A Mixed-Signal Circuit Technique for Cancellation of Interferers Modulated by LO Phase-Noise in 4G/5G CA Transceivers

In RF transceivers operating in carrier-aggregation, spurs are generated on the transceiver chip which may down-convert any blocker signal located at the spur frequency into the receiver baseband. The blocker signal could either be the transceiver's own transmit signal when operating in frequency-division duplex, or a WiFi-related signal received by the antenna. This so-called modulated spur interference contains the phase-noise (PN) of the involved local oscillator harmonics which created the spur and leads to a degradation of the wanted RX signal. The presented mixed-signal circuit mimics the spur building law including the PN of the harmonics and is, therefore, able to provide a replica of the spur interference including PN modulated components. This replica is then used as a reference signal for the digital cancellation of the main and image modulated spur interference using a widely-linear (WL) cancellation structure. The proposed circuit technique is implemented in 28 nm LP CMOS technology, and measurement results show that the mixed-signal solution outperforms a digital-only WL cancellation with respect to PN cancellation even with high blocker power levels of -15 dBm at the input of the low-noise amplifier.