Abstract: Method and apparatus for magnetoresistive (MR) head biasing and output signal detection for reading data recorded in magnetic media. The MR head may be biased by constant current or constant voltage, and an output signal, proportional to the ratio of the instantaneous value of the change in MR head resistance to total MR head resistance when exposed to the magnetic field of the media, is detected.

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: A method for recording high frequency signals representing data with simultaneous readout of low frequency information, such as servo information prerecorded on a magnetic disk, comprises the step of modulating with the data a carrier signal having a repetition frequency displaced significantly from the baseband of the data. The nonlinearity of the recording channel converts the modulated signal spectrum into the low frequency baseband so that the data is magnetically recorded while the low frequency prerecorded information is read out.

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.

Abstract: A servo system provides track following servo information from a buried servo layer disposed under the data recording layer, using the same transducer for simultaneously reading the servo information and writing data. To prevent the voltage generated in the transducer while writing data from masking out the servo information, a dummy voltage having the same magnitude as the transducer voltage is connected so that it cancels the write data voltage in the head.