A Wideband Compact Digitally-Assisted Variable Gain Phase Shifter for Ka-Band Applications

A wideband, compact, digitally-assisted variable gain phase shifter (VGPS) in a 65-nm CMOS process is presented for Ka-band applications. A digitally-assisted variable gain amplifier (VGA) architecture with a wide gain-control dynamic range and minimal input/output impedance variations is proposed by combining bias and digital control. Using only a one-stage digitally-assisted VGA, the VGPS achieves orthogonal phase and gain control with low RMS gain and phase errors in a compact size. Theoretical analysis is explored to provide physical insight into the working mechanism of the VGPS. In this design, the proposed VGPS leverages 3 bits for 18-dB gain tuning and 4 bits for 360° phase control. Measurements show that the VGPS exhibits an average peak gain of 0.6 dB at 28.4 GHz with a 3-dB bandwidth from 25.4 to 35.6 GHz. The measured RMS gain and phase errors is below 0.37 dB and 3°, respectively, from 25.4 to 34 GHz. It is implemented in a 65-nm CMOS process with the core area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.19~{\mathrm { mm}}^{2}$ </tex-math></inline-formula> excluding the pads.