Transceivers operating in frequency division duplex experience a transmitter leakage (TxL) signal into the receiver due to the limited duplexer stop-band isolation. This TxL signal in combination with the second-order nonlinearity of the receive mixer may lead to a baseband (BB) second-order intermodulation distortion (IMD2) with twice the transmit signal bandwidth. In direct conversion receivers, this nonlinear IMD2 interference may cause a severe signal-to-interference-plus-noise ratio degradation of the wanted receive signal. This contribution presents a nonlinear Wiener model recursive-least-squares (RLS) type adaptive filter for the cancellation of the IMD2 interference in the digital BB. The included channel-select-, and DC-notch filter at the output of the proposed adaptive filter ensure that the provided IMD2 replica includes the receiver front-end filtering. A second, robust version of the nonlinear RLS algorithm is derived which provides numerical stability for highly correlated input signals which arise in e.g. LTE-A intra-band multi-cluster transmission scenarios. The performance of the proposed algorithms is evaluated by numerical simulations and by measurement data.

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In RF transceivers operating in carrier-aggregation, spurs are generated on the transceiver chip which may downconvert 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 frequencydivision duplex, or a WiFi-related signal received by the antenna. This so-called modulated spur interference contains the phasenoise (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.

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