Fecha de publicación: 24/09/1991 Fuente: Wipo "digitalization" A digital decimation filter for receiving a stream of input digital samples at an input sample rate, and for delivering a corresponding stream of output digital samples at a different output sample rate stores a plurality of input digital samples, derives samples of the output stream from the stored input digital samples, and makes an output sample available for inclusion in the output stream at all times, whereby the output sample may be delivered with a selectable phase. In other aspects, an analog-to-digital converter has a sigma-delta modulator for generating a high rate stream of digital samples of an analog signal at a rate substantially higher than the Nyquist rate, and a digital decimation filter for receiving the high rate stream and delivering a corresponding stream of filtered output digital samples at a lower rate, the decimation ratio being selectable; and a multiple-mode modem for use with a channel on which a carrier may be modulated in accordance with at least two different possible modulation schemes (the channel being of the kind that induces echo signals, the modulation schemes comprising techniques for avoiding the effects of the echo signals), receives the modulated carrier from the channel and converts it to a corresponding stream of digital samples, using receive circuitry that has an analog-to-digital converter feeding a programmable digital filter for selectively providing filtering functions applicable respectively to the two different modulation schemes, whereby different receive filters applicable to different modulation schemes need not be provided ahead of the analog-to-digital converter.