Magnetic head testing apparatus for detecting occurrences of popcorn

Abstract

A magnetic head tester has a popcorn noise detector for discriminating internally generated popcorn noise events from externally generated noise events. The popcorn noise detector includes a discriminator which receives the magnetic head output signal from the head and generates a comparator pulse for each popcorn noise event detected. A counter counts the number of pulses output from the detector. The discriminator includes a retriggerable noise detection gate circuit for producing a noise detection gate signal when triggered by a comparator pulse. The discriminator responds to a single comparator pulse during the gate period by indicating a popcorn noise event at the output of the discriminator. The discriminator responds to a plurality of comparator pulses during the gate period by indicating that no popcorn noise event has occurred. Embodiments of the discriminator include a first latch configured to toggle from an initial state on each comparator pulse occurring during the gate period, a second latch configured to switch from an intial state to another state on the occurrence of at least one toggle of the first latch back to its initial state during the gate period, and a third latch for storing the state of the second latch at the end of the gate period. A reset circuit resets the initial state of the latches after the trailing edge of the gate signal.