Bidirectional VGA and vector modulator for 5G communication beamforming IC

Abstract

A bidirectional beamforming circuit is being studied to obtain high antenna gain within limited footprints in the millimeter-wave frequency band. Bidirectional wideband variable gain amplifier (VGA) and bidirectional active vector modulator are proposed, which are exploited for millimeter-wave 5G beamforming IC. VGA consists of a symmetrical pair of differential main and auxiliary amplifiers in which the auxiliary amplifiers are cross-connected to have gain control function. The capacitances are added at auxiliary amplifiers to reduce the phase variation while controlling the gain. Transmission line transformers implement wideband matching input and output networks with high coupling coefficients. In addition, a bidirectional vector modulator is designed by applying the structure of the above VGA. A coupled line coupler generates a low-loss quadrature signal with a small amplitude and phase mismatch. Gain of quadrature signal adjusted by phase-invariant bidirectional VGA. Therefore, the vector modulator has a high gain due to using the active bidirectional circuit.