An 18~30 GHz Vector-Sum Phase Shifter With Two-Stage Transformer-Based Hybrid in 130-nm SiGe BiCMOS
Yiming Yu, Yanpeng Wu, Pan Tang, Chenxi Zhao, Huihua Liu, Yunqiu Wu, Wen-Yan Yin, Kai Kang
Abstract
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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 1.9$ </tex-math></inline-formula> dB loss) and an output balun ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 2$ </tex-math></inline-formula> dB loss) at 22 GHz. Also, the input 1-dB compression point and noise figure are tested, which are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\geq $ </tex-math></inline-formula> -1 dBm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\leq 15.5$ </tex-math></inline-formula> dB in the targeting frequency band.