Smart Self-interference Suppression by Exploiting a Nonlinearity

Abstract

A 1.8GHz RF amplifier implemented in 0.14um CMOS with frequency-independent blocker suppression is presented. The blocker suppression functionality is obtained by the adaptation of a nonlinear input-output transfer according to the blocker amplitude. Since superposition does not apply to nonlinear transfer functions, the behavior of such a transfer for strong undesired signals is different from the behavior for weak desired signals, which is exploited here. In the presence of a 0 to +11 dBm RF blocker, a voltage gain for weak signals of respectively 7.6-9.4 dB and IIP3 >4 dBm are measured, while the blocker is suppressed by more than 35 dB. In case of no blocker present at the input, the circuit is set to amplifier mode providing 17 dB of voltage gain and an IIP3 of 6.6 dBm while consuming 3 mW. Application areas are coexistence in multi-radio devices and dealing with TX leakage in FDD systems.

Shifting the Frontiers of Analog and Mixed-Signal Electronics

“…The deliberately introduced strong nonlinearity at the input of the receiver is very well controlled as a function of the known signal (transmitted by the same frontend) that forms a close-by interferer for the receiver. The nonlinearity is controlled in such a way that the fundamental component of the interferer is maximally suppressed (also called "compression"), and "replaced" by one or more if its harmonics outside the channel bandwidth [15,16]. These harmonics are further away from the received signal and can therefore easily be suppressed by a filter.…”