A low-power low-noise direct-conversion front-end with digitally assisted IIP2 background self calibration

Direct conversion receivers offer a high level of integration for multiband applications. For standards operating in full duplex, like WCDMA, a very high IIP2 is needed due to transmit signal leakage. Several circuit, compensation and calibration techniques to improve the IIP2 have been developed, but they usually result in a trade-off between IIP2, area, power and other specifications [1,2]. The IIP2 is very sensitive to manufacturing variations and operating conditions such as supply voltage, LO power or frequency, and temperature. We present a robust automatic background self-calibration technique with minimal overhead and performance penalties on the receiver front-end or baseband due to its digital implementation (Fig. 3.8.1). Such digital IIP2 calibration is also free of mismatch. The 0.13µm 1.8GHz CMOS RF front-end without external filter between LNA and mixer has an IIP2 better than 60dBm-sufficient for WCDMA applications [3]- with a state-of-the-art noise figure and power consumption.