Method for symbol clock recovery in pulse position modulation (PPM) systems

A symbol clock symbol clock recovery circuit for recovering a symbol clock in an M-ary pulse position modulation (PPM) signal received by a receiver, said PPM signal including symbol groups defined by consecutive M number time slots, said symbol clock recovery circuit comprising:

• a slot clock recovery circuit that provides a slot clock pulse for each time slot in the PPM signal;
• a pulse sampler circuit receiving the PPM signal and being controlled by the slot clock pulses to selectively provide sample values for each time slot in the PPM signal;
• M number of sequentially organized delay circuits that each delay the sample values one time slot to provide M number of increasingly delayed sample values;
• a first largest magnitude select circuit responsive to the delayed sample values from the M number of delay circuits and a second largest magnitude select circuit responsive to the sample value from the pulse sampler circuit and M−1 delay circuits, said first and second largest magnitude select circuit each outputting a largest magnitude sample value for each time slot;
• a divider circuit responsive to the slot clock pulses from the slot clock recovery circuit and generating a symbol clock signal including symbol clock pulses for every M number of time slots;
• a first largest magnitude sampler circuit responsive to the largest magnitude sample values from the first largest magnitude select circuit and a second largest magnitude sampler circuit responsive to the largest magnitude sample values from the second largest magnitude select circuit, said first largest magnitude sampler circuit and said second largest magnitude sampler circuit receiving the symbol clock signal and outputting the first and second largest magnitude sample values every symbol clock pulse;
• a summation junction that subtracts the first largest magnitude sample values from the first largest magnitude sampler circuit from the second largest magnitude sample values from the second largest magnitude sampler circuit and provides a difference largest magnitude sample value;
• an averaging circuit that is responsive to the difference between the sample values from the summation junction and that averages the difference between the largest magnitude sample values over a predetermined time period;
• a threshold comparator that compares the averaged difference sample values from the averaging circuit to a predetermined threshold value;
• and
• a position correct circuit responsive to a difference signal from the threshold comparator and providing a control signal to the divider circuit to correct the position of the symbol clock pulses if the difference signal does not exceed the threshold value.

A symbol clock recovery circuit for recovering a symbol clock in an M-ary pulse position modulation (PPM) signal received by a receiver, said PPM signal including symbol groups defined by consecutive M number of time slots, said symbol clock recovery circuit comprising:

• a slot clock recovery circuit that provides a slot clock pulse for each time slot in the PPM signal;
• a pulse sampler circuit receiving the PPM signal and being controlled by the slot clock pulses to selectively provide sample values for each time slot in the PPM signal;
• M−1 number of sequentially organized delay circuits that each delay the sample values one time slot to provide M−1 number of increasingly delayed sample values;
• a magnitude select circuit responsive to the sample values from the pulse sampler circuit and the delay circuits and outputting a largest magnitude sample value for each time slot;
• a divider circuit responsive to the slot clock pulses from the slot clock recovery circuit and generating a symbol clock signal including a symbol clock pulse for every M number of time slots;
• a largest magnitude sampler circuit responsive to the largest magnitude sample values from the largest magnitude select circuit for each time slot and selectively providing that sample value every symbol clock pulse;
• an averaging circuit that is responsive to the largest magnitude sample values from the largest magnitude sampler circuit and that averages the largest magnitude sample values over a predetermined time period
• a threshold comparator that compares the averaged largest magnitude sample values from the largest magnitude select circuit to a predetermined threshold value;
• and
• a position correct circuit responsive to a comparison signal from the threshold comparator and providing a control signal to the divider circuit to correct a position of the symbol clock pulses to identify a first time slot in each symbol group.

A symbol clock recovery circuit for recovering a symbol clock in an M-ary pulse position modulation (PPM) signal, said PPM signal including groups defined by consecutive M number of time slots, said symbol clock recovery circuit comprising:

• a slot clock recovery circuit that provides a slot clock pulse for each time slot in the PPM signal;
• at least M−1 number of delay circuits that consecutively delay signal values in each time slot for one time slot;
• at least one largest magnitude select circuit responsive to the signal values from the delay circuits and outputting a largest magnitude signal value for each group of M time slots;
• a divider circuit responsive to the slot clock pulses from the slot clock recovery circuit and generating a symbol clock signal having a single symbol clock pulse for every M number of time slots;
• at least one largest magnitude circuit responsive to the largest magnitude signal values from at least one largest magnitude select circuit for each time slot and selectively providing that signal value every symbol clock pulse;
• at least one averaging circuit that is responsive to the largest magnitude signal values from at least one largest magnitude circuit and that averages the largest magnitude signal values over a predetermined time period;
• and
• a position correct circuit responsive to the averaged signal values from at least one averaging circuit and providing a control signal to the divider circuit to correct a position of the symbol clock pulses to identify a first time slot in each group.

A method for recovering a symbol clock in an M-ary pulse position modulation (PPM) signal, said PPM signal including groups defined by consecutive M number of time slots, said method comprising:

• recovering a slot clock pulse for each time slot in the PPM signal;
• delaying a signal value in each time slot for one time slot at least M−1 number of times;
• providing a largest magnitude signal value from the delayed signal values for each group of M time slots;
• generating a symbol clock signal having a single symbol clock pulse for every M number of time slots;
• selectively providing the largest signal value every symbol clock pulse;
• and
• correcting the position of the symbol clock pulses to identify a first time slot in each group in response to the selected largest magnitude signal value.