oversampling减低noise floor很容易解释,total power is delta^2/12, assuming white noise 均匀分布在0-fs/2内,增大采样频率当然降低noise floor.
其实无所谓什么sigma delta也无所谓什么Noise shaping.
考虑简单的feedback system,output follows input. noise is added at the output and when referred to input, it should be divided by forward path Hs.