Sigma-delta based IIR filters

A design methodology for realizing IIR (infinite impulse response) filters on sigma-delta modulated signals is proposed. It is shown that only 3N adders together with minor logic are required to implement an Nth-order filter. With the use of examples, it is also shown that a linear noise analysis gives an excellent prediction of noise performance over the frequency band of interest. This type of filtering should prove useful in VLSI technologies where interfaces to analog signals are required. To demonstrate the validity of this approach, a fifth-order prototype filter was simulated for three different oversampling ratios