Tunable Frequency-Division Duplex RF Front End Using Electrical Balance and Active Cancellation

Tunable Duplexers: Downlink Band Isolation Requirements for LTE User Equipment

“…This work deals only with downlink band isolation, assuming that adequate Tx-band suppression is achieved in order to prevent adverse effects due to the Tx blocker (e.g. using filtering or cancellation [3], [4]), and thus a linear Rx can also be assumed. In the following, Section II provides downlink band system noise calculations, developing expressions for the Rx NF as a function of the Tx-Rx isolation and Tx noise.…”

“…With reference to the model, this reduces L Rx and I. Furthermore, this model assumes that the active canceler employs sufficient filtering to avoid desensitization due to active cancellation (see [4]).…”

“…For multi-band frequency division duplexing (FDD), multiple off-chip surface acoustic wave (SAW) duplexers are required, with radio frequency (RF) switches used for band selection. The resultant cost and size of the duplexing hardware has motivated substantial recent work research into tunable duplexing technologies [1]- [4].…”

“…However, the SAW devices used in commercial LTE user equipment (UEs) often exceed this by a substantial margin; state-of-the-art acoustic resonator duplexers can provide 60-70 dB of isolation [5]. Electrical balance duplexers (EBDs) implement a form of feedforward RF self-interference cancellation based on the balancing of signals within a hybrid junction, and have received substantial interest as a potential alternative to SAW duplexers [1], [2], [4]. EBDs can be implemented within the radio frequency integrated circuit (RFIC), can be tuned over wide frequency ranges [1].…”

“…Active RF cancellation uses an additional Tx chain to generate a cancellation signal, which is coupled into the receive path to cancel Tx leakage. In [4], an EBD, operating in the downlink band, is combined with an active RF canceler used for Tx blocker suppression in the uplink band (see Fig. 2b).…”