Integrated active quasi-circulator with 27 dB isolation and 0.8–6.8GHz wideband by using feedback technique

Circulators are widely adopted to decouple the incident and reflected waves. Active circulators have the properties such as small size, low cost and compatibility with Monolithic Microwave Integrated Circuit (MMIC) technology. With the advent of big data, circuits must have wideband characteristics to handle a large number of signals. In this paper, a new topology is proposed to realize an active quasi-circulator. Feedback technology is presented to enhance the isolation from transmitter to receiver (|S
₃₁
|) for wideband utilizations. The proposed circulator is fabricated with a standard 0.18 μm CMOS process. The measured bandwidth is from 0.8 GHz to 6.8 GHz, which to our knowledge is the widest ever reported in integrated circulators. The measured |S31| is higher than 27 dB. The isolations of receiver-to-transmitter (|S
₁₃
|)receiver-to-antenna (|S
₂₃
|), and antenna-to-transmitter (|S
₂₁
|) are better than 15dB, 28 dB and 20 dB, respectively. Power consumption of the core circuit of the circulator is 12.8 mW and the chip size is 0.54 mm × 0.66 mm including bonding pads. The designed active quasi-circulator possesses high isolation and wideband simultaneously.