A Four-Channel Beamforming Down-Converter in 90-nm CMOS Utilizing Phase-Oversampling

Richard Tseng, Hao Li, Dae Hyun Kwon, Yun Chiu, Ada S. Y. Poon
2010 IEEE Journal of Solid-State Circuits  
In this paper, a 4-GHz, four-channel, analog-beamforming direct-conversion down-converter in 90-nm CMOS is presented. Down-converting vector modulators (VMs) in each channel multiply the inputs with complex beamforming weights before summation between the different channels. The VMs are based on a phase-oversampling technique that allows the synthesis of inherently linear, high-resolution complex gains without complex variable gain amplifiers. A bank of simple passive mixers driven by a
more » ... se local oscillator (LO) in each VM performs accurate phase shifting with minimal signal distortion, and a pair of transimpedance amplifiers (TIAs) combines the mixer outputs to perform beamforming weighting and combining. Each individual channel achieves 360 phase shift and gain-setting programmability with 8-bit digital control, a complex gain constellation with a mean error-vector magnitude (EVM) of 2%, and a measured phase error of at a back-off of 4 dB from the maximum gain setting. The beamformer demonstrates 24-dB blocker rejection for blockers impinging from different directions and 17-dB signal EVM improvement in the presence of an in-channel blocker. Index Terms-Beamforming, Cartesian combining, dynamic range, mixer, multiphase local oscillator (LO), phased arrays, phase-oversampling, phase shifter, RF CMOS, receivers, RF variable gain amplifier (RFVGA), vector modulator (VM).
doi:10.1109/jssc.2010.2063971 fatcat:4cakiltpaba57emyexyz6tw3z4