A 71–76 GHz Phased-Array Transmitter with Nested-Coupler-Based Phase Shifter in 65 nm CMOS

This paper presents a four-element phased-array transmitter in 65 nm CMOS operating in the 71–76 GHz band. The transmitter features a nested-coupler-based phase shifter, achieving a full 360° phase-shifting range with a fine 5.625° phase resolution and an rms phase error of 1.01–1.17°. Phase shifting is achieved by vector modulation after the proposed nested coupler, using integrated digital-assisted cancellation-based variable gain amplifiers (VGAs) to adjust the I/Q signal amplitude. The transmitter demonstrates a 12-dB attenuation range with a 1-dB attenuation step, and achieves a peak saturated output power (Psat) of 12.5 dBm at 76 GHz and a maximum output power 1-dB compression point (OP1dB) of 8.3 dBm at 73 GHz. The chip only occupies a 1.55 × 1.61 mm² area and burns 184 mW per channel from a 1-V supply, making it well suited for high-performance, low-power, and highly integrated phased-array applications.