Patent ID: 6240150
Filing Date: 2001-05-29
Classification: H04B,H04L

Abstract:
An apparatus for reducing transmitter feed-through (Tx-FT) interference at a receiver of a modem operating at a first sampling rate to obtain a desired receive (Rx) signal having a spectrum at a carrier frequency for input into a QAM demodulator operating at a second sampling rate, said apparatus comprising:(a) an analog filter having a filter mask for attenuating the Tx-FT interference to a first prescribed level and for passing the Rx signal at the carrier frequency;(b) a converter for converting output from the analog filter to a digital representation;(c) a first digital filter having a mask for passing the Rx signal at the carrier frequency and for attenuating the Tx-FT interference to a second prescribed level;(d) a mixer for shifting the carrier frequency of the spectrum of the Rx signal to an intermediate frequency, said mixer introducing at least one spectral transmitter feed-through image Tx-FT(I) and a receive signal image Rx(I);(e) a second digital filter having a mask for passing the Rx signal at the intermediate frequency and attenuating the image spectrums Tx-FT(I) and Rx(I); and(f) a decimator for downsampling the Rx signal at a downsampling rate from the second digital filter to match the second sampling rate of the QAM demodulator.