Abstract: A magnetoresistive sensor and preamplifier system for sensing magnetization patterns in a magnetic disk based digital data storage and retrieval memory with a grounded magnetoresistive sensor The signals from the magnetoresistive sensor are coupled by a coupling capacitor to a grounded differential amplifier. The structure of the coupling capacitor in a monolithic integrated circuit determines the passband for the system in passing the magnetoresistive sensor signals.

Abstract: The present invention is a dual-input-to-single-output amplifier circuit having a processing amplifier, first and second coupling regions, first and second input impedance circuits, first and second feedback impedance circuits, first and second shunting impedance circuits. The processing amplifier has first and second input regions and an output region. The first and the second input regions each exhibit a relatively high circuit impedance. The output region exhibits a relatively low circuit impedance. The processing amplifier is capable of providing at the output region a signal in a first magnitude direction substantially similar to a signal provided at the second input region in the first magnitude direction but of a greater magnitude in the first magnitude direction.

Abstract: A three-phase generator boost circuit for augmenting the back electromotive force produced by a spindle motor of a disk drive is disclosed. First and second nodes provide normal connection to a source of DC voltage for the spindle motor and a second motor connected between the first and second nodes. A commutator is connected to a sequencer to operate the spindle motor. In the event of catastrophic shutdown, two of the lower commutator switches are operated to short circuit the two stator coils having the highest and lowest voltages to store energy in the coils. The commutator switches are then operated to discharge current through the nodes to a storage capacitor for the second motor.

Abstract: An integrated, tuning circuit for tuning a MOSFET-C filter contains a tuning MOSFET and a differential amplifier. A current source is connected to the drain of the tuning MOSFET. The output of the amplifier is coupled to the drain of the tuning MOSFET and to a terminal that connects to the drains of the MOSFETs of the filter, so that the equivalent resistance of the filter is dependant on the current. The current source is coupled to a reference current generator, such that current supplied by the current source to the tuning MOSFET is proportional to the current supplied in the reference current generator, which in turn varies with process and environmental conditions of a capacitance. As a result, changes in process and environmental conditions oppositely affect the capacitance and resistance in the filter, resulting in a fixed RC product and fixed frequency response from the filter.

Abstract: A write driver, having a pair of head nodes for connection to a write head, includes two diodes connected respectively the head nodes and the emitters of first and second upper drive transistors. The diodes, which are preferably Schottky diodes, increase the voltage necessary to breakdown the emitter pn junctions of the upper drive transistors, thereby enabling a greater head swing voltage, higher switching rates, and ultimately closer spacing of data on a magnetic medium. Additionally, a preferred embodiment of the write driver includes two voltage clamps, each coupled between a respective head node and a first supply node, to limit the magnitude of voltage spikes resulting from self-inductance of the write head.

Abstract: An apparatus for demodulating two pilot tones for use by a servo control for a magnetic read head is disclosed. The apparatus provides positioning information to position the read head adjacent to a desired information track of a magnetic storage medium. The apparatus comprises a first and a second pilot tone demodulation unit. Each pilot tone demodulation unit comprises a band pass filter for providing a first filtered output signal having an amplitude and a phase representative of the first and the second frequency pilot tones, respectively. A delay lock loop receives the first filtered out of the band pass filter and determines a phase of the frequency pilot tone. A multiplier is connected to the output of the band pass filter and the output of the delay lock loop for multiplying the frequency pilot tone with the output signal of the delay lock loop. A low pass filter is connected to the output of the multiplier for filtering out undesired signals and for passing a DC signal.

Abstract: A power supply filter has a primary current source coupled to a node carrying a power supply signal. The second end of the primary current source is coupled to an impedance that is further coupled to a low voltage node. A differential amplifier having an inverting input, a non-inverting input, and an output, has its non-inverting input coupled to the junction between the impedance and the primary current source. The output of the differential amplifier carries the filtered power supply signal and is coupled to a capacitance. The capacitance is coupled between the output and a lower voltage. A feedback path is coupled between the output and the inverting input.

Abstract: A write driver, having a pair of inputs for receiving write data signals, includes a TTL buffer circuit connected to one input and a PECL buffer circuit connected to both inputs. A detector, responsive to a voltage at one of the inputs, selectively operates either the TTL buffer circuit or the PECL buffer circuit. The detector preferably comprises a comparator, a switching circuit, and two current mirrors. The comparator compares the voltage at one of the inputs to a reference voltage and outputs a signal controlling the switching circuit. The switching circuit enables one of the current mirrors, thereby enabling either the TTL or the PECL buffer circuit. In the preferred embodiment, a Schottky diode isolates the TTL buffer circuit from the PECL buffer circuit.

Abstract: A preamplifier circuit, which produces an output signal representative of signals from a magnetoresistive read head, includes a current bias circuit for providing a bias current to the read head, and first and second amplifiers for amplifying signals from the read head. The first amplifier, with an input for coupling to the read head, outputs first signals representative of changes in head resistance. The first signals have an amplitude substantially independent of the head resistance and proportional to a temperature dependent characteristic of the first amplifier. The second amplifier, which is coupled to the first amplifier, outputs a second signal having an amplitude proportional to the amplitude of the first signals and inversely proportional to the temperature dependent characteristic. Thus, the amplitude of the second signal is substantially independent of head resistance and the temperature dependent characteristic.

Abstract: A write driver, having a pair of head pins for connection to a write head, includes two push-pull buffer circuits connected respectively between first and second pull-up resistors and the control nodes of first and second upper drive transistors. The buffer circuits selectively charge and discharge the inherent capacitances of the upper drive transistors, thereby accelerating their turn on and turn off without diminishing head swing. Moreover, connecting the buffer circuits between the pull-up resistors and the upper transistors effectively isolates, or buffers, the pull-up resistors from the self-inductance voltages of the write head, reducing glitching in the write-head output signal.

Abstract: An open-loop biasing circuit for a magnetoresistive element provides high common mode and power supply rejection. Two current sources are connected together by two conduction paths. A first conduction path has two impedances. One impedance is tied between the first current source and ground and the second impedance is tied between the second current source and ground. The second conduction path includes the magnetoresistive element. A capacitive path between the two current sources reduces power supply noise and a voltage follower reduces parasitic capacitance in the capacitive path.

Abstract: A multiplexer selectively connects one of first and second nodes to a third node. The multiplexer includes a first switch coupled between the first and third nodes, a second switch coupled between the second and third nodes, and a control input for receiving a signal to either open the first switch and close the second switch or open the second switch and close the first switch. Additionally, a delay circuit, coupled to the control input and the second switch, delays closure of the second switch until the first switch is open. In a preferred embodiment, the delay circuit includes two field-effect transistors having substantially different width-to-length ratios.

Abstract: The present invention is a system for reading information stored on a plurality of disk surfaces. The system comprises a plurality of channels each containing a preamplifier having first and second terminals for connection to an MR head. A bias circuit is provided common to all of the plurality of channels. The preamplifier in each channel includes first and second channel select circuits responsive to first and second channel select signals and current output from the bias circuit to output currents based on the current's output from the bias circuit. The preamplifier in each channel also includes first and second complementary output transistor circuits responsive to the current's output from the first and second channel select circuits and to the first and second voltages to provide bias current through the respective MR head connected between the first and second terminals of the respective channel. The system is entirely symmetrical around ground for improved common mode rejection.

Abstract: A biasing circuit for a two terminal sensing element has two separate biasing elements. Both biasing elements are controlled by a transconductance feedback circuit that controls feedback currents based upon a voltage associated with the sensing element. Both biasing elements also receive an activation value from an activation circuit. The activation value activates both biasing elements directly, without using the feedback loop.

Abstract: A multiplying digital-to-analog converter produces first and second output currents that have a magnitude difference equal to a gain value multiplied by a magnitude difference between first and second input currents. The multiplying digital-to-analog converter has first and second input nodes for carrying the first and second input currents and first and second output nodes for carrying the first and second output currents. A first input transistor has a first terminal coupled to the first input node, a second terminal with voltage that increases with increases in the first input current, and a third terminal for carrying a first input bias current. A second input transistor has a first terminal coupled to the second input node, a second terminal with a voltage that increases with increases in the second input current, and a third terminal for carrying a second input bias current.

Abstract: The present invention implements a novel emitter scheme that maximizes the emitter perimeter to emitter area ratio of an integrated circuit transistor, thereby achieving improved low noise characteristics over the prior art. Emitter regions are disposed in the transistor in discrete "dotted " segments. The dotted emitter segments may be realized by etching into emitter regions defined by an appropriately formed photoresistive overlay, which can be modified without fabrication process changes. The effect is to reduce the total emitter area by half, while maintaining the total emitter perimeter unchanged. As a result, the noise-capacitance product of the transistor is reduced, improving the overall performance of the transistor.

Abstract: An open-loop biasing circuit for a magnetoresistive element provides high common mode and power supply rejection. Two current sources are connected together by two conduction paths. A first conduction path has two impedances. One impedance is tied between the first current source and ground and the second impedance is tied between the second current source and ground. The second conduction path includes the magnetoresistive element. A capacitive path between the two current sources reduces power supply noise and a voltage follower reduces parasitic capacitance in the capacitive path.

Abstract: A first differential amplifier circuit is provided having a first and second input terminal suited for connection to a magnetic head. The first differential amplifier circuit includes first and second output terminals for providing a read output signal. A second differential amplifier circuit is provided which has first and second input terminals connected to the first and second input terminals, respectively, the first differential amplifier circuit. The second differential amplifier circuit also includes first and second output terminals. A first feedback capacitor is provided which is connected between the first input terminal of the first differential amplifier circuit and the first output terminal of the second differential amplifier circuit. A second feedback capacitor is provided which is connected between the second input terminal of the first differential amplifier circuit and the second output terminal of the second differential amplifier circuit.

Abstract: A magnetoresistive sensor and preamplifier system has an excess differential imbalance detector, (a) for detecting magnitude differences between a pair of signals occurring at the output of a preamplifier subsystem due to modal transitions, and (b) for initiating action to overcome same. The excess imbalance detector changes a threshold therein to become more sensitive to smaller imbalances in the output signals being monitored after detection of a modal transition imbalance.

Abstract: An apparatus conducts current through a two terminal inductive load. The apparatus has a first conduction path, from a first supply voltage to one terminal of the inductive load and a second conduction path from the second terminal of the inductive load to a second supply voltage. The first conduction path includes a switching device that is controlled by a field-effect transistor having a gate terminal, second terminal, and third terminal. The gate terminal of the field-effect transistor is coupled to a reference voltage. The voltage at the second terminal of the field-effect transistor increases when the voltage at the field-effect transistor's third terminal increases.