In a nitride semiconductor device according to one embodiment of the invention, a p-type gallium nitride (GaN) layer electrically connected to a source electrode and extending and projecting to a drain electrode side with respect to a gate electrode is formed on an undoped or n-type aluminum gallium nitride (AlGaN) layer serving as a barrier layer

Nitride semiconductor device

A disk drive is disclosed comprising a velocity extraction circuit for extracting a velocity of an actuator arm from a back EMF voltage across a voice coil of a voice coil motor when embedded servo information is unavailable. The velocity extraction circuit comprises a dual slope integrator for integrating a voltage representing a current flowing through the voice coil and the voltage across the voice coil. The sum of the integrations cancels the resistance of the voice coil from the back EMF measurement. In one embodiment, the dual slop integrator also integrates the reverse polarity of the voltage representing the current flowing through the voice coil and the reverse polarity of the voltage across the voice coil in order to cancel the inductance (L·di/dt) of the voice coil from the back EMF measurement.

Disk drive using dual slope integrator to extract velocity of an actuator arm from a back EMF voltage

A disk drive includes a spindle motor having windings and a spindle motor driver including switching elements connected to the windings. Spin-down instructions are stored in a memory. A microprocessor is responsive to a spin-down command to receive and execute the spin-down instructions. The execution of the spin-down instructions causes the microprocessor to perform the following pulsed braking sequence: (1) providing a brake signal for a first selected period of time (T1); (2) providing a coast signal for a second selected time period (T2); and (3) repeating (1) and (2). The spindle motor driver is responsive to the coast signal to control the switching elements to cause the spindle motor to coast and is responsive to the brake signal to control the switching elements to brake the spindle motor. The pulsed braking sequence preferably maximizes braking time and minimizes coasting time to reduce the time it takes to spin-the down spindle motor while still preventing heat related breakdown of components in spindle motor and power FETs in the spindle motor driver.

Faster spin-down operation in a disk drive by utilizing pulsed braking

A disk drive is disclosed comprising a disk, a head actuated radially over the disk, and a spindle motor for rotating the disk, the spindle motor comprising a plurality of windings and a rotor rotatable at a variable spin rate, wherein the rotor generates a back EMF (BEMF) voltage across the windings proportional to the spin rate of the rotor. A plurality of switching elements are coupled to the windings, and switch control logic generates switch control signals applied to the switching elements for commutating the spindle motor during normal operation and for generating an internal supply voltage from the BEMF during a spin down mode, the internal supply voltage for parking the head. A programmable signal generator generates a periodic signal, the periodic signal for periodically grounding the windings during the spin down mode in order to boost the internal supply voltage, wherein grounding the windings applies a braking torque to the spindle motor. A programmable register is provided for storing a digital value for adjusting a frequency characteristic of the periodic signal, thereby enhancing power management.

Disk drive comprising spin down circuitry having a programmable signal generator for enhancing power and braking control

A disk drive is disclosed comprising a disk, a head, a voice coil motor (VCM) for actuating the head radially over the disk (the VCM having a voltage control input), and a spindle motor for rotating the disk, the spindle motor comprising a plurality of windings and a rotor rotatable at a variable spin rate wherein the rotor generates a back EMF (BEMF) voltage across the windings proportional to the spin rate of the rotor. A plurality of switching elements are coupled to the windings, and switch control logic generates switch control signals applied to the switching elements for commutating the spindle motor during normal operation and for generating an internal supply voltage Vi from the BEMF during a spin down mode, the internal supply voltage Vi applied to the voltage control input of the VCM for parking the head. A demand limit circuit disconnects the internal supply voltage Vi from the voltage control input of the VCM when the internal supply voltage Vi falls below a predetermined level, and reconnects the internal supply voltage Vi to the voltage control input of the VCM once the internal supply voltage Vi recharges to a predetermined level, thereby enhancing power management during the spin down mode.

Disk drive comprising a demand limit circuit for enhancing power management during spin down

A novel switching hysteretic power converter is presented. The power converter combines the function of a capacitive charge pump with the function of an inductive step down converter to obtain a switching boost converter with a much simpler control method with respect to conventional inductive boost power converters. The hysteretic control provides stable operation in all conditions with excellent load transient response. Furthermore the hysteretic control allows high frequency switching reducing the size and cost of the passive components. The Discontinuous Conduction Mode of operation provides very high efficiency even at light loads. The presented power converter can be operated as a boost converter or as a buck converter simply by changing the switching phase of one switch. In both types of operation the efficiency of the hysteretic power converter can be quite high even at high switching frequencies.

Hysteretic CL power converter

A circuit and method for measuring a back EMF voltage of a voice coil in a mass storage device, or the like, includes an amplifier connected across the coil to produce an output signal proportional to a voltage across the coil and a circuit connected to selectively connect the output signal of the amplifier to a circuit output when a driving current is not applied to said coil. A sample window is generated after drive currents within the coil have been allowed to decay to zero, and between a time during which a PWM signal changes from negative to positive and a time when the PWM waveform crosses a voltage error value.

Method and circuit for determining the velocity of a data detector mechanism of a mass storage device, or the like, using a BEMF voltage in the associated voice coil

A novel semiconductor power transistor is presented. The semiconductor structure is simple and is based on a FET structure, where multiple channels and multiple gate regions are formed in order to achieve a lower specific on-resistance, and a higher control on the transport properties of the device. No dielectric layer is present between gate electrodes and device channels, decreasing the parasitic capacitance associated with the gate terminal. The fabrication of the device does not require Silicon On Insulator techniques and it is not limited to Silicon semiconductor materials. It can be fabricated as an enhancement or depletion device with much more control on the threshold voltage of the device, and with superior RF performance.

High performance multigate transistor

In a disk drive, the read-write heads of the disk drive should be parked during a power failure. The kinetic energy of the spinning rotor is used to move the head away from the disk's surface. A high voltage is produce from the low voltage spindle motor by using a BEMF voltage to step up the voltage in a voltage supply capacitor to a higher voltage by enabling or disabling a switch connected to a comparator. When the switch is turned on, it shorts the rectified voltage in the stator windings to ground in order provide a current path for a current formed in the coils by the BEMF. When the current reaches a predetermined level, the switch is turned off. The current flows through the voltage supply capacitor so that its voltage is "kicked-up" by the inductance of the windings and by the BEMF still present in the stator windings. This increased voltage is used to park the heads and to brake the motion of the spindle. Two control feedback loops are used to more efficiently enable the voltage conversion. A current comparator compares the current in coils to a reference current and turns the switch off when the current is at a predetermined level. A voltage comparator compares the voltage across the load with a reference voltage and turns the switch off when the voltage is above a predetermined value.

BEMF rectification voltage when power supply energy fails

A method of operating a vertical DMOS transistor associated with a Schottky diode, the method including diverting current from flowing through a body-to-drain pn junction diode to flowing through the Schottky diode when a metallic source contact becomes more positive than a drain of the DMOS transistor by forward conduction voltage of the Schottky diode to reduce the amount of source current reaching the substrate and reducing operational characteristics of parasitic devices associated with the integrated circuit.

Paolo Menegoli

Papers

Hysteretic CL power converter

Method and circuit for determining the velocity of a data detector mechanism of a mass storage device, or the like, using a BEMF voltage in the associated voice coil

High performance multigate transistor

BEMF rectification voltage when power supply energy fails

Method of operating a vertical DMOS transistor with schottky diode body structure