High IIP2 Adaptive Calibration Technique For Direct Down Conversion Active Mixer

Active mixer has become the prime consideration in direct down-conversion receivers (DCR) for its low power consumption and simple structure. However, it is vulnerable to 2nd order inter-modulation distortion (IMD2), one of the most critical issues for highly integrated DCR design. Commonly, a well-designed CMOS 0.18μm DCR active mixer can achieve IIP2 of about 55dBm, whereas the typical IIP2 requirement of GSM standard is in the range of 50dBm at the receiver input. With the assumption that LNA provides typical gain of 20dB, the minimum requirement of IIP2 translates into 70dBm at DCR mixer input.Methods suppressing IMD2 can be categorized into circuit and calibration techniques. The former includes common-mode feedback (CMFB), LC tank, etc. The latter brings in a beneficial concept of removing the distortion itself.The main tasks of this thesis are: Firstly, quantization analysis for factors affecting IMD2 is done based on models and methodologies proposed by authenticated papers; Secondly, according to the circuit techniques and manual calibrations, practical circuits are designed and simulated for validation. Finally, theories of adaptive calibrations are researched and verified by system simulation. The circuit simulations are under IBM 0.18um CMOS, and system simulations are under Matlab Simulink, with GSM900 standard for receiver as environment.