Linearity- and Gain-Enhanced Wideband Transconductor Using Digitally Auto-Tuned Negative Conductance Load

A wideband, gain enhanced, high frequency, fully differential operational transconductance amplifier (OTA) with enhanced linearity is proposed. The OTA uses a negative conductance to cancel its output parasitic conductance. An automatic, digitally controlled, feedback tuning loop ensures that the parasitic conductance is tracked across corners. High linearity is achieved by voltage biasing the transistors and allowing higher headroom. The OTA uses a common mode feedback (CMFB) loop for common mode stabilization instead of diode connected transistors which enhances the achievable bandwidth. Simulations in a standard 130 nm CMOS process show a dc gain enhancement from 14 dB to 42 dB when negative conductance in incorporated across process voltage and temperature (PVT). The OTA has an unity gain bandwidth of 20 GHz. It has an input referred noise of 1.75 nV/√Hz and has -40dB total harmonic distortion for an input of 330 mVppd.