H - Electricity – 04 – L
Patent
H - Electricity
04
L
340/205
H04L 1/00 (2006.01) H04L 7/027 (2006.01)
Patent
CA 1163005
A B S T R A C T IMPROVEMENTS IN OR RELATING TO TIMING RECOVERY FOR MODEMS The invention is an improvement on a technique of timing recovery from the line signal by envelope detection using double bandpass filtering prior to detection to improve the power ratio of the recovered timing signal to the interfacing by-products of the squaring process as disclosed in BSTJ March 1975 (Vol. 54 No. 3) pp 569-593 by Githin & Hayes entitled "Timing Recover" and Scramblers in Data Transmission". In the method disclosed in the article in addition the difference frequency components which are used to provide the desired timing signal, there are not only the sum-frequency products but also the products of squaring the individual bandpassed signal components, some of which may be in the same frequency region as the difference frequency signal. The invention avoids this problem by taking the outputs of the two bandpass filters used in the Githin & Hayes version and applying them severally to the two input ports of a four-quadrant multiplier. The output from the multiplier will then comprise only sum-frequency and difference-frequency products, the latter being easily separable and providing the desired timing recovery signal free from impairments.
359613
Borden Ladner Gervais Llp
Plessey Overseas Limited
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