Abstract: A signal recording device is provided for transmitting recording data signals via a rotary transformer to a rotary drum having a rotary head for recording data so that control data may be transmitted in a shorter time period and resolution along the time axis may be improved. A 1-bit start bit SB and 2-bit mode setting bits PD are followed by 3-bit group bits GP and 3-bit channel bits CL for a single bit mode, by 3-bit group bits GP and an 8-bit bit patterns BP for a multi-bit mode and by a 4-bit channel number DAN and 8-bit data DAD for D/A data. An even parity PE is appended for each of the respective modes. A continuation flag CF is further appended for the single-bit mode and the multi-bit mode.

Abstract: A recording/reproducing apparatus for a magneto-resistive (MR) head having a playback amplifier, including a capacitor for a dc feedback low-pass filter for do feedback to an initial-stage transistor, and a differential amplifier (gm amplifier), and a switching device for the gm amplifier and for the initial-stage amplifier operable at the time of recording/playback switching. The timing of the switching device is deviated for shortening the switching time interval. To this end, an output of the initial-stage transistor of a playback amplifier for a MR head is compared to reference voltage Vref by a gm amplifier and the low-pass filter is constituted by transconductance gm of the gm amplifier and the capacitance of the capacitor, with the dc output of the gm amplifier being fed back to the base of the initial-stage amplifier.

Abstract: The invention relates to a system for reading magnetic information, comprising at least one read head H0 provided with two magnetoresistive rods (MR10, MR20) whose electrical resistivities (RMR10, RMR20) vary in mutually opposite senses when they are subjected to a same variation in magnetic field. According to the invention, the reading system comprises a detection module DET which comprises two resistors R of substantially the same resistance value, an amplifier A having one input and one output, and a comparator Cp having two inputs and one output. Each resistor R has a terminal connected to the output terminal (M10, M20) of one of the magnetoresistive rods, while the other terminals of the resistors are interconnected so as to form a common junction point NC. The voltage of the common junction point NC is amplified and compared with a reference voltage Vref by the comparator Cp.

Abstract: A magnetoresistive transducer biasing technique that provides high common mode rejection ratio (CMRR) for a dual MR sensor head, while providing for short-circuit protection of the sensor elements within the head for short-circuits between the head and a disk.

Abstract: In data reproducing device, a reproducing signal is detected from a magnetic recording medium in which data is recorded, and an equalizer equalizes the reproducing signal. A sampling circuit samples the reproducing signal from the equalizer, and a filter having a characteristic of linearly delaying a phase of the reproducing signal in a frequency range not higher than a predetermined frequency performs filtering of the resulting sampled value. Thus, phase compensation in a low frequency range of the reproducing signal can be performed satisfactorily in comparison with the conventional device.

Abstract: A recording/reproducing apparatus for a magneto-resistive (MR) head having a playback amplifier, including a capacitor for a dc feedback low-pass filter for dc feedback to an initial-stage transistor, and a differential amplifier (gm amplifier), and a switching device for the gm amplifier and for the initial-stage amplifier operable at the time of recording/playback switching. The timing of the switching device is deviated for shortening the switching time interval. To this end, an output of the initial-stage transistor of a playback amplifier for a MR head is compared to reference voltage Vref by a gm amplifier and the low-pass filter is constituted by transconductance gm of the gm amplifier and the capacitance of the capacitor, with the dc output of the gm amplifier being fed back to the base of the initial-stage amplifier.

Abstract: An amplifier especially suitable for use as a reading-head amplifier in a disc drive employing a magnetoresistive sensor. The amplifier is capable of injecting a fixed current into the magnetoresistive sensor and of providing an output signal dependent on the voltage developed across the magnetoresistive sensor as the resistance of the sensor varies in accordance with its magnetic environment.

Abstract: A switch (380) couples one group of MR channels (340, 342, 344) while decoupling another group of MR channels (340, 342 and 344). Thus, the parasitic capacitance associated with the decoupled group of MR channels does not limit the frequency response of the preamplifier.

Abstract: Momentary contact with a defect site of a data storage disk or free particle by a magnetoresistive read element of a flying head causes momentary heating and unwanted increase in element resistance (thermal asperity) which can disrupt hard disk drive data reading operations. Since the disk carries a predetermined data format, the disk drive controller correlates location of a thermal asperity to the format and thereupon selects from several available thermal asperity recovery methods a method most likely to minimize thermal asperity effect upon disk drive operation during rereading of data at the thermal asperity location.

Abstract: A technique for controlling the write currents of a magnetic disk recording apparatus includes prolonging the write mode for a given time after completing data writing on a disk by supplying a constant write current to a head according to data to write, gradually reducing the write current for the given time, and cutting off the write current.

Abstract: A position sensitivity adjusting method for a disk apparatus and a disk apparatus using the same for adjusting an AGC (Automatic Gain Control) amplifier for amplifying a servo signal on a servo surface of a disk medium, involves positioning a servo head at a boundary of tracks on the servo surface. The method then includes setting a plurality of different adjustment values in the AGC amplifier, reading two position signals through the servo head for each adjustment value, and calculating a dispersion value of the position signals for each adjustment value. After the adjustment value for the AGC amplifier which provides the minimum dispersion value is acquired from the calculated dispersion values, the acquired adjustment value is set in the AGC amplifier. With the adjusting method, even when offset compensation for positioning the servo head at a track boundary is executed, a positioning error can be prevented.

Abstract: A quad burst servo demodulator with adjustable slew rate for hard disk drives. The quad burst servo demodulator includes a peak voltage detecting system for detecting the peak voltages of an input signal, a plurality of storage capacitors for holding voltages proportional to the peak voltages observed by the peak voltage detecting system, and a programmable current source for charging (via an adjustable slew rate) the storage capacitors to voltages proportional to the detected peak voltages of the input signal.

Abstract: A disc drive data recovery system for recovering data from a magnetic disc having asperities is disclosed. The data recovery system includes a magnetoresistive head for reading magnetically encoded data from the magnetic disc and providing in response a signal indicative of the magnetically encoded data. Contact between the magnetoresistive head and an asperity corrupts the signal such that the signal contains thermal asperity noise. The data recovery system includes an asperity recovery filter coupled to the magnetoresistive head for receiving the signal from the magnetoresistive head and reducing the thermal asperity noise in the signal.

Abstract: An open-loop biasing circuit for a magnetoresistive element provides high common mode and power supply rejection. Two current sources are connected together by two conduction paths. A first conduction path has two impedances. One impedance is tied between the first current source and ground and the second impedance is tied between the second current source and ground. The second conduction path includes the magnetoresistive element. A capacitive path between the two current sources reduces power supply noise and a voltage follower reduces parasitic capacitance in the capacitive path.

Abstract: A circuit is disclosed for pre-amplifying signals from an MR sensor in a disk drive without producing output voltage transients as the MR head changes its operational mode. In one preferred embodiment, the circuit includes a bias current source, an input stage, and a voltage clamp across the inputs of the OTA of the input stage. The input stage remains active in all modes of the MR head to avoid transients generated by the thermal responses of the MR sensor. In a second embodiment, the circuit allows the current from a first current source to bypass the input stage and flows directly to the MR sensor in write or idle mode. The bias current remains generally constant in all modes, thus avoiding output transients. In the third embodiment, upon switching to read state, the MR sensor is biased with an additional current source to quickly heat up the sensor.

Abstract: A write driver for an inductive head of a magnetic storage medium that induces a faster write current switch across an inductive head element of a magnetic storage medium comprising having a pair of switches, S.sub.1 and S.sub.2, coupled to a pair of current sources, I.sub.1 and I.sub.2, wherein first switch S.sub.1 is coupled to first current source I.sub.1 and controlled by a first current switch control signal CLK. Second switch S.sub.2 is coupled to second current source I.sub.2 and controlled by second current switch control signal /CLK. First switch S.sub.1 is also controlled by first current control signal CLK to maximize rail to rail voltage swing. Similarly, second switch S.sub.2 is also controlled by second current control signal /CLK. In an alternative embodiment, a current booster is coupled to each current source to boost the write current to offset the otherwise decrease to write current due to damping resistor R.sub.

Abstract: A rigid disk drive unit includes head assemblies having both inductive and magnetoresistive heads. When information is read from a disk surface, signals from the inductive head and the magnetoresistive head are combined to provide an output signal, thereby to overcome disadvantages of using either signal alone. The relative contributions of the magnetoresistive and inductive signals are varied to optimize performance depending on the radial position of the head assembly over a magnetic disk and upon whether the information being read is data or servo position information. The inductive signal is ignored during data recovery procedure head shift operations.

Abstract: The present invention is a system for reading information stored on a plurality of disk surfaces. The system comprises a plurality of channels each containing a preamplifier having first and second terminals for connection to an MR head. A bias circuit is provided common to all of the plurality of channels. The preamplifier in each channel includes first and second channel select circuits responsive to first and second channel select signals and current output from the bias circuit to output currents based on the current's output from the bias circuit. The preamplifier in each channel also includes first and second complementary output transistor circuits responsive to the current's output from the first and second channel select circuits and to the first and second voltages to provide bias current through the respective MR head connected between the first and second terminals of the respective channel. The system is entirely symmetrical around ground for improved common mode rejection.

Abstract: A magnetic disk drive comprises a magnetic recording medium, a magnetic recording head for reading/writing data from/onto the magnetic recording medium, and detecting means for detecting thermal asperity by comparing the data read out from the magnetic recording medium with a predetermined value.

Abstract: A method for reliably measuring preformatted servo patterns, on a magnetic tape, for positioning a magnetic head. The tape has constant frequency stripes marking servo pattern areas. The drive reading the preformatted tape has a read channel amplifier with automatic gain control (AGC). When a stripe is detected, AGC is enabled. Before leaving a stripe, AGC is placed on hold. The amplitudes of two servo bursts are then measured with a gain that has been calibrated by a signal from a stripe. During the time AGC is enabled, the amplifier peak output is limited to less than half the maximum amplifier peak output. The servo pattern signal amplitude is about twice the signal amplitude of a stripe, so that servo patterns are measured with almost the maximum signal-to-noise ratio. When a stripe is detected, a counter counts pulses resulting from the stripe signal, for a fixed time, to ensure that the stripe detection is valid.

Abstract: An amplifier for an MR head comprises a means for switching cut-off frequencies of a plurality of lowpass filters, when a data signal superposed by a disturbance signal (a composite signal) is input from an MR head, a means for extracting the disturbance signal from the composite signal, a means for adding the extracted disturbance signal to the composite signal. Accordingly, it possible to obtain a data signal less influenced and less distorted even if a disturbance signal appears.

Abstract: A magnetic disk apparatus includes a reproducing circuit for reproducing a signal recorded in a medium, a reproduced signal processing controller having a TA compensation mode to effectively control reproduced signal processing in accordance with generation of TA, a reproduced signal processor for processing the reproduced signal output from the reproducing circuit under the control of the reproduced signal processing controller, and an HDC.

Abstract: The present invention relates to an apparatus and method for amplifying a signal from a MR element of a hard disk drive magnetic recording head having a DC component and an AC component. The apparatus includes an amplifier circuit that amplifies the signal. An offset corrector circuit is coupled to the amplifier circuit and generates an offset signal representative of a complement of the dc component of the signal. A circuit is coupled to the amplifier circuit and the offset corrector circuit that combines the signal and the offset signal to provide an output signal representative of the AC component of the signal.

Abstract: A power source control circuit prevents a generation of a spark between a magnetic head and a magnetic disk by accurately controlling an electric potential provided to the magnetic head. A signal processing circuit provides to the magnetic head an intermediate electric potential between a positive source voltage and a negative source voltage supplied by a power source unit. A first circuit provides the positive and negative source voltages to the signal processing circuit. A second circuit controls one of the positive and negative source voltages in response to a reference voltage fed back from the signal processing circuit. The reference voltage is provided from the signal processing circuit to the magnetic head for setting the head at the intermediate electric potential.

Abstract: A preamplifier and its associated biasing circuitry for connection to a magnetoresistive sensor having a first end and a second end is disclosed. The biasing circuitry properly biases the preamplifier such that the preamplifier can properly read signals from the sensor. The preamplifier includes a first transistor. A base of the first transistor is connected to the first end of the magnetoresistive sensor. An emitter of the second transistor is connected to the emitter of the first transistor. A collector of the third transistor is connected to the collector of the first transistor. A base of the fourth transistor is connected to the second end of the magnetoresistive sensor, while the collector of the fourth transistor is connected to the collector of the second transistor, and the emitter of the fourth transistor is connected to the emitter of the third transistor. The preamplifier further includes a voltage source and a first and a second resistor.

Abstract: A circuit for input switching for a read channel is described. The present invention suppresses unwanted signals at the input of a read channel. The present invention uses an open impedance switching circuit to inhibit AC transients during DC bias restoration. One embodiment of the present invention uses a low impedance switching circuit to provide rapid restoration of DC bias levels. Coordination of the operation of the open impedance switching circuit and the low impedance switching circuit is provided to maximize suppression of unwanted signals.

Abstract: Two position signals N and Q having phases different by 90.degree. are demodulated from discrete readout signals of two-phase servo information through a position signal demodulating circuit. A level detecting circuit compares sizes of two position signals (absolute values) N and Q discretely available from the position signal demodulating circuit through seek operation at a certain speed. A cross-point C is calculated on the basis of two smaller discrete values Z and Y immediately prior to reversal of the size relationship of the two signals at the cross-point and a smaller discrete value X immediately after passage through the cross-point, and the thus calculated cross-point value C is set in an AGC amplifier as a reference amplitude value. The AGC amplifier adjusts the positional sensitivity to a certain value by amplifying the cross-point level of the two position signals N and Q so as to agree with the set reference amplitude value.

Abstract: An improved method and apparatus are provided for dc offset trim adjustment of a variable gain amplifier. The VGA has predetermined overall gain endpoints. A minimum gain and a maximum gain are identified for the VGA in a preferred operational range. The identified minimum gain and the identified maximum gain for the VGA in the preferred operational range are spaced apart inwardly from the VGA predetermined overall gain endpoints. The minimum gain for the VGA in operation is set, then trim adjustment of the VGA is provided to minimize an output of the VGA. Then the maximum gain for the VGA in operation is set, then dc offset trim adjustment of the VGA is provided to minimize an output of the VGA.

Abstract: An FET write driver providing high rates of data transfer to a magnetic storage medium by effectively utilizing the voltage swing provided by supply voltage. A first and a second p-channel FET power switch are coupled between the voltage supply and the inductive head, each having a high aspect ratio for low resistance. A first and a second current mirror are coupled at their inputs to the inductive head and a current source, each current mirror having a reference arm coupled to the current source and a mirror arm coupled to the inductive head. Each current mirror has an output coupled respectively to a first and a second mirror enabling FET switch, each having a high aspect ratio for low resistance.

Abstract: Thermal transient signal detection/correction circuitry corrects for errors caused by actual thermal asperities and baseline wander in the analog signal from a magnetoresistive (MR) sensor, such as an MR read head in a magnetic recording disk drive. In a disk drive with an MR head the detection/correction circuitry is located between the MR head signal amplifier and the data readback channel so that the thermal transients are corrected in the analog data signal prior to processing of the analog data signal into digital data. A detection circuit receives the analog data signal from the MR head, low-pass filters the signal and generates a thermal asperity event signal if the filtered signal exceeds a predetermined threshold. A correction circuit also receives the analog data signal from the MR head and includes a high-pass filter whose pole frequency is controlled by the thermal asperity event signal from the detection circuit.

Abstract: An open-loop biasing circuit for a magnetoresistive element provides high common mode and power supply rejection. Two current sources are connected together by two conduction paths. A first conduction path has two impedances. One impedance is tied between the first current source and ground and the second impedance is tied between the second current source and ground. The second conduction path includes the magnetoresistive element. A capacitive path between the two current sources reduces power supply noise and a voltage follower reduces parasitic capacitance in the capacitive path.

Abstract: A power transistor driving circuit for a single power source drives a predetermined load and prevents each of the drive circuit transistors from being damaged because they are not turned on simultaneously.

Abstract: A first differential amplifier circuit is provided having a first and second input terminal suited for connection to a magnetic head. The first differential amplifier circuit includes first and second output terminals for providing a read output signal. A second differential amplifier circuit is provided which has first and second input terminals connected to the first and second input terminals, respectively, the first differential amplifier circuit. The second differential amplifier circuit also includes first and second output terminals. A first feedback capacitor is provided which is connected between the first input terminal of the first differential amplifier circuit and the first output terminal of the second differential amplifier circuit. A second feedback capacitor is provided which is connected between the second input terminal of the first differential amplifier circuit and the second output terminal of the second differential amplifier circuit.

Abstract: A magnetic recording/reproduction apparatus comprises a magnetic tape running apparatus to rotate a rotary drum and run a magnetic tape with the magnetic tape being contact with, at least, part of the circumferential surface of the rotary drum, a plurality of erasing magnetic heads installed on the rotary drum so that the magnetic tape are in contact with the heads and used to erase recording signal, a plurality of recording magnetic heads used for recording, a plurality of erasing circuits installed on the rotary drum to output erasing signal to each of the erasing magnetic heads, a plurality of recording circuits connected to the recording magnetic heads respectively and installed on the rotary drum so that the recording circuits are selectively be gone to enable state and disable state, one or more rotary transformers connected to erasing circuits in common, and a driving circuit to record information signal in the magnetic tape through recording magnetic heads, recording circuits, and rotary transformers.

Abstract: A magnetoresistive sensor and preamplifier system has an excess differential imbalance detector, (a) for detecting magnitude differences between a pair of signals occurring at the output of a preamplifier subsystem due to modal transitions, and (b) for initiating action to overcome same. The excess imbalance detector changes a threshold therein to become more sensitive to smaller imbalances in the output signals being monitored after detection of a modal transition imbalance.

Abstract: A circuit forming part of an arm electronics module installed on an actuator arm that measures the voltage across an MR head A control unit supplies a measurement enable signal that enables a measurement enable circuit. A current bias circuit, responsive to the control unit, supplies a bias current to the MR head. A common node in the circuit provides a voltage signal responsive to the voltage across the MR head, with an added diode V.sub.BE drop across an input transistor. A voltage measurement amplifier has an input node and an output node that supplies an output voltage reduced in voltage by one diode drop (V.sub.BE). An input switch, responsive to the measurement enable signal is coupled between the input node and the common node. An output switch, responsive to the measurement enable signal is coupled between the output node and an output terminal.

Abstract: An innovative differential amplifier circuit, which can control the midpoint potential of a load which does not itself have any midpoint connection. This is achieved by using a proxy load element in parallel with the primary load. The proxy load is of much higher impedance value than the primary load, and does have a center tap. The potential of the center tap of the mirrored load is used for a feedback connection to a control loop which regulates the output to both the primary load and the proxy load.

Abstract: A magnetic head includes an inductive coil electrically partitioned into a plurality of segments by a plurality of conductive leads. During the data reading mode, magnetic flux changes emanating from a record medium are sensed by the magnetic head. The inductive coil transduces the magnetic flux changes into electrical signals at the conductive leads. The signals are amplified by serially cascading the plurality of segments and the signals are then fed into amplifiers. During the data writing mode, the electrical signal is applied to two of the conductive leads via a data writing amplifier. The inductive coil converts the electrical signal into changes in magnetic flux for recording onto a magnetic medium.

Abstract: Disclosed is a rigid disk drive information storage device which includes a rigid disk having an outside diameter in the range of about 33-34 mm., with a housing having a footprint that includes a width of about 35 mm. and utilizing a rotary actuator for positioning read/write recording elements across the surface of the disk. The disk storage devices further includes a footprint with length of about 50.8 mm., and includes in one embodiment dynamic head loading apparatus for loading the read/write recording elements into operative relationship with the disk. In another embodiment the rigid disk drive utilizes contact start stop loading and unloading of the read/write recording elements. An inertial latch is also provided for preventing rotation of the actuator when the drive is subjected to a rotational force.

Abstract: A direct AC-coupled amplifier for use with a plurality of magnetoresistive read elements includes a differential amplifier having first and second inputs and first and second outputs. A plurality of input circuits are provided, one for each MR element. Each input circuit has first and second connections to opposite sides of the respective MR element and a pair of emitter-follower its. Each emitter-follower circuit comprises a transistor having a base connected to one of the connections and a collector arranged to be connected a first voltage source. A capacitor is connected between the emitter of each of the transistors and a respective input of the amplifier. A current is applied to the first and second connections of a selected one of the input circuits to operate the respective MR element.

Abstract: A circuit for converting received input signals to highly symmetrical CMOS level outputs having fast slew rates. The circuit can accept a differential input signal with a wide range of common mode voltages. A first stage level shifts the input signals to provide a ground-based common mode output to a second stage level shifter which centers the input signals around the midpoint between V.sub.cc and ground and which increases their voltage swing. The final stage provides a full, highly symmetric, rail-to-rail output capable of driving highly capacitive loads at high rates and which is immune to temperature, V.sub.cc, and process variations.

Abstract: An apparatus and method for reading an information signal from a magnetic storage medium using a magnetoresistive (MR) element, modifying the signal such that a thermal component of the signal representing a thermal response of the MR element is degraded, and altering the modified signal to produce a restored thermal signal substantially representative of the thermal component of the signal read from the storage medium. The information signal induced in the MR element is communicated from the MR element to an arm electronics (AE) module having a highpass filtering behavior. The AE module passes content of the information signal other than the thermal component content, thereby degrading the thermal component of the information signal. An inverse filter, implemented using an infinite impulse response (IIR) filter, receives the highpass filtered signal from the AE module and produces a restored thermal signal substantially representative of the thermal component of the information signal.

Abstract: A Digital Data Storage (DDS) data storage mechanism for reading DDS tapes containing data at either 61 kbpi or 122 kbpi has two circuits for recovering data from signals induced in a magnetic head by magnetic patterns on the tape. One circuit incorporates a clipping amplifier, a phase-locked loop (PLL), and a latch to sample the two-level signal obtained at 61 kbpi, at times defined by clock pulses from the PLL. The second circuit incorporates a PR-1 partial-response maximum-likelihood (PRML) detector to decode the three-level signal obtained at 122 kbpi. The cosine frequency response characteristic of the PR-1 channel facilitates use of the same rotary head drum and magnetic head gap for reading tapes at either bit density.

Abstract: A disk drive preamplifier unit includes a serial interface circuit for receiving serially formatted control signals from an associated disk drive controller. The control signals contain several types of information, including head select, write current magnitude, bias for MR transducers, gain magnitude for a variable gain amplifier, and test and mode information. The preamplifier unit incorporates several test circuits in addition to the usual write unsafe detector circuit, and a multiplexer controlled by the mode control signals from the serial interface unit is used to select which test circuit or detector is coupled to a common test output terminal whose signals are coupled back to the controller for further processing.

Abstract: The present invention is a magnetoresistive element amplifier circuit for amplifying signals produced by a magnetoresistive element. The amplifier circuit includes a gain setting resistor and a first and second transistor. The first transistor has a pair of controlled terminals connected between first and second supply terminals and in series with the magnetoresistive element. The second transistor is connected to the first transistor in a cascode configuration. The second transistor has a pair of controlled terminals connected between the first and second supply terminals and in series with the gain setting resistor. The magnetoresistive element is in a separate DC current path from the gain setting resistor. The first and second transistors provide small signal current through the gain setting resistor for producing gain adjusted output signals.

Abstract: In a common emitter type amplifier circuit including an input bipolar transistor having an emitter connected to a ground terminal and a collector connected to a load connected to a power supply terminal, a voltage at the collector of the bipolar transistor is fixed by a DC feedback loop, and a current control circuit is provided between the collector of the bipolar transistor and the ground terminal. Thus, a current in proportion to a voltage at the power supply terminal flows from the load to the ground terminal.

Abstract: In a magnetic disk apparatus of high-speed data transfer, in order to cover an uncompensable section of the thermal asperity by error code correction to shorten the uncompensable section, upper and lower envelopes of a reproduced waveform are detected to obtain a level variation waveform due to the thermal asperity and subtract it from the reproduced signal. A thermal asperity processing circuit shown in FIG. 1 for compensating for the thermal asperity is used. In an envelope detection circuit in the thermal asperity processing circuit, a forced charge and discharge current control circuit is used in the thermal asperity portion to thereby be able to improve the follow-up characteristic to level variation of the thermal asperity and shorten the uncompensable section.

Abstract: A peak detector having several novel detection modes including detecting a pair of peaks with opposite polarity and selecting whether or not the peaks must cross programmed thresholds to be detected. The novel detection modes together with several known detection modes are provided in one unit and can be selected by the user. A power down feature is also provided.

Abstract: An innovative disk drive system which provides a regulated bias current to a magnetoresistive read head, and controls the voltage of the magnetoresistive read head terminals so that the CENTER of the resistor is at ground. This halves the peak magnitude of the head-to-disk voltage.

Abstract: A single end input type high frequency amplifier of the present invention decreases noise superposed on a power supply of a pre-amplifier in a read amplifier which amplifies a signal from MR head. The single end input type high frequency amplifier includes a transistor connected to an input side terminal of a differential input amplifier. A single end type resistor is connected to the transistor and a loop amplifier is connected to the single end type resistor to feedback a difference voltage between a reference side terminal and an input side terminal of the differential input amplifier.