4-Bit SiGe phase shifter using distributed active switches and variable gain amplifier for X-band phased array applications

This paper presents a 4-bit digitally controlled phase shifter for X-band (8-12.5 GHz) phased-arrays, implemented in 0.25-μm SiGe BiCMOS process. Distributed active switches are utilized in first three bits. On-chip inductances are used to provide 22.5° phase shift steps. The placement and the geometry of these inductances are optimized for minimum phase error and insertion loss. In order to compensate the gain variations of this stage, a single stage variable gain amplifier is used. The fourth bit which provides 0/180° phase shift is obtained in third amplification stage, with switching between common base-common emitter configuration. With utilization of this technique overall phase error is significantly decreased and overall gain is increased. The phase shifter achieves 7dB gain with 3 dB of gain error. 360° phase shift is achieved in 4 bit resolution with a phase error of 0.5° at center frequency of 10GHz, and maximum 22° phase error in 4.5 GHz bandwidth. The chip size is 2150 μm × 1040 μm including the bondpads. These performance parameters are comparable with the state of the art using similar technology.