US 6,052,420 A · Adaptive multiple sub-band common-mode RFI suppression

Abstract

A noise suppression circuit for a two-wire communications channel comprises a hybrid device, for example a hybrid transformer or circuit, for providing a differential 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 and 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 considerably 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 differential mode signal and subtracts it from the differential mode signal to produce a noise-suppressed output signal. A noise detection and control unit scans the operating band, identifies a frequency band having an instant highest noise level, and sets the noise estimation 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, each comprising a tunable filter, a phase shifter and an amplifier, and the noise detection and control unit sets the channels, in succession, to different frequency bands in descending order of noise level. The noise detection and control unit may cross-correlate the 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 zero.

Claims18

Dependent claims

Apparatus for suppressing noise in signals received from a two-conductor communications channel comprising:

(i) a hybrid device connected to the channel for providing a differential mode signal corresponding to a differential signal received from the channel,
(ii) a device for extracting from the channel a corresponding common mode signal,
(iii) a noise estimation unit responsive to the common mode signal and a frequency control signal for deriving from the common mode signal a noise estimate signal representing a common mode noise level in a selected frequency band having a bandwidth considerably narrower than an operating bandwidth of said differential signal,
(iv) means for providing a noise-suppressed output signal as the difference between the differential mode signal and the noise estimate signal;
and
(v) noise detection and control means responsive to said common mode signal for detecting within the operating bandwidth a narrow frequency band wherein instant noise level is higher than in other parts of the operating bandwidth, such narrow frequency band having a bandwidth significantly less than an operating bandwidth of said differential signal, and generating said frequency control signal for adjusting said noise estimation means so that said selected frequency band corresponds to that of the instant highest noise signal.

3 more elements

Noise suppression apparatus for a two-conductor communications channel comprising:

(i) a hybrid device connected to the channel for providing a differential mode signal corresponding to a differential signal received from the channel,
(ii) a device for extracting from the channel a corresponding common mode signal,
(iii) a noise estimation unit comprising a plurality of noise estimation means for deriving a corresponding plurality of noise estimate component signals for a plurality of selected frequency bands, respectively, each noise estimation means being responsive to the common mode signal and a corresponding one of the plurality of frequency control signals for deriving from the common mode signal a noise estimate signal component representing a common mode noise level in a selected frequency band having a bandwidth considerably narrower than an operating bandwidth of said differential signal,
(iv) means for summing the noise estimate signal components to provide a noise estimate signal;
(v) means for providing a noise-suppressed output signal as the difference between the differential mode signal and the noise estimate signal;
and
(vi) noise detection and control means responsive to said common mode signal for scanning the operating bandwidth a plurality of times to detect, for each scan, that narrow frequency band wherein instant noise level is higher than in other parts of the operating bandwidth, each such narrow frequency band having a bandwidth significantly less than an operating bandwidth of said differential signal, and generating for each scan one of said frequency control signals for adjusting the corresponding one of said noise estimation means so that the corresponding said selected frequency band corresponds to that of the instant highest noise signal, the arrangement being such that the noise estimation means are set to their respective frequency bands in succession.

4 more elements

A method of suppressing noise in a signal received from a two-conductor communications channel comprising the steps of:

(i) using a hybrid device connected to the channel to provide a differential mode signal corresponding to a differential signal received from the channel,
(ii) extracting from the channel a corresponding common mode signal,
(iii) responsive to the common mode signal and a frequency control signal, deriving from the common mode signal a noise estimate signal representing a common mode noise level in a selected frequency band having a bandwidth considerably narrower than an operating bandwidth of said differential signal,
(iv) providing a noise-suppressed output signal as the difference between the differential mode signal and the noise estimate signal;
and
(v) responsive to said common mode signal, detecting within the operating bandwidth a narrow frequency band wherein instant noise level is higher than in other parts of the operating bandwidth, such narrow frequency band having a bandwidth significantly less than an operating bandwidth of said differential signal, and generating said frequency control signal for adjusting said selected frequency band to correspond to that of the instant highest noise signal.