Design of CMOS Integrated Circulator Based on Sequentially Switched Delay Lines With Body-Floating and Clock Boosting Techniques

As the antenna interface of RF communication and radar systems, the performance of the circulator determines the quality of the whole system. This brief demonstrates a circulator based on sequentially switched delay lines with 6 transistor switches using body floating and clock boosting techniques to improve its linearity performance. The proposed circulator is fabricated in a standard $0.18~\mu $ m CMOS process, occupying an area of $1.7~mm^{2}$ including the pads, while consuming 34.9 mW at a supply voltage of 1.8 V, and these power dissipations are contributed by the LO path circuit. The measured Tx-to-ANT and ANT-to-Rx input 1dB compression points of the circulator are 13.44 dBm and 14.32 dBm, respectively, an increase of about 3.7 dB compared to the absence of these two technologies. The measured Tx-to-ANT and ANT-to-Rx insertion loss, and transmitter-to-receiver isolation are 5 dBm, 4.9 dBm, and >20 dB, respectively, for the frequency from 1.95 GHz to 2.55 GHz (with a relative bandwidth of 26.7%). And the measured ANT-to -Rx NF is 6.6 dB.

I. Introduction

Circulators as nonreciprocal devices are often used in RF communication, radar/imaging sensors, and quantum communication systems [1], [2]. As an important antenna interface, the circulator is used in full-duplex communication systems to achieve single-antenna operation [3]. Also, circulators are applied in frequency-modulated-continuous-wave (FMCW) radar systems to separate input and output signals [1]. In addition, circulators are also essential to cryogenic quantum computing systems to excite and read-out the qubits [4]. By connecting one of the ports to a matching load, the circulator can be used as an isolator.