A system includes a sampling circuit, an analog filter, an analog input, a
modulator, and a modulating source. The modulating source includes an
output that generates an impulse response encoded as a sigma-delta
sequence. The output of the modulating source is coupled to the
modulator, which is coupled to the analog input. The analog filter is
coupled to the modulator and the sampling circuit. When the system is
configured as a filter, an analog signal is modulated with the
sigma-delta sequence. The modulated signal is filtered and then sampled.