A 1.5-mW, 2.4 GHz Quasi-Circulator With High Transmitter-to-Receiver Isolation in CMOS Technology

A 2.4 GHz active quasi-circulator is implemented in TSMC 0.18 μ m CMOS technology. We propose a new architecture using current-reuse and adjustable signal cancellation to achieve a low-power, high-isolation and small-size circulator. The measured isolation from transmitter to receiver, |S
₃₁
|, can be as high as 68 dB, which to our knowledge is the highest value ever reported in integrated circulators. Other isolations, such as receiver-to-transmitter, receiver-to-antenna, and antenna-to-transmitter isolations, are all better than 28 dB. The total power consumption is only 1.5 mW with a chip size of 820 μm × 750 μm including bypass capacitors and pads.