Patent ID: 7176754

Claim:
A method for controlling characteristic parameters of an active filter having an operational amplifier and a plurality of first programmable resistors, the method comprising: determining a deviation ε of a second programmable resistor within a control circuit from a value R a , said second programmable resistor having the same structure as said first programmable resistors; generating a plurality of tuning signals to program said first programmable resistors and said second programmable resistor; and programming at least two of said first programmable resistors as a function of said deviation ε toward a predetermined value, wherein determining the deviation ε includes comparing each selected value of the second programmable resistor with a reference value to generate an error signal and count said error signal with a counter to generate said tuning signals, and wherein determining the deviation ε is based on a formula: R a =(1+ε)·( R off +nδR ) where R off is a resistance that avoids a short circuit when outputs of the counter are low, n is a number of first programmable resistors, and δR is a resistance unit.