A functional MOS circuit for achieving the bilinear transformation in switched capacitor filters

Recently, a new technique for filtering in MOS LSI using switched capacitors has been demonstrated (see ibid., vol.SC-12, p.592, 1977). Basically, the technique involves the replacement of resistors, in continuous active RC filter designs, with an analogous circuit using switches and capacitors in a sampled-analog equivalent. The approach creates a problem, however, in that the switched capacitor structures do not directly simulate the equivalent resistors over the useful frequency range. This leads to the necessity for Z-transform analysis, and causes the sampled analog circuit behavior to degrade from the simplicity of the continuous active equivalent. A solution to the problem of realising the bilinear transformation in a switched capacitor network with experimental verification is given. The solution is presented in the context of an active integrator, but is quite general.