Digital phase lock loop for flexible disk data recovery system

In combination with a flexible disk data recovery system wherein an encoded bit stream having data bits and clock bits is obtained from a flexible disk, a means for generating a signal in phase lock with said data bits, comprising:

• means for providing a phase clock signal formed of a sequence of phase clock cycles;
• means responsive to said phase clock signal for producing a bit window to correspond with each bit in said bit stream;
• each of said bit windows having a variable duration defined by a plurality of said phase clock cycles;
• means for providing a signal indicative of the position of a selected bit with respect to the phase clock cycles within the bit window corresponding therewith;
• and
• means for selectively varying the number of phase clock cycles defining a bit window responsive to the position within said bit window of the bit corresponding therewith.

A system for generating a signal in phase lock with data bits within an encoded bit stream having data bits and clock bits comprising:

• means for providing a phase clock signal formed of a sequence of phase clock cycles;
• means responsive to said phase clock signal for providing a bit window to correspond with each bit in said bit stream;
• each of said bit windows having a variable duration defined by a plurality of said phase clock cycles;
• means for providing a signal indicative of the position of a selected bit with respect to the phase clock cycles within the bit window corresponding therewith;
• and
• means for selectively varying the duration of phase clock cycles defining a bit window responsive to the position within the bit window of the bit corresponding therewith.

A method of generating a signal in phase lock with bits within an encoded bit stream having data bits and clock bits, comprising the steps of:

• providing a phase clock signal formed of a sequence of phase clock cycles;
• producing a bit window to correspond with each bit in said bit stream;
• each of said bit windows having a variable duration defined by a plurality of said phase clock cycles;
• determining the position of a bit in said bit stream with respect to the phase clock cycles within the bit window corresponding therewith;
• and
• selectively varying the number of phase clock cycles defining a bit window responsive to the position within said bit window of the bit corresponding therewith.

In combination with a data source providing a stream of bits, means for generating a signal comprised of bit windows occurring in synchronism with said bits, said signal generating means comprising:

• means for producing a first signal comprising successive transitions to define successive bit windows each having a duration defined by the interval between successive transitions;
• means for producing a second signal indicative of the interval between the occurrence time of each transition initiating a bit window and the occurrence time of a bit within that same bit window;
• and
• means responsive to said second signal for adjusting the duration of that same bit window.

In a system for obtaining data bits from an encoded bit stream containing data bits and clock bits, the improvement comprising:

• means for providing a phase clock signal formed of a sequence of ordered phase clock cycles;
• means responsive to said phase clock signal for defining nominal bit windows, each being defined by a predetermined plurality of said phase clock cycles and each corresponding with a different one of said data and clock bits;
• means for determining the position of a selected bit within its corresponding bit window by identifying the order of a phase clock cycle essentially coincident therewith;
• and
• means for adjusting the initiation time of a bit window responsive to the positions of two preceding bits within their respective bit windows.