Bilinear design of fully differential switched-capacitor ladder filters

Fully differential switched-capacitor (SC) analogue blocks are shown to be suitable for implementing SC ladder filters via the bilinear transform of the corresponding analogueRLC passive prototypes. These filters become fully insensitive to parasitic capacitance effects, while the interesting features of the differential implementation, i.e. power supply and common mode rejection ratios and dynamic range improvements, are retained. The technique presented is useful for the exact design of wide-band SC filters, i.e. for filters with a small ratio between the clock frequency and the cut-off frequency. As an example, the bilinear design of an 8th-order Cauer bandpass filter is given, with numerically computed results.