An Ultra-Wideband and Compact Active Quasi-Circulator with Phase Alternated Differential Amplifier

This paper presents a new design for an active quasi-circulator that utilizes a phase alternated differential amplifier to achieve ultra-wideband and compact size in a 28-nm CMOS process. The proposed active quasi-circulator is based on a differential two-stage distributed amplifier, where the differential outputs of the phase alternated amplifier in second stage are cross-connected to the differential outputs of the amplifier in first stage. The use of the phase alternated differential amplifier allows for wideband isolation regardless of frequency. Furthermore, interstage inductor, which is located between two transistors of amplifier makes the circulator more wideband by maintaining frequency response of two transmission lines identically. The measured transmitter (TX) to receiver (RX) isolation is >21 dB, -3 dB bandwidth of TX to antenna (ANT) is from 20 to 38.5 GHz with 4.5 dB of peak gain at 29.8 GHz, minimum insertion loss of ANT to RX is 4.3 dB. The measured TX to ANT output power 1 dB compression point is 7.3 dBm at 28 GHz with DC power consumption of 107 mW. The circulator occupies only 0.07 mm², thanks to coupled inductors which contribute to compact size.