A Wideband CMOS Active Phase Shifter Using a Transformer-Based RL Polyphase Filter

A millimeter-wave CMOS active vector-sum phase shifter (VSPS) with a phase resolution of 5.625 $^{\circ}$ using a two-stage transformer-based resistor and inductor (RL) polyphase filter (PPF) for generating wideband in-phase/quadrature (I/Q) signals is proposed. Theoretical analysis demonstrates that the inductors in RL PPF can resonate with the capacitive loads to boost the passive voltage gain and alleviate the issue of high loss in the traditional RC PPF. Furthermore, the RL PPF provides a larger bandwidth and a better tolerance to process variations. An active VSPS prototype incorporating the proposed RL PPF is implemented in 65-nm CMOS process. The measured results of the phase shifter show a maximum insertion gain of $-$ 2.28 dB with a maximum power consumption of 20.52 mW. The measured root-mean-square (rms) phase error and gain error over the 360 $^{\circ}$ phase shifting range are 0.71 $^{\circ}$ –2.95 $^{\circ}$ and 0.67–0.76 dB, respectively, from 20 to 30 GHz (FBW $=$ 40%). The core size is 0.238 mm $^{2}$ .