Abstract: A portable computer includes a battery and a connection to an external power source, a two-speed data storage device being supplied power from one or more of the battery and the external power source, and a controller attached to the storage device. With the invention, when the storage device is powered by the internal battery, the controller not only reduces the rotation speed and the clock rate of the storage device, but also reduces the power consumption of the read/write electronics module inside the disk drive by lowering the power supply voltage for the write driver inside said module and lowering the tail currents for the amplifier stages in the readback amplifier inside said module.

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: 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 magetic recording system includes a current-tapering circuit which gradually reduces the WRITE current in a magnetic recording head to zero over a time interval on the same order of magnitude as the characteristic relaxation time of the domain patterns in the magnetic recording head, rather than abruptly. Specific embodiments of the current-tapering circuit create a down-sloping ramp, a decaying exponential curve, and a high-frequency burst. The resultant magnetic recording system has reduced Barkhausen noise and reproducible READ performance as well as improved READ sensitivity following a WRITE operation.

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 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: 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 method and apparatus for measuring the flying height of a slider supporting a magnetic transducer in-situ in a direct manner in an operational magnetic disk storage system. The method and apparatus produce relative motion between the magnetic transducer and a magnetic recording medium at a first velocity so that the resulting air bearing positions the magnetic transducer slider at a first flying height from the magnetic medium. A single signal of constant periodicity is written over a predetermined area of the recording medium by the magnetic transducer, and a readback signal is sensed from the predetermined area of the recording medium to produce a first signal. The flying height of the magnetic transducer slider is lowered to substantially zero, and a readback signal is sensed at the lowered flying height to produce a second signal. The first flying height is then calculated as the ratio, expressed in decibels, of the first and second signals times the wavelength divided by a constant.

Abstract: Apparatus and a method are presented for contactless measurement of charge concentrations and potential differences in biological organisms, with the electrode being spaced from the organism. Relative movement between the organism and the probe results in alteration of the electrostatic field which is measured in an external circuit to determine potential differences in the organism.

Abstract: Transducer for converting mechanical vibrations into corresponding electrical signals. Two separate coils are disposed in permanent magnetic fields produced by a magnet assembly. The coils on the one hand and the magnetic assembly on the other are mounted for movement relative to each other. The magnet assembly is structured and disposed relative to said two coils respectively so as to reduce the electromagnetic coupling between the two coils to zero, while having an electromagnetic coupling only between a respective one of said coils and said magnet assembly. In a composite seismometer comprising a transducer of the above-described type and an amplifier, one of said coils is connected to the amplifier input, while the other one of said coils is included in a feedback circuit for said amplifier.