A data recovery system includes means for injection locking a variable frequency oscillator directly with raw data from a magnetic recording disc during the beginning of a read data operation in order to rapidly lock the variable frequency oscillator in phase with the incoming raw data signals. Desirably, the variable frequency oscillator includes an LC oscillator circuit, which provides excellent noise immunity.

Data recovery circuit

A system is disclosed for sensing a single moving magnetic track, to provide two distinct binary signals (clock and binary data) representative of digital information. Magnetically recorded signals in the Manchester or F/2F code format are selectively processed into electrical representations, using time and amplitude criteria to verify and distinguish between clock (sync) pulses and binary data pulses. An amplitude discriminator is controlled on the basis of the amplitude of immediately prior signals as well as the character of prior binary data pulse signals. A time discriminator is controlled (to segregate clock and data pulse signals) on the basis of the interval of immediately prior signals as well as the character (1 or 0) of prior binary data pulse signals. Consequently, the system is tolerant with regard to signal quality and speed consistency of the relative motion.

Self-clocking magnetic record sensing system

An apparatus is provided for removing invalid read signal peaks which are detected during a disk read operation. In one embodiment, the apparatus converts the analog read-back signal from the disk into a pair of signals, a raw data signal being indicative of the signal peaks read from the disk and a raw polarity signal being indicative of the polarity of such peaks. The raw data signal is inputted to a phase lock loop, which outputs a strobe signal. The raw data signal and the raw polarity signal are made synchronous with the strobe signal in a reclocking circuit. The data and polarity signals outputted by the reclocking circuit are synchronously applied to a qualifying circuit, the output therefrom being free of invalid data.

Method and apparatus for qualifying data

Apparatus for reading data from a rotating magnetic disk whereon data has been recorded at either "single" or "double" density rate, or at both rates on different sectors of the same disk. Density rate information is used to control the frequency of a timing signal generated by a phase locked loop (PLL). The PLL times the reading of data according to a synchronizing signal recorded on the disk. To accommodate the bit shift associated with such plural density data recording, the phase locked loop is provided with a dual gain low pass filter. A high gain is used in the phase locked loop filter until lock-in is achieved, to increase acquisition range and reduce acquisition time; the gain of the loop filter is reduced upon acquisition, to provide a greater lock-in range and to reduce system sensitivity to bit shift of the data, thereby obviating the need for pre-compensation of the bit recording positions.

Reader for data recorded on magnetic disks at plural densities

A digital data encoding and reconstruction circuit is improved by substantially eliminating erroneous and unwanted data readings due to imperfections in the magnetic recording media, excessive shoulders, electronic noise and the like by the use of pulse width discrimination. Since the time between successive transitions caused by valid data is greater than the time duration between transitions caused by erroneous signals, a counter or timer is used to determine and select only transitions caused by valid data in the read signal.

Digital data encoding and reconstruction circuit

A voltage controlled oscillator output frequency is constrained to follow the highest component of significant transitions in an input signal by allowing the input signal to change oscillator-controlling voltages only within a predetermined period after receipt of an input signal transition. The output frequency is maintained at its last corrected value between periods of change. The oscillator forms part of a phase lock loop for establishing a clock to recover variable frequency recorded information.

Sollman George H

Papers

Voltage controlled oscillator with constrained period of frequency change