A 1.0-to-4.0GHz 65nm CMOS four-element beamforming receiver using a switched-capacitor vector modulator with approximate sine weighting via charge redistribution

Phased-array receivers provide two major benefits over single-antenna receivers. Their signal-to-noise ratio (SNR) doubles for each doubling in the number of elements, resulting in extended range. Secondly, interferers can be rejected in the spatial domain for increased link robustness. These arrays can be implemented by phase shifting and summing the signals from antenna elements with uniform spacing. For accurate interference rejection, a phase shifter with uniform phase steps and constant amplitude is desired. Several types of continuous-time phase shifters have been published, e.g. using injection locking, phase selection and vector modulation. This paper proposes a phased-array receiver architecture with a discrete-time vector modulator that takes advantage of the high linearity and good matching of switched-capacitor circuits, which are highly compatible with advanced CMOS. A simple charge redistribution circuit is presented that performs a rational approximation of the sine and cosine needed for the vector modulator weights.