A high IIP2 doubly balanced sub-harmonic mixer in 0.25-μm CMOS for 5-GHz ISM band direct conversion receiver

This paper presents a new low power and high IIP2 0.25- μm CMOS doubly balanced sub-harmonic mixer for a 5 GHz Industrial Scientific Medical (ISM) band direct conversion-zero IF receiver. Using a 1/2×LO frequency generation scheme, the sub-harmonic mixer, designed and fabricated, overcomes the LO self-mixing problem common in conventional direct conversion receivers (DCR). Measurements show the sub-harmonic mixer is able to achieve voltage conversion gain of 8.2 dB, input compression, P_1dB of -8 dBm and IIP₃ of -2.5 dBm while consuming only 1.35 mA of DC current. Measured results correlate well with simulated results where with 1% g_m mismatch, 0.5 % load mismatch and 2° LO phase error, the mixer is able to achieve high IIP₂ of 55.3 dBm, IIP₃ of -6.5 dBm, and voltage conversion gain of 8 dB. The proposed mixer takes up less than 1 mm² of silicon real estate, including test die pads.