A Compact CMOS <i>W</i> -Band Transmitter Front-End With 7-Bit Phase Shifter Resolution

Vector modulation circuits such as cartesian phase shifters and IQ modulators are integral components of mm-wave transceivers, relying on quadrature signal summation. This work analyzes conventional quadrature summation techniques and provides an in-depth study of the widely used current-summation method, identifying its limitations and the resulting distortion of the output constellation. Guided by these insights, we present a W-band 65 nm bulk CMOS transmitter front-end that integrates a voltage-summation vector modulator (VM) and a power amplifier. The VM features a transformer-based combiner with a single secondary inductor that performs a weighted summation of the quadrature fluxes generated by two primary inductors. Using a low-complexity predistortion algorithm, a linear and predictable 1024-point constellation is achieved with 9% Error Vector Magnitude (EVM). Additionally, phase shift keying (PSK) constellations were measured, demonstrating true 7-bit phase resolution across the 95–97.5 GHz range with minimum 1° phase RMSE.