A 5 GHz BiCMOS I/Q VCO with 360° variable phase outputs using the vector sum method

A 5 GHz in-phase/quadrature (I/Q) voltage controlled oscillator (VCO) with multiple independently tunable phase outputs is presented. The VCO is realized using an LC oscillator with a ring structure and has a tuning range of between 4.6 and 5.3 GHz. The variable phase shift is achieved by varying the amplitudes of the two quadrature signals independently and then combining these signals together. Using multiple Gilbert cells as variable gain amplifiers (VGAs), multiple tunable phase outputs are achieved using only a single coupled I/Q VCO. The entire circuit is designed using a 3.3 V SiGe BiCMOS process. This VCO can be used as a phase shifter in adaptive phase array antenna systems, whereby the beam is formed by controlling the phase of individual antenna elements.