Generating index pulses proportional to disk drive motor revolutions

摘要

The pick-up (13), pref. an inductive type having a permanent magnet sensor working in conjunction with a coil, passing one another at each revolution of the disk drive motor, delivers its output signal pulses to the evaluating circuit (21 to 26). This has a differential amplifier (22). The non-inverting input accepts one end of the pick-up coil via a resistance (21). The other end of the coil is connected to the inverting input and earth.The outlet (23) of the amplifier is connected through a resistance (24) with a positive supply potential and through a resistance (25) with the non-inverting input. Together the amplifier and three resistances form a comparator with asymmetrical hysteresis. This is tuned to the pick-up output signal so that the comparator's output jumps from a first to a second potential when the amplitude of the pulse at a predetermined polarity exceeds a predetermined unblocking potential amount. When the signal pulse passes through its zero passage to the opposite polarity, the comparator's output jumps back to the first potential