Electronically Programmable Inductorless Ladder Filters

A technique is presented for the design of a programmable filter instrument in which the frequency response may be electronically programmed by an external analog or digital signal. The active ladder structure is used because the passband insertion loss is highly insensitive to element tolerances. The basis of the method is the selection of a set of electronically switched conductances within the general active ladder structure, which is directly related to the frequency domain characteristics of the transfer function. The frequency response is controlled by accurately programming the values of the conductances in this set. An instrument is presented which embodies these principles and illustrates the versatility which is possible with programmable active ladder structures.