Highly Linear Tunable CMOS Gm}C Low-Pass Filter

A comprehensive analysis of tunable transconductor topologies based on passive resistors is presented. Based on this analysis, a new CMOS transconductor is designed, which features high linearity, simplicity, and robustness against geometric and parametric mismatches. A novel tuning technique using just a MOS transistor in the triode region allows the adjustment of the transconductance in a wide range without affecting the voltage-to-current conversion core. Measurement results of the transconductor fabricated in a 0.5- mum CMOS technology confirm the high linearity predicted. As an application, a third-order Gm-C tunable low-pass filter fabricated in the same technology is presented. The measured third-order intermodulation distortion of the filter for a single 5-V supply and a 2-V pp two-tone input signal centered at 10 MHz is -78 dB.