Abstract: A preamplifier system is provided for use with a magneto-resistive (MR) sensor. Included is an alternating current (AC) coupling module connected to the MR sensor for blocking a direct current (DC) voltage associated with an input signal, and filtering low frequency noise associated with the input signal. Also provided is a gain stage module coupled to the AC coupling module. The gain stage module includes a plurality of cascode field effect transistors (FETs) configured for amplifying the input signal, while reducing intrinsic noise and increasing operational bandwidth. Coupled to the gain stage module is a control circuit for feeding back an output of the gain stage module for bias regulation and disturbance rejection.

Abstract: A preamplifier system is provided for use with a magneto-resistive (MR) sensor. Included is an alternating current (AC) coupling module connected to the MR sensor for blocking a direct current (DC) voltage associated with an input signal, and filtering low frequency noise associated with the input signal. Also provided is a gain stage module coupled to the AC coupling module. The gain stage module includes a plurality of cascode field effect transistors (FETs) configured for amplifying the input signal, while reducing intrinsic noise and increasing operational bandwidth. Coupled to the gain stage module is a control circuit for feeding back an output of the gain stage module for bias regulation and disturbance rejection.

Abstract: In a magnetoresistive read/inductive write magnetic transducer, magnetic stability of the magnetoresistive read sensor is improved by reducing the bias current to the magnetoresistive read sensor to a predetermined value during a period when a write current signal is applied to the inductive write head. The reduced bias current is greater than zero, but less than that required for reading data stored in a magnetic storage media. The reduced bias current is about 30% of the full bias current applied during the read operation of the magnetoresistive head.

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: Writing of data on a storage disk by an inductive magnetic transducer is modulated by write driver circuitry that includes a supply voltage as low as three volts provided by a source referenced to ground, and a bias current source connected to either the supply voltage source or ground. Two bias control switches respectively direct the bias current to one or the other of two current gain circuits according to whether a positive or a negative input terminal has a preselected polarity. The gain circuits selectively respond to the bias currents supplied by the associated control switch for amplifying the bias current to remove a write current from a respective associated terminal of the transducer.

Abstract: An optical data storage system including an amplifier which (i) provides a differential current input having a low impedance over the full range of frequencies for which amplification is required in an optical detector that includes a photodiode that senses the intensity of an optical signal generated by data on the optical storage medium; (ii) reverse biases the photodiode; (iii) amplifies the signal current from both sides of the photodiode to improve signal-to-noise ratio; and (iv) is isolated from and unaffected by power supply noise.

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: 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: 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 circuitry for suppressing additive transient disturbances in an analog differential input signal, such disturbances being due, for example, to thermal asperity transients caused by an MR transducer contacting a moving storage surface. The input data signal is algebraically summed with a corrective feedback signal for providing as output signal. The output signal is fed back to a circuit including an envelope detector and differentiator and converted into another signal that is the derivative of an amplitude envelope corresponding to the output signal. Nonlinear signal-adaptive filter means converts said other signal into the corrective feedback signal, which substantially replicates the additive transient disturbance and is subtracted from the data input signal to render the output signal substantially free of the transient disturbance.The input, output and corrective signals are preferably differential signals.

Abstract: A circuit for producing a signal whose magnitude is a chosen amplitude compensation characteristic of the signals produced by a magnetoresistive (MR) element comprising an input stage which produces an amplified output signal which is coupled to the output stage, and control signals proportional to the resistance of the MR element and inversely proportional to the resistance of the MR element which are coupled to a feedforward circuit. The feedforward circuit generates a chosen amplitude equalization characteristic of the signals coupled to the feedforward circuit, and this signal is coupled to a bias terminal of the output stage so that the output stage produces a signal representing the chosen amplitude compensation characteristic of the signals produced by the MR element.

Abstract: A method and circuitry are disclosed for suppressing additive transient disturbances in a data channel; e.g., due to thermal transients caused by an MR transducer contacting moving a storage surface. Positive and negative envelope detectors each have their inputs connected to the channel, and provide respective outputs which are summed and contain an envelope component and a residue component. A buffer interconnects the detectors to allow both detectors to follow rapid positive excursions of the data channel signal. A nonlinear signal-adaptive filter is connected to the summed output to further reduce the residue component. The data channel signal (or preferably the output from a delay means connected to the channel) is summed with the output from the filter. The relative amplitudes of these two outputs is set such that the resulting summed output signal is free of additive disturbances.

Abstract: A protective circuit for a magnetoresistive (MR) element having a first and a second terminal in which a first current source is coupled to the first terminal of the MR element to produce a bias current through the MR element and a second current source is coupled to the second terminal of the MR element to produce a reference current. Circuit means coupled across the MR element senses the center potential of the MR element substantially midway between the first and second terminals, and a feedback circuit responsive to the sensed center potential is coupled to adjust the current output of the first current source to maintain the center potential to a selected reference voltage to protect the MR element from short circuits to a conductive area of the magnetic recording medium.

Abstract: An amplifier for voltage biasing and amplifying the signals produced by a magnetic sensor is provided. Electrically, the resistance of the sensor is disposed between the bases of a differential pair comprising the input stage of the amplifier. Constant bias voltage for the sensor is provided independently of sensor resistance. DC feedback to the input stage balances current flow in both paths of the differential input stage to correct for DC offset arising in the output from input stage emitter resistor. The amplified signal, representing .DELTA.R.sub.h /R.sub.h, is sensed as a voltage across the magnetoresistive sensor, where .DELTA.R.sub.h is the change in steady-state resistance, R.sub.h, of the sensor.

Abstract: A frequency response compensation circuit includes a first forward gain stage and second reverse gain stage coupled to the first stage in negative feedback mode. The reverse gain stage depresses the gain of the first stage at low frequencies. When the frequency response of the reverse gain stage begins degrading, which corresponds to the frequency of the real zero of the compensation circuit, the gain of the compensation circuit begins increasing and increases until the gain of the reverse stage is zero. The circuit utilizes a pair of NPN transistors in the first stage, a pair of PNP transistors in the second stage and includes no capacitors or inductors. Thus, the circuit can be implemented as a semiconductor integrated circuit. By proper selection of the resistance values of the resistors in the circuit, the zero of the compensation circuit can be chosen to correspond generally to the frequency of the pole of the uncompensated input signal, so as to increase the bandwidth of the resultant signal.

Abstract: A transimpedance amplifier for biasing and amplifying the signals produced by a magnetoresistive element is provided. Electrically, the resistance of the element is disposed as degenerative feedback in the emitter circuit of a differential pair comprising the input stage of the amplifier. Bias current for the element is supplied by the same current source that supplies current to the differential pair. DC feedback to the input stage balances current flow in both paths of the differential input stage to correct for DC offset arising in the output from variations transistor characteristics and the steady-state value of the magnetoresistive element. The amplified signal, representing .DELTA.R.sub.h /R.sub.h, is sensed as a current through the magnetoresistive element, where .DELTA.R.sub.h is the change in steady-state resistance, R.sub.h, of the element.

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.