Abstract: A fourth-order Butterworth low-pass filter with accurate tunable frequency is designed using CMOS operational amplifier.Utilize the liberalized model behavior of an MOS transistor operating in the triode region instead of a passive resistor.Through tuning the grid-voltage of MOS transistor,we can tune the equivalent resistance,accordingly accurately tuning the cut-off frequency of the filter.The filter’s cut-off frequency is 500 kHz.

Key words: R-MOSFET-C filter;Butterworth low-pass filter;PSPICE , simulation