Opamp based broad band phase shifter for use in detecting flaws in the media of disks for use in disk drives

摘要

An electronic system for detecting flaws in the magnetic media of raw disks prior to assembly into disk drives which works in conjunction with an electro-mechanical apparatus that performs the functions of spinning the disk, impressing a sinusoidal signal onto the media of the spinning disk and subsequently reading back the signal from the spinning disk. The signal read from the disk is supplied as the electrical output of the electro-mechanical apparatus. The system includes a divider circuit to divide the read signal into two signal channels. An op amp based impedance matching circuit is connected to the output of the dividing circuit in each channel and matches the electrical impedance of the electro-mechanical apparatus with the impedance of the remainder of the electronic detection system. It passes the two signals through substantially unaltered. A two stage op amp based phase shifter circuit is connected to each of the impedance matching circuits and generates two output signals having substantially the same amplitude as the two input signals, but a phase difference with respect to each other of substantially 90° over a frequency range of approximately 3 to 22 megahertz. A multiplier circuit is connected to each phase shifter circuit. These circuits square each of the two output signals from the phase shifting circuits. A summing circuit sums the two output signals from the two multiplier circuits. This produces a DC signal value which is low pass filtered with a large time constant filter. The voltage value of the DC signal is used to determine the reference of a comparator circuit. The comparator circuit compares the amplitude of the output signal of the summing circuit with upper and lower limit values based on the reference and each time the output signal of the comparator circuit exceeds either the upper or lower limit, the comparator supplies an output signal to a computer which keeps track of the defects so determined.