H - Electricity – 04 – B
Patent
H - Electricity
04
B
H04B 3/20 (2006.01) H04B 3/30 (2006.01) H04M 3/18 (2006.01)
Patent
CA 2239675
A noise suppression circuit for a two conductor communications channel comprises a hybrid device (11) coupled to the channel for providing a differential output signal corresponding to a signal received from the channel. A delay unit (12) coupled to the output of the hybrid device delays the differential signal by a suitable amount to allow for the generation and subtraction of a noise estimate. A summing device (13) coupled to the channel extracts a digital common mode signal from the channel, and a noise estimation unit (16) provides a common mode noise estimate signal in dependence upon a history of the common mode signal over a predetermined period of time and over a plurality of frequency bands. The common mode noise estimate signal is combined subtractively with the delayed input signal to cancel common mode noise elements of the delayed differential signal. The noise estimation unit may comprise an analysis filter bank (20) responsive to the digital common mode signal for producing a plurality of subband signals S1-S M, each at a different one of a plurality of different frequencies, a plurality of noise detection circuits (23 1-23M), each coupled to the analysis filter bank to process a respective one of the plurality of subband signals and provide a component of the common mode noise estimate signal, and a synthesis filter bank (24) for processing the common mode noise signal components from the plurality of noise detection circuits to provide the noise estimate signal. Each noise detection circuit may monitor and sum a plurality of previous samples of the corresponding subband signal, compare the sum with a predetermined threshold, select, in dependence upon said comparison, either a zero value or an instant value of the subband signal, and supply the selected value to a respective one of a plurality of subband inputs of the synthesis filter bank (24).
Adams Thomas
Bell Canada
Yeap Tet Hin
LandOfFree
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