An 18~30 GHz Vector-Sum Phase Shifter With Two-Stage Transformer-Based Hybrid in 130-nm SiGe BiCMOS

This article presents an 18~30 GHz vector-sum phase shifter for wireless application in the millimeter-wave regime. It is composed of an I/Q signal generator, two variable-gain amplifiers (VGA), and a digital-to-analog converter with a quadrant selector. To attain wideband quadrature signal, a two-stage hybrid based on transformers is proposed to realize the I/Q signal generator. The first- and second-stage hybrids are designed with different resonating frequencies. As a result, the amplitude and phase errors of the I/Q signal generator are significantly decreased in a wide frequency band. In addition, theoretical analysis based on a simplified equivalent-circuit model is performed to guide the circuit implementation, and its correctness is demonstrated by electromagnetic simulation. To mitigate the impact of the VGAs’ parasitics on the phase performance, a capacitive-neutralization technique is applied to cancel parasitics of transistors in the VGAs. A prototype circuit is designed using a 130-nm SiGe BiCMOS process. The measured results show that the circuit achieves a root-mean-square (RMS) amplitude error of less than 1.4 dB and an RMS phase error of 1.4°~3.4° across 18~32 GHz. The tested peak gains of all the phase states are −1~4.5 dB with an input balun ( <tex-math notation="LaTeX">≈ 1.9 </tex-math> dB loss) and an output balun ( <tex-math notation="LaTeX">≈ 2 </tex-math> dB loss) at 22 GHz. Also, the input 1-dB compression point and noise figure are tested, which are <tex-math notation="LaTeX">≥ </tex-math> -1 dBm and <tex-math notation="LaTeX">≤ 15.5 </tex-math> dB in the targeting frequency band.