Analog Devices,inc.

Peter Real

Mairtin Walsh

Philip Eugene Quinlan

Kenneth T Deevy

David Philip Burton

Brian Keith Russell

Patrick Griffin

Michel Steyaert

Jan Craninckx

Wim Dehaene

A control circuit ( ) controls the operation of a laser diode ( ) for controlling the average power output (P ) and the extinction ratio. A state machine ( ) controls the control circuit ( ) which reads the current from a monitor photo diode ( ) which is coupled to the laser diode ( ). An amplifier ( ) determines the average power output of the laser diode ( ) which is fed to a first comparator ( ). The first comparator ( ) compares the average power output with a reference value set by a resistor (R ). The output from the comparator ( ) is fed to the up/down pin of a first counter ( ) which is clocked by the state machine ( ). In the event that the average power output is too high the first counter ( ) decreases the bias current to the laser diode ( ) outputted by a constant current source ( ), and vice versa. To determine the extinction ratio of the laser diode ( ) the slope of the operating portion of the power/current characteristic curve is determined by applying an incremental increase (&Dgr;I ) to the modulation current (I ) of the laser diode ( ), which is a small percentage of the modulation current (I ). The increase (&Dgr;P ) to the average power output (P ) of the laser diode ( ) resulting from the increase &Dgr;I to the modulation current I is determined through a latch ( ) and an adder ( ) and is fed to a second comparator ( ) which compares the increase &Dgr;P in the average power output with a reference value (&Dgr;P ) set by the resistor (R ). A second up/down counter ( ) increases the modulation current (I ) applied to the laser diode ( ) by a constant current source ( ) if the value of (&Dgr;P ) is less than (&Dgr;P ) and vice versa.

Method and a control circuit for controlling the extinction ratio of a laser diode

A servo system for controlling the position of a read/write head in a disk drive is provided. The servo system includes an input terminal for sequentially receiving a plurality of input signal bursts of a burst pattern, wherein the input signal bursts include positional information of the head. Demodulation circuitry, coupled to the input terminal, sequentially demodulates each input signal burst and provides a demodulated signal for each burst. An ADC, coupled to the demodulation circuitry, sequentially converts each demodulated signal. The ADC converts a first demodulated signal corresponding to the first of the plurality of input signal bursts before the demodulation circuitry completes demodulating the next of the plurality of input signal bursts. In a preferred embodiment, the ADC converts a demodulated signal corresponding to a first input signal burst while the demodulation circuitry demodulates a signal corresponding to a second, and subsequent, input signal burst. Thus, a pipelined demodulation and conversion scheme is disclosed in which time delays between demodulation and conversion are reduced. In the preferred embodiment, the demodulation circuitry includes area detect circuitry having an integration circuit and a single track-and-hold amplifier.

Pipelined demodulation and ADC conversion scheme for disk drive servo

A servo system for controlling the position of a read/write head in a disk drive is provided. The servo system includes two input terminals for sequentially receiving a plurality of input signal AC voltage bursts of a burst pattern, wherein the input signal bursts include positional information of the head. Demodulation circuitry, coupled to the input terminals, sequentially demodulates each input signal burst and provides a demodulated signal for each burst. The demodulation circuitry includes translation circuitry, coupled to the input, for sequentially translating each input voltage burst to a translated current. A rectifier circuit, coupled to the translation circuitry, including an absolute value circuit and a current mirror circuit, sequentially rectifies each translated current and produces a driving signal. An integrator, coupled to the rectifier circuit, sequentially integrates each driving signal. The integrator includes an integration capacitor which is sequentially charged by each driving signal. In the preferred embodiment, the current mirror circuit includes an operational amplifier and a gain circuit. Also in the preferred embodiment, the voltage to current translation circuit includes a folded cascode circuit arrangement of a plurality of CMOS transistors.

Rectifier and integrator circuit for disk drive servo system

A CMOS DAC with means to avoid leakage current. In one embodiment, the back gates of the CMOS switches are held at -200 mV with respect to the output lines, and the logic low level to the off switch also is set at -200 mV relative to the output lines. In another embodiment, the CMOS switches are ion-implanted. In a still further embodiment, the output lines are held at a potential 200 mV more positive than the P- well of the CMOS switches.

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Limerick, Ireland

Peter Real