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

Abstract

A hybrid transformer-based integrated tunable duplexer is demonstrated. High isolation between the transmit and receive ports is achieved through electrical balance between the antenna and balance network impedances. A novel high-power-tolerant balance network, which can be tuned at both the transmit and receive frequencies, allows high isolation in both the transmit and receive bands even under realistic antenna impedance frequency dependence. To maintain high isolation despite antenna impedance variation, a feedback loop is employed to measure the transmitter leakage and correct the impedance of the balance network. An isolation 50 dB in the transmit and receive bands with an antenna voltage standing-wave ratio within 2:1 was achieved. The duplexer, along with a cascaded direct-conversion receiver, achieves a noise figure of 5.3 dB, a conversion gain of 45 dB, and consumes 51 mW of power. The insertion loss in the transmit path was less than 3.8 dB. Implemented in a 65-nm CMOS process, the chip occupies an active area of 2.2 mm .

Electrical balance duplexing for small form factor realization of in-band full duplex

“…The hardware duplexer shows comparable performance to that predicted by the simulation, although there is some additional reduction in transmit to receive isolation due to the increased frequency domain variation in the balancing impedance. Simulations recently presented in [13] use a more realistic printed inverted F antenna (PIFA) model (Fig.4.b); these simulation results are in much closer agreement with measured performance. Furthermore, the isolation achieved by the prototype EB duplexer exceeds that of small form factor antenna separation architectures (~30dB) and circulators (~15dB).…”

“…Furthermore, the isolation achieved by the prototype EB duplexer exceeds that of small form factor antenna separation architectures (~30dB) and circulators (~15dB). [10], b) Simulation with lumped element PIFA antenna model [13], c) Simulation with measured antenna data [6], d) Measurement of hardware prototype EB duplexer.…”

“…Deep submicron CMOS implementation is possible [10], however microelectromechanical (MEMS) tunable components may offer advantages in terms of linearity, power handling, and resolution. Recent publications [13] have also introduced balancing impedance designs which can match the antenna impedance at two frequency points, which is of clear benefit for FDD applications, but should also be investigated to determine the possible improvement in IBFD isolation bandwidth.…”

Dynamic Performance of Electrical Balance Duplexing in a Vehicular Scenario

“…This measurement bandwidth was chosen as the simulated EBD (described in the following section) operates over a 20 MHz bandwidth, this being the largest bandwidth used by long term evolution (LTE). Each measurement/simulation operates over a single contiguous 20 MHz band, corresponding to an IBFD system, however since the tunable balancing impedances presented in [4], [11] allow for simultaneous independent impedance control in the uplink and downlink bands this analysis is also directly relevant to the FDD application.…”

Impact of small antenna on linear power amplifier performance in a co-design approach

“…Different methods to optimize the RFFE have been presented and discussed in various studies [1][2]. Small antennas could be a part of the solution and a co-design power amplifier (PA) with small antenna may be a method to tackle the challenges associated with an optimized compact RFFE.…”