Applied Magnetics, LLC

Phase Metrics, Inc.

Calient Technologies, Inc.

Michael Inbar

Optical scanning systems and methods of controlling a resonant scanning mirror are disclosed. A rotatable mirror may oscillate about a rotation axis in response to a drive signal. A reference source may provide a reference light beam directed to the rotatable mirror. A reference detector may be disposed to receive the reference light beam reflected from the rotatable mirror twice during each oscillation of the rotatable mirror. A controller may set both an amplitude and a frequency of the drive signal based on an output of the reference detector.

Multichannel optical power meter using a synchronous scanner

There is disclosed a driver circuits and method for driving a micro-electro-mechanical system. A driver circuit may include a converter to convert a digital input value into a pulse-width modulated signal with precise amplitude. A low pass filter may extract an average DC component of the pulse-width modulated signal. An amplifier may amplify the average DC component to provide an output voltage to drive the MEMS.

Precision driver circuits for micro-electro-mechanical system

A disk certifier which analyzes a read signal generated from a disk of a hard disk drive. The read signal typically has a sinusoidal waveform with modulated peak amplitudes. The waveform is generally defined by the equation A.multidot.sin(wt).multidot.(1-m(t)), where the term m(t) is the amplitude modulation of the signal. The peak signal is provided to a phase lock loop circuit which generates a multiplier peak signal generally of the form sin(wt). The certifier includes a multiplier which multiplies the read signal by the multiplier read signal to provide a multiplied read signal described by the equation A/2.multidot.(1-cos 2(wt)).multidot.(1-m(t)). The multiplied read signal is filtered by a low pass filter which has a cut-off frequency Wc below w. The low pass filter provides a filtered multiplied read signal which is described by the equation A.multidot.(1-g(t)), wherein the term g(t) is the portion of m(t) with frequencies below Wc. The filtered multiplied read signal is then compared to a threshold value(s) to determine a pass/fail error condition of the read signal. The certifier also has a histogram circuit which detects, counts and stores the occurrence of each peak amplitude value of the read signal. The peak amplitude data can be processed to plot a histogram which shows how many times the read signal produced various peak amplitudes. The histogram can be used to determine the actual performance of the disk certifier.

Magnetic media tester which includes a filter that filters the product

The present invention relates to a method and apparatus for the measurement of defects in magnetic recording disks using a logarithmic amplifier. A magnetic head senses a magnetic field of a magnetic disk and creates a read signal having a varying amplitude. The test apparatus has a squarer which receives and squares the read signal. A logarithmic amplifier coupled to the squarer converts the squared signal to a logarithmic signal. The logarithmic signal is filtered by a first filter. A second filter coupled to the logarithmic amplifier provides an average of the peaks of the logarithmic signal. A digital-to-analog converter coupled to the second filter scales the output of the second filter. The test apparatus further comprises a comparator having a first input and a second input, where the first input is coupled to the first filter, and the second input is coupled to the digital-to-analog converter. The comparator provides an output signal in response to receiving a signal from the first filter having an amplitude that is lower than an average of a predetermined number of peak values of the signal, thereby indicating an error in the disk. In another embodiment, the test apparatus is implemented using a rectifier instead of a squarer.

Method and apparatus for the measurement of defects in magnetic

An apparatus and method for demodulating an amplitude modulated read signal generated by a magnetic head of a hard disk drive. The apparatus includes a pair of serially connected track and hold circuits that receive the read signal. The track or hold state of each circuit is controlled by a phase lock loop circuit which also receives the read signal. The first track and hold circuit initially tracks the read signal to a peak value. The circuit then switches to a hold state and provides a constant output signal that corresponds to the peak voltage of the read signal. While the first track and hold circuit is in the hold state, the second track and hold circuit is in a tracking state. The second track and hold circuit tracks the output of the first circuit. Because the output of the first circuit is a constant value, the second circuit also provides a constant output signal in the tracking state. The first circuit is switched back to the tracking state to again track the amplitude of the read signal, and the second circuit is switched to the hold state. The process is repeated to create a 'stepped' demodulated signal. The output signals are compared to a threshold value to detect bit errors in the signal. The constant output signals provide additional energy to the detection circuit to minimize the number of false error signals from the comparator circuit.

Method and apparatus for the coherent demodulation of an amplified

A tester for measuring the resistance of magnetoresistive heads as a function of the magnetic field applied to the heads. The tester applies a time varying magnetic field to the magnetoresistive head to be tested and filters the resulting time varying (AC) voltage signal indicative of the resistance of the head with a capacitor to remove the DC component of the signal. The AC component of the signal is then amplified, digitized, and analyzed to obtain the resistance properties of the magnetoresistive head.

Method and apparatus for testing the resistive properties of magneto

An apparatus and a method for determining the time difference between electrical events utilizes a sinusoidal signal as a reference from which to determine the elapsed time between events represented as electrical pulses. A sine wave and a cosine wave are multiplexed to produce the sinusoidal reference signal. When an event occurs, as indicated by an electrical pulse, the sine wave and the cosine wave are sampled to produce two digital values. A comparator determines which of the two digital values falls within a predetermined range, and transmits a select signal to multiplexer. The multiplexer selects the digital value which falls within the predetermined range. The selected digital value corresponds to an angle value which can be uniquely determined within one cycle of the sinusoidal reference signal. A cycle counter accounts for the number of full cycles which elapse until the next event is detected. The digital information for each event, including the angular position of each event within a cycle of the reference signal, and the number of cycles between events, is stored within a random access memory (RAM) and transmitted to a computer. The time difference between events is then advantageously calculated in real time within the computer using the known frequency of the effective reference signal.

Method and apparatus for measuring time elapsed between events

A digital peak detecting circuit for receiving a pulse train of electrical signals having a frequency within a known frequency range and for converting the same into digital signals is shown. The digital peak detecting circuit includes an input circuit having a phase-locked loop for producing clock pulses at a frequency which is a preselected integer of the electrical signals frequency and for deriving therefrom an analog input signal. A pulse control circuit receives and counts a predetermined number of clock pulses and produces count enabling signals. A peak detecting circuit is provided which includes a comparator which has the analog input signal and a analog output signal voltage applied to the inputs thereof and which has an output coupled to the pulse control circuit. A digital counting circuit is responsive to count enabling signals by changing count direction and produces discrete digital output signals which are stored in a latch register at the time the digital counting circuit changes its count direction. A digital-to-analog converter produces the analog output signal voltage and it is applied to the comparator input for comparing the analog input signal with the analog output signal voltage and the comparator enables the digital counting circuit as long as the analog input signal is of a greater magnitude than the analog output signal voltage, and when this condition is reversed, the digital counting circuit is reversed in counting direction, and the binary value thereof is stored in the latch register.

Digital peak detecting means for a pulse train of electrical signals

A method of converting a pulse train of electrical signals having a frequency within a known frequency range into digital signals is shown. The method comprises the steps of deriving with a phase-locked loop the frequency of the electrical signals and producing clock pulses at a frequency which is a preselected integer of the electrical signals frequency; deriving an analog input signal from the electrical signals; receiving and counting clock pulses with a pulse scaling circuit for producing count enabling signals; detecting with a peak detecting circuit having a comparator receives as inputs the analog input signal and a analog output signal voltage and an output coupled to and enabling the pulse scaling circuit; producing with a digital counting circuit which is responsive to count enabling signals by changing count direction discrete digital output signals which are stored in a latch register at the time the digital counting circuit changes its count direction; applying the discrete digital output signals to a digital-to-analog converter which produces the analog output signal voltage; and comparing with the comparator the analog input signal with the analog output signal voltage for enabling the digital counting circuit as long as the analog input signal is of a greater magnitude than the analog output signal voltage, and when this condition is reversed, the digital counting circuit is reversed in counting direction, and the binary value thereof is stored in the latch register.

Method of converting a pulse train of electrical signals into digital

An electrical measuring system for measuring selected parameters of electrical signals derived from magnetic recording and having a frequency within a known frequency range wherein the system includes an input stage having an automatic amplifier for selectively amplifying the electrical signals to a preselected amplitude level, a first circuit which includes a digital peak detecting circuit for producing digital signals representing peak amplitude and the amplitude of the electrical signals sampled at closely spaced intervals and wherein the digital peak detecting circuit includes circuitry for sampling the preselected amplitude level electrical signals at a frequency which is less than the frequency of the electrical signals, a second circuit which includes a first phase-locked loop circuit, a frequency dividing circuit and a second phase-locked loop circuit for producing an output signal representing the frequency of a remnant signal in the electrical signals which is applied to the digital peak detecting circuit for producing a digital signal representing the remnant signal magnitude, a third and fourth stage for producing direct current voltage signals representing the power magnitude of noise spectra and the DC content of a pulse train for deriving from the pulse widths of the electrical signals, respectively, and for applying the same to the digital peak detecting circuit to produce a digital representation thereof is shown. A method for processing electrical signals to produce digital representations of the amplitude, read-over-write ratio, signal-to-noise ratio and the average pulse widths thereof is shown.

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Santa Barbara, CA, United States of America

Michael Inbar