Hybrid transformer-based tunable integrated duplexer with antenna impedance tracking loop

Tunable CMOS Integrated Duplexer With Antenna Impedance Tracking and High Isolation in the Transmit and Receive Bands

“…The balance network can be tuned to match the antenna impedance in the transmit and receive bands to achieve high isolation in both bands. We also introduce a calibration loop that can detect the TX leakage generated due to imbalance in the duplexer and correct the balance network impedance to track antenna impedance variation [6]. Toward that goal, we propose the tracking feedback loop shown in Fig.…”

“…These intermodulation products will couple to the LNA input in the same manner as the received signal couples from the antenna, i.e., with ideally 3-dB power loss, degrading the effective isolation. To keep the coupled third-order intermodulation (IM3) distortion lower than the fundamental components leaked directly from the PA to LNA side, the balance network should satisfy dBm dB dBm dB -dB (6) and by definition the third-order intercept point (IIP3) is dBm dBm dB dBm (7) and thus dBm dBm -dB dB (8) For a maximum PA output power of 27 dBm and to maintain 55 dB of isolation, the IIP3 of the balance network should exceed 45.5 dBm. This high linearity requirement was achieved by making use of highly linear switched capacitors and other …”

RF Self-Interference Reduction Techniques for Compact Full Duplex Radios

“…This section proposes an electrical balance duplexer (EBD) instead of a circulator. This hybrid junction circuit provides an attractive duplexing performance for FD (and potentially FDD operation [14]), can be densely implemented in CMOS technology and can be co-integrated with the transceiver circuitry.…”

RF Self-Interference Cancellation for Full-Duplex

“…The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 316369 -project DUPLO: www.fp7-duplo.eu For FD concurrent Tx and Rx operation at the same frequency is required. Recently, the use of hybrid transformers to achieve signal cancellation based on electrical balance (EB) has been proposed to achieve tunable duplexer filters for FDD [10]- [12]. In this paper, we apply this technique in the context of full-duplex and show how it provides RF self-interference cancellation for compact radio devices.…”

“…The principle of electrical balance is applicable to both FDD and FD: the Tx-to-ZANT path as well as the ZANT-to-Rx path have a wideband transformer response, while Tx-to-Rx cancellation is required at both the Tx and Rx frequencies simultaneously (FDD) [12] or instead at a single frequency only (FD), a grace of FD operation. The on-chip impedance tuning range must cover the frequency-dependent impedance of a real antenna, which varies across environmental conditions.…”