A novel technique to improve amplitude imbalance in mixers

Stringent I/Q matching requirement and large dynamic range of RF signals are two challenges in low-IF and direct conversion receivers. This paper analyzes a technique in detail used to alleviate both challenges. This technique can achieve a large range of variable linear-in-dB conversion gain easily by incorporating a modified R-2R ladder. Amplitude imbalance between the I- and Q-path can be adjusted using this technique. The procedure to design general fine linear-in-dB R-2R ladder is also discussed. It is shown that altering the conversion gain has little effect on the operating point of the mixer. The output resistance of the mixer seen by the following stage is a constant independent of variable range and step size. This technique can also be incorporated with AGC to accommodate large dynamic range of RF signals.