Synchronization correction circuit for correcting the period of clock signals
A transmission interval counter measures the period of a packet sync generated in a sync generator. A comparator compares the period of the packet sync to a reference interval as selected by a type selector to calculate a period error. A correction value calculator calculates a correction value based on the period error. An adder sums the correction value to a predetermined value to output a sum. A frequency dividing counter counts the high-speed clock signals to output its count, and is reset by a pulse. A comparator outputs the pulse when the count coincides with the sum. A circuit generates clocks synchronized with the pulses. A circuit frequency-divides the clocks by ⅛ to generate synchronization signals.
1. A synchronization correction circuit comprising:
a synchronization signal generator for detecting a synchronization word contained in a received packet to generate a packet synchronization signal synchronized with the received packet;
a period error detector for measuring a period of the packet synchronization signal generated in said synchronization signal generator to calculate a period error with respect to a reference interval;
a cumulative error counter for cumulating the period error as calculated by said period error detector every plural periods of the packet synchronization signal to calculate a cumulative period error;
a correction value calculator for calculating a period correction value per one clock signal and a number of clock signals to be corrected for a clock period so that a sum of the period correction values per one clock signal will be coincident with the cumulative period error; and
a clock signal generator for generating clock signals of a predetermined reference period when the period correction value is zero, and for generating, when the period correction value is different than zero, a number calculated in said correction value calculator of clock signals, a period of which has been corrected based on the period correction value.
2. The synchronization correction circuit according to claim 1 , wherein said clock signal generator comprises:
an adder for summing a predetermined value with the period correction value as calculated in said correction value calculator;
a counter for counting high-speed clock signals;
a comparator for outputting pulses when a count of said counter coincides with a sum obtained in said adder; and
a synchronization pulse generator for wave-shaping a waveform of pulses output by said comparator to generate the clock signals,
said counter resetting the count by pulses output from said comparator.
3. The synchronization correction circuit according to claim 1 , wherein said period error detector includes a header analysis part for detecting a packet type from the received packet, and wherein a value of the reference interval is determined from the packet type detected by said header analysis part.
4. The synchronization correction circuit according to claim 2 , wherein a period of said high-speed clock signals and the sum obtained in said adder are set so that a product of a period of the high-speed clock signals and the sum obtained in said adder will be equal to the predetermined reference period.
5. A synchronization correction circuit comprising:
a synchronization signal generator for detecting a synchronization word contained in a received packet to generate a packet synchronization signal synchronized with the received packet;
a period error detector for measuring a period of the packet synchronization signal generated in said synchronization signal generator to calculate a period error with respect to a reference interval;
a cumulative error counter for sequentially cumulating the period error calculated in said period error detector and sequentially outputting the cumulated period error each time the period error has been cumulated;
a first comparator for comparing the cumulated period error output from said cumulative error counter to a threshold value to output a trigger when the cumulated period error has exceeded the threshold value;
a correction value calculator for calculating a period correction value per one clock signal and a number of clock signals to be corrected for a clock period, when a trigger is output from said first comparator, so that a sum of the period correction values per one clock signal will be coincident with the threshold value; and
a clock signal generator for generating clock signals of a predetermined reference period when the period correction value is zero, and for generating, when the period correction value is different than zero, a number calculated in said correction value calculator of clock signals, a period of which has been corrected based on the period correction value,
said cumulative error counter subtracting the period correction value from the cumulated period error when the trigger is output from said first comparator.
6. The synchronization correction circuit according to claim 5 , wherein said clock signal generator comprises:
an adder for summing a predetermined value with the period correction value as calculated in said correction value calculator;
a counter for counting high speed crock signals;
a second comparator for outputting pulses when a count of said counter coincides with a sum obtained in said adder, and
a synchronization pulse generator for wave-shaping a waveform of pulses output by said second comparator to generate the clock signals,
said counter resetting the count by pulses output from said second comparator.
7. The synchronization correction circuit according to claim 5 , wherein said period error detector includes a header analysis part for detecting a packet type from the received packet, and wherein a value of the reference interval is determined from the packet type detected by said header analysis part.
8. The synchronization correction circuit according claim 5 , wherein the threshold value used in said first comparator is stored in a register, and wherein the threshold value stored in said register can be set externally to any optional value.
9. The synchronization correction circuit in accordance with claim 6 , wherein a period of said high-speed clock signals and the sum obtained in said adder are set so that a product of a period of the high-speed clock signals and the sum obtained in said adder will be equal to the predetermined reference period.