Exact design of stray-insensitive switched-capacitor LDI ladder filters from unit element prototypes

A new technique is described by means of which stray-insensitive switched-capacitor (SC) low-pass and highpass ladder filters of the LDI type may be designed without the need for network synthesis. These filters exactly simulate the response of a unit element cascade prototype filter and may be designed with a usable frequency range up to one-half the sampling frequency. The method operates by establishing an equivalence between the signal flowgraphs (SFG's) of a voltage-wave filter and a leapfrog LDI filter, and a simple algorithm to effect this transformation is described. Since the resulting SFG contains the original wave filter parameters in symbolic form, the transformation need only be carried out once for each order of prototype.