06501405 is referenced by 8 patents.
An apparatus and method is disclosed for minimizing in band distortion in the transmit path of an XDSL modem. The transmit path of an XDSL modem introduces various non-linearities into transmissions in both the frequency and time domains. The current invention provides a means for both determining and correcting for distortion in the time domain. In an embodiment of the invention the apparatus may include a calibrator which may be implemented using the existing analog-to-digital (ADC) conversion and demodulation capabilities on the receive path of the modem or alternately, a dedicated module. During a calibration phase a training signal is injected digitally into the digital-to-analog converter of the transmit path. The analog portion of the transmit path is coupled to a calibrator which measures the corresponding analog response. The correlation between input and response is stored in an analog model. During subsequent training and run-time phases of modem operation an oversampled digital input stream is subject to digital Delta Sigma Modulation (&Dgr;&Sgr;M) with the analog model injected into the feedback path from the quantizer. The injection of the analog model into the feedback improves the noise transfer function (NTF) associated with the &Dgr;&Sgr;M.