Principle of switched-capacitor circuits
Filtres à capacités commutées

In MOS integrated technology, we know how to make good operational amplifiers, fairly accurate capacitors (better than 10%) and analog gates, but we don't know how to make the inductors and resistors needed to synthesize analog filters. Feasible inductances have very low values (in the nanohenry range). Resistors are not very precise and have insufficient dynamic range if they are made by diffusion or in polysilicon, or, if they are made in the form of MOS channels, they are highly non-linear as a function of the voltage applied to their terminals.

The basic idea behind switched-capacitor filters is to replace resistors with a circuit comprising only capacitors and switches alternately opened and closed...