A 6-bit CMOS Active Phase Shifter for Ku -Band Phased Arrays

A 6-bit high-accuracy active phase shifter is developed in 0.13- $\mu \text{m}$ CMOS technology for Ku -band phased arrays. Improved transformer balun with wriggly stub is applied to split the single input to differential and achieve high balance with reduced chip area. Two-stage polyphase filter (PPF) generates broadband I/Q signals with high accuracy. A main digital-to-analog convertor (DAC) controls the I/Q amplitude to achieve 6-bit phase resolution, while an auxiliary DAC compensates the amplitude/phase error introduced by balun and PPF. Consequently, high resolution along with low phase/gain error can be achieved. The phase shifter shows measured rms phase error of $0.75 \times 0.32$ mm 2 excluding pads.