In this article, a 40-GHz subharmonic Gilbert down-conversion mixer with an accurate quadrature local oscillator (LO) input is demonstrated using a standard 0.13-μm CMOS technology. The quadratureoutput frequency divider is realized by injection-locked oscillators and is used at the LO port to replace conventional RC-CR polyphase filters at higher frequencies. Furthermore, the proper Marchand balun at an RF stage is suitable for the standard Si-based process to generate precisely balanced signals despite the substrate loss. The measured conversion gain is 4 dB at 40 GHz. The IP 1dB and IIP 3 of-7 dBm and 2 dBm, respectively, are achieved. The measured 3-dB RF bandwidth is very broad and about 12-GHz bandwidth when the 10-MHz IF frequency is fixed. The die size is about 1 mm × 1 mm.