Adaptive variable threshold qualification level circuit for signal

Abstract

A pulse qualification apparatus and method provides for qualifying signal pulses from a raw data signal by comparison to a variable qualification level. Pulse qualification is done on a read signal developed by moving a magnetic transducer relative to addressable portions of a magnetic disk. A qualification level generator circuit generates a qualification level signal which varies in value depending upon the addressed portion of the magnetic disk. A threshold detector is used in qualifying pulses from a transducer read signal by comparision to the qualification level signal to generate an encoded pulse signal representing occurrences of qualifying pulses. Error recovery is accomplished by increasing or decreasing the qualification level of the address portion of the magnetic disk where the error occurs. This process is repeated until qualifcation channel requirements are met. Using variable qualification for defect on a magnetic disk consists of running a manufacturing test process with qualification levels raised slightly from normal operation to detect defects which are caused by reduced amplitude. Likewise, operation with reduced qualification levels detects extra amplitude defects. The address locations of these defects are then mapped into memory.