Abstract: A read preamplifier for use in reading data in a magnetic storage system uses positive feedback to reduce the preamplifier's input capacitance. The read preamplifier includes first and second voltage supply terminals. An input is coupled to the second voltage supply terminal and receives input signals from a connected magnetic head. An output is coupled to the first voltage supply terminal and to the input for producing output signals based upon the input signals. A positive feedback circuit, coupled to the input reduces the input capacitance of the read preamplifier.

Abstract: A magnetic head driving circuit is provided which has first and second transistors having the bases respectively connected to first and second input terminals and the collectors supplied with a power source voltage, third and fourth transistors having the collectors respectively connected to the emitters of the first and second transistors, and a magnetic head and surge absorbing resistor disposed in a parallel connection with each other between the emitters of the first and second transistors. Delay circuits are respectively disposed between the input terminal and the base of the fourth transistor and between the second input terminal and the base of the third transistor. If there has a time delay in inverting action generated between the first and second transistors, the reverse bias voltage acting between the base and emitter of the first and/or second transistor will be impossible to be increased, so that the switching time of the magnetic head current can be shortened.

Abstract: An amplifier for biasing and amplifying the signals produced by a magnetoresistive element is provided. The input stage of this circuit includes two transistors in a differential common base configuration having a low input impedance. Since the two transistors are coupled to separate identical current sources, balance between the currents through the two transistors is maintained. The currents are balanced without the use of a feedback loop. Additional input stages may be added to allow signals from additional magnetoresistive elements to be selected and amplified. By using a common mode switching configuration, switching transients are greatly reduced.

Abstract: A write circuit in a magnetic disc drive writes data to a magnetic disc based on a write signal received. The write circuit includes a magnetic write head, an H-switch, and a headroom assistance circuit. The headroom assistance circuit includes a voltage divider, a capacitor, and a charging circuit for charging and discharging the capacitor based on the write signals so that increased voltage appears across the magnetic recording write head during switching of the current polarity by the H-switch.

Abstract: A read/write amplifier provides a magnetic disk unit capable of reducing variations of the bias voltage. An output stage provides a DC bias circuit for the read signal and a circuit for producing a high impedance for the read signal. A switch circuit is in a closed circuit operation only when a chip select signal is received. The output stage provides a switching order to connect a constant current circuit to the amplifier circuit at read time and to connect the DC bias circuit at the write time.

Abstract: A preamplifier circuit amplifies signals from a magneto-resistive element. The preamplifier circuit utilizes a voltage regulator to regulate one terminal of a magneto-resistive element at a predetermined voltage. A first feedback loop is used to minimize a differential DC component and a differential low frequency component of the differential output signal. A second feedback loop is utilized to cause a common mode component of the differential output signal to track an externally supplied reference voltage. The preamplifier of the present invention protects the magneto-resistive elements from short circuits of the disc medium, is powered by a single-ended power supply, and is capable of being coupled with other circuitry without physical coupling capacitors.

Abstract: A data storage system comprises magnetoresistive (MR) sensing elements for sensing data from a recording medium that is referenced to ground, and an amplifier circuit including a biasing stage, an amplifying stage, and a matching stage, each referenced to a common supply voltage source and to ground. The biasing stage includes a reference current source for selectively biasing each MR element with a constant current and, in so doing, developing a single-ended voltage signal having a first dc component. The amplifying stage converts the single-ended voltage signal into an amplified single-ended output voltage signal having a second dc component but in which the first dc component is eliminated. The matching stage creates a bias and imposes said bias on the amplifying stage for converting the single-ended output voltage signal to a differential output voltage signal in which the second dc component is eliminated.

Abstract: According to this invention, in a magnetic disk device for recording/reproducing data using a magnetic head, a position of which is controlled by a sector servo method, a tracking speed of an AGC amplifier is set to be a first speed (about 10 .mu.s) in an AGC address area and an AGC burst area, and the tracking speed of the AGC amplifier is set to be a tracking speed (about 20 ms) lower than the first tracking speed in an intersector gap, a gap, a block address area, and a data area.

Abstract: A dual head type magnetic disk according/reproducing apparatus, in which a magnetic disk is inserted and/or from which the magnetic disk is ejected, the magnetic disk having a first surface and a second surface each of which is segmented into a plurality of tracks, each track having a corresponding track number, the dual head type magnetic disk recording/reproducing apparatus includes a first magnetic head which reproduces an information signal from a first track on the first surface, a second magnetic head which reproduces an information signal from a second track on the second surface, a track number of the second track corresponding to that of the first track, and a predetermined number of tracks being between the first track and a radial location of the second track, a low pass filter, coupled to the first and second magnetic heads, to which the information signals reproduced by the first and second magnetic heads are supplied, and control means, coupled to the low pass filter, for adjusting a cut-off fre

Abstract: Circuitry for eliminating magnetic instability of an inductive magnetic transducer during sensing of data from a magnetic recording medium to prevent distortion of the readback signal by hysterically moving domain walls. An inductive sensing coil has an impedance constituting the output impedance of the transducer. Means connected to the coil amplifies a data signal generated by the magnetic flux changes and produces a selected input impedance. The sum of these input and output impedances is selected to be small enough to substantially eliminate motion of the domain walls in the yoke of the transducer while the transducer is sensing data from the medium.

Abstract: A method and apparatus are provided for biasing a non-center tapped magneto-resistive head at a constant voltage using two separate biasing stages to provide independent control over the voltage at each of the two terminals of the head. A first control device detects the voltage at a first head terminal and directs changes to the output of a current source, interconnected with a first terminal of the head, to maintain the voltage at the first terminal at a first predetermined voltage. A second control device detects the voltage at second terminal of the head and directs changes to the input of a current sink, interconnected with the second terminal, to maintain the voltage at the second terminal at a second predetermined voltage. Each control device is interconnected to a separate reference voltage source; by appropriate selection of the voltages of the reference voltage sources, the voltages at the two head terminals and the potential across the head can be established and maintained.

Abstract: A power amplifier of a digital cassette tape reproducing device is set to a value suitable to amplify an amplitude level of an audio signal from an analog signal reproducing system thereof and, when a digital signal reproducing system is selected, an audio signal therefrom is supplied to the power amplifier circuit without attenuation while increasing an amount of negative feedback of the power amplifier circuit, hence reducing amplification thereof to match an output level of the power amplifier circuit with that of the analog signal reproducing system to thereby improve S/N ratio and maintain high tone quality of the digital source.

Abstract: A system which records and reproduces a digital signal in the form of a magnetic reversal on and from a recording medium includes a magnetic head for reproducing data recorded on the recording medium; an automatic gain control unit for controlling the reproduced signal so as to have a constant amplitude; an equalizer for processing the output waveform from the automatic gain control unit; a differentiator for changing the output from the equalizer to a differentiated waveform; a low pass filter for limiting the signal band of the differentiated waveform; a low pass filter for limiting the signal band of the equalizer output; a pulser for receiving the equalizer output, the band of which is limited by the low pass filter and the differentiated waveform, the band of which is limited; a differentiator for receiving the output from the automatic gain control unit and producing a differentiated signal from the output signal; an attenuator for attenuating the differentiator output; and a waveform processor for addi

Abstract: A hard disk drive is disclosed in which the disk has tracks each divided into alternating data sectors and servo sectors, with the control data such as track addresses on the servo sectors being normally recorded more stably than the main data on the data sectors. In order to obtain read pulses representative of the peaks of the output waveform of a transducer, this waveform is directed on one hand into a differentiator circuit and thence into a wave shaping circuit for the provision of data pulses which rise and decay in synchronism with the peaks of the transducer output waveform. On the other hand, the transducer output waveform is sent into a gate pulse circuit, in which the waveform is compared with a reference signal in order to provide gate or window pulses. A logic circuit is provided for ascertaining whether the data pulses rise and decay within the durations of the gate pulses and, if they do, for producing read pulses indicative of the rises and decays of the data pulses.

Abstract: An information signal reproducing apparatus for reproducing from a recording medium information signals recorded on recording tracks formed on the recording medium. The boosting ratio at which an information signal reproduced from the recording medium is boosted before it is output is selected in response to changes in the state of reproduction, thereby minimizing deterioration of the reproduced information signal as well as stabilizing the reproduction operation.

Abstract: A driver circuit for providing drive current to a coil for positioning a read/write head of a memory disk system and method are presented. The driver circuit includes a pair of high side driver transistors having current paths connected between respective terminals of the coil and a voltage source, a first pair of low side driver transistors having current paths connected between respective terminals of the coil and a first voltage sense node, and a second pair of low side driver transistors having current paths connected between respective terminals of the coil and a second voltage sense node. A first sense resistor is connected between the first and second voltage sense nodes, and a second sense resistor is connected between the second sense node and a reference potential.

Abstract: A method of, and an apparatus for, positioning a record/playback head assembly in a transverse reference position on one edge of a multitrack magnetic tape having no track identification data or other positioning patterns prerecorded thereon. A stream of transverse head positioning data, typically representative of serial numbers 1-255, is first written by the record/playback head assembly longitudinally on the tap in a selected transverse position intermediate the opposite edges of the tape. The data are subsequently read and checked for errors. If the thus detected errors are less than a predetermined number, the record/playback head assembly is moved a unit distance toward one tape edge. A similar cycle of operations is repeated until errors are found in the read stream of transverse head positioning data to the predetermined number or more.

Abstract: A base current compensation circuit is configured for connection to a first current mirror that has lost base current. The compensation circuit includes a compensation mirror coupled in a feedback loop to the first current mirror. A current sensing transistor senses the lost base current. A current duplicating mirror is coupled to the current sensing transistor and generates a compensation current in response to the sensed lost base current. The compensation current is fed back into the first current mirror to compensate for the lost base current. A voltage clamp is coupled to the current sensing transistor and the current duplicating transistor. The voltage clamp maintains approximately equal collector-base voltages in the current sensing transistor and the current duplicating transistor to increase accuracy of the compensation mirror.

Abstract: A magnetic head drive circuit includes a first MOS transistor of a first conductivity type, a bipolar transistor of a second conductivity type, a second MOS transistor of the second conductivity type, a second bipolar transistor of the first conductivity type. The first MOS transistor of a first conductivity type has a source connected to a first power supply. The first bipolar transistor of a second conductivity type is connected in series with the first MOS transistor and has a common node thereof as a first output terminal, an emitter connected to a second power supply, and a collector current controlled as a constant current. The second MOS transistor of the second conductivity type has a source connected to the first power supply.

Abstract: An amplifier is compensated for variations in element values. A trim signal is generated based on element values of filter elements of a filter in the amplifier. An RC product in the amplifier is controlled based on the trim signal. The RC product corresponds to a product of a dynamic resistance value of a dynamic resistance element in the filter in the amplifier, and a capacitance value of capacitive elements in the filter. The RC product also determines a pole position of the amplifier. Gain in the amplifier is controlled based on the trim signal so that a desired gain is maintained.

Abstract: Low noise, low power, low voltage amplifier circuits with a single ended input having no common mode rejection for concurrently biasing and amplifying signals generated by magnetoresistive (MR) elements in a disk file. The amplifier circuits comprise a single (grounded) supply voltage source. One terminal of each MR element and the conductive substrate of each MR element and the conductive substrate of each disk in the disk file are grounded to minimize transient conductive asperity currents. The head/disk assembly of the disk file is completely enclosed by a highly conductive electrostatically shielded metallic enclosure that operates as a Faraday cage and isolates leads connecting the MR elements with the amplifier circuit from large, fast rise/fall time voltage transients.

Abstract: Disclosed herein is a magnetic read/write circuit which causes only small fluctuation of an output offset in mode switching. When a head (HD3) is switched to a head (HD6) in read mode, amplifiers (2) and (5) are turned off and on respectively. An offset caused by the amplifier (5) is reduced by negative feedback which is provided by an offset detection circuit (46) and an offset adjusting circuit (5) so that an amplifier (19) will not enhance an offset caused by difference between the amplifiers. During a constant period after mode switching, outputs of an amplifier (40) are transmitted to differential output terminals (26, 27). Input ends of the amplifier (40) are so shorted that an offset of the outputs thereof is suppressed small. After a lapse of the constant period, the outputs of the amplifier (19) are transmitted to the differential output terminals (26, 27).

Abstract: A magnetic head swing clamp configured for interconnection with a read/write preamplifier of the type including a read differential transistor pair connected to an inductive head. The collectors of the transistors in the read differential transistor pair provide first and second read output signals at first and second read output terminals for connection to a read amplifier. The magnetic head swing clamp comprises a reference voltage generator which produces first and second reference voltage levels at first and second reference voltage output terminals. Positive and negative voltage clamps are electrically connected to the first and second reference voltage output terminals, respectively, and to the first and second read output terminals. The positive and negative voltage clamps clamp voltage swings in the first and second read output signals as functions of the first and second reference voltage levels.

Abstract: A reproduction waveform signal l(having a frequency f) containing perpendicular and longitudinal components is reproduced from a recording medium which is magnetized in the vertical direction, thereby recording digital information. The signal is processed through a waveform processing circuit including an operational amplifier having an input side connected to a time constant-setting circuit comprising a capacitor and a resistor, thereby obtaining a processed waveform signal having a constant amplitude and a phase shifted by 2.times.(tan.sup.-1 2.pi.fA).degree. . Bits of the digital information is detected from the processed waveform signal.

Abstract: A recording and reproducing apparatus in which signals are recorded onto and reproduced from a magnetic tape wound around a peripheral surface of a rotary drum by magnetic heads which are attached to the peripheral surface of the rotary drum corresponding to a plurality of channels, respectively, comprises at least: a detector to detect an envelope level of a reproduced RF signal which is derived from the magnetic head every channel; a comparator to compare the detection output and a reference level and to generate a control voltage corresponding to the magnetic head every channel; a latch to store the control voltage; and a circuit to make the envelope level of the reproduction RF signal constant in accordance with a predetermined timing for supplying the control voltage.

Abstract: An apparatus for reproducing information converts read signals for servo fields and read signals for data fields recorded on an optical disk to digital data. The input range of the A/D converter at the time of A/D conversion of the read signals for servo fields and that at the time of A/D conversion of the read signals for data fields are controlled so as to be different from each other.

Abstract: A series resonant AC erase head drive circuit apparatus for use with a miniaturized cartridge-type tape drive includes apparatus for generating a non-overlapping pulse wave forms and for driving switches, power switches and a voltage controlled DC current source. The pulse form generating and power switch driving apparatus includes a clock frequency input coupled to an externally supplied clock frequency signal and an enable input coupled to an externally supplied enable signal, and includes a plurality of power switch driving outputs. The power switch driving outputs provide a plurality of power switch control signals which include a non-overlapping interval.

Abstract: A prewrite compensation circuit for use with a hard disk drive wherein surfaces of disks of the drive are formatted for writing data to the surfaces at different frequencies selected for different concentric zones on the surface. Data to be written is passed through a shift register to a series of delay elements and a multiplexer that passes the output of a delay element selected in relation to a data word received by the multiplexer to a write circuit that writes the data to the disc. The delay words, or elements of delay words, are stored in latches that are selectively connected to the multiplexer, or a delay word accumulator connected to the multiplexer, in relation to the pattern of bits surrounding a bit to be written.

Abstract: In a disk drive servo, position slope is adjusted automatically, by referencing on the amplitude of position signals at the "half-track point".

Abstract: The present invention discloses an amplifier which can amplify signals based on a specific amplification factor at high speed without inhibiting electrical characteristics. A first switch 22 is connected in parallel with a third resistor 10. A second switch 24 is incorporated into an operational amplifier 6 between the inverted input and the noninverted input. A switch controlling means 26 regulates the switching of the first switch 22 and the second switch 24. When the second capacitor 14 is charged to obtain the reference voltage V.sub.REF, the switch controlling means 26 closes the first switch 22 and the second switch 24.

Abstract: An automatic gain control circuit in which the gain of the gain controlled amplifier is controlled in an inverse exponential relationship with the amplitude of the output of said amplifier to provide a loop bandwidth that is essentially constant over variations in the strength of the input signals. The circuit is used in a magnetic disk drive to control amplification of detected servo signals to provide position and velocity error signals.

Abstract: A circuit for concurrently producing low noise electrical output signals which are amplified representations of signals produced by a magnetoresistive (MR) element and protecting said element from electrical short circuits which can occur between said element and its environment. A first feedback loop comprises (a) an input amplifier for amplifying a signal current from the MR element and (b) a source of bias current for biasing the MR element with a bias voltage. An input amplifier is concurrently biased by said current and amplifies a signal current from the MR element for producing a circuit output signal corresponding to dRh/RhRh and in which any differential direct current (dc) output offset error is minimized. (RhRh is the square of the time-averaged resistance of the MR element and dRh is the magnetic-signal-induced change in the resistance of the MR element.

Abstract: A magnetic recording and reproducing circuit comprises a recording and reproducing head including a recording coil; an erasing head disposed upstream of the recording and reproducing head and including an erasing coil; a flip-flop which receives pulse-shaped record data and outputs an output signal which reverses the state in accordance with the pulses of the recording data; a delay circuit which receives the output of the flip-flop and delays such output by a predetermined period of time; a record driver which receives the output of the delay circuit for causing a recording current to flow through the recording coil of the recording and reproducing head; and an erasing circuit for causing an erasing current to flow through the erasing coil of the erasing head at the time of recording.

Abstract: In recording systems in which video and audio signals are recorded in tape layers having different depths, a method and apparatus is provided which serves to ensure that the video recording bias for a video signal is always selected and adjusted for optimum results, allowance being made for an audio signal already recorded in the same tracks and for tolerances of the record carrier, the heads and the head amplifier with respect to the playback sensitivity. During recording of the video signal, the video recording bias is varied step-wise. After every change in the video recording bias, a d.c. signal is derived from the playback envelope of the audio signal, the value of the d.c. signal being a measure of the playback amplitude of the audio signal. As soon as the d.c. signal value has reached a predetermined minimum value, the video recording bias is ceased to be changed and the last value of the video recording bias is stored for the next recording process.

Abstract: A sum signal processing device for use in an optical disk drive for detecting a sum signal which is a groove-crossing signal used to detect a relative position of a beam spot for recording and reproducing information from a medium and the medium and a relative velocity in the radial direction of the medium. The device identifies a recorded portion on the basis of high-frequency components and, in the recorded portion, processes the high-frequency components to generate a groove-crossing signal, thereby detecting an accurate sum signal.

Abstract: A slew rate converter is provided in a video signal recording circuit for limiting a signal having a high frequency and a high amplitude so as to avoid an over-modulation when the signal is reproduced. The high frequency and high amplitude component exceeding a pre-determined amplitude is detected and applied to the slew rate converter for reducing its slew rate so that the signal component having the high frequency and high amplitude is suppressed.

Abstract: A head amplifier is integrated into an IC with a minimum number of pins and outside parts as well. An offset cancellation circuit cancels offset voltages to prevent distortion of playback signals. An amplifier amplifies a playback signal to produce an output signal that is fed to one input of a differential amplifier. A reference voltage is fed to the second input of the differential amplifier. The input of the differential amplifier is compared in a comparator with the reference voltage to produce a feedback signal for cancelling offset voltages. The feedback path is frequency sensitive to reduce frequency response at low frequencies, and to compensate for distortions produced at high frequencies from using PNP transistors in the comparator.

Abstract: Data signals recorded in oblique tracks on a magnetic tape, after they are picked up, preamplified and prefiltered, are rectified and converted to digital values representative of amplitude in respective segments distributed over track lengths. For each segment position in a track, the values are averaged and inverted by a ROM and stored in a RAM at track segment addresses. The values thus stored are converted into analog form and then used as multipliers in a multiplication stage following the preamplification and prefiltering. The output of the multiplier can readily be shaped into unambiguous data signals for further processing.

Abstract: A magnetic reproducing head amplifier includes a differential amplifier referred to as one of these three types: a balanced input type, a balanced output type, or a balanced input/output type. The amplifier has at least one positive feedback circuit for passing a positive feedback current to the differential amplifier, and at least one negative feedback circuits for passing a negative feedback current to the differential amplifier and is configured so that a positive feedback and a negative feedback are simultaneously performed by the positive feedback circuit as well as the negative feedback circuit. A resonance peak characteristic at the input part of the differential amplifier is dumped by the negative feedback current, and therefore a frequency characteristic as well as a group delay characteristic of the output of the differential amplifier becomes flattened.

Abstract: A reading circuit used for a floppy disk unit capable of reading data by converting data stored upon the surface of a floppy disk in the form of magnetic variations of a residual magnetism into voltage variations by using a magnetic head. While one of the voltage signals read by a magnetic head is differentiated by a differentiating circuit with a predetermined differential property, the other voltage signal is supplied to a level slicer and is output after being converted into rectangular pulses at a predetermined threshold value. The pulse signals are delayed in accordance with a phase shift period caused by a differential of a differentiating circuit. The delayed signals are then delivered to a comparator, which detects a signal output from the differentiating circuit by performing a comparison, so as to activate the comparator intermittently. The pulse signals, a peak value of which is detected by the comparator, are shaped by a pulse shaping circuit, and are output.

Abstract: A variable bandwidth differentiating amplifier comprises a differential amplifier and a variable filter comprising a capacitor and a pair of diodes. A current source, having a current value derived from the track postion information in the track count register of a disk drive forward biases the diodes to alter the frequency response of the filter. A Gilbert multiplier may also be included to maintain a constant voltage gain for the differential amplifier.

Abstract: A read head arrangement comprising n first read heads (h.sub.a.1, . . . , h.sub.a.n) and n second read heads (h.sub.b.1, . . . , h.sub.b.n) of the magnetoresistance type, n transistors (Tr.sub.1, . . . , Tr.sub.n) and switching means (S), where n is an integer greater than two. The first main electrode (collector) of a transistor (Tr.sub.i) is coupled to an i-th output (U.sub.i) of the arrangement. The second main electrode (emitter) of the transistor (Tr.sub.i) is coupled to a first terminal (t.sub.1) of a first read head (h.sub.a.i) and a second read head (h.sub.b.i). The second terminal (t.sub.2) of the first read head (h.sub.a.1) is coupled to a first terminal (a) of the switching means (S). The second terminal (t.sub.2) of the second read head (h.sub.b.1) is coupled to a second terminal (b) of the switching means (S), of which a third terminal (c) is coupled to a point of constant potential (earth), while i ranges from 1 to n.

Abstract: A low frequency component restoration circuit of a digital VTR restores cut off low frequency component of a reproduced digital signal. The low frequency component restoration circuit includes a first low frequency compensation path for performing feed-back low frequency compensation to an input digital signal and a second low frequency compensation path for performing low frequency compensation to the input digital signal, and wherein an output of the first low frequency compensation path is selectively supplied when a normal reproduction mode is selected where the amplitude of the input digital signal wanders slightly, and an output of the second low frequency compensation path is selectively supplied when a special reproduction mode is selected where an amplitude of the input digital signal greatly wanders in a short time period.

Abstract: A direct-coupled grounded-base amplifier comprising two or more grounded-base amplifying circuits. The same circuit used as the output stage of a first grounded-base amplifying circuit is mounted in each of second and subsequent grounded-base amplifying circuits. The base potentials of output stges of the second and subsequent grounded-base amplifying circuits are applied by the same circuit, thereby equalizing the DC potentials at both ends of an input resistor of the second and subsequent grounded-base amplifying circuits. Therefore, a capacitor outside of the IC is unnecessary.

Abstract: The present invention discloses a circuit for reproducing a digital signal which is recorded on a recording medium with high density. The reproducing circuit of the present invention adds an output obtained by differentially amplifying the signal, picked up with a playback head, with respect to a predetermined reference voltage, an amplified output delayed by a predetermined time 1T and a different amplified output delayed by 2T, thereby widening the pulse width of the reproduced waveform to be equalized. Accordingly, even a feeble isolated pulse of high density can be exactly reproduced, and the deterioration of the reproducing picture quality or the sound quality can be prevented.

Abstract: A preamplifer for use with a magneto-resistive playback head in which a d.c. current source provides current through a field effect transistor and the magneto-resistive element to ground. An operational transconductance amplifier included in a feedback loop provides a bias voltage for the field-effect transistor, whereby the voltage across the said magneto-resistive element is held constant while the resistance of said element changes. The resulting a.c. current flowing through the magneto-resistive element flows only through the feedback loop and an output resistor connected across the inputs of the operational transconductance amplifier. The amplification of the circuit is approximately the resistance of the output resistor divided by the resistance of the magneto-resistive element.

Abstract: An apparatus and method are provided for controlling the level of an audio output signal which has been recorded and is played back from a magnetic tape at a low or zero tape speed, such as utilized in jog mode or variable speed playback during editing. A gain control signal is provided to eliminate a disturbing repetitive audio signal which accompanies stop motion playback and to reduce that signal level at low tape speed playback. The gain control signal is made dependent on the magnitude of tape speed, and it is applied to adjust the audio output gain of the playback channel.

Abstract: A read channel detector circuit for recovery of digital data from a readback waveform produced by a magnetic recording head is disclosed. The detector circuit includes a forward filter for slimming the rising edge and slurring the falling edge of an isolated input magnetic pulse. Quantized feedback techniques are then used to produce a compensating waveform which is substantially complimentary to the portion of the filtered waveform occurring after T.sub.min. The complimentary waveform is then added to the forward filter output to produce a waveform which is substantially a step function. This step function corresponds to a single digital transition, either positive-going or negative-going in a digital output sequence. The equalized waveform is then limited by a comparator to produce the desired digital output sequence.

Abstract: An amplifier circuit is disclosed for simultaneously producing electrical output signals whose magnitude is representative of signals produced by a magnetoresistive (MR) element and protecting said MR element from electrical short circuits between said element and its environment. A means including a first feedback loop biases the MR element with a bias current and amplifies a signal current for causing the MR element to produce a circuit output signal corresponding to dRh/Rh and in which any dc offset error is minimized. Rh is the resistance of the MR element and dRh is the magnetic-signal-induced change in the resistance of the MR element. A second feedback loop insures that the MR element is held at a preselected reference potential and concurrently insures that no current will flow sufficient to damage the element in event of a short circuit between the element and its environment.

Abstract: A method and apparatus for equalizing a signal with weighted first and second derivative signals extracted from a resistance-capacitance-inductance series circuit.