Periodic-switching filter networks-a means of amplifying and varying transfer functions

A technique of periodically switching filter networks makes continuously variable filter parameters possible; at the same time capacitor or time-constant multiplication is obtained. With this method the time constants are multiplied by the switching period to switch aperture-time ration. Because the aperture time is usually small compared to the switching period, the active elements can be shared. A typical first-order system is analyzed for its step and sine response by the difference equation method. Phase and gain error expressions are established as a function of the various parameters. Limiting cases are then investigated to give a measure of a pulse- switched system performance. Finally an application of a multiplexed system is presented where three independent transfer functions are realized using one operational amplifier.