US Patent 7825842 Digital sigma-delta modulators

A digital sigma-delta modulator (100) for modulating a digital input signal (x) is described. The digital sigma-delta modulator (100) comprises a quantizer (115) for quantizing an input signal (s) and producing a quantized output signal (y) at a first output (110) and an error output signal (−q) at a second output (165), at least one feedback loop (120, 125) connected to an input adder (140) and the first outputs (110) and the second output (165) of the quantizer (115) and a feedback filter (130, 135) in the at least one feedback loop (120, 125). The input adder (140) produces the sum signal (s) by adding the digital input signal (x) at an input (105) and output signals of the at least one feedback loop filters (130,135).