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-mu m SiGe BiCMOS process. Distributed active switches are utilized in first three bits. On-chip inductances are used to provide 22.5 degrees 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 degrees 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 degrees phase shift is achieved in 4 bit resolution with a phase error of 0.5 degrees at center frequency of 10GHz, and maximum 22 degrees phase error in 4.5 GHz bandwidth. The chip size is 2150 mu m x 1040 mu m including the bondpads. These performance parameters are comparable with the state of the art using similar technology.