Abstract: An apparatus for setting a threshold voltage for determining bit positions of digital data stored on an optical recording device utilizing pulse width modulation. The optical recording device reads a pattern from an optical medium. The read pattern has a fixed, known duty cycle. A feedback circuit processes the pattern according to an initial threshold voltage. The feedback signal is then input to a comparator. The comparator compares the feedback signal against the pattern. Based on this comparison, the amount of current input to and output from a compensation circuit is adjusted. Thereupon, the compensation circuit sets the threshold voltage accordingly.

Abstract: An optical recording system having a DC restored read signal for qualifying pulses in the read channel. The equalized and filtered read signal is input to a differentiator and a DC restore circuit. The zero crossings of the differentiated signal which represent the peaks of the pulses are detected. The DC restore circuit inverts the read signal, generates a reference voltage, and compares the negative pulses peaks of the read signal to the reference voltage. The charge of a capacitor is adjusted according to the difference in voltages of the pulse peaks to that of the reference voltage in order to maintain a constant DC level. The DC restored signal is qualified according to a threshold. Only those pulses which have zero crossings and which have been qualified are considered to be valid.

Abstract: In an optical recording system employing a laser for writing digital data onto a storage medium, an apparatus and method for calibrating a laser to a power level which minimizes write errors. A calibration profile is generated by writing test data patterns onto the storage medium by using a number of different predetermined laser power levels. The test data patterns are then read back. The number of write errors is determined for each of the different laser power levels by comparing the written data patterns to the read back data patterns. The calibration profile denotes the number of write errors as a function of laser power levels. Next, an optimum laser power is determined corresponding to an average of an upper and a lower knee of the calibration profile. The laser is calibrated to this optimum power level.

Abstract: An apparatus and method for compensating for dust particles on the surface of an optical disk during a write operation includes a circuit for sensing the reflected laser light back from the optical storage medium, and a negative peak detection circuit for determining when the reflected laser light drops below the average read power level. The reflected laser power is reduced below the average read level whenever a dust or dirt particle is blocking a portion of the incoming laser light. An additonal circuit means then increases the power of the laser beam by an amount proportional to the detected reduction so that the data can be effectively recorded.

Abstract: A disk drive control system incorporating an internal microprocessor and internal testing capabilities. The disk drive control system is capable of simulating drive operation without carriage motion so as to test substantially all functional subsystems of the disk drive. The test technique comprises the exercising of subsystems and a diagnosis of operations according to a hierarchy of interdependence of subsystem operation.

Abstract: In a digital information storage system or the like, start up power sequencing for independently operable machines such as disk drives each equipped with a microprocessing unit is provided through a simplified power sequencing circuit. The power sequencing circuit is operatively coupled with an independent preprogrammable micropocessing unit in each machine and to a single control line common to all disk drives. The microprocessing unit is preprogrammed to interact with the power sequencing circuit to provide Enable/Disable signals to the control line and to sense the state of the control line. In particular, the microprocessing unit executes a preprogrammed sequence of steps in interaction with the control line to sequence the start-up of each spindle motor irrespective of the number of disk drives coupled to the control line, thereby preventing electrical power overload.