International Business Machines Corporation

Paik Saber

Paul Wingshing Chung

Klaas Berend Klaassen

Michael O Jenkins

Stephen A Jove

Jacobus C Van Peppen

Ralph L Gee

David S Lowrie

Chorng K Wang

Luke C Lang

A method and circuitry for suppressing additive transient disturbances in an analog differential input signal, such disturbances being due, for example, to thermal asperity transients caused by an MR transducer contacting a moving storage surface. The input data signal is algebraically summed with a corrective feedback signal for providing as output signal. The output signal is fed back to a circuit including an envelope detector and differentiator and converted into another signal that is the derivative of an amplitude envelope corresponding to the output signal. Nonlinear signal-adaptive filter means converts said other signal into the corrective feedback signal, which substantially replicates the additive transient disturbance and is subtracted from the data input signal to render the output signal substantially free of the transient disturbance. The input, output and corrective signals are preferably differential signals.

Method and circuitry to suppress additive disturbances in data channels

A digital-to-analog converter for use in a timing control loop. The converter includes a plurality of cells, each activated in response to a timing loop control signal. The converter also includes a resistive current mirror, with a first resistance R1, providing a reference curent which is mirrored in each cell by a current source FET. Each cell is constructed to switch the current from its current source FET through an output FET when a respective control bit provided to the cell is positive. Otherwise, the current is diverted through a sink FET. All of the cell output FETs are tied to a single resistance R2 which collects the currents of the active cells and provides the AC output of the converter. The converter's output is related only to the ratio R2/R1, thereby decoupling process, temperature, and voltage effects from the output of the converter.

BiCMOS digital-to-analog converter for disk drive digital recording

A method and means for setting the free-running frequency of a voltage controlled oscillator (VCO) without requiring laser trimming or the like is described. The VCO forms part of an interconnected phase-locked loop (PLL) and frequency-locked loop (FLL). At system power on, the PLL is automatically disabled and a digital-to-analog (DAC) in the PLL is set to a value corresponding substantially to the center of a preselected lock range. The FLL, which includes a second DAC, then operates to generate a bias voltage for incrementing or decrementing the VCO output frequency until the VCO pulse count stored in a register equals an expected count; whereupon the VCO will be set at its free-running frequency. When the PLL is enabled, a phase error generator generates a digital phase error signal from the input data. A digital integrator converts the phase error signal to a digital frequency error signal. These error signals are added and the result is supplied to the DAC in the PLL for providing an analog output indicative of PLL frequency error. The outputs from both DACs are summed and the resultant current is converted to a bias voltage to adjust the VCO frequency as necessary for normally maintaining it within said lock range. If the VCO frequency deviates from said range, the frequency error signal to the PLL DAC is zeroed, and the frequency error signal is supplied to the FLL DAC. The phase error signal from the PLL DAC and the signal from the FLL DAC as modified by the frequency error signal are summed, and the resultant current in converted to a bias voltage to adjust the VCO frequency to within said lock range.

Setting and dynamically adjusting VCO free-running frequency at system

A voltage controlled oscillator (VCO) having high temperature stability and wide voltage/frequency linearity is provided. The VCO comprises a multivibrator being switched by a bipolar type device, and temperature fluctuations of the bipolar type means are compensated by a FET current source coupled thereto. To provide a linear relationship of frequency vs. voltage over wide voltage range, the bipolar device is further regulated by a plurality of resistor and diode networks.

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Paik Saber