Abstract: A hard disk drive system (10) includes a read/write head (21) for reading and writing data to and from a rotating magnetic disk (12). The read/write head includes a portion which is a magneto-resistive read head (36), the output of which is supplied through a preamplifier (26) to a read channel circuit (27). The read head has a nonlinear transfer function. The read channel circuit includes an asymmetry compensation circuit (62), which generates an analog compensation signal by squaring an output signal from the read head and scaling by an asymmetry factor (.alpha.'). The analog compensation signal is combined with the analog output signal in order to obtain a corrected analog signal, which is substantially free of the distortion introduced by the read head.

Abstract: The present invention is a new design for transconductance elements useful in high-frequency filters such as fully differential state-variable biquads. The present invention enjoys a large dynamic range. It is built with simple circuitry to reduce parasitic capacitance which impedes high-frequency operation. It is easily tunable for use in programmable filters. It is configured in a fully differential circuit and operates on five volts. The present invention is also very useful for implementing dual-input or multiple input transconductance elements. By incorporating additional current sources in the present invention, another degree of freedom is added to the determination of pole frequency and pole quality factors, when the transconductance is used as a biquad filter building block.