A wide tuning range operational transconductance amplifier (OTA) using tail current offset in two differential pairs is proposed. SPICE simulations of the designed fifth-order Butterworth low-pass filter (LPF) using OTA in a mixed-signal 0.25 /spl mu/m CMOS process with a single 3.3 V power supply shows the cut-off frequency range from 1.5 to 50 MHz, which is wider than that of conventional filter. Total harmonic distortion (THD) for differential input voltage of 0.1 V/sub pp/ at 1 MHz is less than -57 dB.