A high-frequency transconductor using a robust nonlinearity cancellation

This brief deals with the design of a linear operational transconductance amplifier (OTA) intended for high-frequency continuous-time filters. Three source-degenerated differential pairs are used to reduce the third-order distortion components regardless of process parameter tolerances and bias current. Experimental results for an OTA fabricated in the TSMC 0.35-mu m CMOS process are presented and compared with recently reported topologies. Draining 2.8 mA from a single supply voltage of 3.3 V, the transconductor achieves IM3 < - 70 dB for a two-tone input signal of 1.3 Vpp measured at 70 MHz. The input referred noise density is only 7 nV/root Hz, leading to an SNR of 75 dB.