Low distortion active filters using the Gm-assisted OTA-RC technique

The linearity of conventional active-RC filters is limited by the operational transconductance amplifiers (OTAs) used in the integrators. We propose the Gm-assisted OTA-RC technique, which is a way of combining Gm-C and active-RC integrators in a manner that enhances the linearity and speed of the latter, while adding negligible extra noise or power dissipation. Measurements from a fifth order Chebyshev filter with 20 MHz bandwidth designed in a 0.18μm CMOS process show a 30 dB reduction in intermodulation distortion when Gm-assistance is added to an active-RC filter.