Decimating SC filter for high speed sigma-delta D/A converters

A decimating switched capacitor filter for sigma-delta D/A converters based on a passive FIR and an active IIR filter is presented. The main advantage of the proposed circuit technique is that all analog components run at a lower sampling rate than the digital modulator, while maintaining a low sensitivity to capacitor mismatch, thus simplifying the design. The low sensitivity to capacitor mismatch is achieved by implementing the FIR filter as a cascaded filter comprising two low order FIR filters. Several filters have been designed and fabricated based on the technique.