W-band phase shifter in 28-nm CMOS

Abstract

In this article, a compact W-band differential I---Q phase shifter is designed and implemented using 28-nm CMOS technology. The phase shifter is capable of achieving phase shifts ranging from 45° to 315° with a resolution of 90°. The design employs transmission-line baluns for creating a differential signal, Gilbert-cell-type active switches for generating 0° and 180° phase shifts and a 90° differential hybrid for obtaining differential I---Q signals. The hybrid is developed using capacitive-loaded slow-wave differential lines, thereby making it 75 % smaller than a conventional 90° hybrid. Furthermore, the modelling of a slow-wave differential line for odd-mode and even-mode propagation is explained. The phase shifter exhibits 12 dB of insertion loss, and the root-mean-square (RMS) gain and phase error are 0.55 dB and 16.6°, respectively, at 100 GHz. The total power consumption is 39 mW when using a 1-V supply. The chip size of the implemented design is 0.48 mm2 including the probing pads. The phase shifter design is further modified by replacing the baluns with single-stage differential buffer amplifiers to mitigate the signal loss. This modified version of the design shows +1 dB insertion gain with a total power consumption of 122.9 mW from a 1-V supply and realized at 0.565 mm2. A 13-dB gain improvement is obtained from the modified version and the measured RMS gain and phase error are 1.5 dB and 13°, respectively, at 100 GHz. After redesigning the layout, a minimum RMS phase error of 1.7° is expected in the simulations.