Robust highly linear high-frequency CMOS OTA with IM3 below - 70 dB at 26 MHz

Abstract

An enhanced configuration for a linearized MOS operational transconductance amplifier (OTA) is proposed. The proposed fully differential OTA circuit is based on resistive source degeneration and an improved adaptive biasing technique. It is robust to process variation, which has not been fully shown in previously reported linearization techniques. Detailed harmonic distortion analysis demonstrating the robustness of the proposed OTA is introduced. The transconductance gain is tunable from 160 to 340 /spl mu/S with a third-order intermodulation (IM3) below -70 dB at 26 MHz. As an application, a 26-MHz second-order low-pass filter fabricated in TSMC 0.35-/spl mu/m CMOS technology with a power supply of 3.3 V is presented. The measured IM3 with an input voltage of 1.4 Vpp is below - 65 dB for the entire filter pass-band, and the input referred noise density is 156nV//spl radic/Hz. The cutoff frequency of the filter is tunable in the range of 13-26 MHz. Theoretical and experimental results are in good agreement.