Cancellation of OpAmp virtual ground imperfections by a negative conductance applied to improve RF receiver linearity

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    Abstract

    High linearity CMOS radio receivers often exploit linear V-I conversion at RF, followed by passive down-mixing and an OpAmp-based Transimpedance Amplifier 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 cancel 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 derived 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 IIP3 from 9dBm to >20dBm, and IIP2 from 51 to 61dBm, at the cost of increasing the noise figure from 6 to 7.5dB and <10% power penalty. In 1MHz bandwidth, a Spurious-Free Dynamic Range of 85dB is achieved at <27mA up to 2GHz for 1.2V supply voltage.
    Original languageEnglish
    Pages (from-to)1112-1124
    Number of pages13
    JournalIEEE journal of solid-state circuits
    Volume49
    Issue number5
    DOIs
    Publication statusPublished - 1 May 2014

    Keywords

    • EWI-24666
    • IR-91061
    • METIS-304065
    • Receiver linearity
    • Interference robustness
    • Compression
    • Blocking
    • in-band and out-band IIP3
    • IIP2
    • Mixer-first receiver architecture
    • transimpedance amplifier (TIA)
    • Negative conductance technique
    • CMOS
    • Wideband base station receiver
    • Software radio
    • Software defined radio
    • Cognitive radio (CR)

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