A self-calibrated LC quadrature VCO in a current-limited region

This paper presents a self-calibrated LC quadrature VCO (LC QVCO) which operates in a current-limited region. Our steady-state phasor analysis shows that phase and amplitude errors of an LC QVCO are linearly related to each other if the LC QVCO is designed to operate in a current-limited region. Based on this linear relationship, we propose a self-calibration technique which uses a low speed amplitude error detector instead of a conventional high speed phase error detector for I/Q error compensation of an LC QVCO. As a prototype, a 2.7 GHz self-calibrated LC QVCO was implemented in a 0.18 mum CMOS process. The LC QVCO core and the self-calibration loop consume 7.6 mA and 0.4 mA from a 1.8 V supply, respectively, and successfully compensate for phase and amplitude errors.