METHOD FOR MEASURING RELATIVE AND ABSOLUTE AMPLITUDES OF A SIGNAL READ FROM A DATA STORAGE MEDIUM

AN APPARATUS AND METHOD FOR MEASURING AN AMPLITUDE OF A READBACK SIGNAL OBTAINED FROM A DATA STORAGE MEDIUM INVOLVES TRANSMITTING THE READBACKSIGNAL TO A GAIN MODIFYING AMPLIFIER, SUCH AS A VARIABLE GAIN AMPLIFIER (VGA)(76), PREFEREBLY PROVIDED IN THE READ CHANNEL. A VOLTAGE SIGNAL ASSOCIATED WITH A LOOP GAIN OF THE AMPLIFICATION CIRCUITRY IS SENSED AND COMPARED WITH A NUMBER OF CONTROL VOLTAGE SIGNALS, EACH OF THE CONTROL VOLTAGE SIGNALS BEING ASSOCIATED WITH A CORRESPONDING DIGITAL WORD VALUE. THE DIGITAL WORD VALUE ASSOCIATED WITH A CONTROL VOLTAGE SIGNAL THAT IS EQUAL TO THE SENSED VOLTAGE SIGNAL REPRESENTS THE RELATIVE AMPLITUDE OF THE READBACK SIGNAL. GAIN CHARACTERIZATION CIRCUITRY MAY FURTHER BE COMBINED WITH READBACK SIGNAL AMPLITUDE MEASURING CIRCUITRY (75), PREFERABLY IN-SITU A READ CHANNEL, TO OBTAIN THE ABSOLUTE AMPLITUDE OF A READBACK SIGNAL. GAIN CHARACTERISTICS OF THE AMPLIFICATION CIRCUITRY ARE DETERMINED BY APPLYING REFERENCE VOLTAGE SIGNALS ASSOCIATED WITH CORRESPONDING PRE-ESTABLISHED GAIN VALUES TO THE SIGNAL INPUT OF THE GAIN MODIFYING AMPLIFIER. A CONTROL VOLTAGE SIGNAL IS SELECTIVELY APPLIED TO THE AMPLIFIER FOR EACH OF THE REFERENCE VOLATGE SIGNALS UNTIL THE AMPLIFIER OUTPUT VOLTAGE SIGNAL IS SUBSTANTIALLY EQUAL TO A PRE-ESTABLISHED REFERENCE VOLTAEGE SIGNAL. AMPLITUDE MEASUREMENTS MAY THEREAFTER BE TAKEN TO OBTAIN THE ABSOLUTE AMPLITUDE OF READBACK SIGNALS. READBACK SIGNAL AMPLITUDE MEASUREMENTS MAY BE PERFORMED WHEN THE READ CHANNEL IS IN A READ MODE, IDLE MODE, OR SERVO MODE OF OPERATION.(FIG 3B)