial to parallel shift register and clocked through to a ROM at a frequency corresponding to the data bit cell width. The ROM examines the incoming data, which is also clocked from an intermediate stage in the first shift register to a second serial-to-parallel shift register having a data clock frequency substantially greater than the data clock frequency of the first shift register.

Abstract: In a system for recording bits in elements along a moving magnetic medium wherein a first valued bit is represented by a pulse of a first width, length or duration, and a second valued bit is represented by a pulse of a second width, length or duration, there is included the improvement of changing either the first width or said second width when the bit to be recorded and the bit previously recorded have the same value.

Abstract: The invention relates to a device for reading digital information which is stored as a bivalent state of a moving carrier, for example, the magnetization direction of a tape. Reading causes a differentiating effect. A coil of the read member constitutes, in conjunction with a parallel connected capacitor, a resonant filter having a mediocre Q factor, so that the signal components of comparatively high frequency are slightly amplified. The output of the resonant filter has connected thereto an amplifier. A branch line for comparatively low frequencies with a filter having a drooping amplitude/frequency characteristic is connected to the amplifier. A branch line for comparatively high frequencies in which a filter having a rising amplitude/frequency characteristic is included is also connected to the amplifier.

Abstract: A system is disclosed for sensing a single moving magnetic track, to provide two distinct binary signals (clock and binary data) representative of digital information. Magnetically recorded signals in the Manchester or F/2F code format are selectively processed into electrical representations, using time and amplitude criteria to verify and distinguish between clock (sync) pulses and binary data pulses. An amplitude discriminator is controlled on the basis of the amplitude of immediately prior signals as well as the character of prior binary data pulse signals. A time discriminator is controlled (to segregate clock and data pulse signals) on the basis of the interval of immediately prior signals as well as the character (1 or 0) of prior binary data pulse signals. Consequently, the system is tolerant with regard to signal quality and speed consistency of the relative motion.