High-Linearity RF Canceller With Precision Control for L-Band Full-Duplex Transceivers

This article presents the design and characterization of a four-channel integrated radio frequency (RF) canceller with simultaneous amplitude and phase control, implemented in a 0.25-$\mu $m gallium nitride (GaN) high-electron-mobility transistor (HEMT) process. Each channel integrates a 7-bit digital step attenuator (DSA) and a 7-bit digital phase shifter (DPS), both employing switched-type circuit topologies. To address inherent amplitude and phase deviations in the GaN process, circuit optimization techniques are applied to mitigate HEMT parasitic effects. To address inherent amplitude and phase deviations in the GaN process, circuit optimization techniques are applied to mitigate HEMT parasitic effects through customized compensation strategies for different circuit blocks. Furthermore, a key innovation enables straightforward logic control of asymmetric depletion-mode HEMTs using a resistive voltage divider structure combined with switch-HEMTs. By adjusting the external control voltage, this architecture facilitates flexible linearity tuning. Measurements from 1 to 2 GHz show excellent input/output matching, channel isolation exceeding 33.2 dB. The rms amplitude error of DSA and the rms phase error of DPS are less than 0.24 dB and 4.4 °, respectively, and high linearity with an input 1-dB compression point (IP1dB) of 31 dBm and input third-order intercept point (IIP3) of 40.8 dBm. Finally, in response to direct path interference between transmitting and receiving antennas, the experiment demonstrated a 31 dB RF self-interference cancellation (RFSIC) capability. This integrated RF canceller demonstrates superior resolution, accuracy, and linearity, making it suitable for in-band full-duplex (IBFD) communication systems.