Integrated Quasi-Circulator with RF Leakage Cancellation for Full-Duplex Wireless Transceivers

Seyyed Amir Ayati, Debashis Mandal, Bertan Bakkaloglu, Sayfe Kiaei

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


An integrated reconfigurable CMOS quasi-circulator operating at 2.4 GHz is presented. A passive structure delivers transmit power amplifier (PA) output signal to the differential low-noise amplifier (LNA) input as a common-mode signal and simultaneously delivers received signal as a differential-mode signal at the LNA input. The leakage of the PA output signal at the LNA input is reduced in two steps. First, the use of a reconfigurable impedance matching circuit, instead of a fixed 50-Ω resistance reduces the leakage by compensating the antenna impedance mismatch, and improves transmitter-receiver isolation. Second, a reconfigurable summing stage adds amplitude and phase adjusted PA output signal to LNA output to cancel the residual PA output leakage. Measurement results show that the receiver achieves a reduction of 90 dB for a single tone and more than 50 dB for a QPSK modulated 40-MHz bandwidth transmit signal. The receiver gain is more than 10 dB and the noise figure in the receiver path is 4.5 dB. The reconfigurable quasi-circulator along with the receiver LNA is designed and fabricated on a 130-nm CMOS technology. The cancellation circuitry occupies 0.27 mm2 and consumes 30-mW quiescent power, while the total active area of the chip is 1 mm2, and it consumes 65-mW power.

Original languageEnglish (US)
Pages (from-to)1421-1430
Number of pages10
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number3
StatePublished - Mar 2018


  • Full-duplex wireless
  • impedance tuner
  • on-chip circulator
  • reconfigurable circuit
  • self-interference cancellation
  • transmit leakage cancellation

ASJC Scopus subject areas

  • Radiation
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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