Cancellation of OpAmp Virtual Ground Imperfections by a Negative Conductance Applied to Improve RF Receiver Linearity Dlovan H. Mahrof , Student Member , IEEE , Eric A. M. Klumperink , Senior Member , IEEE

Abstract

High linearity CMOS radio receivers often exploit linear V-I conversion at RF, follo wed by passive down-mixing and an OpAmp-based Transimpedance Ampli fier at baseband. Due to nonlinearity and finite gain in the OpAmp, virtual ground is imperfect, inducing distortion currents. This paper proposes a negative conductance concept to c ancel such distortion currents. Through a simple intuitive analysis, the basic operation of the technique is explained. By mathematical analysis the optimum negative conductance value is de rived and related to feedback theory. In- and out-of-band linearity, stability and Noise Figure are also analyzed. The technique is applied to linearize an RF receiver, and a prototype is implemented in 65 nm technology. Measurement results show an increase of in-band IIP from 9d B mt o 2 0d B m ,a n dI I P 2f r o m5 1t o6 1d B m ,a tt h ec o s to f increasing the noise figure from 6 to 7.5 dB and 10% power penalty. In 1 MHz bandwidth, a Spurious-Free Dynamic Range of 85 dB is achieved at 27 mA up to 2 GHz for 1.2 V supply voltage.