An Automatic LO Leakage Calibration Method for Class-AB Power Mixer Based RF Transmitters

Mixers in a transmitter typically use pseudo differential common-source baseband amplifiers driving local oscillator (LO) switches. The common-source amplifiers are biased near cut-off for class-AB operation which yields higher efficiency. To mitigate their non-linearity, they are usually preceded by feedback controlled pre-distortion circuitry. DC bias differences between the two pseudo-differential halves of the common-source amplifiers turns out to be a major source of LO leakage. This paper presents an automatic calibration method to reduce the LO leakage. Major contributors of LO leakage in class-AB based power mixers with enhanced linearity and baseband noise filtering is analyzed. Monte Carlo analysis shows that LO leakage is less than -35dBc for 17% of the cases without calibration and 98% of the cases with calibration.