Programmable RC filter

Abstract

A programmable resistive-capacitive filter circuit enabling on-chip digital control of the frequency response includes a switched resistive type voltage divider network where one of the resistors forms an element of an RC filter and wherein the voltage divider additionally provides a DC bias on an output terminal. One preferred embodiment of the invention is directed to a programmable bandpass filter including MOSFET type semiconductor devices which are utilized as switched resistive elements of the filter.

What is claimed is:  
     
         1 . A programmable RC filter, comprising: 
 a plurality of switched circuit elements which respectively operate both as a resistor and series connected switch with each of the plurality of switched circuit elements connected in parallel between an input terminal and an output terminal; and    a capacitor connected between one side of said active circuit element common to the output terminal and a point of reference potential or ground;    wherein at least one of said active circuit elements is switched into circuit relationship with said capacitor so as to provide an active low pass filter circuit having a programmable frequency response.A    
     
     
         2 . A programmable filter according to  claim 1  wherein said active circuit elements are comprised of semiconductor devices.  
     
     
         3 . A programmable filter according to  claim 2  wherein said semiconductor devices are comprised of transistors.  
     
     
         4 . A programmable filter according to  claim 2  wherein said semiconductor devices are implemented in an integrated circuit.