A CMOS Passive LPTV Nonmagnetic Circulator and Its Application in a Full-Duplex Receiver

Negar Reiskarimian, Jin Zhou, Harish Krishnaswamy

Research output: Contribution to journalArticlepeer-review


Recently, we demonstrated the first CMOS nonmagnetic nonreciprocal passive circulator based on N-path filters that uses time variance to break reciprocity. Here, the analysis of performance metrics, such as loss, isolation, linearity, and tuning range, is presented in terms of the design parameters. The analysis is verified by the measured performance of a 65-nm CMOS circulator prototype that exhibits 1.7 dB of loss in the transmitter-antenna (TX-ANT) and antenna-receiver (ANT-RX) paths, and has high isolation [TX-RX, up to 50 dB through tuning and 20-dB bandwidth (BW) of 32 MHz] and a tuning range of 610-850 MHz. Through an architectural feature specifically designed to enhance TX linearity, the circulator achieves an in-band TX-ANT input-referred third-order intercept point (IIP3) of +27.5 dBm, nearly two orders of magnitude higher than the ANT-RX IIP3 of +8.7 dBm. The circulator is also integrated with a self-interference-canceling full-duplex (FD) RX featuring an analog baseband (BB) SI canceller. The FD RX achieves 42-dB on-chip SI suppression across the circulator and analog BB domains over a 12-MHz signal BW. In conjunction with digital SI and its input-referred third-order intermodulation (IM3) cancellation, the FD RX demonstrates 85-dB overall SI suppression, enabling an FD link budget of -7-dBm TX average output power and -92-dBm noise floor.

Original languageEnglish (US)
Article number7866009
Pages (from-to)1358-1372
Number of pages15
JournalIEEE Journal of Solid-State Circuits
Issue number5
StatePublished - May 2017


  • CMOS
  • Circulator
  • full-duplex (FD) wireless
  • interference cancellation
  • nonreciprocity

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


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