Low-distortion 4th order programmable Butterworth filter

A highly linear 4th order low-pass filter with one decade frequency programmability and 39 dB gain programmability is presented in this paper. Low distortion is achieved through the use of the inherently linear current division principle. The paper provides the basic equations of the Butterworth filter and shows how to achieve programmability. A prototype was fabricated in a 0.35 μm–3.3 V CMOS process and experimental measurements prove the high linearity of the system. A distortion level better than −65 dB for 2 Vp-p output signal is obtained.