US 7,469,026 B2
Random walk filter timing recovery loop
Tien M. Nguyen, Placentia, Calif. (US); James Yoh, Palos Verdes Peninsula, Calif. (US); Ashok Mathur, Duarte, Calif. (US); and Gary W. Goo, Rolling Hills Estate, Calif. (US)
Assigned to The Aerospace Corporation, El Segundo, Calif. (US)
Filed on Mar. 07, 2002, as Appl. No. 10/92,758.
Prior Publication US 2003/0169834 A1, Sep. 11, 2003
Int. Cl. H04L 25/38 (2006.01); H03D 3/22 (2006.01)
U.S. Cl. 375—354  [375/362; 375/373; 375/375; 375/376] 10 Claims
OG exemplary drawing
 
1. A timing recovery loop for generating adjusted timing pulses from a baseband signal waveform encoding a self clocking digital bit stream, the timing recovery loop comprising,
a pulse detector for generating data transition pulses from the baseband signal waveform, the pulse detector for comparing the data transition pulses with the adjusted timing pulses for generating lead signals and lag signals, the lead signals and lag signals being generated from the data transition pulses occurring within a window period of time referenced to the adjusted timing pulses, the data transition pulses corresponding to respective data bits of the self clocking digital bit stream with each of the data bits having a bit period, the data transition pulses being synchronized to the baseband waveform,
a random walk counter for counting the early signals and lag signals over a plurality of bit periods for generating a running count, the lead signals and lag signals being generated when the data transition pulses lead and lag the adjusted timing pulses,
a threshold comparator for determining when the running count exceeds a predetermined first threshold count value, and
a timing pulse delay adjustor for adjusting an adjusted timing pulse delay communicated to the pulse detector for delaying the adjusted timing pulses for synchronizing the adjusted timing pulses with the data transition pulses and with the baseband signal over a plurality of bit periods when the running count exceeds the predetermined threshold count value,
a data transition pulse generator for generating the data transition pulses,
a window delay for delaying the data transition pulses by half of a search window to center the data transition pulses within respective search windows,
a timing delay for delaying by a timing pulse delay the reference timing pulses into the adjusted timing pulses, the timing pulse delay being generated by the timing delay adjustor, the timing pulse delay being adjusted when the running count exceeds predetermined threshold value,
a data transition pulse counter for counting the number of data transition pulses within the search window following an adjusted timing pulse, and
a lead and lag generator for generating lead and lag signals for early and late arrivals of the data transition pulses relative to the adjusted timing pulses when one and only one data transition pulse occurs within a respective one of the search windows following a respective one of the adjusted timing pulses.