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This paper presents a 4-path LO generation system with automatic phase tuning for 60 GHz phased-array receivers. Each path employs a linear phase-shift generation chain composed of an injection-locked-oscillator-based phase shifter cascaded with an injection-locked frequency tripler. The frequency tripler with a proposed locking-range enhancement technique is employed to relax both the frequency and the phase shift of the phase shifter for high linearity and low power. Finally, a novel successive-approximation algorithm is proposed to perform automatic phase detection and tuning. Fabricated in a 65 nm CMOS process and occupying a core area of 1.4 ×2.0 mm ² , the proposed 4-path LO generation system measures linear phase shift range larger than ±90°, amplitude variation within ±0.4 dB, phase resolution of 22.5°, and maximum phase errors of 22.0° and 1.5° before and after automatic phase …