A 4-bit CMOS phase shifter using distributed active switches

Abstract

This paper presents a novel 4-bit phase shifter using distributed active switches in 0.18-mu m RF CMOS technology. The relative phase shift, which varies from 0 degrees to 360 degrees in steps of 22.5 degrees, is achieved with a 3-bit distributed phase shifter and a 180 degrees high-pass/low-pass phase shifter. The distributed phase shifter is implemented using distributed active switches that consist of a periodic placement of series inductors and cascode transistors, thereby obtaining linear phase shift versus frequency with a digital control. The design guideline of the distributed phase shifter is presented. The 4-bit phase shifter achieves 3.5 +/- 0.5 dB of gain, with an rms phase error of 2.6 degrees at a center frequency of 12.1 GHz. The input and output return losses are less than -15 dB at all conditions. The chip size is 1880 mu m x 915 mu m including the probing pads.