A Wideband Switched-Capacitor Circulator Based on Isolation Improvement Technique With Transformers

Based on four-path switched-capacitor networks architecture, an isolation improvement technique using the transformers (center-tapped inductors) is presented in the circulator design. The proposed circulator is fabricated in a standard 55-nm CMOS process, occupying an area of 0.225 mm2 including the pads. It only consumes 4.1 mW at a supply voltage of 1.2 V, which is contributed by the clock generation circuit. Measurement results show that 19.6-dB isolation is obtained over a wide frequency range from dc to 1.4 GHz, while the insertion loss (IL) is 3.9–5.3 dB and the noise figure (NF) is 3.9–7.1 dB. Due to the body-floating technique, the measured input 1-dB compression points (IP1 dBs) of the circulator are more than 2.5 dBm.