Interference Cancellation in Broadband Wireless Systems Utilizing Phase-Aligned Injection-Locked Oscillators

We demonstrate an interferer suppression method based on feed-forward cancellation that uses an injection-locked oscillator (ILO) to extract interferers from the incident spectrum in an auxiliary receiver. The technique is expected to be useful in environments where a strong narrowband interferer appears along with a wideband desired signal, such as ultra-wideband (UWB) and emerging cognitive-radio applications. The ILO is further embedded within a phase-locked loop which allows self-tuning of the ILO center frequency and automatic phase alignment between the main signal path and auxiliary path. An IC that uses this approach is implemented in a 0.18 mum CMOS process. In measurement, the chip demonstrates 20 dB suppression for phase- and frequency-modulated interferers while maintaining around 18 dB power gain and a noise figure below 5 dB, including an off-chip balun for the desired signal. Techniques for canceling amplitude modulated interferers, though not included in the fabricated chip, can also be implemented by adding an amplitude tracking gain-control loop.