The invention provides a sigma-delta modulator (SDM) and associated system improving spectrum efficiency of wired interconnection. The SDM may comprise a main circuit for transferring an aggregated signal by a signal transfer function, and a noise shaping circuit for shaping noise away from a low-pass band by a modified noise transfer function. A frequency response of the modified noise transfer function may have a notch at a passband, and the passband may not overlap with the low-pass band.