| 摘要 |
A noise suppression circuit for a two-wire communications channel comprises a hybrid device, for example a hybrid transformer or circuit, for providing a diff erential mode signal corresponding to a differential signal received from the two-wire channel . A summing device extracts from the two-wires of the channel a common mode signal a nd supplies it to a noise estimation unit which derives from the common mode signal an estimate of a noise level in at least one frequency band having a bandwidth cons iderably narrower than an operating bandwidth for the channel. The noise estimation unit adjusts the amplitude of the noise estimate to correspond to the residual noise in the d ifferential mode signal and subtracts it from the differential mode signal to produce a nois e-suppressed output signal. A noise detection and control unit scans the opperating band, ide ntifies a frequency band having an instant highest noise level, and sets the noise estimat ion unit to the detected noisy band. The noise estimation unit suppresses the noise in that band. In preferred embodiments, the noise estimation unit comprises several channels, eac h comprising a tunable filter, a phase shifter and an amplifier, and the noise det ection and control unit sets the channels, in succession, to different frequency bands in d escending order of noise level. The noise detection and control unit may cross-correlate t he common mode signal and the noise-suppressed output signal and adjust the amplification of the noise estimation signal to reduce residual differential mode noise substantially to ze ro.
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