Abstract: A magnetic head reader circuit comprises a gain stage that is configured to effect multiple functions. In a preferred embodiment, the gain stage is a single stage circuit that includes programmable gain, programmable bandwidth and high-frequency boost, and squelch control. The single stage circuit also includes a folded cascode current drive that provides an increased dynamic range of the gain stage. To provide a low DC offset, the reader also includes an integrator that is operated in closed loop to appropriately attenuate the currents from the cascode current drive. By employing a multi-function single stage reader, a substantial reduction in circuit area, and a substantial increase in bandwidth, is achieved.

Abstract: A feedback system includes an emitter-follower as a gain stage in the forward path. The emitter-follower has a very wide band width and does not, by itself, effectively narrow the bandwidth of an information channel in which it is used. Emitter-followers are frequently used as buffers in many gain systems so using an emitter-follower which is already present effectively reduces die area for the feedback system. In an embodiment, the feedback system includes a differentiator with a programmable zero in the feedback path. The zero in the feedback path creates a pole in the forward path and the programmed location of the zero influences the pole and controls the bandwidth of the forward path. The emitter-follower also buffers the differentiator so that it does not effect the operation of any prior gain stages in which the feedback system is used.

Abstract: A preamplifier for a multi-head disk drive includes a circuit that tests the connectivity of each magnetic head in the disk drive by driving each head with a small current, and detecting the flow of this current. By driving and sensing the current flowing through the magnetic heads, both open-circuit faults and bridging faults can be detected. In a preferred embodiment, each head is tested sequentially. The result of each test is stored as a bit value in a register, for subsequent access. The circuit may be activated by a test device, or by a microcontroller in an assembled disk drive. To minimize costs, the circuit is integral to the circuitry that is conventionally used to read and write information via the magnetic heads. The oscillator that is conventionally used to characterize the read heads of a disk drive is used in a preferred embodiment to control the sequencing of tests through each head.

Abstract: An integrated circuit includes a filter with switched capacitors to dynamically adjust a corner frequency of the filter. Such dynamically adjustable filters are typically included in circuits to reduce noise, and consequently such filters should not themselves generate noise. An equalization circuit is included in the filter to equalize the potential on each terminal of the switched capacitors prior to being switched into circuit, thereby removing a source of transient current. Another source of noise is a transient current induced by the application of control signals to the transistors used to switch the capacitors into circuit. A compensation circuit is included which generates a compensation current of opposite sense and substantially the same magnitude as the induced transient currents, to thereby effectively cancel noise at the filter output.

Abstract: A device for writing information to a magnetic medium includes an inductive head and a write amplifier coupled to the inductive head. The write amplifier receives an information signal, and amplifies the signal to provide a current through the inductive head to generate a flux at the inductive head which flux writes a bit of the information on the magnetic medium. The current for each bit of information is characterized by a rising portion, a peak portion, and a settling portion. A damping network is coupled to the inductive head, and couples a low impedance path to the head and the write amplifier, after the current reaches the peak portion, to divert current from the head to reduce a duration of the settling portion of the current. The write amplifier and damping network are embodied together in an integrated circuit, and are programmable via a serial interface.