H - Electricity – 04 – L
Patent
H - Electricity
04
L
H04L 7/00 (2006.01) H04L 7/027 (2006.01)
Patent
CA 2114408
"METHOD AND APPARATUS FOR ACCURATELY ESTIMATING A CLOCK FREQUENCY AND FOR SIMULATING A PRECISION CLOCK OSCILLATOR" Abstract of the Disclosure A method for estimating the frequency of the symbol clock in an incoming signal so as to match the frequency of the local symbol clock to the frequency of the remote symbol clock. An analog front end (15) samples an incoming signal to provide a sampled signal. A frequency estimator and clock recovery circuit (16) recovers the symbol clock in the incoming signal and performs a Discrete Time Fourier Transform (DTFT) at two frequencies, F1 and F2. The amplitude of the DTFT at F1 is compared with the amplitude of the DTFT at F2 to provide an estimate of the frequency of the symbol clock in the incoming signal. A master clock (20) provides a clock signal to a clock adjustment circuit (23), which divides the clock signal to provide the transmitter symbol clock for the modem (10). The estimate of the frequency of the symbol clock in the incoming signal is used to adjust the divide ratio in the clock adjustment circuit (23) so that the frequency of the transmitter symbol clock of the modem (10) matches the frequency of the symbol clock of the incoming signal. The present invention matches these frequencies within 10 parts per million (ppm). Therefore, a precision symbol clock can be generated using a master clock having an accuracy of only 100 ppm.
Easley Matthew F.
Rife David C.
Tjahjadi Taruna
Finlayson & Singlehurst
Hayes Microcomputer Products Inc.
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