Adaptive Cancellation of Digital Power Amplifier Receive Band Noise for FDD Transceivers

In frequency division duplex systems, spurious emission from transmitter (TX) can fall into receive band and lead to significant receiver desensitization. In this paper, a DSP-based solution that relies on a linear auxiliary receiver to cancel receive band noise (RxBN) from the received signal is demonstrated. This technique allows reduction of duplexer rejection requirements in the receiver band, and associated reduction of insertion loss in the TX band, thus resulting in high-power amplifier (PA) efficiency and small duplexer footprint. The PA architectures that inherently have high RxBN (such as envelope tracking and the digitally modulated PAs) can substantially benefit from this technique. Experimental results based on off-the-shelf system implementation are demonstrated using a digital PA, and more than 22 dB cancellation is achieved to reduce RxBN below thermal noise floor at 836 MHz with 45 MHz duplex spacing.