An E-Band Subradix Active Phase Shifter with <0.69° RMS Phase Error and 16dB Attenuation in 28nm CMOS

This paper proposes an E-band active phase shifter, which leverages a subradix-2 gm array to achieve low gain and phase errors. The phase shifter stacks differential couplers for high precision quadrature signals. It employs extensive (215) vector modulation control states provided by the subradix-2 arrangement for high accuracy that is not available in conventional vector modulation (VM) based phase shifters. The proposed E-band phase shifter is fabricated in 28-nm CMOS with a chip area of 0.078 mm². It provides a 5.625° phase accuracy with root mean square (RMS) phase error of 0.38~0.69°, and RMS gain error of 0.49~0.83 dB at 67–79 GHz. In addition, the phase shifter supports 16 dB attenuation range with a 2 dB step. Measurements show it can also provide a 1.4° phase accuracy with RMS phase error of less than 0.77°. The phase shifter consumes 28.5 mW from a 1.2 V supply.