Olin Lathrop wrote: > A switched capacitor filter just switches in/out elements of cascaded R/C > lowpass filters. No, Olin, a switched-capacitor filter replaces each resistor in a filter network (and not just low-pass configurations) with a capacitor and two switches. Since the capacitor transfers a fixed amount of charge between two circuit nodes on each cycle of the clock, it functions as a precise amount of conductance that's directly proprotional to the clock frequency. (Or think of it as a resistance that's inversely proportional to the clock frequency.) Multiple such elements within a network track very closely, making it possible to build high-order filters that maintain their performance over a wide range. The big advantage is that these are easy to build on an IC, as it is very difficult to make precise large-value resistors in silicon, but very easy to make precise (and well-matched) small-value capacitors. Their biggest drawback is that they are discrete-time, so you do need to think about sampling issues such as aliasing, etc. However, these issues tend to be minimized by the fact that the clock frequency is usually several hundred times the signal frequencies of interest. -- Dave Tweed -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.