An even harmonic image rejection mixer using an eight-phase polyphase filter

Since an even harmonic mixer is pumped by LO with half the frequency compared with the fundamental mixer, LO can be generated and amplified easily with lower current consumption. When it is applied to the quadrature mixer (QMIX) or the image rejection mixer (IRM), a 90 degree phase shifter in the RF signal path or a 45 degree phase shifter in the LO path is required. As a 90 degree phase shifter for RF path increases loss of the RF signal and degrades noise figure of the receiver, a configuration with a 45 degree phase shifter is better for QMIX or IRM. In this paper, a novel LO divider using eight-phase polyphase filters (PPF) and the even harmonic IRM using the proposed LO divider are presented. A proposed LO divider divides the input differential signal into the four differential signals with 45 degree phase difference and it can be applied for the IRM using even harmonic mixer. A developed even harmonic IRM with an eight-phase PPF fabricated by SiGe BiCMOS process achieved more than 20dB of the image rejection ratio in 5.8GHz-band.